Investigations of the crystalline phase and photoluminescence properties of white-light CaxZnMoO4+x phosphors

Abstract

In this study, the solid-state reaction method was used to synthesize the undoped CaxZnMoO4+x (without the addition of activators) compositions (x = 0, 0.5, 1.0, and 1.5) at different temperatures and investigate them as the new luminescent phosphors. XRD patterns revealed that no raw materials were residual and no secondary phase was observed in the synthesized ZnMoO4 powder. The applicable synthesis temperature of ZnMoO4 powder was 800 °C˜900 °C because it was melted as temperature was higher than 900 °C. As 800 °C and 900 °C were used as the synthesis temperatures of Ca0.5ZnMoO4.5 composition, the CaMnO4 was observed as the predominant crystalline phase and ZnMoO4 was observed as the secondary phase. As the x value of CaxZnMoO4+x powders increased from 0 to 1.0, the applicable synthesis temperatures were raised from 900 °C to 1200 °C. The important novelties for all CaxZnMoO4+x compositions are that they have special emission properties, and we call them as CaxZnMoO4+x phosphors. The PL spectra of all CaxZnMoO4+x phosphors show that they had only one broad peak with centered optical wavelengths occurred at around 490 nm. The bandwidths and central wavelengths of all PL spectra were unchanged as the CaO content and synthesis temperature were changed. The approximate emission bandwidths of all CaxZnMoO4+x phosphors were in optical wavelengths of 350 nm˜650 nm and their maximum emission intensities increased with CaO content. Even the crystalline phases of CaxZnMoO4+x phosphors were different from their original compositions, all of them would emit the white light. Keywords: CaxZnMoO4+x compositions, Luminescence properties, Emission peak, Broad band