Effect of heat treatment on photoluminescence behavior of Zn2SiO4 : Mn phosphors

The thermal treatment in reducing atmospheres gives rise to the increase bo th in emission intensity and 10% decay time in ZnzSiO(4):Mn phosphors. The present investigation aims to take account of such changes in association w ith the structural change. For this sake, X-ray absorption spectroscopy tec hniques such as XANES and EXAFS were conducted to the ZnzSiO(4):Mn phosphor s. The Zn2SiO4:Mn phosphors were fired in the air and then thermally treate d in two different reducing atmospheres (hydrogen or carbon). The photolumi nescent (PL) behavior was closely related to the X-ray absorption data. The XANES and EXAFS prove that the oxidation state (+2) remains identical rega rdless of whether or not the samples are treated, but that the Mn-O distanc e was reduced by the heat treatment. In order to give a plausible interpret ation to the change in PL results, two possible suggestions are presented. Firstly, it is conceivable that the thermally activated diffusion process o f manganese ions splits Mn-Mn pair during the heat treatment. Another possi bility is that the thermal treatment annealed out some quenching site, whic h is related with defects and impurities. Such hypotheses can be rationaliz ed systematically by considering the results from lifetime measurement, Deb ye-Waller factor calculation, and XANES pre-edge peaks. (C) 2000 Elsevier S cience Ltd. All rights reserved.