Optical thermometry based on anomalous temperature-dependent 1.53 μm infrared luminescence of Er3+ in BaMoO4: Er3+/Yb3+ phosphor

The temperature dependences of 1.53 mu m near infrared and green upconversion (UC) emissions of Er3+ ion have been investigated in Er3+/Yb3+: BaMoO4 powders upon 980 nm excitation. Interestingly, an anomalous enhancement of 1.53 mu m luminescence intensity with increasing temperature is observed, which is interpreted based on the phonon-assisted nonradiative process from I-4(11)/2 to I-4(13/2) level. Moreover, the emission intensities from various Stark transitions I-4(13/2)(Y-i) -> I-4(15/2)(Z(j)) show different changing rates with temperature, which is in favor of optical thermometry application based on fluorescence intensity ratio (FIR) technique. The results show that the utilization of FIR-1 (I-1504/I-1531) from two Stark transitions with the same power-dependence is beneficial to obtain consistent results at different excitation power densities, and avoid measurement error resulted from the power density variation. Besides, when FIR-Green (I-533/I-557) is used as the thermometric index, a high absolute sensitivity of 115 x 10(-4) at 430 K can be obtained. Therefore, Er3+/Yb3+: BaMoO4 is promising for optical thermometry.