Red photoluminescence and blue-shift caused by phase transformation in multilayer films of titanium dioxide and zinc sulfide

The most versatile methods for altering the properties and behavior of materials involve a phase transformation in the solid state. In this article, we report multilayered films of ZnS/TiO₂/ZnS on amorphous SiO_x/Si substrates by pulsed laser deposition (PLD). After sequential vacuum annealing at various temperatures, we investigated the effects of TiO₂ on the phase transformation of ZnS films and the consequential changes in photoluminescence (PL) property. PL spectra of the film revealed red emission centered at 686 nm after annealing at 600°C, however, this emission disappears, and the color shifts to blue after annealing at 700°C. Detailed analysis identified that TiO₂ acts as a catalytic agent for the phase transformation of ZnS at this temperature, and that the color shift to blue resulted from decreased red emissions attributed to oxygen in the film. The present results show that catalytic agent-mediated phase transformation has strong potential for the modification of material properties.