52

Optical and structural investigation of Sm3+–Nd3+ co-doped in

Magnesium lead borosilicate glasses

3.1 Introduction:

Magnesium lead borosilicate glasses have extensive applications in various

fields such as astronomical, thick film technology, dielectrics and sealant

materials for solid oxide fuel cells. These glasses are one of the choices in

thermal technology due to heat resistance and also for fluorescence centers in

optical devices [1-6]. More over an extensive research activity has been

conducted on the borosilicate glasses for immobilization of the different

streams of nuclear wastes. Due to the ability of glasses to act like a solvent for

high-level wastes (HLW), the fairly low processing temperatures involved, as

well as their good chemical durability and radiation resistance. Recently glass

materials are one of the possible alternatives to concrete because they can be

transparent to visible light and their properties can be modified by composition

and preparation techniques.

The properties of glasses are closely related to inter-atomic forces and

potentials in lattice structure. Thus, any change in lattice due to doping and/or

irradiated can be directly noted using spectroscopic techniques. Rare-earth

ions are incorporated in these glasses, further increases their potential

applications in optoelectronic and high-density optical memory devices

because of abundant number of the absorption and emission bands arising

from the transitions between the energy levels [7, 8]. Among different rare

53

earth ions, samarium containing glasses exhibits to have an unusual elastic

behavior due to valance instability and widely used with different potential

application for high-density optical memory like under sea communication,

color display and gives red color emission, sometimes shifted to longer

wavelengths glass matrix that provide high gain for producing efficient laser

host material [9-12]. The spectral studies of Sm3+ ion (4f5) doped in glasses are

complicated when compared with other rare earth ions. Because a large

number of energy levels lying close to each other make the interpretation of

the absorption spectrum of this ion rather difficult for the determination of

meaningful intensity parameters needed in the calculation of various radiative

properties. On the other hand luminescence intensity in the spectral region can

be increased by co-doping in the host.

In this paper, Nd3+ ions are used as co-dopant along with Sm3+ ions in

magnesium lead borosilicate glasses. Most of the research has concentrated on

the Nd3+ ions incorporated amorphous and crystalline materials due to their

efficient infrared 4F3/2→4I13/2, 11/2, 9/2 with emissions at wavelengths around

1350, 1064 and 946 nm which finds potential applications in tunable, ultrafast

laser medium and promising materials for a high-efficiency solid-state laser.

First of all Snitzer [13] investigated on the trivalent neodymium (Nd3+) -

doped glasses, which turned as considerable progress in evaluating the effect

of the amorphous host matrices on the Nd3+ ion. Over the past several decades,

lot of work has been reported on the luminescent properties of Nd3+ ions in

54

different glass matrices which include phosphates, silicate, borates, sulphates,

tellurites, chalocogenides, and bismuth-borate, germinate [14-23]. Whatsoever

the spectroscopic characteristics of a trivalent rare-earth ion depend on the

surrounding host matrix due to considerable influence of ligand field effect. In

this paper, we are investigating spectroscopic and structural characteristics of

Sm3+ ions in MgO–PbO–B2O3–SiO2 glasses co-doped with Nd3+ ions using

XRD, Optical absorption, Luminescence, FT-IR, Raman spectral technique.

As mentioned in chapter-II, the details of the compositions of investigating

glasses (MgO–PbO–B2O3–SiO2–Nd2O3/Sm2O3 glasses) are given in the

following Table 1.

Table 1

Summary of glass compositions

S. No Glass codes MgO PbO B2O3 SiO2 Nd2O3 Sm2O3

mol% mol% mol% mol% mol% mol%

1 Pure 9.5 40.0 25.0 25.0 0.5 -

2 Sm1 9.0 40.0 25.0 25.0 0.5 0.5

3 Sm2 8.5 40.0 25.0 25.0 0.5 1.0

4 Sm3 8.0 40.0 25.0 25.0 0.5 1.5

5 Sm4 7.5 40.0 25.0 25.0 0.5 2.0

55

3.2 Brief review of previous work on the glasses containing Samarium ions:

M. Jayasimhadri et al [24] studied on the spectroscopic characteristics of

Sm3+-doped alkali fluorophosphate glasses. In their investigation, these glasses

suitable for strong orange-red luminescence with high potential laser

applications. P. Raghava Rao et al [25] investigated on the fluorescence

features of Sm3+ ions in Na2SO4–MO–P2O5 glass under the influence of

different modifier oxide (MgO/ CaO/ BaO). They concluded that the structural

changes in the vicinity of the Sm3+ ion is higher for MgO mixed glasses

whereas the quantum efficiency is found to be the highest for BaO mixed

glasses, indicating that these glasses exhibit better luminescence efficiency.

