Vacancy-Enhanced Self-Reduction of Eu in Pyrophosphate Phosphor

Abstract

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-xZn_1-yP₂O₇:xEu^2+/3+, yMg 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 BaZnP₂O₇ to BaMgP₂O₇ with increasing Mg²⁺ 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 Eu³⁺ → Eu²⁺ phenomenon but also provides a supplementary explanation and data support to complete the effect of the oxygen vacancy on self-reduction.