Er3+/Yb3+ codoped phosphor Ba3Y4O9 with intense red upconversion emission and optical temperature sensing behavior†
Abstract
The Ba3Y4O9 host matrix with a low cutoff phonon energy of 585 cm−1 is first applied to upconversion (UC) luminescence (UCL) by codoping Er3+/Yb3+. The new phosphor shows an intense red UC emission which is 6.8-fold and 5.9-fold stronger than that of Y2O3 and β-NaYF4, respectively, under 980 nm GaAs laser diode (LD) excitation at a low density. A broad absorption band centered at 976 nm is observed, meaning a high adaptability to the GaAs LD required in actual applications. The optical thermometry behaviors based on the temperature dependent fluorescence intensity ratios of thermally coupled green UC bands 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 as well as the thermally coupled red UC emission bands originating from the Stark sublevels of 4F9/2 manifold have been explored. The results show that green emissions are suitable for temperatures above 350 K with the maximum sensitivity of 0.00248 K−1 at 563 K and the red emissions are appropriate for temperatures below 350 K with the maximum sensitivity of 0.00371 K−1 at 143 K in our experimental range, indicating their complementary temperature sensing ranges. Moreover, a new method is proposed for evaluating the radiative lifetime of the Er3+ 4F9/2 state based on the analysis of photoluminescence (PL) spectra and fluorescence decay curves. The radiative lifetime of 879 μs for the red emitting level in Ba3Y4O9 is achieved. Thereby, the emission efficiency of 4F9/2 in the new UCP is a little higher than that in Y2O3. Our results imply that Ba3Y4O9:Er3+/Yb3+ is a promising UCP, which could be applied to wide scope optical thermometry using a dual-color scheme.