Therefore the modifier strongly influences the optical properties of Sm3+. Y. K

Sharma et al [26] investigations also supported these results. M. Nogami et al

[27] studied the redox reaction of the samarium ions by means of first-order

kinetics and they observed that the modifier like Al2O3 effectively influences

the redox equilibrium. E. Malchukova et al [28, 29] also suggested that γ- rays

also influence the redox reaction.

B. H. Rudhrama devi et al [30] invented novel optical glasses for

applications as potential luminescent amorphous material by using Sm3+ ions

in B2O3-BaO-LiF/AlF3. B. C. Jamalaiah et al [31] in their investigation, at

lower concentration of Sm3+ (0.1 mol %) the decay curves show single-

exponential whereas for higher concentrations they become non-exponential.

The decrease of lifetime at higher concentrations is due to the cross-relaxation

56

between excited Sm3+ ions unexcited Sm3+ ions in the ground state and atoms

of host lattice. They concluded that 1.0 mol % Sm3+-doped LBTAF glass may

be used as laser active medium for emission at 600 nm corresponding to the

4G5/2→6H7/2 transition. The energy transfer processes between Sm3+ ions and

different sites in the host lattice is also investigated by Fuxi Gan et al [32],

Siby Mathew et al [33]. G.-H. Lee et al [34] used Sm3+ ions as optical

sensitizer for white light emission in europium ions doped potassium

tungstate. R. Van Deun et al [35] mentioned that samarium ions doped glasses

are sitable for orange emission. M. Seshadri et al [36] investigated on the

spectroscopy and laser properties of Sm3+ doped different phosphate glasses,

they concluded that calcium phosphate glass shows higher spectral intensity

whereas sodium potassium glass matrix shows higher spectral intensity for the

hypersensitive transition indicating higher covalency of RE–O bond in these

glass matrices. C. K. Jayasankar et al [10] investigated on the high-pressure

fluorescence study of Sm3+-doped borate and fluoroborate glasses, in this work

they observed that with an increase in pressure, the positions of the emission

bands are shifted to the lower-energy side (red shift) due to changes in the

overlap of the ligand orbitals with the 4f wave functions of the Sm3+ ions.

K.S.V. Sudhakar et al [37] studied the effect of different modifiers on the

spectroscopic and thermo luminescence characteristics of Sm3+ ion in

antimony borate glasses, finally they suggested that CaO mixed glasses

indicating that these glasses exhibit better lasing action.

57

In the same way number of researcher like K. Bhargavi et al [12] Takayuki

Hirao et al [38], Shunsuke Murai et al [39], Hongpeng You et al [40] and

Zhijian Shen [41] also done a lot of work on the Sm3+ ions doped glasses/

cramics and given important results which are help us for the future studies.

3.3 Results:

3.3.1 Physical parameters:

The density is one of the important physical properties of the material

that can be used to derive thermal conductivity, elastic properties and

important parameter to know about the materials (glasses). Using conventional

formulae [42-45], practically measured density (d) and refractive index (The

error in density measurements and refractive indices are estimated to be ±

0.004 g/cm3 and ± 0.0001 respectively) various physical parameters such as

samarium ion concentration (Ni), mean separation (ri), polaron radius (rp), field

strength (Fi), electronic polarizability (α), reflection loss and optical dielectric

constant (ε) in the present glass network can be calculated and are furnished in

the Table 2.

3.3.2 X-ray diffraction spectra:

Fig. 1 shows the typical X-ray diffraction patterns of MgO–PbO–B2O3–

SiO2–Nd2O3/Sm2O3 glasses. The patterns consist of a broad bump centered at

around 270 (= 2θ) and no shape lines are observed which suggests that all the

prepared glass samples confirm the amorphous (glassy) nature.

58

Table 2

Various physical parameters of Sm3+ ions in MgO–PbO–B2O3–SiO2–Nd2O3 glasses.

