Strong green up-conversion luminescence and optical thermometry of Ho3+/Yb3+ Co-doped AlN submicron towers

Rare-earth (RE) doped aluminum nitride (AlN) holds great promise for integrated optoelectronic devices. Here, the Ho and Yb co-doped AlN (AlN:Ho3+/Yb3+) submicron towers were prepared by a direct nitridation route. XRD, Raman, XPS and EDS studies showed successful doping of Ho and Yb ions into AlN. SEM images show that the submicron towers have an interesting layered structure by layer-by-layer stacking of hexagonal AlN nanosheets. Under excitation at 980 nm, AlN:Ho3+/Yb3+ submicron towers exhibit up-conversion (UC) luminescence at 540, 550, 659, and 762 nm, which are due to Ho3+/Yb3+ system from 5F4, 5S2→5I8, 5F5→5I8, and 5F4, 5S2→5I7 respectively. Based on the intensity ratio and decay lifetime of UC luminescence, the optical temperature sensing characteristics are investigated from 298 K to 548 K. The maximum relative sensitivities associated with the intensity ratio of I540, 550 and I659 and decay lifetime of 659 nm are as high as 2.73% K−1 and 0.43% K−1, respectively. This work broadens the optoelectronic properties of RE doped AlN.