Multicolor luminescence of undoped zinc sulfide nanocrystalline thin films at room temperature

Thin films containing luminescent undoped zinc sulfide (ZnS) nanoparticles, with and without silica capping, were prepared via a simple method using sol-gel technique. Average particle size changed from 3 to 10 nm for the set of ZnS films and 2.5 to 7 nm for the set of ZnS-SiO2 films when they were annealed from 473 to 673 K in a step of 50 K. The films containing ZnS nanoparticles without silica capping showed sizedependent blue emission at room temperature. The doublet fine structures in the Photoluminescence (PL) spectra were resolved and a qualitative approach was taken to explain the variation in the PL emission with change in the annealing temperature. The films containing ZnS nanoparticles embedded in silica matrix showed ultra violet (UV) and red emissions upon excitation at different energy levels. The UV emission experienced red shift; whereas, the red emission was found to be blue shifted for the films synthesized at higher annealing temperatures. PL intensity decreased with aging for the films containing ZnS particles without silica capping when they were exposed in relatively humid atmosphere (relative humidity 80%) for 6 weeks. The films containing ZnS particles embedded in silica matrix showed much more stable behavior since the emission intensity practically remained constant with aging and the films also restored their quality when exposed to a humid atmosphere. (c) 2006 Elsevier B.V All rights reserved.