S.No Physical Properties Glasses

Pure Sm1 Sm2 Sm3 Sm4

1 Density D (g/cm3) (± 0.004)

5.2248 5.2342 5.2373 5.3505 5.3552

2 Rare earth ion concentration Ni(1019ions/cm3)(± 0.005)

=(%)

- 1.24 2.42 3.67 4.79

3 Refractive index nd (± 0.0001)

1.7862 1.7865 1.7892 1.7897 1.7898

4 Interionic distance ri (A

0) (± 0.005)

r = 1

/

- 43.24 34.57 30.10 27.53

5 Polaron radius rp (A

0) (± 0.005) r =

1

2

6/

- 17.42 13.93 12.13 11.09

6 Field strength Fi (1013cm-2) (± 0.005)

=

- 9.88 15.46 20.39 24.38

7 Electronic polarizability αe

(10-21ions/cm3) (± 0.005) =3(n

− 1)

4(n + 2) - 8.24 4.18 2.76 2.11

8 Reflection loss = n − 1

n + 1

0.0796 0.0797 0.0801 0.0801 0.0801

9 Molar refractivity RM (cm− 3) (± 0.005)

= n

− 1

n + 2

10.28 10.38 10.53 10.43 10.64

10 Optical dielectric constant (± 0.005)

= 3.1905 3.1916 3.2012 3.2030 3.2015

59

3.3.3 Fourier Transmission Infrared Spectra:

The FT-IR spectra of the Sm3+-Nd3+ co-doped magnesium lead borosilicate

glasses are given as Fig 2. The data related to FT-IR spectra is given in Table

3. The characteristics of FT-IR spectra are presented as follows

1. In the FT-IR spectra, we observed conventional bands at about 527-

532, 566-575, 605-609 and 692-696 cm-1 their intensities are modified

with content of MgO in the glass network.

60

2. After that an intensive wide band is observed at around 900 cm-1. Due

to Sm3+ ions doping a degeneracy of this band is visualized.

3. The spectra reveal intense broad bands at about 1690, 1550/1520, 1320,

1240 cm-1 in the range 1200-2000 cm-1.

4. Weak OH— vibrations are observed in the range 2000-4000 cm-1.

3.3.4 Raman spectra:

Fig 3 represents the Raman spectra of the Sm3+-Nd3+ co-doped in

magnesium lead borosilicate glasses. The vibrational band intensities in the

spectra are increased with the varying content of Sm3+ ions in glass network.

The data related to the Raman spectra is furnished in the Table 4. The main

features of the Raman spectra in the present investigation listed as

1. In the pure glass, intensive bands are revealed at around 973 and 1250-

1460 cm-1. Along with these bands weak bands are observed at lower

wave number side.

2. By the addition of Sm3+ ions, the sharp band at 973 cm-1 becomes wider

and weak bands at lower wave number side clearly resolved with

increasing the content of Sm3+ ions in the glass network.

61

62

Table 3

Observed FT-IR band positions (cm-1) Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses

Glasses Band assignments

pure Sm1 Sm2 Sm3 Sm4

1693 1693 1690 1695 1689 Water molecular vibrations

1546 1549 1546 1547 1549 Stretching modes of Si–OH/ B–O bond stretching of the

tetrahedral BO4units 1516 1512 1514 1515 1514

1326 1326 1326 1325 1328 Symmetric stretching relaxation of the B–O band of trigonal

BO3units

1236 1239 1234 1235 1239 Stretching vibrations of B–O of the BO3 units from the boroxol

rings

897 897 895 898 896 Si–O–Si Anti-symmetric stretching of bridging oxygen within the

tetrahedra - 858 856 859 857

696 692 694 693 695 Bending vibrations of B–O–Si linkages

605 605 609 606 604 Symmetric stretching vibration of Si–O–Si

566 572 568 570 575

527 527 528 530 532 Bending vibrations of Si–O–Pb

63

64

Table 4 Raman band positions (cm-1) of Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses

Glasses Band assignments

pure Sm1 Sm2 Sm3 Sm4

1455/1402 1451 1453 1453 1451 Stretching vibrations of B–O–B bond in BO4 units from different

borate groups 1366 1347 1360 1352 1354

- - 1275 1272 1270

- - 1165 1164 1162 Asymmetric vibration of Si-O in Q4 groups.

