High Efficiency Green Phosphor Ba9Lu2Si6O24:Tb3+: Visible Quantum Cutting via Cross-Relaxation Energy Transfers

Tb3+-doped phosphors are widely used in fluorescent lamps and plasma display panels (PDP) due to the strong vacuum ultraviolet (VUV)/UV light absorption of Tb3+. Most of these phosphors are fluorides. The quantum efficiency (QE) of these phosphors is more than 90%; however, it is still too low. Theoretically, one VUV/UV photon can convert two visible photons or more by visible quantum cutting (QC), and the QE can reach 200% or more. Usually, the oxides have a higher QE than fluorides. In this work, we obtained a novel oxide phosphor Ba9Lu2Si6O24:Tb3+ (BLS:Tb3+). Under the 251 nm UV-light excitation, QC processes occur in BLS:Tb3+ via cross-relaxation energy transfers (CRET) between Tb3+ ions, leading to intense green emissions around 552 nm. Based on an indirect method, the ideal QE is calculated nearly to be 171%. When the UV light absorption and energy losses are considered, the practical QE is near 144% estimated by a direct method. This value is much higher than that of the commercial phosphors of 90%, indicating the promising application of BLS:Tb3+ for fluorescent lamps and PDP. The CRET processes were investigated according to the luminescence spectra and decay curves.