Rational Design of the Electronic Structure of CdS Nanopowders

In this study, varioustechniques, such as energy-dispersive X-rayspectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, andspectrophotometry, were used to analyze the properties of nanometricCdS particles synthesized with varying precursor concentrations. EDXanalysis revealed the nonstoichiometric composition manifested byan increase in the Cd/S ratio from 1.02 up to 1.43 with increasingprecursor concentration. The growth of lattice parameters and unitcell volume accompanying preferential crystallization of the hexagonalphase along with an increasing Cd/S ratio was confirmed by XRD analysis.This indicated the presence of interstitial cadmium in nonstoichiometricCd(1+x )S. The formation of shallow Cd-i donor levels below the bottom edge of the conduction bandimpacts the bang-gap energy; a decrease from 2.56 to 2.21 eV alongwith increasing nonstoichiometry was observed. This is accompaniedby a widening of the range of absorption of light, which creates conditionsthat can lead to an increase in the efficiency of redox reactionsin photochemical processes. Precipitationof nanometric CdS led to nonstoichiometriccomposition manifested by cadmium-to-sulfur ratio > 1. The reasonfor this is the presence of a shallow donor level in the forbiddenband which was confirmed by decreasing value of E-g . This in turn led to the extension of the light absorptionrange and a potential increase in the efficiency of photochemicalprocesses.