CHAPTER 3 - DOPED IN LEAD BISMUTH ALUMINUM-BORATE...
Transcript of CHAPTER 3 - DOPED IN LEAD BISMUTH ALUMINUM-BORATE...
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CHAPTER 3
SPECTROSCOPIC PROPERTIES OF Nd3+
- DOPED IN
LEAD–BISMUTH–ALUMINUM-BORATE GLASSES WITH
CONCENTRATION VARIATION
ABSTRACT
________________________________________________________________________
The effect of Nd3+
ion concentration on the physical and spectroscopic properties of
lead–bismuth–aluminum-borate glasses have been studied for the compositions:(70-
x)B2O3+20PbO+5Bi2O3+5Al2O3+xNd2O3 where x= 0.1, 0.5, 1.0, 1.5, 2.0 and 3.0 mol%.
From the room temperature absorption spectra, various spectroscopic parameters have
been computed. The Judd-Ofelt intensity parameters Ωλ (λ=2,4 and 6) have been evaluated
and used to obtain the radiative transition probabilities (AR), radiative life-times (τR),
branching ratios (βR) and absorption cross-sections (σa). Stimulated emission cross-
sections (σe) for the lasing levels 4F3/2→
4IJ (J=9/2, 11/2 and 13/2) were evaluated from
fluorescence spectra. Optical band gap values were estimated. FT-IR spectra were
recorded and analyzed.
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3.1. Introduction
Physical and spectroscopic properties of silicate, phosphate and borate glasses doped
with various rare earth ions offer many commercial and technological applications.
[21,91,92]. Heavy metal oxide (HMO) glasses find their importance as host matrices for
good lasing candidates because of their low phonon energy, high density, high refractive
index, optimum band width, high mechanical and thermal stability, corrosion resistance
and good solubility of rare earth ions [15,21-23]. Initially the laser efficiency increases
with the concentration, maximum at optimum level and decreases at higher concentrations
due to non radiative self-quenching processes [21]. Hence, the incorporation of HMOs such
as PbO or Bi2O3 into the borate glass matrix leads to an increase in its luminescence
quantum efficiency [21]. The effect of lead-borate, bismuth-borate and lead-bismuth-
borate glasses on the optical properties of Nd3+
ion have been reported [21, 23-25].
Motivated by these works lead-bismuth-aluminum-borate glasses doped with Nd3+
were
prepared and their physical and spectroscopic properties were studied with variation of
Nd3+
concentration.
Laser active medium should have high gain, high energy storage capability, low optical
losses which depend on stimulated emission cross-section, fluorescence life-times and
optical efficiency [15, 93]. The absorption spectrum of Nd3+
ions in a typical glass range
from ultraviolet to the infrared region. The stimulated emission cross-section is in the
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intermediate range [94]. The compatibility of borate glasses as host materials for rare earths
is encouraging in the areas like wave guide lasers and optical amplifiers [93, 94].
For all the present glass matrices optical absorption and emission spectra were recorded
at room temperature. The spectroscopic parameters like Racah (E1, E
2 and E
3), Slater-
Condon (F2, F4 and F6) and bonding parameter (δ) were evaluated from the spectral data.
The Judd-Ofelt (JO) intensity parameters (Ω2 , Ω4 and Ω6 ), transition probabilities (A), life
times (ηR), branching ratios (βR) and absorption (ζa) and emission (ζe) cross-sections have
been computed. The significant lasing transitions 4F3/2
4IJ (J = 13/2, 11/2 and 9/2) have
been studied. Optical band gap values were estimated. FT-IR spectra were recorded and
studied for structural changes in the 3D glass network. The present results are compared
with some of the reported glasses doped with varying Nd3+
ion concentration.
3.2. Experimental details
BLABIN1-6: (70-x) B2O3+20PbO+5Bi2O3+5Al2O3+xNd2O3 (where x = 0.1, 0.5,
1.0, 1.5, 2.0 and 3.0 mol%) glasses were prepared by melt quenching technique.
Appropriate amounts of B2O3, PbO, Bi2O3, Al2O3 and Nd2O3 of 99.9% purity were
thoroughly mixed and grinded using an agate mortar in 10g batches. This mixture is
transferred into a silica crucible and kept in an electric furnace initially for 30 min between
400 and 4500C then for 1 hour at 1000
0C for melting and then poured onto a pre-heated
brass plate and air quenched. The glasses so obtained were annealed at about 4000C for 8 h
to remove internal mechanical stress and then after cooling to room temperature samples of
good optical quality were selected and polished in order to study the physical and
spectroscopic properties. Refractive indices were determined by Brewster angle method at
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a wavelength of 543 nm. The amorphous nature of the samples was confined by XRD
spectra obtained by using Shimadzu - XD 3A diffractometer. Perkin Elmer Lambda 950
UV-Vis-NIR spectrophotometer is used to record the absorption spectra at room
temperature in the wave length range of 400-900 nm. The NIR emission spectra were
recorded in the range of 800-1500 nm by JOBIN-YVON Fluorolog-3 spectrofluorimeter, at
room temperature. The FT-IR spectra were recorded using KBr pellet method on Thermo
Nicolet-5700 FT-IR Spectrophotometer in the wave number range 4000– 400 cm-1
.
3.3 Results and discussion
3.3.1 Physical properties
Physical properties such as density (d), molar volume (VM), neodymium ion
concentration (N), dielectric constant ( ), reflection loss (R), molar refractivity (Rμ), inter-
ionic distance (ri), polaron radius (rP), field strength (F), electric susceptibility (χe) and
numerical aperture (NA) were evaluated using relevant expressions 2.1- 2.12 for the glass
matrices BLABIN:1-6 and are presented in Table 3.1.
The laser beam emanating from the lasing material is affected mainly by RE ion
concentration. The variation of density and molar volume with concentration of Nd2O3 is
graphically presented in Fig 3.1. The density decreases from 0.1 to 0.5 mol%, then
increases up to 1.5 mol%, again decreases up to 2.0 mol% and then increases at higher
concentrations. The possible reason of decrease in density of the host material could be the
formation of non-bridging oxygen atoms around 0.5 and 2.0 mol% concentration of
Nd2O3. The clustering of RE ions can be one of the factors which contribute to the
variation of the density at higher concentrations. The behavior of molar volume follows an
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opposite trend to the density as expected. The concentration of the number of luminescent
centers (N) is found to be densely distributed because of the higher values of the glass
density (d) and refractive index (n) and is comparable to other host glasses [21,25,94].
The polaron radius (rP) is less than inter-ionic distance (ri) and hence high field strength
(F). Polaron radius and inter-ionic distances decrease with increase of Nd3+
concentration.
