Li₄ Zn(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 Li₄ Zn(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 Li₄ Zn(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 Li₄ Zn(PO₄ )₂ :Mn²⁺ phosphor has potential application in optical thermometry.