Aierpati Taximaimaiti,Aierken Sidike,Halizati Abulimiti,Qingling Wang
In this paper, a SrAl2Si2O8:Tm3+,Yb3+ upconversion (UC) phosphor was prepared with a high-temperature solid-phase method, and proved that the strontium feldspar structure was an excellent UC matrix. The Tm3+ were shown to have a maximum relative thermometric sensitivity (Sr) of 1.67% K−1 at 298 K and a maximum absolute thermometric sensitivity (Sa) of 1.34% K−1 at 573 K. The non-thermally coupled energy level corresponded to the maximum relative thermometry sensitivity (Sr) of 2.4% K−1 at 298 K and a maximum absolute sensitivity (Sa) of 13% K−1 at 423 K. The use of the fluorescence intensity ratio of the nonthermally coupled energy levels of Tm3+ for temperature measurements improved the temperature measurement sensitivity of the same material. These results indicated that the phosphor has good temperature sensing performance with a wide sensing range and good stability and has potential thermometry applications in the first biological window.
Upconversion luminescent (UCL) materials have broad application prospects in the field of temperature sensing; thus, improving the luminescence performance and temperature measurement sensitivity of upconversion phosphors is highly important. In this study, SrAl 2 Si 2 O 8 with good thermal stability was doped with Ho 3+ and Yb 3+ , and the optimal concentration was determined to be SrAl 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ (in mole fraction). A series of (Sr 0.87‒ x Ba x )Al 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ phosphor samples was prepared by using a cationic substitution strategy and further doping Ba 2+ to replace the Sr 2+ lattice in the matrix. The results show that the introduction of Ba 2+ effectively replaces Sr 2+ and significantly increases the upconversion fluorescence emission intensity of SrAl 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ by approximately 2.9 times. The temperature sensing properties of SrAl 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ and Sr 0.37 Ba 0.50 Al 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ were investigated. The Ho 3+ -based 5 F 5 and 5 S 2 / 5 F 4 nonthermal coupled energy level fluorescence intensity ratio (FIR) techniques in the Ba 0.37 Sr 0.50 Al 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ phosphors show a maximum temperature measurement absolute sensitivity of 4.32%/K at 573 K and a maximum relative sensitivity of 1.08%/K at 373 K; these values are 5.8 and 3.2 times greater, respectively, than that of the non-Ba 2+ -doped SrAl 2 Si 2 O 8 :1%Ho 3+ , 12%Yb 3+ phosphor. These results not only confirm the effectiveness of the cation substitution strategy in enhancing the upconversion luminescence performance and temperature sensing characteristics but also provide a scientific basis for the design of high-performance optical temperature sensors.
In this paper, monoclinic SrAl 2 Si 2 O 8 ceramics with porous structures were prepared based on ion-exchanged geopolymer precursor technique. Micron-level pores with a homogeneous pore-size distribution were introduced into the inorganic framework using foaming agents. The results demonstrated that the apparent density, pore-size distribution and specific surface area of porous geopolymer precursors can be well-engineered via tailoring the category and concentration of the foaming agent. After being treated at 900°C, hexagonal SrAl 2 Si 2 O 8 first-crystallized from the amorphous geopolymer matrix and then gradually converted into monoclinic SrAl 2 Si 2 O 8 between 1100°C and 1200°C. The resulting monoclinic SrAl 2 Si 2 O 8 ceramics maintained the porous structures during high-temperature treatments and exhibited high porosity, specific surface area, and compressive strength. The aforementioned strategy not only achieves monoclinic SrAl 2 Si 2 O 8 ceramics with well-defined and robust microstructures, but also provides an alternative route to prepare other porous ceramics, with potential applications in fields of high-temperature filters, adsorbents, and heterogeneous catalysis.
To achieve high-color-rendering WLED devices, exploration of blue‒cyan phosphors that can be excited by near-ultraviolet (NUV) chips is particularly important to compensate for the cyan gap. In this work, feldspar-structured Sr 1-y Al 2- x Ga x Si 2 O 8 :yCe 3+ blue-cyan phosphors were prepared via a high-temperature solid-phase method and a cation substitution strategy. The luminescence performance of the Sr 0.96 Al 2 Si 2 O 8 :0.04Ce 3+ sample was improved by applying the cation substitution strategy of partially replacing Al 3+ with Ga 3+ , and the representative sample Sr 0.96 Al 1.4 Ga 0.6 Si 2 O 8 :0.04Ce 3+ was obtained. The luminescence intensity increased threefold for the Sr 0.96 Al 1.4 Ga 0.6 Si 2 O 8 :0.04Ce 3+ compound compared to Sr 0.96 Al 2 Si 2 O 8 :0.04Ce 3+ , and a broadband blue‒cyan phosphor with a half-height width of 100 nm was obtained. The representative sample Sr 0.96 Al 1.4 Ga 0.6 Si 2 O 8 :0.04Ce 3+ showed relatively good thermal stability. Sr 0.96 Al 1.4 Ga 0.6 Si 2 O 8 :0.04Ce 3+ was combined with 365 nm NUV LED chips and commercial (Sr, Ca)AlSiN 3 :Eu 2+ to obtain WLED devices with color rendering index (Ra) as high as 94.8 and correlated color temperatures (CCTs) as high as 4831.4 K. These results show that the blue-cyan phosphor complements the cyan component while simplifying the manufacturing process of WLEDs.
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