Insight into the photoluminescence properties and formation mechanism of Ca4(PO4)2O crystal: Design of Eu2+-doped multi-color phosphors

Abstract The photoluminescence properties and formation mechanism of oxygen vacancies in Ca 4 (PO 4 ) 2 O crystal were studied. X-ray diffraction, photoluminescence spectra, and Fourier transform-infrared spectra were used to investigate the formation process of Ca 4 (PO 4 ) 2 O crystal. Pure Ca 4 (PO 4 ) 2 O crystal prepared in reducing atmosphere shows an intense emission at 405 nm under excitation of 330 nm, which is originated from oxygen vacancies in the lattice. It can be concluded that oxygen vacancies in Ca 4 (PO 4 ) 2 O crystal exhibit a high thermal stability and the strong photoluminescence emission can be observed for the sample recalcined in air at 400 °C. The results of XRD and FTIR indicate a phase transformation process between Ca 4 (PO 4 ) 2 O, Ca 10 (PO 4 ) 6 O and Ca 10 (PO 4 ) 6 (OH) 2 phase and oxygen vacancies are also formed during this process. Furthermore, a novel Eu 2+ singly doped phosphate phosphor with multi-color emission can be firstly developed through strictly controlling phase transformation of the host. Under NUV excitation, the color coordinates are calculated to be (0.3427, 0.3229) and (0.3872, 0.3429) closely corresponding to white/warm white light. The warm white light with high color rendering index ( R a : 87.6) and low correlated color temperature (3510 K) can be achieved based on the Eu 2+ singly doped phosphate phosphor.