The local symmetry of trivalent europium ion activated Li4Ca2B8O16 red-emitting phosphors with high color purity and excellent thermal stability

Exploring for red-emitting phosphor materials with supper property plays a key role in the development of white light-emitting diodes (WLEDs). Simultaneously, the crystal structure has a crucial effect on its luminescence properties. In this work, we synthesized a type of new red-emitting Li4Ca2B8O16: Eu3+ phosphor via the solid-state reaction. The phase purity, crystal structure, surface morphology, decay behavior, thermal stability, the correspondence between local symmetry and luminescence properties were investigated in detail. Under the optimal 393 nm excitation, Li4Ca2B8O16: 0.33Eu3+ shows a strong red emission located at 612 nm ascribed to the 5D0→7F2 transition of Eu3+. The calculated Judd-Ofelt parameters (Ω2 and Ω4) have clarified that Eu3+ has lower symmetry without an inversion center, resulting in the high value of R/O (the emission intensity ratio of 5D0→7F2 to 5D0→7F1) of 7.95 at x = 0.33 mol. The Li4Ca2B8O16: 0.33Eu3+ phosphor exhibits a high color purity of 94.99% with the chromaticity coordinates of (0.6547, 0.3449), perfect internal quantum efficiency (99.75%) and excellent thermal stability at high temperature (90.91% at 150 °C). The results indicate that this new Li4Ca2B8O16: Eu3+ phosphor can be used as the potential red component for pc-WLEDs.