UVB upconversion of LiYO 2 :Ho 3+ ,Gd 3+ for application in luminescence thermometry.

Development of novel ultraviolet (UV) upconversion materials has been emerging as a hot research topic for application in tunable UV lasers, photocatalysis, sterilization, tagging, and most recently luminescence thermometry. We readily synthesized a series of Ho 3+ /Gd 3+ co-doped LiYO 2 upconversion phosphors by a traditional high-temperature reaction. Under excitation from a blue ∼445 nm laser, LiYO 2 :Ho 3+ ,Gd 3+ polycrystalline powders yield intense sharp ultraviolet B (UVB) upconversion luminescence from Gd 3+ 6 P j ( j = 7/2, 5/2, 3/2) excited states. By means of steady and dynamic photoluminescence spectra, we systematically investigated the involved two-photon absorption upconversion as well as the accompanying energy transfer processes between Ho 3+ and Gd 3+ ions in the LiYO 2 host lattice. Interestingly, the distinguishable UVB luminescence constituents from Gd 3+ 6 P j excited states exhibit sensitive temperature dependence in a 353-673 K range. Shedding light on thermal equilibria between Gd 3+ 6 P j UV-emitting levels, their luminescence intensity ratios follow Boltzmann statistics for the application of new luminescence thermometry. For the scheme of 6 P 7/2 - 6 P 3/2 thermally coupled levels, it works over a temperature range of 373-673 K with a maximum relative sensitivity ( S r ) of about 1.07% K -1 at 373 K, and its 6 P 7/2 - 6 P 5/2 counterpart works over 353-533 K with a maximum S r of about 0.83% K -1 at 353 K. Overall, our study provides a new pathway to develop UV upconversion materials, and promotes the application of Gd 3+ -related UV luminescence constituents in sensitive temperature sensing over a wide temperature range.