Colloidal and photonic crystals

Colloidal and photonic Colloidal and photonic crystalscrystals

Prepared by group 4:

Anna Kaczmarczyk

Aleksandra Jayko

Katarzyna Mocniak

Michał Kaczmarek

Paweł Lis

Outline:

1. Colloidal crystals with tunable colors and their use as photonic papers

2. Photonic crystals from core-shell colloids with incorporated highly fluorescent quantum dots

3. Dye-containing polymer beads as photonic crystals

4. Heterostructures of polymer photonic crystal films

5. Laboratory nanoparticles - report

Colloidal and photonic Colloidal and photonic crystalscrystals

Colloidal crystals with tunable colors and their use as photonic papers

What are the colloidal crystals?

They are long-ranged ordered lattice assembled from spherical colloids such as polymer latexes and silica spheres.

By organizing such colloids into crystalline lattice it is possible to obtain interesting functionality. This beautiful indescent color of an opal orginates from Bragg diffraction of a crystalline lattice assembled from silica colloids that display no color by themselves.

The similar mechanism has also been used by a variety of insects – butterflies, bees to decorate their skins with shiny colors without involving the use of any conventional pigments.

Colloidal crystals with tunable colors and their use as photonic papersColloidal crystals with tunable colors and their use as photonic papers

Bragg equation

Where:m – diffraction order- wavelength of the diffracted lightna- a mean refractive index of the crystalline latticedhkl – the interplanar spacing along the [hkl] direction - the angle between the incident light and the normal to the [hkl] planes

This equation suggests that of light diffracted from a colloidal crystal is directly proportional to the lattice constant.


Printing colorful patterns without using convetional pigments

The concept of this new paper ink system has already been reported in communication

Basically the „paper” is a colloidal crystal of polymer beads embedded in an elastomer matrix made of PDMS, whereas the „ink” is a liquid capable of swelling the

elastomeric matrix.

As the elastomer is swollen by the ink molecules, the lattice constants are changed.


If the colors of these states are sufficiently different to be distinguished by the naked eye, the contrast can be exploited to write and display color letters and patterns with certain spacial resolutions.

As the ink molecules are evaporating the PDMS matrix will gradually shrink back to its orginated state and the color patterns will be automatically erased.

Photonic crystals from core-shell colloids Photonic crystals from core-shell colloids withwith

incorporated highly fluorescent quantum incorporated highly fluorescent quantum dotsdotsWe are presenting the synthesis of composite Photonic Crystals (PCs) from

polymer core-shell spheres with incorporated highly fluorescent monodisperse CdSe QDs in the core. The steps how to prepare are listed below:

1. Synthesis of CdS/ZnS Coated CdSe Quantum Dots using succesive ion layer adsorptions reaction (SILAR), keeping up the light-emitting properties of the PC on the Photoluminescens.

2. Synthesis of PS Core Colloids with incorporated CdS/ZnS QDs with modyfied miniemulsion polymerization.

3. Synthesis of PS/PMMA Core-Shell Colloids with incorporated CdS/ZnS Coated CdSe QDs in the Core prepared by a core-shell polymeryzation.

4. Crystalization of the Core-Shell Spheres to Colloidal Crystals.

Photonic crystals from core-shell colloids withPhotonic crystals from core-shell colloids with incorporated highly fluorescent quantum incorporated highly fluorescent quantum dotsdots

Schematic illustraton of QD incorporation into the core of core-shell colloids.

Photonic crystals from core-shell colloids Photonic crystals from core-shell colloids withwith incorporated highly fluorescent quantum incorporated highly fluorescent quantum dotsdots

Up to now semiconductors QDs have been incorporated into the voids of colloidal crystals by:

1. In-situ growth methods (chemical vapor and chemical or electrochemical bath deposition).

2. Electrostatic fixation on the surface of the polymer sphres being subsequently crystalized to artificial opals.

There are several disadvantages of this process:

1. Incorporation of QDs into the voids of colloidal crystals does not protect the QDs from oxidation.

2. In-situ growth methods do not allow the formation of high-quality QDs known for low polydyspersity and strong photoluminescence (PL).

