In this work, the nitriding method was used to improve the up-conversion (UC) luminescence intensity and temperature sensing sensitivity of phosphor materials. Yb 3 Al 5 O 12 : Er 3+ and partially nitrided Yb 3 Al 5 O 12-1.50 x N x : Er 3+ phosphors by using AlN as nitrogen source were prepared via solid-state reaction method. The influence of nitridation on the UC luminescence and temperature sensing properties of Yb 3 Al 5 O 12 : Er 3+ phosphors upon 980 nm excitation were discussed. Almost pure red UC emission was obtained, and the intensity of the red UC emission of the samples was enhanced by 25 % after nitridation. Meanwhile, the absolute temperature sensitivity respectively derived from the intensity ratios of the green and red emissions increased by 5 % and 50 % after nitridation. Judd-Ofelt theory was utilized to analyze the change of the crystal field environment around Er 3+ and confirmed that the introduction of N 3– reduced the symmetry around Er 3+ and strengthened the covalence between Er 3+ and ligands, which may result in the enhancement of UC emission intensity and temperature sensing sensitivity. The experiment proved that Yb 3 Al 5 O 12 : Er 3+ red UC phosphors had potential application in luminescence imaging and temperature sensors.
The high solar reflectance and good colour performance are requisite for the practical application of the colour-cool pigment. In this work, Ce-doped Yb 3 Al 5 O 12 and (Y, Yb) 3 Al 5 O 12 ceramic pigments were prepared by the sol-gel method. Both Ce 3+ and Ce 4+ ions coexist in the doped pigments. Due to the 4f→5d electron transition of Ce 3+ , the Ce-doped pigments have a selective absorption at around 400–520 nm, which is responsible for the yellow hue. The content of the Ce 3+ ion determines the colour performance of the pigment. The size effect from the smaller Yb 3+ ion results in an increased content of Ce 3+ in the Ce-doped pigments, leading to an improved colour performance. The incorporation of Y 3+ ion can effectively decrease the absorption at 975 nm, thereby enhancing the solar reflectance to 80.6 %, while maintaining good colour performance (Yb 0.7 Y 2.1 Ce 0.2 Al 5 O 12 , L* = 91.40, a* = -4.89, b* = 45.33). In a simulation experiment, the ceramic glaze coating based on the prepared pigment showed a temperature reduction of 5.2 °C compared to the commercial yellow pigment ceramic coating .
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