Er3+/Yb3+ codoped phosphor Ba3Y4O9 with intense red upconversion emission and optical temperature sensing behavior

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 beta-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 H-2(11/2) -> I-4(15/2) and S-4(3/2) -> I-4(15/2) as well as the thermally coupled red UC emission bands originating from the Stark sublevels of F-4(9/2) 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+ F-4(9/2) state based on the analysis of photoluminescence (PL) spectra and fluorescence decay curves. The radiative lifetime of 879 mu s for the red emitting level in Ba3Y4O9 is achieved. Thereby, the emission efficiency of F-4(9/2) 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.