Articles you may be interested in Investigation on the near-infrared-emitting thermal stability of Bi activated alkaline-earth aluminoborosilicate glasses J. Appl. Phys. 117, 053107 (2015); 10.1063/1.4907565 In-situ characterization of femtosecond laser-induced crystallization in borosilicate glass using time-resolved surface third-harmonic generation

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A new organometallic “cold−slow” route to strongly fluorescing CdTe/CdS (core−shell) colloids and transparent films is presented. Based on the optical absorption, fluorescence, FTIR, micro-Raman, XPS, and XRD data collected on these nanostructures before and after thermal annealing, a mechanistic path of the core−shell formation and thermal break up is proposed and discussed. The processing of the CdTe/CdS nanostructures starts with 0.5 M tributylphosphine (TBP) stabilized CdS colloid in dichloromethane as a solvent. This yellow colloidal oil composed of 3−4 nm CdS clusters is reacted with liquid Bis(trimethylsilyl)-telluride (TMS2Te) in the presence of excess insoluble CdCl2 salt. During this reaction, a rapid chalcogen atom exchange occurs within a few seconds which produces a new CdTe “core”. The expelled sulfide reacts slowly with the CdCl2 salt to form new CdS clusters after several hours. Furthermore, this “CdS-formation-driven CdCl2 salt dissolution” activates a strong green-yellow fluorescence indicating a possible evolution of a “core−shell”-like CdTe/CdS structure. Thermal sintering of the subsequently prepared CdTe/CdS films between 100 and 200 °C completely suppresses the fluorescence and initiates CdTe cluster growth, reflecting a high thermal sensitivity of the “core−shell” interfaces. By further raising the sintering temperature to 300−400 °C, the TBP ligands are released and, consequently, bare CdS- and CdTe nanocrystals, as well as ternary nanocrystalline CdTe x S1 - x phases, start forming. Above 400 °C, the CdTe part of the nanostructures sublimates, yielding (111)-oriented CdTe films.

Two novel metal alkoxide-derived routes were developed for the synthesis of nanocrystalline CdSe layers with quantum dot sizes between 1 and 4 nm. The first route, where cadmium ethoxy−acetate is reacted with bis(trimethylsilyl)selenium in the presence of aminopropyltriethoxysilane (AMEO), yields highly concentrated alcoholic 0.5 M sols for direct coatings. The second route allows to grow CdSe clusters by infiltrating the selenium precursor into Cd-enriched organosilicate gel layers. The resulting optically transparent films with thicknesses near 10 μm (obtained in a single-step coating) were characterized by steady-state optical absorption and photoluminescence spectroscopy, high-resolution electron microscopy (HRTEM), X-ray diffraction (XRD), resonance Raman, and time-resolved photoluminescence spectroscopy. The experimental data reveal the presence of nanocrystals exhibiting a tetrahedral shape. The quantum dot films are strongly fluorescing, with a quantum yield near 10%. The decay characteristics of the photoluminescence signal after pulsed excitation is discussed taking into account the splitting of the quantum dot ground state as well as the influence of surface states. Furthermore, a size-dependent shift of the Raman band, attributed to the longitudinal optical phonon of the consolidated CdSe clusters, could be observed. This shift is accompanied by a broadening of the corresponding Raman line width. Both effects, the size-dependent shift as well as the broadening of the Raman line width, indicate that phonon confinement is present for the clusters under consideration.