Simultaneous Thermal Enhancement of Upconversion and Downshifting Luminescence by Negative Thermal Expansion in Nonhygroscopic ZrSc(WO4)2PO4:Yb/Er Phosphors

Thermal quenching (TQ) is still a critical challenge for lanthanide (Ln³⁺)-doped luminescent materials. Herein, we report the novel negative thermal expansion nonhygroscopic phosphor ZrSc(WO₄)₂PO₄:Yb³⁺/Er³⁺. Upon excitation with a 980 nm laser, a simultaneous thermal enhancement is realized on upconversion (UC) and downshifting (DS) emissions from room temperature to 573 K. In situ temperature-dependent X-ray diffraction and photoluminescence dynamics are used to reveal the luminescence mechanism in detail. The coexistence of the high energy transfer efficiency and the promoted radiative transition probability can be responsible for the thermally enhanced luminescence. On the basis of the luminescence intensity ratio of thermally coupled energy levels ²H_11/2 and ⁴S_3/2 at different temperatures, the relative and absolute sensitivities of the targeted samples reach 1.10% K^-1 and 1.21% K^-1, respectively, and the low-temperature uncertainty is approximately 0.1-0.4 K on the whole temperature with a high repeatability (98%). Our findings highlight a general approach for designing a hygro-stable, thermostable, and highly efficient Ln³⁺-doped phosphor with UC and DS luminescence.