Stokes and Anti-Stokes Luminescence in Heat-Treated CdS Nanopowders

Abstract

Here we are presenting our experimental results on CdS nano powders, heat-treated at different temperatures in air environment. We used different spectroscopic studies like XRD, TGA-DTA, FT-IR, Raman, FE-SEM-EDAX, TEM-SAED, and DRS to characterize the heat-treated powders. From XRD results, we conclude that increasing temperature from 200 to 400 °C or above allows changing from cubic to hexagonal phase. During heat treatment in an air environment, oxygen diffuses into the crystal lattice inducing the oxidation of powders. The chemical groups of the samples have been identified by FTIR studies. FWHM of Raman peaks (1-LO and 2-LO) decreases and 2-LO mode intensity increases in the case of hexagonal compared to their cubic phase due to increasing its crystallite size. Morphology, elemental, stoichiometric ratio, and crystallinity of the samples studied by using FE-SEM-EDAX and TEM-SAED. Structurally dependent Stokes and anti-Stokes luminescence were studied by using 6 ns Nd:YAG and 100 fs Ti:sapphire laser. Heat treatment at 400 and 600 °C, powders show only a band edge emission with relatively narrow full-width half-maximum, which means that they possess good optical property. Dependence of the anti-Stokes luminescence (upconversion) on heat treatment of the powders was studied through laser excitation.