Fig. 3.1 Variation of (a) Density and (b) Molar Volume with Nd2O3 Concentration
Luminescent centers (N) are found to be densely distributed because of the higher values
of the glass density (d) and refractive index (n) and is comparable to other host glasses
[21,25,94]. The polaron radius (rP) is less than inter-ionic distance (ri) and hence the high
field strength (F). Polaron radius and inter-ionic distances decrease with increase of Nd3+
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Table 3.1: Various physical properties of Nd3+
: BLABIN 1-6 glasses
S.No. BLABIN→
Parameter↓
1 2 3 4 5 6
1 Refractive index, n 1.740 1.741 1.743 1.744 1.746 1.749
2 Density d (gm/cm3) 4.094 3.970 4.050 4.174 3.966 4.779
3 Average molecular wt (g) 203.58 185.28 207.45 209.55 211.67 215.57
4 Molecular volume (VM)
(cm3)
49.73 50.65 50.51 50.20 53.37 45.11
5 Optical path length(cm) 0.280 0.257 0.292 0.268 0.290 0.295
6 Nd3+
conc. (1020
ions /cc) 0.21 0.95 1.93 2.96 3.46 5.85
7 Optical dielectric constant,
ε
3.028 3.031 3.038 3.042 3.049 3.059
8 Reflection loss R (%) 7.294 7.308 7.337 7.352 7.380 7.424
9 Molar refractivity Rµ
(cm3)
20.057 18.841 20.721 20.331 21.659 18.358
10 Inter-ionic distance ri (Å) 36.538 21.749 17.233 14.953 13.859 11.953
11 Polaron radius rP (Å) 14.727 8.766 6.946 6.027 5.586 4.818
12 Field strength F (10+15
cm-
2)
0.598 1.687 2.687 3.568 4.154 5.583
13 Electric susceptibility χe 0.1613 0.1616 0.1621 0.1624 0.1630 0.1638
14 Numerical aperture (NA) 0.25 0.25 0.25 0.25 0.25 0.25
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concentration. All the glasses under investigation have numerical aperture (NA) about 0.25
indicating that optical fibers made of these glass compositions will accept large amount of
light from the source. Hence these transparent glasses are suitable as core material for
optical fibers [84].
3.3.2. Absorption spectroscopic parameters
The absorption spectra of the Nd3+
: BLABIN 1-6 glass matrices in the wavelength range
of 400-900 nm are shown in Fig. 3.2. A comparison of the optical absorption spectra of the
present glasses with the standard wavelength chart of Nd3+
[14,21,53,63,98] results in the
identification of the spectroscopic transitions 4F3/2,
4F5/2+
2H9/2,
4F7/2+
4S3/2,
4F9/2,
2H11/2,
4G5/2+
2G7/2,
4G7/2+
4G9/2+
2K13/2,
2G9/2+
4G11/2,
2P1/2 ←
4I9/2 [53]. The experimental energy
levels of Nd3+
ions in the present glasses are obtained from the absorption spectra and are
collected in Table 3.2. The rms deviation range from ± 40.13 to ± 57.47 and is in good
agreement with the literature. The variation of total intensity with Nd2O3 concentration of
some selected bands is shown in Fig.3.3. The energy level analysis [15, 63, 92, 99, 100] by
the Hamiltonian model expressed in the form of free-ion (HFI) with the help of f- shell
empirical program [14,15]. The HFI representing the energy level structure of Nd3+
(4f 3)
ion is defined as
…(3.1)
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where k=2,4 and 6; i = 2,3,4,6,7 and 8; and j = 0,2 and 4. The operators and their associated
parameters were written according to conventional notation and meaning [14,15,92].
Among the various interactions that contribute to the total free-ion Hamiltonian, the inter-
electronic (Fk) and the spin-orbit (ξ) interactions are the major contributors and they govern
the 2S+1
LJ contributions to the energy level positions [15, 96]. The other terms will only
give corrections to the energy of these levels without removing their degeneracy. In Table
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3.3 the best-fit free-ion parameters Fk, ξ, α, β and γ values are collected. The sum of Slater
integrals ΣFk
indicating the net electrostatic interaction experienced by Nd3+
ions in the
host matrix, is also given in this table. ΣFk
trend suggests that Nd3+
ions experience
relatively more electrostatic bonds in BLABIN:1 than in other glass hosts [15,53,63,99].
The ΣFk
value shows the decreasing tendency with the increase in the concentration of
Nd3+
except for 2 mol%. The hydrogenic ratios, F2/F
4 (~1.45) and F
2/F
6 (~1.89), for
Lasing
level BLABIN1 BLABIN2 BLABIN3 BLABIN4 BLABIN5 BLABIN6
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Table 3.2 : Experimental energies of Nd3+
: BLABIN 1-6 glasses
BLABIN:1-6 glass systems are in good agreement with those Nd3+
doped glass systems
[15] indicating that the radial integral part of the f-orbital of Nd3+
ions remains unchanged
even though the concentrations are changed. This may mainly due to shielding effect
experienced by the 4f electrons by the 5s25p
6 orbitals [15].
Nephelauxetic ratio cn
a
where c and a refer to the spectral energies (cm
-1) in the
host under investigation and the aqua-ion respectively, and bonding parameter
4F3/2 11494 11481 11481 11481 11468 11468
4F5/2 12500 12500 12500 12500 12484 12484
4F7/2 13550 13500 13531 13531 13531 13513
4F9/2 14815 14749 14749 14749 14749 14728
2H11/2 16000 16000 16000 16000 16000 16000
4G5/2 17212 17212 17212 17212 17212 17212
4G7/2 19120 19083 19083 19083 19083 19083
4G9/2 19569 19569 19569 19569 19569 19569
2G9/2 21186 21142 21142 21097 21097 21097
4G11/2 21598 21505 21598 21598 21598 21598
2P1/2 23310 23364 23310 23310 23310 23310
rms
dev.
±50.14 ±40.13 ±56.89 ±57.32 ±56.54 ±57.47
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Table 3.3 : Spectroscopic parameters of Nd3+
: BLABIN 1-6 glasses
Parameter 1 2 3 4 5 6
E1(cm
-1) 5710.20 4993.41 4881.05 4872.24 5100.45 4874.63
E2(cm
-1) 25.38 25.74 25.53 25.65 25.71 25.74
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…(3.2)
E3(cm
-1) 490.08 489.17 489.21 489.78 490.02 490.11
ξ4f (cm-1
) 922.77 904.71 914.38 910.55 913.23 909.12
α (cm-1
) 0.15 -3.92 -3.65 -3.87 -2.78 -3.91
β (cm-1
) 307.38 446.50 460.83 475.52 455.33 508.06
γ(cm-1
) -3611.17 71.54 432.46 502.49 -610.82 505.89
E1/E
3 11.65 10.21 9.98 9.95 10.41 9.95
E2/E
3 0.05 0.05 0.05 0.05 0.05 0.05
F2 (cm-1
) 350.72 334.63 331.26 331.63 337.31 332.05
F4(cm-1
) 56.77 46.81 45.71 45.41 48.29 45.31
F6 (cm-1
) 6.86 5.35 5.09 5.07 5.56 5.08
F2/F4 0.01 0.01 0.01 0.01 0.01 0.01
F4/F6 1.22 1.30 1.33 1.33 1.28 1.32
F2
(cm-1
) 78912.5 75292.6 74533.3 74616.0 75895.0 74712.3
F4
(cm-1
) 61821.6 50976.0 49772.8 49449.2 52588.7 49346.3
F6
(cm-1
)
ΣFk
50478.3
191212.4
39357.1
165625.7
37446.1
161652.2
37312.3
161377.5
40952.9
169436.6
37361.3
61419.9
δ 0.828 0.961 0.923 0.947 0.963 0.983
n 1.7401 1.7413 1.7428 1.74424 1.74572 1.74868
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where n is the average value of n, have been evaluated. The RE ion-ligand bond will be
covalent or ionic depending respectively on positive or negative sign of value [43,74].
