Dual-mode optical ratiometric thermometer based on rare earth ions doped perovskite oxides with tunable luminescence

Rare earth ions doped luminescent materials have drawn considerable attention as they can generate both upconversion and downshifting emissions. Here, the rare earth ions Pr3+/Er3+ codoped perovskite oxide Bi4Ti3O12 is proposed as a dual-mode temperature sensor and anti-counterfeiting material based on its up/down-conversion luminescence. Under 481 nm excitation, the intensity ratio of green emission (∼523 nm in Er3+) and red emission (∼611 nm in Pr3+) brings about a very high absolute sensitivity (Sa) of 2% K−1 at 568 K and a maximum relative sensitivity (Sr) of 1.03% K−1 at 478 K in the temperature range of 298–568 K. In addition, the upconversion green emissions of Er3+ yield a relatively-high Sr of 1.1% K−1 at 298 K with 980 nm excitation, which can provide self-calibration coupled with down-conversion luminescence temperature sensing mode. Besides, this phosphor also shows tunable luminous colors for the potential application in the anti-counterfeiting field under various excitation wavelengths.