Effect of alkali metal ions on the spectra of CaZn2(PO4)2: Sm3+ phosphor analyzed by J-O theory

Abstract

To investigate the effect of alkali metal ions on the spectra of CaZn2(PO4)2: Sm3+ phosphor. Here, we prepared a series of doped and undoped CaZn2(PO4)2 were prepared by the high temperature solid-state reaction method. The microstructure and luminescence properties were systematically investigated by the experimental and theoretical methods. Rietveld refinement of XRD data was performed to indicate the crystal parameters variation, caused by introducing rare earth ions (Sm3+) and charge compensation ions (Li+, Na+, K+). To further understand the role of doped ions, we applied density functional theory to calculate the band structure and density of states of CaZn2(PO4)2. The excitation and emission spectra showed the intense excitation peak at 402 nm and emission peak at 598 nm. The intensities of those spectra were enhanced after adding the charge compensation ions. The Judd-Ofelt theory based on the absorption spectra was applied to predict the transition probability, branching ratio and quantum efficiency, and to explain the improved luminescence properties. The mechanism of concentration quenching was investigated by the optical luminescence system of CaxZn2-x(PO4)2: xSm3+, xLi+. The results showed that the dipole-dipole interaction dominated in non-radiative energy transfer when the concentrantion of Sm3+ ions was higher than the quenching concentration 3 mol%. This work has the potential application in n-UV excited LED and other orange-red luminescent devices.