For the present glass matrices value ranging from + 0.828 to + 0.983 indicates that the
RE ion-ligand bonds are strong and covalent.
3.3.3. Spectral intensities and Judd-Ofelt parameters
The experimental oscillator strengths of the absorption transitions can be obtained
from the relation [53, 63,100] fexp = 4.318 x 10-9
( ) d where ε (ν) = OD/ct is the
molar extinction coefficient at mean energy ν (cm-1
), with OD being the optical density, c
being the molar concentration of the RE ions and t is the optical length of the glass[15].
The intensities of all absorption bands have been evaluated using the area method. The rms
deviations between experimental and calculated oscillator strengths (fexp and fcal) presented
in Table 3.4 range from ± 0.7 to ± 2.43 show the validity of Judd-Ofelt theory. Using the
oscillator strengths, the values of the reduced matrix elements and other parameters, JO
intensity parameters Ωλ (λ = 2,4,6) have been computed by the least- square fit [51,52] and
are collected in Table 3.5. Since the reduced matrix elements are host invariant, the values
reported in literature [53, 63, 84] have been used for the calculations. Some of the
absorption bands overlap with each other and in those cases the matrix elements
2
U
of
the corresponding transitions were summed for JO analysis [15]. In crystals and glasses
the RE ions are distributed over a large number of non-equivalent sites and the intensity
parameters are the average values of Ωλ ( λ = 2,4,6) from all the sites [21]. The obtained
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values of Ωλ are in the order 6 2 4 for all the glasses under study .
Table 3.4 : Experimental and calculated oscillator strengths ( x 10-6
) and rms
deviation of Nd3+
: BLABIN 1-6 glasses.
According to Krupke [101] Ω2 and Ω6 values mainly depend on the transition
intensities of 4I9/2 →
4G5/2+
2G7/2 and
4I9/2 →
4F7/2+
4S3/2 respectively. These transitions in
the absorption spectra split into two peaks by Stark-splitting due to crystal-field. From
Fig. 3.2, it is evident that the resolution of Stark-splitting of the hypersensitive transition
4I9/2→
4G5/2+
2G7/2 decreases with increasing concentration. Hence for BLABIN: 1-4 there
is visible resolution and for BLABIN: 5 and 6 the resolution is poor indicating for
Level
BLABIN1 2 3 4 5 6
f exp f cal f exp f cal f exp f cal f exp f cal f exp f cal f exp f cal
4F3/2 - 1.74 1.65 2.57 2.57 2.86 2.86 2.22 1.84 2.13 3.29 2.46
4F5/2+
2H9/2 8.86 8.21 9.40 9.14 9.14 10.30 10.30 10.39 12.89 11.45 11.50 11.6
4F7/2+4S3/2 9.11 9.83 9.62 9.95 9.95 11.24 11.24 11.71 8.04 12.32 12.42 13.5
4F9/2 0.53 0.73 0.80 0.77 0.77 0.86 0.86 0.85 1.60 0.85 0.96 0.85
2H11/2 0.15 0.20 0.19 0.21 0.21 0.24 0.24 0.22 0.41 0.22 0.26 0.24
4G5/2+
2G7/2 22.0 22.2 26.0 26.0 26.0 24.6 24.6 28.1 28.4 28.5 28.6 29.0
4G7/2+
4G9/2+
2K13/2 8.23 5.63 8.40 7.00 7.00 7.48 7.48 10.27 4.77 10.42 8.54 10.9
2G9/2+
4G11/2 1.71 0.86 2.28 1.12 1.12 1.25 1.25 2.39 1.63 2.44 1.42 2.60
2P1/2 - 0.35 0.36 0.62 0.62 0.69 0.69 0.42 0.08 4.33 0.80 0.51
rms dev. ±1.1 ±0.7 ±0.77 ±1.56 ±2.43 ±0.99
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BLABIN: 1-4 glasses Ω2 parameter value is mainly contributed by covalence parameters
rather than crystal-field parameters whereas for BLABIN: 5 and 6 the converse is true.
Stark-splitting of the transition 4I9/2 →
4F7/2+
4S3/2 is well resolved for BLABIN: 3-6
glasses.
Table 3.5 : Judd-Ofelt intensity parameters (Ωλ , λ = 2,4,6 )
( x 10-20
cm2) Nd
3+ : BLABIN 1-6 glasses
The Ω2 parameter indicates the covalent nature of the RE ion-ligand bond as well as
the asymmetric nature of the Nd3+
ion local environment. Increase of asymmetric nature of
RE ion site and increase of covalency of chemical bonds with the ligands cause an increase
in Ω2 value [14]. For the present glass systems Ω2 values are in the order of BLABIN: 1 <
BLABIN: 2 > BLABIN: 3 < BLABIN: 4 >BLABIN: 5 <BLABIN: 6 indicating BLABIN:
BLABIN →
Parameter ↓ 1 2 3 4 5 6
Ω2 5.70 5.91 5.09 6.16 5.95 6.28
Ω4 2.29 4.06 4.54 4.78 5.30 4.95
Ω6 6.09 6.05 6.84 7.09 7.54 8.15
Ω4 / Ω6 0.38 0.67 0.66 0.67 0.70 0.61
Ω2 + Ω4 + Ω6 14.08 16.03 16.47 18.03 18.79 19.38
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4,5 and 6 (higher concentration) glasses exhibit more covalence and higher asymmetry of
Nd3+
ion local environment compared to other three glasses (lower concentration). The Ω4
and Ω6 parameters are related to rigidity of the host matrix [14]. These values indicate that
the rigidity of the present glasses under study increases with increasing concentration.
Spectroscopic quality factor χ = Ω4 / Ω6 determines the lasing efficiency of the host.