973 971 971 971 971 The vibrations of SiO4tetrahedra with two non-bridge oxygen

atoms Q2

919 920 924 920 920 Symmetric stretching vibrationsfrom an Si2O76- unit

- - 849 845 843 Symmetric stretching vibrations from an SiO44- units

721 726 733 733 737 Symmetric breathing vibrations of six members rings with two

BO4units (ditri- or dipenta-borate)

632 656 656 660 662 Symmetric breathingvibrations of meta-borate rings

- 612 614 612 590 Symmetric stretching and partially deformation vibrations of Si–

O–Si bridges

455 460 464 464 468 B–O–B bending vibrations along with Si–O network vibrations

65

3.3.5 Optical absorption spectra:

Fig 4 is the optical absorption spectra of pure and Sm3+ ions doped glasses

respectively. The MgO–PbO–B2O3–SiO2–Nd2O3 (pure) glass exhibits absorption

bands (Vis-NIR region) at 431, 473, 512, 526, 583, 624, 683, 747, 804 and 876 nm

[46, 47]. These bands are attributed to the neodymium ions (Nd3+) in the glass

network which act as spectra material and the assignments of these transitions

have been made on the basis of the Carnall et al [48-50].

Nd3+: 4I9/2 → 2P1/2, 4G11/2 + 2D3/2+ 2G9/2+ 2K15/2,

4G9/2, 4G7/2,

2G7/2+ 4G5/2, 2H11/2,

4F9/2, 4S3/2+ 4F7/2,

4F5/2+2H9/2 and 4F3/2

Intensive broad bands are revealed in the range 1000-1900 nm are due to host

glass absorption. Non-crystalline disorder is obviously responsible for the

significant inhomogeneous broadening of the absorption features. When Sm3+ ions

are introduced into the glass network, additionally we observed absorption bands

at 402, 944, 1078, 1225, 1372, 1479, 1526 and 1583 nm. This is due to samarium

ions and corresponding transitions are given as follows [30, 51 and 52].

Sm3+: 6H5/2→4F7/2,

6F11/2, 6F9/2,

6F7/2, 6F5/2,

6F3/2, 6F1/2 and 6H15/2

The intensity half widths of all the bands in NIR region are slightly modified

by the increasing contents of Sm3+ ions in the glass network. Theoretical and

experimental oscillatory strengths are presented in the Table 5.

66

67

Table 5

Theoretical and experimental oscillatory strengths of Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses

Transitions

6H5/2→

Sm1 Sm2 Sm3 Sm4

fexp,(x 10-6) fcal, (x 10-6) fexp, (x 10-6) fcal, (x 10-6) fexp, (x10-6) fcal, (x 10-6) fexp,(x 10-6) fcal, (x 10-6)

6F1/2 1.46 1.59 1.41 1.53 1.39 1.44 1.37 1.31

6F3/2 1.61 1.73 1.65 1.74 1.58 1.69 1.62 1.57

6F5/2 2.33 2.37 2.28 2.35 2.36 2.42 2.28 2.39

6F7/2 4.66 4.79 4.64 4.62 4.54 4.72 4.59 4.44

6F9/2 2.87 2.96 2.90 2.95 2.74 2.88 2.84 2.76

6F11/2 0.74 0.82 0.78 0.77 0.72 0.67 0.69 0.59

Rms deviation ± 0.1035 ± 0.0712 ± 0.1101 ± 0.0976

68

3.3.6 Luminescence spectra:

Fig 5 shows the luminescence spectra of Sm3+-Nd3+ co-doped magnesium lead

borosilicate glasses recorded with an excited wavelength 355 nm in the region

375-1200 nm. Sm3+ ions free glass network shows an intensive luminescence band

at about 900 nm and a weak band are observed at 1060 nm. The luminescence

spectra of glasses containing Sm3+ ions exhibits four luminescence bands (at about

562, 599, 646, 708 nm) [24, 31, 53- 57] in the visible-NIR range and other one at

about 900 nm. By introduced of Sm3+ ions following changes are observed in

spectra

1. In the range 750-1200 nm, the intensity of emission band at about 900 nm

is reduced and neighboring weak bands are diminished.

2. In the visible range, a weak broad band from 400-500 nm is observed.

3. On the basis of Judd–Ofelt theory, J–O intensive parameters, transition

probabilities (A) and branching ratios (β) of emission transitions are

estimated and given in Table 6, 6A.

4. Table 6B is the comparison of branching ratio of 4G5/2→6H7/2 transition

with earlier data.

69

70

Table 6

J–O parameters of Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses.

