الفهرس 
CHAPTER 1 GENERAL THEORETICAL INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Lithium-Zinc-phosphate glasses of the composition: x Li2O – (45 – x) ZnO – 55 P2O5 (where 0 ≤ X ≤ 45 mol. %) were prepared by the normal melt-quenching method. The structural characterization of amorphous materials are normally extracted from the analyses of X-ray diffraction (XRD), glass density, (ρ), differential thermal analysis DTA, optical spectra (UV – vis and infrared) and electrical conductivity σdc.
In the present studies all the above mentioned techniques are applied for carrying out the planned required measurements and analyses. The compositional dependences of all measured optical and electrical properties with Eopt, λcutoff, ΔE, σdc, and Eg revealed the occurrence of two structural regions at about 15 mol. % Li2O. This is explained based on changes in the nature of the oxygen bonds in glass network as well as the manner by which the lithium oxide does enter the glass structure whether substitution or interstitial.
PbTe nanoparticles with diameter from 4.0 up to 24.6 nm were grown within a Li2O-ZnO–p2O5 glass matrix prepared by melt quenching method. The size of nanoparticles can be adopted by tuning annealing temperature and time in the process of the heat treatment. We confirmed the presence of PbTe nanoparticles by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The optical absorption spectra of host glass matrix with PbTe nanoparticles grown in it, exhibit structure reflecting distinct quantum transition on the optical spectra which are dependent on their particle sizes. With increasing temperature of annealing and/or annealing time, the optical energy gap Eopt (for direct allowed transition) in PbTe nanoparticles decreases (from 5.5 to 4.4 eV). The Urbach energy ΔE increases from (0.92 to 1.92 eV). Also, the DC conductivity measurements on the tested glass containing PbTe nanoparticles revealed that an increase in the PbTe nanoparticle size, leads to a decrease in the energy of activation Eg of electrical conduction from 0.1633 to 0.1219 eV.
The controlled synthesis of PbSe nanocrystals quantum dots (QDs) in lithium–zinc phosphate glass matrix was achieved through phase decomposition of PbSe solid solution. The specific features in the formation of PbSe quantum dots are investigated by high resolution X–ray diffraction, transmission electron microscopy (TEM) and optical absorption spectroscopy. A complete characterization of the PbSe quantum dots (their sizes, morphology and distribution over the matrix bulk and sizes) is performed on the basis of the results obtained. PbSe quantum dot size has also been manipulated by tuning annealing time and temperature in the processing of thermal heat–treatment. The size of PbSe quantum dots has been calculated from, X–ray diffraction, transmission electron microscopy (TEM) and absorption analysis data. The obtained results show that the dots have mean diameters between 6.4 and 33.2 nm. The exciton Bohr radius = 46 nm in PbSe, so these quantum dots provide unusual perhaps unique access to the regime of strong quantum confinement. The inference is made that spherical PbSe nanocrystals with a cubic lattice are formed with uniformly distributed over the bulk matrix and are characterized by a narrow size distribution. Optical and electrical properties of PbSe quantum dots embedded in the studied glass were investigated. It was observed that their optical absorption spectra exhibit structure reflecting distinct quantum transition and the variation of the optical spectra depends on the PbSe nanoparticle sizes and they are showed a red shift in the absorption edge. The obtained values of both the optical energy gap (Eopt) and activation energy (Eg) of electric conduction for PbSe nanoparticle-doped-glass samples are found to be decreased with increasing their particle size. This behavior due to the splitting of both the valence and conduction band into sub-bands i.e the energy band in the PbSe nano-crystals becomes discrete. So the energy gap in this case should be increased with decreasing the nanoparticle sizes.Finally, it can be said that the effects of applying different heat treatments on the growth of nano-crystals of semiconductor materials in a lithium-Zinc-phosphate glass has provide us with nano-crystals of different sizes which confirms a strong quantum confinement regime in consistent with the observed optical absorption data for both studied cases of PbTe and PbSe nano-crystals which were grown in our prepared lithium-Zinc- phosphate glass. This makes this glass of the present work is very promising in future technologies such as, optical gain media, photonic devices and molecular electronics.