Local structure distortion enhanced the emission intensity of KBaYSi2O7:Eu2+ phosphor for full-visible-spectrum LED lighting

Abstract

Due to Eu2+ and Eu3+ ions often co-exist in the crystal lattices, the luminous intensity of some phosphors is limited greatly. In this work, we propose a crystal-site engineering approach to reduce Eu3+ to Eu2+ in the KBaYSi2O7 lattice through substitution of Ba2+ by Ca2+ or Sr2+. The mechanism between the local environmental regulation of the crystal structure around Eu2+ as well as the luminous intensity and thermal stability of the phosphor was systematically explored. The results of XRD, Rietveld refinement and EDX confirmed that Ca2+ and Sr2+ are dissolved into the crystal lattice effectively without changing the main phase structure. As a result, the luminous intensity of samples doped Ca2+ and Sr2+ increased by 39.7% and 41.2%, respectively. The mechanisms for such improvement is ascribed to the reduction of Eu3+ into Eu2+ under the lager volume of [EuO9]2 polyhedron. The treated samples exhibited relatively superior thermal stability with I150°C > 70%, indicating that doping with Ca2+ or Sr2+ have no effect on the thermal stability. A pc-WLED device fabricated by combining (Ba,Sr)2SiO4:Eu2+, (Ca,Sr)AlSiN3:Eu2+, BaSi2O2N2:Eu2+ and KBa0.86Ca0.1YSi2O7:Eu2+ with 380 nm chip exhibits CCT (5010 K) and high CRI (96.6). These results indicate that this phosphor has potential for applications in full-spectrum warm white lighting.