LiYF4-nanocrystal-embedded glass ceramics for upconversion: glass crystallization, optical thermometry and spectral conversion

UVB upconversion of LiYO2:Ho3+,Gd3+ 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 Ho3+/Gd3+ co-doped LiYO2 upconversion phosphors by a traditional high-temperature reaction. Under excitation from a blue ∼445 nm laser, LiYO2:Ho3+,Gd3+ polycrystalline powders yield intense sharp ultraviolet B (UVB) upconversion luminescence from Gd3+ 6Pj (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 Ho3+ and Gd3+ ions in the LiYO2 host lattice. Interestingly, the distinguishable UVB luminescence constituents from Gd3+ 6Pj excited states exhibit sensitive temperature dependence in a 353-673 K range. Shedding light on thermal equilibria between Gd3+ 6Pj UV-emitting levels, their luminescence intensity ratios follow Boltzmann statistics for the application of new luminescence thermometry. For the scheme of 6P7/2-6P3/2 thermally coupled levels, it works over a temperature range of 373-673 K with a maximum relative sensitivity (Sr) of about 1.07% K-1 at 373 K, and its 6P7/2-6P5/2 counterpart works over 353-533 K with a maximum Sr 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 Gd3+-related UV luminescence constituents in sensitive temperature sensing over a wide temperature range.

Dual-wavelength enhanced upconversion luminescence properties of Li+-doped NaYF4:Er,Yb glass-ceramic for all-optical logic operations

Rare earth-doped oxyfluoride glass-ceramic (GC) demonstrate the physical, chemical, and mechanical stabilities of oxide glass and excellent optical properties of fluoride crystals and is regarded as a potential material for developing advanced optical devices. In the present study, Li⁺-doped NaYF₄:Er,Yb GC was prepared by the traditional melt-quenching method. Upon the excitation of single 980 and 1550 nm lasers, the upconversion (UC) luminescence intensities of green and red emission were enhanced due to the introduction of the crystal field symmetry reducing available Li⁺ ions of the use of dual-wavelength (980 and 1550 nm) co-excitation and could further enhance the UC luminescence intensity owing to its synergetic effect, which is suitable for the design of all-optical logic gates. The all-optical UC logic gates and complex logic operations ("YES + OR", "INH + YES", "XOR + YES", and "INH + AND + YES + OR") are designed by taking the two excitation sources as input signals and UC emission as output signals. The results provide a novel strategy to enhance UC luminescence and further information for the design of novel photonic logic devices for future optical computing technologies.

Luminescence properties of Ba4Yb3F17:Er3+ nanocrystals embedded in glass ceramics for optical thermometry

Transparent glass ceramics (GCs) containing Ba₄Yb₃F₁₇:Er³⁺ nanocrystals were successfully fabricated by a traditional melt-quenching method. The formation of Ba₄Yb₃F₁₇ nanocrystals was confirmed by X-ray diffraction, transmission electron microscopy, and selected area electron diffraction. Compared with the precursor glass, the enhanced emission intensity and lifetime of GCs indicate that the Er³⁺ ions incorporate into the Ba₄Yb₃F₁₇ nanocrystals after crystallization. The color tuning properties with doping under 980 nm excitation have been systematically discussed. It was found that the red/green ratio increased with Er³⁺ ion doping and the corresponding color changed from greenish-yellow to yellow-green. Furthermore, the temperature-dependent luminescence properties were studied in detail by the fluorescence intensity ratio (FIR) technique. The monotonic change of FIR with temperature indicates that this material is suitable for temperature sensing. At a temperature of 450 K, the relative sensitivity of the prepared sample reached its maximal value of 0.20% K⁻¹. The results show that the GCs containing Ba₄Yb₃F₁₇:Er³⁺ nanocrystals are candidate materials for temperature sensing.

Transparent glass ceramic embedded with Ba₄Yb₃F₁₇:Er³⁺ nanocrystals can be applied as a promising temperature sensor.