Abnormal anti-thermal quenching of Mn2+ and reverse thermal response of Mn2+/Mn4+ luminescence in garnet phosphor for wide-range temperature sensing

Herein, we explored the diverse temperature-dependent luminescence, thermal quenching, and decay kinetics of Mn2+/Mn4+ emission centers in a Y3Al2Ga3O12 garnet host. Emission color tuning was achieved from red to deep red region as a function of the Mn doping amount. The tuning of the Mn valence state as a function of doping concentration in Y3Al2Ga3O12 was investigated in detail, and the mechanism of self-reduction of Mn4+ has been discussed. Interestingly, the temperature-dependent photoluminescence study of Y3Al2Ga3O12:Mn2+/4+ revealed the abnormal anti-thermal quenching of the Mn2+ emission band with increasing temperature. In contrast, Mn4+ emission displayed thermal quenching with increase in temperature. The interplay of self-reduction and defects in the anti-thermal quenching of Mn2+ has been discussed. Benefiting from the reverse temperature-dependent luminescence behaviour of Mn2+/4+, luminescence ratiometric and lifetime thermometry have demonstrated a promising wide temperature sensing range, from cryogenic conditions (10 K) to 490 K. A high relative sensitivity of 2.35% K-1 (190 K) and 3.10% K-1 (390 K) could be achieved for ratiometric and lifetime thermometry, respectively. The lifetime thermometer based on the lifetime of Mn2+ and Mn4+ ions offered good temperature resolution (<0.30 K). This work proposed the use of dual-emitting single-doped materials for highly sensitive wide sensing range thermometry and offers meaningful advancement in the design of orange-red emitting phosphors.