Glasses Ω2(x 10-20) cm-2 Ω4(x 10-20) cm-2 Ω6(x 10-20) cm-2

Sm1 4.58 4.23 3.27

Sm2 4.36 4.01 3.42

Sm3 4.44 4.18 3.25

Sm4 4.26 3.94 3.01

Table 6 B

The comparison of branching ratio of 4G5/2→6H7/2 transition with earlier data

Glass systems Branching ratio

β (%)

Reference

Present work (Sm4) 51.25 -

Alkali fluoro phosphate glasses (NaTFP) 50.14 24

LBTAF glasses 50.0 31

P2O5–PbO–Nb2O5 glasses 52.0 53

Bi2O3-B2O3 glasses (BBS60) 37.4 54

Fluoride containing phosphate glasses 56.0 55

71

Table 6 A

Various radiative properties of Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses.

Transitions Glass samples

Sm1 Sm2 Sm3 Sm4

A (S-1) β(%) A (S-1) β(%) A (S-1) β(%) A (S-1) β(%)

4G5/2→6H11/2 30.2 11.97 31.2 13.00 28.9 11.18 29 11.48

4G5/2→6H9/2 67.2 26.65 68.6 28.57 69.2 26.78 69.2 27.38

4G5/2→6H7/2 126.3 50.08 119.2 49.65 132 51.08 129.5 51.25

4G5/2→6H5/2 28.5 11.30 21.15 8.81 28.3 10.95 25 9.90

AT (S-1) 252.2 240.15 258.4 252.7

τR (ms) 3.965 4.164 3.870 3.957

72

3.4 Discussions:

The physical properties are very interesting and offer valuable

information regarding the conduction mechanism of glasses due to transport of

ions. In the present work, the density and refractive index are varied linearly

(increased) with Sm2O3in the glass network because heavy metal oxide is

replaced by alkali earth oxide which has comparatively low density.

In borosilicate glasses, SiO2, B2O3 are the basic glass formers because

of their higher bond strength. PbO in general acts as modifier (normally the

oxygens of PbO break the local symmetry while Pb2+ ions occupy interstitial

positions). The structural units such SiO4, BO3, BO4 and PbO4 units in the

Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses are responsible for

the infrared spectra. Generally SiO2 is expected to exhibit four fundamental

absorption bands ν1 (755–800 cm−1), ν2 (680 cm−1), ν3 (1020–1175 cm−1), and

ν4 (460 cm−1) which can be attributed to symmetric stretching vibration,

symmetrical bending vibration, asymmetrical stretching vibration, and

asymmetrical bending vibration of Si–O–Si respectively. On the other hand,

the borate network have strong vibrational modes which are active in three

infrared spectral regions, (i) the first group of bands which occur at 1200–1600

cm–1 is due to the asymmetric stretching relaxation of the B–O band of

trigonal BO3units, (ii) the second group lies between 800 and 1200 cm–1and is

due to the B–O bond stretching of the tetrahedral BO4 units and (iii) the third

73

group is revealed around 700 cm–1 and is due to bending of B–O–B linkages

in the borate networks. It is also quite likely that the vibrations due to PbO4

structural groups are also present; in fact the vibrational band due to PbO4

units lies at around 470 cm−1 [58-61].

1. We observed four conventional bands at around 527, 600/ 560-580, 700

cm-1. These bands are attributed to the Si–O–Pb bending vibrations,

Symmetric stretching vibration of Si-O-Si, Bending vibrations of B–O–

Si linkages respectively.

2. An intensive wide band is observed at about 900 cm-1. Additional band

is observed at 858 cm-1 in case of Sm3+ doped glasses which are due to

Si–O–Si anti-symmetric stretching of bridging oxygen within the

tetrahedra.

3. We observed intensive wide peaks at about 1690, 1550, 1520, 1320,

1240 cm-1. Molecular water, stretching modes of Si–OH/ B–O bond

stretching of the tetrahedral BO4 units, symmetric stretching relaxation

of the B–O band of trigonal BO3 units, stretching vibrations B–O of the

BO3 units from the boroxol rings are responsible for these bands

respectively.

