Investigation of temperature sensing based on luminescence intensity ratiometric and lifetime of Zn0.9Mn0.1Al2O4:Cr3+phosphors with various reducing time

Zn0.9Mn0.1Al2O4:Cr3+ phosphors with pure spinel structure were fabricated by using co-precipitation method. The influence of reducing time on the structure, photoluminescence and temperature sensing properties were investigated by using X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence (PL). With the reducing time increasing, the diffraction peak reveals a shift toward lower angle, and the isolated six refined peaks of EPR assigned to Mn2+ in spinel lattices reveal a large increasing overlap, indicating the increasing concentration of Mn2+. A red emission assigned to 2Eg -> 4A2g of Cr3+ is observed, but its intensity is very tiny in the as-synthesized Zn0.9Mn0.1Al2O4 phosphors, and with reducing time increasing, the emission intensity is enhanced sharply. The energy level of 2Eg is split into 2E(2 A) and 2E(E) corresponding to 687 nm (R1) and 689 nm (R2) emissions due to the high crystal field in ZnAl2O4 lattices. The emission assigned to Mn2+-Vo (Oxygen vacancy) at 530 nm reveals a strong temperature dependence, and the highest relative sensitivity of 2.55 %K  1 is achieved based on the luminescence integral intensity ratio of I530nm/Mn2+, which is higher than that based on the lifetime of 512 nm emission peak assigned to Mn2+ and based on the luminescence integral intensity ratio of the excitation peaks of I427nm/I530nm, indicating that the potential application in multi-reading temperature nanoprobe.