3. Requirement of thioglycolic acid that are well-known PL reducing agents.

Photonic crystals from core-shell colloids Photonic crystals from core-shell colloids withwith incorporated highly fluorescent quantum incorporated highly fluorescent quantum dotsdots

The effect of the colloidal crystal photonic stop band on the PL of the integrated QDs was investigated by angular-dependent fluorescence measurements. The measurements were performed in reflection and the PL was excited with an argon ion laser at 457,9 nm.

Photonic crystals from core-shell colloids withPhotonic crystals from core-shell colloids with incorporated highly fluorescent quantum incorporated highly fluorescent quantum dotsdots

By doping PCs with fluorescent QDs, discrete electronic and photonic states can be combined as well as separately engineered within a single structure. This presents a powerful platform for the creation of novel nanoscaled light sources its controllable spontanous emission.

Dye-containing polymer beads as photonic crystalsDye-containing polymer beads as photonic crystals

Photonic crystals are periodic dielectric structures that are designed to control the propagation of electromagnetic waves by defining allowed and forbidden energy bands in the phonon dispersion spectrum.

Photonic crystals are prepared from PMMA

Monodisperse PMMA beads of a size varying between 200-400 nm have been prepared by a modified emulsion polimerization sediment well on hydrophilic substraces to form 3- dimentional face-centered cubic packages. This method allows it to cover large films with opaline structure with can be used as photonic crystals.


Advantages of using PMMA are:

1. PMMA photonic film can be precisely patterned by e-beam lithography with the feature resolution down to one bead in width and various fluorescent dyes can be incorporated in PMMA balls.

2. Dye-impregnated PMMA opaline photonic films demonstrate the incomplete photonic band gap structure and related modification of dye photoluminescence spectrum.

3. PMMA is more polar as compared with polystyrene and thus a better sovent for the fluorescent dyes.Incorporation of dye molecules in PMMA balls can be performed much easier as compared with the similar procedure used in the case of silica balls.


Preparation of the PMMA Beads:

• preparation of films• determination of the size of the beads• patterning by electron beam writing

Conclusion:PMMA beads are ideal candidates for the preparation of thin film photonic structures with optical properties comparable to the best bulk opals. They have the advantage that they can be patterned as e-beam resists. In addition they are more polar than polystrene and thus a better matrix for various fluorescent laser dyes.

Heterostructures of polymer photonic crystal filmsHeterostructures of polymer photonic crystal films

Photonic crystals are attracting a lot of attention as materials for optical switches, data storage, chemical sensors and lasers with low threshold.

We describes multilayer opaline films composed from functional opal layers of spheres with different lattice constants.

Various monodisperse colloids can be crystallized into large, well oriented opaline films by the method of crystallization in a moving meniscus.

After annealing, a second opaline film can be crystallized on top of these films and so on.


Schematic illustration of the crystallization in a moving meniscus:


Electron microscopy inspection shows a sharp borderline between the sublayers and no disorder on both sides athough the lattice constants in both films can be incommensurable.


Generally, the film thickness depends on such parameters as:

Lifting speed,

Solution concentration,

Temperature,

Air humidity,

Sphere size.

Dependence of the film thickness on the suspension concentration for PMMA latice

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Transmission and reflection measurements prove the high quality of the films.

The use of a combination of thermolabile and thermostable colloids opens the possibilty to prepare functional opaline heterostructures.

Laboratory nanoparticles - reportLaboratory nanoparticles - report

Substance Purity

Zinc acetate ~98 %

Mangan acetate ~98 %

Sodium sulphide ~60 %

Cysteamin ~97 %

Ethanol Technical

Acetic acid Technical

Absolute mass

2,253 g Zn(Ac)2

0,478 g Mn(Ac)2

0,941 g Cysteamin

0,465 g Na2S

In 125 ml H2O

In 25 ml H2O

Chemicals which were used in experimental part

Preparation and charakterization of ZnS:Mn nanoparticles


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Record 75: ZnS:Mn grupa 4 -pH 4.82 Record 76: ZnS:Mn grupa 4 -pH 4.82

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Record 75: ZnS:Mn grupa 4 -pH 4.82 Record 76: ZnS:Mn grupa 4 -pH 4.82

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Thank you for your attention !!!Thank you for your attention !!!

Colloidal and photonic crystals

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