Achieving High Quantum Efficiency Narrow-Band β-Sialon:Eu2+ Phosphors for High-Brightness LCD Backlights by Reducing the Eu3+ Luminescence Killer

Abstract

β-Sialon:Eu 2+ has been reported to be the most promising narrow-band green phosphor for wide color gamut LCD backlights, but the coexistence of the Eu 3+ luminescence killer with the Eu 2+ luminescence center limits its luminescence performance to a great extent. In this study, we propose a direct reduction strategy to successfully realize the reduction of Eu 3+ to Eu 2+ and, finally, increase the effective concentration of Eu 2+ in the crystal lattice and greatly minimize the amount of Eu 3+ on the particle surface. As a result, the luminescence of treated β-sialon:Eu 2+ is enhanced by 2.3 times, and the internal quantum efficiency significantly increases from 52.2 to 96.5%. The mechanisms for such large enhancements in luminescence are clarified by investigating the microstructure, luminescence spectra, valence state, concentration, and distribution of Eu using a variety of chemical analyses. We find that the low efficiency is ascribed to the coexistence of the Eu 3+ luminescence killer with the Eu 2+ luminescence center. The white LED backlight using the treated β-sialon:Eu 2+ demonstrates a high luminous efficacy of 136 lm W –1 (22.5% up) and a wide color gamut (∼96% National Television System Committee standard (NTSC)), which thus promises high brightness and energy saving. We believe that the strategy proposed in this work would also work for other luminescent materials containing mixed valence of dopants.