Nickolaevich, Vadim. (Professor)Gemechu, Nebiyu2018-07-022023-11-092018-07-022023-11-092017-06http://10.90.10.223:4000/handle/123456789/5293Analytical, numerical and experimental results of thermoluminescence (TL) from nanomaterials are studied and correlated. In particular, theoretical investigation of TL from silicon quantum dots in the presence of multiple trap states is compared to the TL properties of Ca3Y2(Si309)2 : x Ce3+ nanophosphor of average crystallite size 28 nm synthesized by solution combustion technique. The TL properties of the silicon quantum dots of diameters in the range of 2-8 nm are investigated in the model of two active electron traps and one recombination center. The rate equations corresponding to the active electron traps which are, in general, located at different trap depths below the edge of the conduction band are written. The assumption of negligible retrapping results in the analytically solvable rate equations, whereas, the consideration of the retrapping terms complicates the rate equations requiring numerical solutions. The TL measurements of Ca3Y2(Si309)2 : x Ce3+ nanophosphor are measured and analyzed. Samples are heated from 0 to 400 oC for different UV doses. Measurements of TL fading are done after keeping the sample for different storage times before heating. Peak shape and initial rise methods are employed to evaluate the different TL kinetic parameters such as activation energy (E), the frequency factor (s) and the order of kinetics (b). Moreover, the experimental data is fitted in the analytical solution of TL glow curves obeying general order kinetics using Kitis et al equation. The optical band gap of the synthesized sample (not doped) is estimated from Kubelka-Munk (K-M) function for both direct and indirect allowed transitions. The TL intensity of the silicon quantum dots increases with a decrease in the dot xiv xv size, indicating that quantum confinement effect enhances the radiative recombination rate. For the TL kinetic parameters used in the theoretical approach, the number of peak maxima of the glow curve corresponding to a given quantum dot is the same as the number of active electron traps taken in to account. For first order kinetics, the simulated variation in the concentration of electrons in all the traps decreases with temperature, whereas, it considerably increases with temperature in the deeper traps for general order kinetics due to retrapping. This result bridges the experimental gap where the TL glow curves are generated and the variation of concentration of electrons in traps remain unknown. Analysis of the glow curve deconvolution shows that the TL glow curves of Ca3Y2− (Si309)2 host material (x = 0) can be well fitted by three constituent peaks which obey general order kinetics; indicating the presence of three active electron trap levels. The TL intensity of the synthesized phosphor (not doped) increases for all the UV doses applied up to 50 minutes. Simulation of the TL glow curve of this material is performed by using the rate equations corresponding to the determined active electron trap levels and employing the evaluated TL kinetic parameters. This glow curve is broad and much similar to the experimentally obtained glow curve. The isothermal decay analysis of this host material shows that it suffers from fast phosphorescence decay. Moreover, the incorporation of Ce3+ into the host material resulted in a broad TL glow curves over a wide temperature range. The photoluminescence (PL) emission spectra of the doped samples (x = 0, 0.01, 0.02, 0.04, 0.08 and 0.16) monitored at excitation wavelength of 365 nm show a broad band extending from about 350 to 600 nm and this band can be ascribed to the allowed [Xe]5d1-[Xe]4f1 transition of Ce3+. Moreover, the PL intensity increases up to critical concentration of x = 0.08 and then decreases. The reflectance spectra of the doped samples show a red shift in their optical band gap compared to the hostenInvestigation of Thermoluminescence PropertiesThesis