BLABIN: 1 glass has χ = 0.38 equivalent to that of Nd: YAG laser [102] indicating it as a
good lasing material. For BLABIN:1-6 glasses χ range from 0.38 to 0.70 indicating these
are better lasing hosts than those like fluoride, oxide and phosphate glasses reported in
literature [15,102-104]. The variation of total intensities of the bands of the transitions
4F5/2+
2H9/2,
4F7/2+
4S3/2,
4G5/2+
2G7/2 and,
4G7/2+
4G9/2+
2K13/2 ←
4I9/2 with Nd2O3
concentration, is the fingerprint of changes in the structure of the glass. The changes in
the line profiles indicate that small change in the concentration of Nd2O3 causes more
changes in the network structure of the glass and the local environment of the optically
active ion.
3.3.4 Radiative properties
The obtained Ωλ (λ = 2,4,6) values from the absorption measurements have been
used to calculate the radiative transition probabilities (AR), radiative life-times (ηR),
branching ratios (βR) and absorption cross-sections (ζa) of the excited state 4F3/2. The
equations for the radiative transition probabilities A(SLJ, S1L
1J
1) for emission between J
manifolds, the electric dipole line strength and the magnetic dipole line strength are given
in chapter 1. For Nd3+
ion, the bands produced by the magnetic dipole mechanism have
very low spectral intensity compared to those produced by electric dipole mechanism.
Hence the term n3 Smd in the equation for A(SLJ, S
1L
1J
1) can be omitted [5]. Electric
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dipole line strengths and radiative transition probabilities of certain lasing transitions of
Nd3+
: BLABIN 1-6 glasses are given in Table 3.6.
The radiative life times (R) [97] for certain lasing transitions presented in Table
3.7 indicate the order 2
H11/2 > 4F3/2 >
4F9/2 >
4F5/2 >
4G7/2 >
4G9/2 >
4G5/2 for all
the glasses. Transition probabilities are used to evaluate the fluorescence branching ratio
(R) [5, 15, 96, 97]. Branching ratios (βR) and integrated absorption cross-sections (ζa) of
certain lasing transitions of Nd3+
are given in Table 3.8.
Fluorescence spectra are given in Fig 3.4. The experimental and calculated
branching ratios (βR) and computed radiative lifetimes (ηR) for 4F3/2
4IJ (J = 13/2, 11/2
and 9/2) lasing transitions are presented in Table 3.9. The radiative property of the
transitions 4F3/2
4I13/2,
4I11/2 and
4I9/2 are characterized by the spectroscopic quality
factor χ and not by 2, as the tensor operator 2
2U is zero for all these transitions,
according to the triangle rule | J-J’| ≤ λ ≤| J+J’| [21,105-107]. 4F3/2
4I11/2 is a potential
lasing transition for Nd3+
ion (λ =1.06 μm). The radiative lifetime (ηR) has lowering trend
with increase in concentration of Nd2O3. Minimum values of ηR for BLABIN:6 glass with
3 mol% of Nd2O3 , reflect higher values of 4 and 6 with χ < 1. The transition 4F3/2 →
4I11/2 exhibits higher R value compared to other transitions. The magnitude of R did not
vary significantly whereas R decreases with increase of Nd3+
concentration (Fig 3.5) for
the above transition, indicating BLABIN: 1-6 glasses are good laser hosts.
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The fluorescence band was integrated and divided by the peak intensity to yield an
effective line width [14, 74]. The stimulated emission cross–section of the laser transition
can be determined from the expression [15, 84,107]
4P 4 4
P 3/ 2 J2
eff
( ) A[( F );( I )]8 cn
…(3.3)
where P is the peak fluorescence wavelength, n is the refractive index, eff is the
effective line width of the transitions 4
F3/24IJ (J=13/2, 11/2 and 9/2) and
4 4
3/ 2 JA[( F );( I )]
is the radiative transition probability determined from the JO theory. The luminescence
properties (λP, ∆ λeff, (p),R) for the lasing transitions 4F3/2
4IJ (J = 13/2, 11/2 and 9/2)
are collected in Table 3.10. Spectroscopic quality factor helps to identify the channel
through which the excited metastable state 4F3/2 of Nd
3+ relaxes to the ground state. χ < 1
implies that the transition 4F3/2
4I11/2 is more intense than
4F3/2
4I9/2 and vice versa for χ
>1. For the potential lasing transition 4F3/2
4I11/2, (p) values exhibit the lowering order
with increase in Nd2O3 concentration and are comparable to those of commercial laser
glasses [15,22]. The high values of (p) and R indicate these glass matrices may be good
laser hosts. Experimental branching ratios (R exp) are obtained from the relative areas
under the emission peaks and are comparable with those predicted from the JO theory and
are collected in Table 3.9. The values of (p) for the 4F3/2
4IJ (J=13/2, 11/2 and 9/2)
transitions are comparable to the glasses reported in literature for phosphate and borate
glass host materials [87, 88, 89]. As can be seen from Fig 3.4, the emission bands are
affected by sizeable inhomogeneous broadening due to the large crystal-field distribution
around the RE ions which is the characteristic of the glasses under study [104].
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20
Fig. 3.5 Variation of radiative lifetime of 4F3/2
4I11/2 transition with
Nd3+
concentration
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Table 3.6 : Electric dipole line strengths (S’ed cm2x10
-22) and radiative transition probabilities A (s
-1) of certain lasing
transitions of Nd3+
: BLABIN 1-6 glasses
BLABIN→
Transition ↓
1 2 3 4 5 6
S’ed A S’ed A S’ed A S’ed A S’ed A S’ed A
4G9/2→
2K13/2 90.87 0.03 98.74 0.04 108.00 0.04 114.12 0.04 121.05 0.05 127.15 0.05
4G7/2 140.77 0.05 166.80 0.06 181.74 0.06 192.80 0.07 205.87 0.07 210.79 0.07
4G5/2 174.41 8.07 191.96 8.88 216.35 10.01 225.02 10.41 241.51 11.18 253.11 11.71
