Effect of annealing on the grain growth and luminescent properties of SrS:Cu blue phosphors

Abstract

Systematic studies of the postgrowth annealing of molecular beam epitaxial deposited SrS:Cu films are reported. In the as-grown SrS:Cu films, the grain size was small and the luminescence very weak. A step-annealing procedure in a H2S atmosphere was developed and found to be a very efficient way to improve the crystallinity and luminescent properties without damage to the low temperature glass substrate and insulator layer of the device. A model is presented in terms of the free energy of formation and the reaction kinetics of Cu with H2S. It was proposed that the weak luminescence in the as-grown films was attributed to Cu atoms segregated at the grain boundaries in the SrS film. The oxidation of atomic Cu by H2S and the diffusion of Cu+ into the SrS lattice during annealing were responsible for the grain growth and the improved luminescent properties.