The gradual increase of Sm3+ ions, strongly influence the local field of the

lead ions which may disrupt the bonds connecting neighboring [BO3], [BO4]

74

and [SiO4] groups and can be incorporated into the glass as network-forming

Pb-O groups which causes coordinate defects known as dangling bonds along

with non-bridging oxygen ions. The variation of the intensities and band

position are not seen clearly which suggested that the introduction of Sm3+

ions into the glass network; these ions are occupied in the structural frame

work of the glass by means of making connection with the two additional

oxygens through dative bond. Stoch and Sroda [62] suggested that the glass

network gradually polymerized with reducing the content of the modifier ions

like Na+, Ca2+ and Mg2+ and MgO contributes to the weakening of glass

network and reduces the stability of the glass structure. Since the additional

oxygen required for the coordination conversion (B3+↔ B4+) to polymerization

of network are naturally provided by rare earth oxide (Nd2O3, Sm2O3) present

in the glass or even by a further molecule of lead oxide.

The Raman spectroscopy is more sensitive than FT-IR spectroscopy; it

provides direct information on the changes in the glass structure and is applied

to probe structural and dynamics of the glasses. The observed vibrational

bands are assigned to different structural groups according to various authors

as follows [63-68]

1. The band at about 464 cm-1 is due to B–O–B bending vibrations.

2. The weak bands in the range 590-615 cm-1 are attributed to Symmetric

stretching and partially deformation vibrations of Si–O–Si bridges.

75

Whereas 636–662 cm-1 is due to Symmetric breathing vibrations of

meta-borate rings.

3. The vibrational band at 721–737 cm-1 are assigned as symmetric

breathing vibrations of six members rings with two BO4 units (ditri- or

dipenta-borate)

4. The broad band at about 916–919 and 843–849 cm-1 presumably due to

symmetric stretching vibrations of Si2O76–, SiO4

4– units respectively.

5. An intensive sharp band in the range 969–973 cm-1 are assigned to SiO4

tetrahedra with two non-bridge oxygen atoms (Q2)

6. A weak broad band is observed at about 1162–1165 cm-1 this may be

due to symmetric vibration of Si–O in Q4 groups.

7. Broad bands are observed in the range 1270–1460 cm-1. Stretching

vibration of B–O bonds are responsible for these bands in which are

involving non-bridging oxygen (NBO) and being part of a connected

boron-oxygen network

In the Raman spectra, widening bands and increase of band intensities are

due to increase of non-bridging oxygen (NBO). Here Sm3+ ions are doesn’t

enter into glass matrix, occupies the interstials of the network.

76

All the spectra of the rare earth ions arise due to the intra-configurational

transitions within incompletely filled 4f shell. The 4f orbital lies inside the ion

and is shielded from the surroundings by the filled 5s2 and 5p6 orbitals.

Therefore the influence of the host lattice on the optical transitions within 4fn

configuration is small but essential. In the present work neodymium and Sm3+

ions are responsible for the optical absorption bands in spectra. The energy

level transition of Nd3+, Sm3+ are shown in the Fig 6.The optical absorption

spectrum for pure glass shows intensive absorptions bands in Vis-NIR regions.

When Sm2O3 is doped along with Nd2O3 in glass network, the intensity of

Nd3+ bands gradually decreases with Sm2O3 concentrations. Conversely Sm3+

ions bands intensities are increased. The peak at 402 nm tentatively attributed

to the absorption from the 6H5/2 to 4F7/2. The seven absorption bands from 900

to 1900 nm are spin-allowed transitions whereas samarium ions have spin-

forbidden transitions in the visible region and they have low intensities. Due to

the presence of PbO content, the intensity of the absorption peaks may also

decrease [69]. Hence neodymium ion transitions are dominating in the visible

range. The majority of the transitions in the spectra initiate from induced

electric dipole interactions with selection rule ΔJ≤6. Certain transitions also

contain magnetic dipole (6H5/2 to 4F7/2) contribution with selection rule ΔJ=0,

±1 [70-72]. More over most of the f–f transitions of the trivalent Sm3+ ions are

little affected by the environment. However some transitions are very sensitive

to the environment and become more intense which are called hypersensitive

77

transitions. Due to these isolated, well resolved absorption bands, we used J-O

intensity calculation to study the bonding environment of Sm3+ ions. The

spectral intensities for the observed bands in the optical absorption spectra are

often expressed in terms of oscillator strength of forced electronic dipole

transitions. Oscillator strength (f) can be expressed in terms of molar

extinction coefficient (ε) and energy of the transition in wave number (n) by

the relation [73, 74]

fexp =4.32*10−9∫ ε (υ) dυ…………………………………..(1)

