The crystal structure and luminescence properties of a novel green-yellow emitting Ca1.5Mg0.5Si1-xLixO4-delta:Ce3+ phosphor with high quantum efficiency and thermal stability

Ji, Weiwei; Xia, Zhiguo; Liu, Ke; Khan, Sayed Ali; Hao, Luyuan; Xu, Xin; Yin, Liangjun; Molokeev, Maxim S.; Agathopoulos, Simeon; Yang, Wenyun; Ma, Xiaobai; Sun, Kai; da Silva, Ivan Source: DALTON TRANSACTIONS, 47 (29):9834-9844; 10.1039/c8dt02241k AUG 7 2018

A novel green-yellow emitting Ca1.5Mg0.5Si1−xLixO4−δ:Ce3+ phosphor with high quantum efficiency and thermal stability was discovered for applications in near ultraviolet pumped white light-emitting diodes. Its crystal structure was determined with a single-particle diagnosis approach. The Si sites in the SiO4 tetrahedra are reported for the first time to accommodate Li+ ions. This substitution, confirmed by 6Li solid-state NMR and T.O.F. neutron powder diffraction, causes a disordered occupation of Ca/Mg in the Ca3MgSi2O8 host and favors a phase transformation at ∼330 °C, which results in the formation of the novel phosphor. The produced phosphor was efficiently excited by near UV light peaking at 365 and 410 nm and produced broad green-yellow emission with peaks at 500 and 560 nm, respectively. Its quantum efficiency reached 88.4% (internal) and 55.7% (external) under excitation at 365 nm, and 80.5% (internal) and 42.7% (external) under excitation at 410 nm, while the decrease of luminescence intensity at 200 °C was small (∼26%). A WLED lamp with a high color rendering index of Ra = 92.8 was produced with the combination of a 365 nm emitting chip with blue emitting BaMgAl10O17:Eu2+, green-yellow emitting CMSL:0.01Ce, and red emitting Sr2Si5N8:Eu2+ phosphors.