Remarkable enhancement of upconversion emissions by thermal stimulation in Er-doped Yb₂Mo₃O₁₂ microcrystals

Lanthanide-doped luminescent materials have drawn great attention due to their lighting, display, and sensing applications. However, their emission intensity usually decreases with increasing temperature, leading to a weaken performance. In this work, the Er³⁺-doped Yb₂Mo₃O₁₂ microcrystals with optical temperature sensing properties have been synthesized by a solid-phase sintering route. Under the excitation of a 980 nm laser, the sample shows enhanced upconversion emissions as temperature rises, which is attributed to the negative thermal expansion in the crystal structure and enhanced crystal field strength. At the same time, based on the luminous intensity ratio of two thermally coupled energy levels (Er³⁺:²H_11/2,⁴S_3/2), the temperature sensing properties of the prepared microcrystals were studied. This work achieves high S_R (1207.4/T) in the range from 313 to 573 K, and it is accompanied by a 21-fold enhancement of the upconversion emission intensity. As a whole, this is an excellent material that can be used for optical temperature sensing with highly sensitive and enhanced upconversion emission.