Improved optical thermometric sensitivity of Eu3+-doped calcium niobate phosphor via nonstoichiometric control

Eu3+-doped calcium niobate CaNbxO6 phosphors were successfully prepared by a solid-state reaction, and the crystal structure, morphology, energy transfer process, and temperature-dependent behaviors were systematically investigated. The CaNbxO6 host matrix presents the self-activated characteristic emission at 470 nm due to the charge transfer transition of Nb5+-O2+, and the corresponding photoluminescence intensity reaches the maximum intensity when the nonstoichiometric ratio of Ca2+/Nb5+ ions is 1:1.9. Moreover, the energy transfer process from the host (470 nm) to Eu3+ (612 nm) ions in the CaNb1.9O6:Eu3+ phosphor is demonstrated, and the corresponding energy transfer efficiency is significantly enhanced compared with that of stoichiometric sample. Furthermore, it is observed that nonstoichiometric ratio of Nb5+ ions deteriorates the thermal quenching of the matrix while guaranteeing the thermal stability of the activators, resulting in the relative sensitivity (S-r) of CaNb1.9O6:Eu3+ being greatly improved from 2.235% to 3.673% K-1. Herein, these results provide an effective strategy for manipulating the sensitivity of optical thermometers of phosphors based on the induced modulation of the temperature-response performance via nonstoichiometric control.