Judd and Ofelt independently derived expression for the oscillator strength of

the induced electric dipole transition. It can be represented as a linear

combination three Judd–Ofelt parameters (Ω2, Ω4 and Ω6) and given as [75,

76]

=

()

∑ ,, <

>………… (2)

Here all the terms in the above equations have standard meaning, <

>are the matrix elements of the reduced unit tensor operators which

are insensitive to the ion environment in the glass and calculated by means of

intermediate coupling approximation. We have used the values of the matrix

elements as given by Carnallet al [48-50]. The J–O parameters (Ωλ) are

calculated using least squares fitting manner and the estimated values are in

the order of Ω2=4.78x10-20 cm-2, Ω4=4.43x10-20 cm-2, Ω6=3.47x10-20 cm-2

78

(Sm1). The summary of the J–O intensity parameters for all the glasses doped

with Sm2O3 is mentioned in Table 5. These crystal field parameter

determines the symmetry and the distortion associated to the structural

change in the vicinity of Sm3+ ions. Here, one thing may be understood as

follows: stronger the electrostatic attraction between cation (Si4+, B3+and Pb2+)

and anion (O2-) in glass network which leads to the average distance between

Si–O–Si, Si–O–Pb, B–O–B chains become shorter that causing the average

Sm–O distance to decrease. Such decrease in the bond lengths produces

stronger field around Sm3+ ions leading to a higher value of Ω2.

Additionally the variations in the concentration of silicate and borate

groups with different number of non-bridging oxygens and also changes

of the higher order electrostatic ligand fields as discussed above, also

play an important role in the variation of value of Ω2for glasses. Ω4 is

related to the long-range effects [77-79].

Luminescence spectra give detailed information about energy levels

splitting of dopant ions in MgO–PbO–B2O3–SiO2–Nd2O3/Sm2O3 glasses. In

the luminescence spectrum of Sm3+ ions free glass network, two luminescence

bands are noticed at 900, 1060 nm due to 4F3/2→4I9/2,

4F3/2→4I11/2 transitions of

neodymium ions respectively. On other hand, Sm3+ ions doped glasses reveal

four luminescence bands at around 562, 599, 646, 708 nm in addition to the

earlier discussed bands. These bands are attributed to 4G5/2→6H5/2,

4G5/2→6H7/2,

79

4G5/2→6H9/2,

4G5/2→6H11/2 transitions of Sm3+ ions in the glass network, the

intensities of the bands are gradually increased with Sm3+ ions concentration in

the glass network [80-82]. Moreover it is observed that the bands intensities at

900nm is rapid fall and at 1060 nm is disappeared in Sm3+ ions doped glass.

As it appears in the Fig. 6, it is quite possible for the energy transfer from 4F3/2

level of Nd3+ ion to 6F9/2 level of Sm3+ ion. Thereby Sm3+ ion get excited from

6F9/2 to 4G7/2 and subsequently de-excites to 4G5/2 via non radiative decay and

strengthens the emission transitions from 4G5/2 of Sm3+ ions. This may be the

reason for the increase in the intensity of the Sm3+ emission lines at the

expense of Nd3+ emission lines The branching ratio β value is found to be the

highest for the transition 4G5/2 →6H7/2 (near orange emission) for all the glasses

and it is found to be ~50% and found to be slightly enhanced with increase in

the concentration of Sm2O3. In several other glass systems the highest value of

β is reported for this transition of Sm3+ ions. Finally, the overall analysis of the

results of the present study indicate that the co-doping of Sm3+ ions containing

glasses with Nd3+ ions causes a significant enhancement of orange emission

transitions of Sm3+ ions in the studied glass system and makes the glasses

suitable for orange emission devices.

80

3.5 Conclusions:

Sm3+-Nd3+ co-doped magnesium lead borosilicate glasses are prepared

by using melt quenching technique. XRD spectrum reveals that the prepared

81

glasses are amorphous in nature. using Optical absorption, luminescence

spectra have been recorded and Several radiative parameters were evaluated

and the values obtained were compared with those of several Sm3+ ions doped

glass systems. The quantitative analysis of the results, with the support of FT-

IR and Raman spectral data, suggested that the co-doping of Sm3+ ions mixed

glasses with Nd3+ ions causes a significant improvement in the orange

emission of Sm3+ ions in the magnesium lead borosilicate glass system.

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