The Er 3+ doped double perovskite Ba 2 CaWO 6 crystal is a promising ratiometric thermometer based on the fluorescence intensity ratio (FIR) of transitions from 2 H 11/2 and 4 S 3/2 to the lowered 4 I 15/2 level. However, the Ca 2+ vacancy defect caused by the charge difference between rare-earth ions and the substituted alkaline-earth ions gives rise to the non-radiative probability and limits the thermal sensitivity. Here, the up-conversion luminescence and thermometric performance of Er 3+ , Yb 3+ doped Ba 2 CaWO 6 are tuned by tri-doping with alkaline ions. The Ca 2+ vacancy defect can be eliminated by the introduction of Na + , which occupies the Ca 2+ site when it is doped into Ba 2 CaWO 6 with Er 3+ and Yb 3+ . On the contrary, the doping of Cs + into Ba 2 CaWO 6 with Er 3+ and Yb 3+ enhances the defect concentration because it occupies the site of Ba 2+ . Thus, the tri-doping of Na + reduces the non-radiative probability and enhances the quantum efficiency of Er 3+ , leading to the improvement of the thermometric sensitivity of Ba 2 CaWO 6 . As a result, we get an excellent thermometric Ba 2 CaWO 6 :8%Yb 3+ ,3.5%Er 3+ ,6%Na + powder with a luminescence lifetime of 515 μs and maximum thermal sensitivity ( S r ) of 1.45%/K, which is more than three times higher than that of the BCWO:Er 3+ powder.
Currently, Mn 4+ -activated phosphors have attracted extensive attention for their versatile applications in general lighting, display and plant cultivation. Owing to 3d 3 electronic configuration of Mn 4+ ion, modifying its local coordination environment emerges as a potent method to tailor its luminescence behavior. Herein, a heterovalent substitution strategy is reported to greatly enhance the photoluminescence (PL) of Ba 2 CaWO 6 :Mn 4+ . The effects of the substitution of rare-earth ions (Ln 3+ = Lu 3+ , Y 3+ , Gd 3+ , La 3+ ) for Ca 2+ ions on the PL properties of the phosphor are studied in detail. The PL spectral change of Mn 4+ induced by Ln 3+ substitution is clarified in terms of the local structure of [WO 6 ] octahedron and the valence state of Mn. By selection of Ln 3+ ions and optimization of Ln 3+ doping concentration, the emission intensity of Ba 2 Ca 0.85 Gd 0.15 WO 6 :0.25Mn 4+ phosphor reaches up to 46.3 times as that of Ba 2 CaWO 6 :0.25Mn 4+ . Besides, the Ba 2 Ca 0.85 Gd 0.15 WO 6 :0.25Mn 4+ phosphor exhibits an internal quantum yield of 56.9 % and a thermal stability of 72.6 %@423 K. Finally, Ba 2 Ca 0.85 Ln 0.15 WO 6 :Mn 4+ based phosphor conversion LED devices are demonstrated, which can be potentially employed for indoor plant lighting.
This research focuses on the fluorescent powder materials based on a single matrix of this type of LED. Taking Ba2CaWO6 as an example, mixing Dy3+ alone can produce blue and white light at 318nm UV excitation. At the same time, mixing Dy3+
with Eu3+ can make the fluorescent powders realize the emission of 491 nm/577 nm of Dy3+ and 588 nm of Eu3+. Dy3+ is set to 0.06 and the ratio of Eu3+ is adjusted to make the luminous color gradually close to white. In the study of Ba3Y(PO4)3
· xDy3+ · yEu3+, x is set as 0.07, and the content of y is set as 0.01∼0.08. Dy3+ alone will emit blue and white light under the laser at 391 nm. By increasing the content of Eu3+, polychromatic emission
can be carried out, and white light can be obtained by adjusting the concentration of Eu3+. At the same time, the application functions of white LED packaging are tested for the above materials. The results show that both Ba2CaWO6 · xDy3+
· yEu3+ and Ba3Y(PO4)3 · xDy3+ · yEu3+ materials can realize white lighting by adjusting the ratio of Eu3+ · Dy3+, increasing the proportion of Eu3+
can improve the color rendering of white LED.
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