Anomalous luminescence from Yb2+-doped Ca2PO4Cl

The photoluminescence of Ca2PO4Cl:Yb2+ has been investigated and compared with that of Ca2PO4Cl:Eu2+, and the application of Ca2PO4Cl:Yb2+ for white LED has been evaluated. The excitation spectra of Ca2PO4Cl:Yb2+ are dominated by an intense excitation band at 395 nm. Under near-UV excitation at 395 nm, Ca2PO4Cl:Yb2+ shows a broad asymmetric emission with maximum at 490 nm. This emissions result from two different Yb2+ centers is evidenced by the low temperature (T=100 K) emission spectrum. Yb2+ luminescence differs significantly from that of Eu2+, most notably in the structure of emission spectra, and is characterized by a much broader emission band and lower quenching temperature. Such anomalous luminescence from Yb2+ is ascribed to the de-excitation process of the Yb2+-trapped exciton state. Ca2PO4Cl:Yb2+ has external quantum efficiency of 24% and exhibits 40% of luminescence quenching at 100 °C in the air and, therefore, these results reveal its limited potential in the fabrication of white-light LEDs.