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/Gd co-doped LiYO upconversion phosphors by a traditional high-temperature reaction. Under excitation from a blue ∼445 nm laser, LiYO:Ho,Gd polycrystalline powders yield intense sharp ultraviolet B (UVB) upconversion luminescence from GdP ( = 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 and Gd ions in the LiYO host lattice. Interestingly, the distinguishable UVB luminescence constituents from GdP excited states exhibit sensitive temperature dependence in a 353-673 K range. Shedding light on thermal equilibria between GdP UV-emitting levels, their luminescence intensity ratios follow Boltzmann statistics for the application of new luminescence thermometry. For the scheme of P-P thermally coupled levels, it works over a temperature range of 373-673 K with a maximum relative sensitivity () of about 1.07% K at 373 K, and its P-P counterpart works over 353-533 K with a maximum of about 0.83% K at 353 K. Overall, our study provides a new pathway to develop UV upconversion materials, and promotes the application of Gd-related UV luminescence constituents in sensitive temperature sensing over a wide temperature range.