Synthesis and properties of ZnTe and Eu3+ ion co-doped glass nanocomposites

Abstract

In this study, ZnTe (II-VI) semiconductor and Eu+3-ion co-doped borosilicate glass has been prepared in the SiO2-K2O-CaO-BaO-B2O3 glass system followed by controlled heat-treatment to produce glass nanocomposites. Glass transition temperature and crystallization peak temperature have been evaluated using DSC analysis. Dilatometric studies were carried out to evaluate thermal expansion co-efficient, glass transition temperature, and dilatometric softening temperature and found to be 10.7 × 10−6/K, 580° C and 628° C, respectively. TEM micrographs demonstrate formation of nano sized crystallites of less than 50 nm. The ZnTe crystal formation also established through selected area electron diffraction (SAED) analysis and high resolution images obtained through TEM studies. With increasing heat treatment time, optical transmission cut-off wavelength (λcut-off) shifted towards higher wavelength. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5D0 → 7F2 transition. An intense 394 nm excitation band corresponding to the 7F0 → 5L6 transition was observed. Emission spectra were then recorded by exciting the glass samples at 394 nm. When the glass is heat-treated for 30 min at 610° C, a 6-fold increase in the intensity of the red emission at 612 nm has been observed, which is attributed to the segregation of Eu3+ ions into the low phonon energy ZnTe crystallites and as the size of the nanocrystals is smaller than the size of the exciton, quantum confinement effect is visible. Further increase in heat-treatment duration led to decrease in luminescence intensity due to the growth of larger size crystals. 5D1 → 7F0 transition is visible only in the samples heat-treated for 30 min and 1 h, which is a characteristic of presence of Eu3+ ions in the low phonon energy ZnTe crystal sites. The micro hardness of the precursor glass and glass nanocomposites was evaluated; base glass shows hardness of 6.7 GPa and hardness of heat-treated glass nanocomposites has been found to decrease with increase in heat-treatment duration (5.5-5.3 GPa). However, mechanical properties are found to be suitable for device applications.