Single band ratiometric thermometry of K2BaCa(PO4)2:Mn5+ phosphor with near infrared excitation and emission

Transition metal as an activator is susceptible to influences of external environment, which make it sensitive to temperature and enable it to be used as a thermometer. However, its excitation spectra could hardly extend to near-infrared (NIR) region, which restricts its application in the field of biology. Additionally, ratiometric thermometry based on dual luminescent bands suffers from a low reliability due to the impacts of optical dispersion. To overcome the above challenges, single band ratiometric thermometry is adopted, which can render the thermometer immune to optical dispersion, resulting in a high reliability. Meanwhile, Mn⁵⁺ activated K₂BaCa(PO₄)₂ (KBCP) phosphor is successfully synthesized, whose excitation and emission are in the NIR region. The influence of the excitation light fluctuations can be excluded by monitoring and screening the excitation intensity. Under 970 and 806 nm excitation, its temperature sensing behaviors are investigated in the range of 300–480 K. The maximum relative sensitivity is 1.69 % K⁻¹ at 413 K under 806 nm excitation. These results indicate that KBCP:Mn⁵⁺ phosphor is an excellent NIR thermometer and can achieve highly reliable measurement.