Finely-tuned NIR-to-visible up-conversion in La2O3:Yb3+, Er3+ microcrystals with high quantum yield

Up-conversion (UC) materials whose emission color can be finely-tuned while a high UC quantum efficiency is maintained are desirable for many applications. Herein, we report near-infrared-to-visible La2O3:Yb3+, Er3+ (LYE) UC materials with a high internal quantum yield (UCQY) of 3.8%, external UCQY (brightness) of 1.6% and tunable emission color. UC emission colors from pure green to reddish-orange can be precisely tailored by simply controlling synthesis conditions, whilst maintaining the high UCQY. The internal UCQY and external UCQY of LYE yield better performance than both commercially available and other record UC phosphors reported in the literature under the same excitation conditions. The facile preparation combined with the color-tuning and high UCQYs make these materials attractive candidates for solar energy harvesting, sensors, 3D volumetric displays, solid state lasers and bio-imaging.