Vacancy-Enhanced Self-Reduction of Eu in Pyrophosphate Phosphor.

The self-reduction mechanism in pyrophosphate phosphors is currently explained through nonequivalent substitution for charge compensation. Nevertheless, the impact of oxygen vacancies on the self-reduction enhancement requires further investigation. Herein, heterovalent Ba 1- x Zn 1- y P 2 O 7 : x Eu 2+/3+ , y Mg phosphors with rigid structures were prepared through conventional solid-phase technology in air. The cation substitution strategy leads to different chemistry electronegativity and adjustable crystal field environments and creates vacancy defects. Crystal structure and component analysis indicate the gradual phase segregation change from BaZnP 2 O 7 to BaMgP 2 O 7 with increasing Mg 2+ content. The CIE coordinates that are tuned from (0.514, 0.334) to (0.326, 0.152) and realize color-tunable emission from red-orange to blue-violet can be used as multicolor functional materials. Besides, the phosphor demonstrates its maximum S a of 0.4725% K -1 (498 K) and S r of 1.376% K -1 (423 K). These results demonstrate that the phosphors have the potential for contactless optical temperature measurement and anticounterfeiting. This work not only investigates the self-reduction of the Eu 3+ → Eu 2+ phenomenon but also provides a supplementary explanation and data support to complete the effect of the oxygen vacancy on self-reduction.