Enhanced upconversion emission of Er3+/Yb3+ and Er3+/Yb3+/Zn2+ doped calcium aluminate for use in optical thermometry and laser induced optical heating

Abstract

There are two key factors to design an efficient green upconversion (UC) emission based optical sensor for temperature. The primary need is to develop a thermally stable and economical material, for a stable sensor, and the second essence is to get an efficient green UC emission, for high sensitivity of the sensor. The proof of this concept is demonstrated on a model system CaAl2O4: Er3+, co-doped with Yb3+ and Zn2+. UC emission of Er3+ion is enhanced, primarily, through co-operative energy transfer from Yb3+to Er3+ ions. Secondly, we prove that, incorporation of Zn2+ ions alters local crystal field environment around Er3+ ions which causes an enhancement in green UC emission. The variation in intensity ratio of 2H11/2 → 4I15/2 (green) and 4S3/2 → 4I15/2 (green) transitions with temperature is studied to report the sensing property. We show that, sensitivity becomes better with an increase in UC efficiency and the best sensitivity is attained for CaAl(0.793)2Er0.007Yb0.05Zn0.15O4 sample, ∼0.0154 K-1 at 308 K. The obtained result is compared with other works and implies its better suitability. Further, the laser induced optical heating is also observed. The laser induced optical heating has been observed experimentally at 400 K above 1 W laser power. This has been further verified by theoretical justification of heating at various pump powers. © 2018 IOP Publishing Ltd.