Improvement in white light emission of Dy3+ doped CaMoO4 via Zn2+ co-doping

Abstract

The research in developing a single ingredient phosphor for white-light emission is progressively increasing. It is well known that the 4F9/2 → 6H13/2 (yellow) and 4F9/2 → 6H15/2 (blue) transitions of Dy3+ ions give near-white light emission. The white light emission of Dy3+ ions can be enhanced via improving the crystallinity of the host phosphor via co-doping of transition metal ions. In this paper, we report a significant improvement in the white light emission of Dy3+ doped CaMoO4 by co-doping Zn2+ ions. The x-ray diffraction pattern confirms the tetragonal phase of pure and doped CaMoO4 phosphor. The peak broadening and a red-shift in the absorption peak are observed by UV–vis absorption analysis of Zn2+/Dy3+ doped CaMoO4. From Photoluminescence studies, we have observed that in Dy3+ doped CaMoO4, the 4% Dy3+ doped CaMoO4 exhibits maximum emission. The Zn2+ ions are co-doped to further increase the luminescence intensity of CaMoO4:4%Dy3+ and the maximum luminescence is obtained for 0.25% Zn2+ concentration. Two intense emission peaks centered at 484 nm and 574 nm related to transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 of Dy3+ ion are observed for Dy3+ doped phosphor. The 4F9/2 → 6H13/2 transition is the forced electric dipole transition which is affected by its chemical environment. After Zn2+ co-doping, the 4F9/2 → 6H13/2 transition is affected due to a change in asymmetricity around the Dy3+ ions. The 0.25% co-doping of Zn2+ gives 34% enhancement in luminescence emission of 4% Dy3+ doped CaMoO4. As a result, the CIE coordinates of chromaticity diagram and the color purity of the 0.25% Zn2+ co-doped CaMoO4:4Dy3+ show improvement in the overall white light emission. We have shown that with Zn2+ co-doping, the non-radiative relaxations are reduced which results in improved white light emission of Dy3+ions.