Li₄Zn(PO₄)₂:Mn²⁺ thermosensitive phosphor with dual luminescent centres for optical thermometry

An optical thermometry strategy based on Mn2+-doped dual-wavelength emission phosphor has been reported. Samples with different doping content were synthesized through a high-temperature solid-phase method under an air atmosphere. The electronic structure of Li4Zn(PO4)(2) was calculated using density functional theory, revealing it to be a direct band gap material with an energy gap of 4.708 eV. Moreover, the emitting bands of Mn2+ at 530 and 640 nm can be simultaneously observed when using 417 nm as the exciting wavelength. This is due to the occupation of Mn2+ at the Zn2+ site and the interstitial site. Further analysis was conducted on the temperature-dependent emission characteristics of the sample in the range 293-483 K. Mn2+ has different responses to temperature at different doping sites in Li4Zn(PO4)(2). Based on the calculations using the fluorescence intensity ratio technique, the maximum relative sensitivity at a temperature of 483 K was determined to be 1.69% K-1, while the absolute sensitivity was found to be 0.12% K-1. The results showed that the Li4Zn(PO4)(2):Mn2+ phosphor has potential application in optical thermometry.