2G7/2 75.61 3.26 101.90 4.39 102.78 4.43 114.08 4.91 119.90 5.16 117.71 5.07
2H11/2 149.45 23.57 154.21 24.32 173.58 27.37 180.39 28.45 192.32 30.33 205.51 32.41
4F9/2 116.39 47.09 147.08 59.51 146.56 59.30 163.59 66.19 170.28 68.89 169.94 68.76
4F7/2 366.61 295.68 377.99 304.85 338.95 273.37 400.16 322.74 392.53 316.58 415.76 335.32
4S3/2 44.52 32.80 78.64 57.93 87.81 64.69 92.56 68.19 102.47 75.49 95.92 70.66
4F5/2 133.14 165.09 154.80 191.95 144.00 178.55 166.89 206.94 168.18 208.54 171.17 212.24
2H9/2 92.93 100.13 101.91 109.80 108.70 117.12 116.46 125.48 122.55 132.04 128.19 138.12
22
4F3/2 101.34 188.74 110.97 206.69 125.09 232.98 130.08 242.27 139.55 259.91 146.47 272.80
4I15/2 178.55 1503.22 203.07 1709.62 228.69 1925.32 238.12 2004.73 256.26 2157.47 266.04 2239.76
4I13/2 642.19 8300.42 730.40 9440.54 671.44 8678.46 783.16 10122.5 784.03 10133.8 803.09 10380.1
4I11/2 110.69 2058.12 172.57 3208.80 193.10 3590.42 202.94 3773.51 223.17 4149.53 214.24 3983.58
4I9/2 39.18 991.19 49.51 1252.62 54.93 1389.70 57.78 1461.87 62.42 1579.17 62.90 1591.33
4G7/2→
4G5/2 81.76 1.40 104.93 1.80 117.82 2.02 123.18 2.11 133.77 2.29 134.41 2.30
2G7/2 58.13 0.91 59.48 0.93 57.14 0.89 64.80 1.01 65.17 1.02 69.41 1.09
2H11/2 222.53 16.46 221.47 16.38 249.18 18.43 258.78 19.14 274.86 20.33 297.07 21.97
4F9/2 188.59 40.32 197.19 42.16 218.41 46.70 229.02 48.96 243.10 51.97 258.53 55.27
4F7/2 117.77 53.53 134.42 61.10 123.73 56.24 144.22 65.56 144.51 65.69 147.86 67.21
4S3/2 47.48 19.56 83.44 34.38 92.85 38.26 98.05 40.40 108.39 44.66 101.51 41.83
4F5/2 219.43 158.46 224.57 162.17 212.94 153.77 243.31 175.70 243.49 175.83 259.19 187.17
2H9/2 265.64 165.00 275.11 170.88 302.51 187.90 318.37 197.75 336.74 209.17 359.10 223.05
4F3/2 74.95 83.49 88.35 98.42 82.61 92.02 95.48 106.37 96.54 107.54 97.86 109.01
4I15/2 64.98 351.42 64.80 350.45 73.22 395.98 75.87 410.33 80.72 436.58 87.20 471.61
4I13/2 41.01 345.45 56.43 475.33 63.29 533.10 66.30 558.41 72.35 609.36 71.45 601.81
23
4I11/2 300.00 3673.92 339.52 4157.95 319.19 3908.92 367.44 4499.81 370.67 4539.34 380.89 4664.60
4I9/2 96.34 1618.30 128.27 2154.63 132.77 2230.20 145.22 2439.32 153.84 2584.10 151.92 2551.87
4G5/2→
2G7/2 81.76 0.00 104.93 0.00 117.82 0.00 123.18 0.00 133.77 0.00 134.41 0.00
2H11/2 8.87 0.09 8.86 0.09 10.01 0.10 10.37 0.10 11.03 0.11 11.92 0.12
4F9/2 82.38 7.57 83.24 7.65 93.61 8.60 97.28 8.94 103.46 9.51 111.28 10.22
4F7/2 144.69 45.08 163.53 50.96 178.15 55.51 188.82 58.84 200.75 62.55 208.35 64.92
4S3/2 41.01 11.01 72.54 19.48 80.88 21.72 85.33 22.91 94.42 25.35 88.35 23.72
4F5/2 182.08 111.07 210.78 128.57 195.02 118.96 226.71 138.29 227.92 139.03 232.20 141.64
2H9/2 4.85 2.39 7.24 3.57 7.92 3.90 8.42 4.15 9.17 4.52 8.86 4.36
4F3/2 286.83 316.23 304.70 335.94 266.89 294.26 319.75 352.53 312.03 344.02 326.46 359.93
4I15/2 2.80 21.94 2.78 21.82 3.15 24.65 3.26 25.54 3.47 27.17 3.75 29.38
4I13/2 37.34 488.79 43.25 566.15 48.68 637.31 50.72 664.01 54.67 715.64 56.46 739.11
4I11/2 124.07 2484.02 174.65 3496.72 195.79 3919.92 205.22 4108.68 224.27 4490.20 220.30 4410.62
4I9/2 627.26 17884.14 719.22 20506.1 667.82 19040.7 774.55 22083.7 778.92 22208.1 796.27 22702.8
2H11/2→
4F9/2 65.72 0.43 71.74 0.47 67.06 0.44 77.38 0.51 77.59 0.51 80.69 0.53
4F7/2 101.00 5.01 104.01 5.16 112.11 5.57 119.25 5.92 125.16 6.21 133.61 6.63
24
4S3/2 13.85 0.55 23.84 0.95 26.64 1.06 28.06 1.12 31.02 1.24 29.19 1.16
4F5/2 16.37 2.08 16.28 2.07 18.40 2.34 19.06 2.42 20.27 2.57 21.92 2.78
2H9/2 207.68 19.73 208.85 19.84 225.07 21.38 239.29 22.74 250.51 23.80 269.49 25.61
4F3/2 4.95 1.36 4.94 1.35 5.58 1.53 5.79 1.58 6.16 1.69 6.65 1.82
4I15/2 89.45 248.60 104.36 290.03 97.00 269.58 112.48 312.61 113.36 315.05 115.24 320.26
4I13/2 8.06 39.60 11.12 54.65 11.79 57.95 12.74 62.58 13.64 67.03 13.38 65.76
4I11/2 8.38 65.47 10.11 79.06 10.69 83.59 11.54 90.18 12.21 95.46 12.41 97.00
4I9/2 6.95 79.57 7.39 84.66 8.34 95.50 8.66 99.20 9.27 106.16 9.81 112.39
4F9/2→
4F7/2 121.78 0.85 139.66 0.98 142.48 1.00 156.62 1.10 162.92 1.14 167.64 1.17
4S3/2 1.20 0.01 1.60 0.01 1.80 0.01 1.88 0.01 2.05 0.01 2.04 0.01
4F5/2 84.00 3.15 92.88 3.48 103.00 3.86 108.07 4.05 115.39 4.33 120.66 4.52
2H9/2 29.53 0.69 31.06 0.72 27.34 0.64 32.65 0.76 31.89 0.74 33.49 0.78
4F3/2 68.91 8.14 69.35 8.20 78.34 9.26 81.21 9.60 86.47 10.22 93.14 11.01
4I15/2 396.02 859.47 483.25 1048.77 543.34 1179.19 567.07 1230.70 613.63 1331.73 624.77 1355.90
4I13/2 361.27 1499.85 397.76 1651.35 447.84 1859.25 466.04 1934.80 500.03 2075.92 523.97 2175.30
4I11/2 232.84 1621.52 237.43 1653.45 268.11 1867.07 278.07 1936.45 296.45 2064.49 317.99 2214.45
25
4I9/2 27.32 289.40 28.84 305.46 32.40 343.13 33.72 357.16 36.01 381.37 38.21 404.65
4F5/2→
2H9/2 13.75 0.00 19.33 0.00 20.69 0.00 22.23 0.00 23.92 0.00 23.39 0.00
4F3/2 56.28 0.36 67.36 0.43 63.54 0.40 73.10 0.46 74.25 0.47 74.95 0.47
4I15/2 139.97 206.38 139.20 205.24 157.29 231.93 162.97 240.31 173.35 255.61 187.43 276.37
4I13/2 285.60 980.75 316.51 1086.93 356.67 1224.83 371.05 1274.20 398.47 1368.38 416.77 1431.21
4I11/2 61.30 399.11 91.33 594.59 102.27 665.85 107.36 698.98 117.74 766.58 114.16 743.28
4I9/2 296.19 3183.53 336.36 3615.31 378.72 4070.59 394.37 4238.83 424.33 4560.84 440.70 4736.72
4F3/2→
4I15/2 17.04 22.14 16.95 22.01 19.15 24.88 19.84 25.78 21.10 27.42 22.82 29.64
4I13/2 127.37 443.14 126.67 440.70 143.14 498.00 148.31 515.99 157.75 548.85 170.56 593.42
4I11/2 281.02 2006.98 304.92 2177.65 343.79 2455.21 357.38 2552.25 383.11 2736.01 403.20 2879.54
4I9/2 85.94 1065.56 126.29 1565.83 141.46 1753.91 148.45 1840.53 162.67 2016.85 158.21 1961.58
26
Table 3.7 : Computed radiative lifetimes τR (µs) of certain lasing levels of Nd3+
:
BLABIN glasses.
