Structure tailoring and defect engineering of LED phosphors with enhanced thermal stability and superior quantum efficiency

The discovery of phosphors with high quantum efficiency and high thermal stability is in high demand for facilitating the next generation high-power white light-emitting diodes (WLEDs). Herein, we report the design and synthesis of a high-performance blue-emitting K2Sr1.25Ba0.75(PO4)2: Eu2+ phosphor with an excellent quantum efficiency (IQE = 96.4%) and high thermal stability (93%@200 °C) via a defect engineering approach. The internal quantum efficiency was effectively enhanced through the symmetric stretching vibration of the crystal framework, preventing energy transfer loss from activator (Eu2+) to killer centers. Combining density functional theory (DFT) calculation and experimental investigation, we unravelled the intrinsic mechanism for the improvement of IQE thermal stability and proposed a model for the thermal stability enhancement. It is revealed that the induced size mismatch defects (SrBa) stimulate the excited electrons to transfer from defect levels to the conduction band of the matrix. The results arising from this study demonstrate the effectiveness of the defect engineering approach for enhancing the overall performance of LED phosphors.