Giant Photoluminescence Improvement and Controllable Emission Adjustment in Bi3+-Activated Ca4ZrGe3O12 Phosphors for High-Quality White Light-Emitting Diodes

High-performance and thermally stable phosphors play an important role in high-quality white light-emitting diode (pc-WLED) lighting. In this work, we proposed a cation substitution strategy to improve the luminescence performance of blue-emitting Bi3+-doped Ca4ZrGe3O12 (abbreviated as CZGO) phosphor. As expected, the introduction of Sr2+ and Si4+ can improve photoluminescence intensity and thermal stability. The photoluminescence intensity can be increased by 6.7 times. The internal quantum efficiency (IQE) can achieve 88.1%. Based on Rietveld refinement results, the corresponding enhancement mechanism is ascribed to the local lattice modification and the improved structure rigidity. In addition, controllable color tuning from blue to red light is successfully realized through designing Bi3+ -> Eu3+ energy transfer. The energy transfer efficiency (eta(T)) is 0.55 in CZGO:2% Bi3+, 15% Eu3+ phosphor. The energy transfer mechanism is discussed in detail. The prototype pc-WLEDs with blue/red dual-emitting CZGO:2% Bi3+, 10% Eu3+ possess a high color rendering index (CRI = 90.8) and low correlated color temperature (CCT = 4372 K). The above investigations indicate that CZGO:Bi3+ and CZGO:Bi3+, Eu3+ are promising blue-to- red tunable phosphor candidates for pc-WLED applications.