BLABIN→
Lasing level↓
1 2 3 4 5 6
4G9/2 73 60 60 54 52 52
4G7/2 153 129 130 117 113 111
4G5/2 47 40 41 36 36 35
2H11/2 2163 1858 1855 1670 1614 1577
4F9/2 233 214 190 183 170 162
4F5/2 210 182 161 155 144 139
4F3/2 283 238 211 203 188 183
27
Table 3.8 : Branching ratios ( β) and integrated absorption cross sections (σa x 1018
cm-1
) of
certain lasing transitions of Nd3+
: BLABIN 1-6 glasses
BLABIN→
Transition↓
1
β σa
2
β σa
3
β σa
4
β σa
5
β σa
6
β σa
4G9/2→
2K13/2 0.00 0.07 0.00 0.07 0.00 0.08 0.00 0.08 0.00 0.09 0.00 0.09
4G7/2 0.00 0.10 0.00 0.12 0.00 0.13 0.00 0.14 0.00 0.15 0.00 0.15
4G5/2 0.00 0.64 0.00 0.70 0.00 0.79 0.00 0.82 0.00 0.88 0.00 0.92
2G7/2 0.00 0.27 0.00 0.36 0.00 0.37 0.00 0.40 0.00 0.42 0.00 0.42
2H11/2 0.00 0.82 0.00 0.85 0.00 0.95 0.00 0.99 0.00 1.05 0.00 1.12
4F9/2 0.00 0.88 0.00 1.11 0.00 1.10 0.00 1.23 0.00 1.27 0.00 1.27
4F7/2 0.02 3.47 0.02 3.57 0.02 3.20 0.02 3.77 0.02 3.69 0.02 3.90
4S3/2 0.00 0.41 0.00 0.72 0.00 0.80 0.00 0.85 0.00 0.94 0.00 0.87
4F5/2 0.01 1.46 0.01 1.69 0.01 1.57 0.01 1.82 0.01 1.83 0.01 1.85
2H9/2 0.01 0.97 0.01 1.06 0.01 1.13 0.01 1.21 0.01 1.27 0.01 1.32
4F3/2 0.01 1.27 0.01 1.39 0.01 1.56 0.01 1.62 0.01 1.74 0.01 1.82
4I15/2 0.11 3.70 0.10 4.20 0.12 4.72 0.11 4.91 0.11 5.27 0.12 5.45
4I13/2 0.61 15.33 0.57 17.42 0.52 15.98 0.55 18.61 0.53 18.60 0.54 18.99
4I11/2 0.15 2.98 0.19 4.65 0.22 5.19 0.20 5.44 0.22 5.98 0.21 5.72
4I9/2 0.07 1.17 0.08 1.48 0.08 1.64 0.08 1.72 0.08 1.85 0.08 1.86
4G7/2→
4G5/2 0.00 0.17 0.00 0.22 0.00 0.25 0.00 0.26 0.00 0.28 0.00 0.28
2G7/2 0.00 0.12 0.00 0.12 0.00 0.12 0.00 0.13 0.00 0.13 0.00 0.14
2H11/2 0.00 0.76 0.00 0.75 0.00 0.85 0.00 0.88 0.00 0.93 0.00 1.00
4F9/2 0.01 0.92 0.01 0.96 0.01 1.06 0.01 1.11 0.01 1.17 0.01 1.24
4F7/2 0.01 0.74 0.01 0.84 0.01 0.77 0.01 0.90 0.01 0.90 0.01 0.92
4S3/2 0.00 0.29 0.00 0.50 0.00 0.56 0.00 0.59 0.01 0.65 0.00 0.61
4F5/2 0.02 1.60 0.02 1.64 0.02 1.55 0.02 1.77 0.02 1.76 0.02 1.87
2H9/2 0.03 1.84 0.02 1.91 0.02 2.09 0.02 2.20 0.02 2.32 0.02 2.47
4F3/2 0.01 0.63 0.01 0.74 0.01 0.69 0.01 0.80 0.01 0.81 0.01 0.82
4I15/2 0.05 0.93 0.05 0.92 0.05 1.04 0.05 1.08 0.05 1.14 0.05 1.23
4I13/2 0.05 0.68 0.06 0.93 0.07 1.04 0.07 1.09 0.07 1.19 0.07 1.17
28
4I11/2 0.56 5.62 0.54 6.35 0.51 5.96 0.53 6.85 0.51 6.90 0.52 7.07
4I9/2 0.25 2.01 0.28 2.67 0.29 2.76 0.28 3.01 0.29 3.18 0.28 3.13
4G5/2→
2G7/2 0.00 0.01 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02
2H11/2 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.04
4F9/2 0.00 0.53 0.00 0.54 0.00 0.60 0.00 0.62 0.00 0.66 0.00 0.71
4F7/2 0.00 1.40 0.00 1.58 0.00 1.72 0.00 1.82 0.00 1.93 0.00 2.00
4S3/2 0.00 0.38 0.00 0.67 0.00 0.74 0.00 0.78 0.00 0.87 0.00 0.81
4F5/2 0.01 2.21 0.01 2.55 0.00 2.36 0.01 2.74 0.00 2.75 0.00 2.79
2H9/2 0.00 0.05 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10 0.00 0.10
4F3/2 0.01 4.24 0.01 4.50 0.01 3.93 0.01 4.70 0.01 4.58 0.01 4.78
4I15/2 0.00 0.08 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10 0.00 0.11
4I13/2 0.02 1.26 0.02 1.46 0.03 1.64 0.02 1.70 0.03 1.83 0.03 1.88
4I11/2 0.12 4.82 0.14 6.77 0.16 7.58 0.15 7.93 0.16 8.65 0.15 8.47
4I9/2 0.84 27.41 0.82 31.38 0.79 29.09 0.80 33.68 0.79 33.81 0.80 34.45
2H11/2→
4F9/2 0.00 0.11 0.00 0.12 0.00 0.11 0.00 0.13 0.00 0.13 0.00 0.14
4F7/2 0.01 0.33 0.01 0.34 0.01 0.37 0.01 0.39 0.01 0.41 0.01 0.44
4S3/2 0.00 0.04 0.00 0.07 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.09
4F5/2 0.00 0.07 0.00 0.07 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10
2H9/2 0.04 0.85 0.04 0.86 0.04 0.92 0.04 0.98 0.04 1.02 0.04 1.10
4F3/2 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.04 0.00 0.04
4I15/2 0.54 1.13 0.54 1.32 0.50 1.22 0.52 1.42 0.51 1.43 0.51 1.45
4I13/2 0.09 0.12 0.10 0.17 0.11 0.18 0.10 0.19 0.11 0.21 0.10 0.20
4I11/2 0.14 0.15 0.15 0.18 0.16 0.19 0.15 0.21 0.15 0.22 0.15 0.22
4I9/2 0.17 0.14 0.16 0.15 0.18 0.17 0.17 0.18 0.17 0.19 0.18 0.20
4F9/2→
4F7/2 0.00 0.24 0.00 0.27 0.00 0.28 0.00 0.30 0.00 0.31 0.00 0.32
