Solution combustion synthesis of high-entropy rare earth oxide Ce 0.2 La 0.2 Gd 0.2 Y 0.2 Lu 0.2 O 1.6:Eu 3+phosphor with intense blue-light excitable red emission for solid-state lighting

Red-light-emitting phosphors capable of being well excited with blue light are highly desirable in solid-state lighting. In this work, a novel Eu3+-activated high-entropy rare earth oxide Ce 0.2 La 0.2 Gd 0.2 Y 0.2 Lu 0.2 O 1.6 : x Eu 3+ (x = 4-16 mol%) phosphor was successfully prepared by solution combustion reaction for the first time. The multi-composition rare earth oxide has a specific cubic fluorite structure, which is almost the same as that of the pure CeO2 despite the tiny ceria composition in the sample, demonstrating the formation of a high-entropy composite solid solution. To our surprise, the high- entropy phosphor exhibits extremely intense red emission at 613 nm, corresponding to the 5 D 0 -> 7 F 2 characteristic transition of Eu3+ under the excitation of blue light at 466 nm. The luminescence internal quantum yield (QY) for the optimal high- entropy phosphor (x = 12 mol%) reaches nearly 50% and can further increase to 67.8% through a subsequent heat- treatment process at 1400 degrees C. The QY result is much superior to that of previously reported Eu3+-activated CeO2 as well as Y2Ce2O7 and La2Ce2O7 low-entropy composite oxides (QYs are approximately 10%-20%). Moreover, the high-entropy oxide phosphor also shows better luminescence thermal stability than low-entropy oxides, as confirmed from the temperature-dependent photoluminescence emission spectra. The tremendous improvement in optical properties depends closely upon the high-entropy and other related effects. The novel high-entropy rare earth oxide phosphor is beneficial to be used in the field of solid-state lighting owing to the coincidence of excitation of blue light with the emission of InGaN light- emitting diode (LED) chips.