4S3/2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4F5/2 0.00 0.29 0.00 0.32 0.00 0.35 0.00 0.37 0.00 0.39 0.00 0.41
2H9/2 0.00 0.09 0.00 0.09 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10
4F3/2 0.00 0.34 0.00 0.35 0.00 0.39 0.00 0.40 0.00 0.43 0.00 0.46
4I15/2 0.20 5.22 0.22 6.36 0.22 7.14 0.22 7.43 0.23 8.03 0.22 8.15
4I13/2 0.35 5.91 0.35 6.50 0.35 7.30 0.35 7.58 0.35 8.12 0.35 8.48
4I11/2 0.38 4.52 0.35 4.61 0.35 5.19 0.35 5.38 0.35 5.72 0.36 6.12
4I9/2 0.07 0.61 0.07 0.64 0.07 0.72 0.07 0.75 0.06 0.80 0.07 0.85
29
4F5/2→
2H9/2 0.00 0.01 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02
4F3/2 0.00 0.15 0.00 0.18 0.00 0.17 0.00 0.19 0.00 0.20 0.00 0.20
4I15/2 0.04 2.28 0.04 2.26 0.04 2.55 0.04 2.64 0.04 2.80 0.04 3.02
4I13/2 0.21 6.16 0.20 6.82 0.20 7.67 0.20 7.97 0.20 8.54 0.20 8.90
4I11/2 0.08 1.64 0.11 2.44 0.11 2.72 0.11 2.85 0.11 3.12 0.10 3.02
4I9/2 0.67 9.35 0.66 10.60 0.66 11.92 0.66 12.39 0.66 13.31 0.66 13.77
4F3/2→
4I15/2 0.01 0.35 0.01 0.35 0.01 0.39 0.01 0.40 0.01 0.43 0.01 0.46
4I13/2 0.13 3.62 0.10 3.59 0.11 4.05 0.10 4.19 0.10 4.45 0.11 4.80
4I11/2 0.57 10.14 0.52 10.99 0.52 12.37 0.52 12.84 0.51 13.74 0.53 14.41
4I9/2 0.30 3.73 0.37 5.47 0.37 6.12 0.37 6.41 0.38 7.01 0.36 6.80
30
Table 3.9 : Computed radiative lifetimes τR (µs), computed and experimental branching ratios ( β ) of certain lasing
transitions of Nd3+
doped glasses
BLABIN→
Transition↓ 1 2 3 4 5 6
4F3/2 → τR
cal
βR
cal
βR
exp
τR
cal
βR
cal
βR
exp
τR
cal
βR
cal
βR
exp
τR
cal
βR
cal
βR
exp
τR
cal
βR
cal
βR
exp
τR
cal
βR
cal
βR
exp
4I13/2 2149 0.13 0.02 2161 0.10 0.11 1913 0.11 0.09 1846 0.10 0.12 1735 0.10 0.12 1605 0.11 0.13
4I11/2 404 0.57 0.90 379 0.52 0.74 336 0.52 0.82 323 0.52 0.76 302 0.51 0.77 286 0.53 0.76
4I9/2 283 0.30 0.07 238 0.37 0.15 211 0.37 0.09 203 0.37 0.12 188 0.38 0.11 183 0.36 0.10
31
Table 3.10: Fluorescence peak wavelengths (λP, nm ), effective line widths (Δλeff, nm) and stimulated emission cross
sections (σe, x10
-20cm
2 ) of Nd
3+ in BLABIN glasses
Transition BLABIN→1 2 3 4 5 6
4F3/2 → λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe
4I13/2 1334 51.14 1.20 1331 54.44 1.11 1328 59.24 1.14 1331 56.57 1.25 1330 52.79 1.42 1332 57.74 1.40
4I11/2 1060 5.69 19.51 1063 8.86 13.73 1065 13.17 10.45 1060 33.59 4.18 1065 25.67 5.96 1061 34.65 4.57
4I9/2 900 56.10 0.55 904 54.44 0.84 904 54.30 0.94 907 45.08 1.21 909 41.24 1.45 914 33.60 1.80
3.3.5 Optical band gap
The optical energy band gap and cut-off wavelength were evaluated from the
absorption coefficient (α) near the edge of absorption curve for all the glasses, given by
α = 2.303 A/t where ‘A’ is the absorbance and‘t’ is the thickness of the glass sample in
cm.
The relation between α and photon energy (hν) of the incident radiation is given by [90]
α = B(hν – Eopt )2 / hν …(3.4)
where B is a constant and Eopt is optical energy band gap.
To obtain indirect band gap, (α hν)2 vs hν graph, shown in Fig 3.6(a), is drawn and
the linear region is extrapolated. Direct band gap is obtained by the extrapolation of the
linear region of the plots of (α hν)1/2 vs hν, shown in Fig 3.6(b).
Values of indirect and direct mobility gap and cut-off wavelength for BLABIN:1-6
samples are collected in Table 3.11. Both indirect and direct mobility band gap values
show a maximum for 0.5 mol% and a minimum for 3 mol% concentration of Nd2O3 .
Both the band gaps show the same trend of variation with concentration i.e. 0.1 to 0.5
mol% increase , 0.5 to 1.0 mol% decrease, 1.0 to 1.5 mol% increase and then up to 3.0
mol% decrease is observed, similar to the earlier report [21]. Cut-off wavelength has
opposite trend to both direct and indirect optical band gaps. It is interesting to note that
the variation of optical energy band gap and 2 with Nd3+
ion concentration (Tables3.5
and 3.11) have similar trend. Small increase in Nd2O3 and corresponding small decrease
in B2O3 influence the optical band gap on which switching action depends.
Table 3.11: Optical band gaps and cut-off wavelengths of Nd3+
doped glasses
Parameter BLABIN1 BLABIN2 BLABIN3 BLABIN4 BLABIN5 BLABIN6
Indirect mobility
gap(eV) 3.64 3.68 3.66 3.67 3.65 3.63
Direct mobility gap
(eV) 3.61 3.66 3.62 3.64 3.62 3.61
Cut-off wavelength
(nm) 337 334 336 335 336 338
The variation in optical band gap values can be attributed to similar variation in
the phonon-assisted indirect transition [85]. The decrease in optical band gap at higher
concentrations of Nd2O3 might be due to the increase in the number of non-bridging
oxygen atoms [25]. Lower band gap values indicate the low phonon energies and high
lasing efficiency.
3.3.6 FT-IR spectral analysis
In order to obtain more information about the local structure of the present borate
glasses FT-IR spectra were recorded in the region 4000-400 cm-1
, Fig 3.7. The absorption
peaks in FT-IR spectra can be divided into four main groups in the ranges 3600-2300
cm-1
, 1600-1200 cm-1
, 1200-800 cm-1
and 700-400 cm-1
[87]. The various IR peaks
observed in the glass systems are given in Table 3.12. It is known that boron exhibits
more than one stable configuration. The addition of PbO, Bi2O3 and Al2O3 to the borate
network, changes the boron coordination from three (BO3-) to four (BO4
-) [5]. This
result in the formation of di-, tri-, tetra- and pentaborate groupings, linked together, form
the glass 3D network. The broad bands extending from 3900-3300 cm-1
are due to
hydroxyl groups whose presence may be due to the KBr pellet technique used to record
the IR spectra. The group of bands in the region 1600-1200 cm-1
is due to the asymmetric
stretching relaxation of the B-O bond of trigonal BO3 units, the group of bands in the
region 1200-800cm-1
is due to the B-O bond stretching of the tetrahedral BO4 units and
the other group of bands in the region around 700 cm-1
is due to the bending of B-O-B
linkages in the borate networks [5]. The absence of absorption peak at 806 cm-1
in all the
samples of glasses indicates that there is no boroxol ring formation [87]. This indicates
that the glass structure consists of BO3 and BO4 groups [87-89]. The variation of the
doping concentration of Nd3+
ions result in the structural changes in the 3D glass
network as well as in the local environments of the Nd3+
ions, evident from Fig 3. 7. The
presence of Nd3+
ions seems to influence the surroundings of Bi3+
cations favoring the
formation of BiO6 units [88]. With increasing concentration of Nd3+
ion the vibrations of
BO3 units, Al-O vibrations ~ 1734 cm-1
, Al-O vibrations at ~ 762 cm-1
, BiO6 units due to
Bi-O bend at nearly 580 cm-1
and octahedral units due to Bi-O bend at nearly 473 cm-1
are much affected. The stretching of vibrations at nearly 1048, nearly 1384 nearly 1461
and nearly 1631 cm-1
are unaffected due to increasing concentrations. The stretching
vibrations of network forming oxides result large phonon energies and these effectively
reduce probabilities of radiative processes and luminescent efficiencies of the systems.
Table 3.12: Assignments of FT-IR in Nd3+
doped BLABIN :1-6 glasses
Wavenumber
(cm-1
)
FT- IR assignment
~ 473 Bi-O bend in BiO3 units [36] and stretching vibration in PbO4 [37]
~578 Bi-O bend in BiO6 units [36]
~694 B-O-B angle bending vibrations from pentaborate groups [37]
~762 Al-O vibrations [35]
~1048 BO4 vibrations and stretching vibrations of B-O-Bi linkages [8]
~1384 B-O vibrations various borate rings [8]
~1461 B-O stretching vibrations of BO3 units in chain and ring type
metaborate groups [37]
~1631 Bending modes of OH groups [37], Vibrations of bridging oxygen
atoms between BO3 and BO4 groups [ 38]
~1734 Vibrations of BO3 units [37]
~2330 O-H bond stretching vibrations [8]
~2854 Hydrogen bonding [34]
~2924 Hydrogen bonding [34]
~3437 Characteristic stretching of OH- groups [34]
~3852 Characteristic stretching of OH- groups[34]
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
0.0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100.0
cm-1
%T
NDC1
3437
2924
2854
2330
1734
1631
1461
1384
1048
784
762
694
578
473
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
0.0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100.0
cm-1
%T
NDC2
3432
2924
2853
2321
1629
1462
1382 1044
719
588
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
0.0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100.0
cm-1
%T
NDC33852
3436
2924
2854
2332
1457
1384 1049
690
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
0.0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100.0
cm-1
%T
NDC4
3428
2923
2853
2334
1628
1508
1460
1377
1048
721
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
0.0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100.0
cm-1
%T
NDC6
34392924
2854
2322
1626
1456
1383
1053
684
494
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
0.0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100.0
cm-1
%T
NDC5
3438 2924
2853
2345
1461
1384
1046
686
Fig . 3.7. FT-IR spectra of BLABIN : 1-6 (NDC:1-6) glasses.
3.4. CONCLUSIONS
The Nd3+
doped heavy metal oxide lead-bismuth-aluminum-borate glasses have
been fabricated and characterized for their lasing potencies. The numerical aperture is
0.25 for all the glasses indicating these are potential candidates for core material of
optical fiber. The low rms deviation values obtained in the fitting analysis for
experimental and calculated band positions support the validity of the evaluated
spectroscopic parameters. The Slater integrals F2/F
4 and F
2/F
6 are in agreement with the
other reported works. The bonding observed in the glasses is of covalent in nature. The
spectroscopic quality factor χ less than unity indicates these glasses are good lasing
candidates. Ω4 and Ω6 values indicate that the rigidity of the present glasses under study
increases with increasing concentration. BLABIN:1 glass has χ = 0.38 equivalent to
that of Nd:YAG laser indicating it as a good lasing material. The values of branching
ratios (R) and emission cross sections (e) obtained for all the glasses are of high in
magnitude for the lasing transition 4
F3/24I11/2 indicating the investigated glasses may
be good laser hosts. The indirect and direct mobility gap values show a maximum for 0.5
mol% and minimum for 3.0 mol% concentration and decreasing trend from 1.5 to 3.0
mol% of Nd2O3, indicating the decrease in the phonon energy and hence increase in
lasing efficiency with increase of concentration. Hence these glasses have good switching
action and lasing potencies.
The structural changes in the 3D glass network as well as in the local
environments of the Nd3+
ions take place due to the variation of the doping concentration
of Nd3+
ions, evident from FT-IR spectra. The coexistence of trigonal BO3 and
tetrahedral BO4 units was evidenced by FT-IR spectroscopy and the increase of PbO
content to the glass matrix promotes the conversion of some BO3 units to BO4.