| Summary: | Highly transparent Ho:Y<sub>2</sub>O<sub>3</sub> ceramics for laser diode lighting were prepared using the vacuum sintering method with 0.3 at.% Nb<sub>2</sub>O<sub>5</sub> as a sintering additive. The microstructures, transmittance, and luminescence properties of the Ho:Y<sub>2</sub>O<sub>3</sub> ceramic samples were investigated in detail. The transmittance levels of all samples with various Ho<sup>3+</sup> concentrations reached ~81.5% (2 mm thick) at 1100 nm. Under the excitation of 363 nm (ultraviolet) or 448 nm (blue) light, Ho:Y<sub>2</sub>O<sub>3</sub> transparent ceramic samples showed that green emission peaked at 550 nm. The emission intensity was strongly affected by the concentration of Ho<sup>3+</sup> ions, reaching its highest level in the sample doped with 1 at.% Ho<sup>3+</sup>. The CIE coordinates of the luminescence were in the green region (i.e., the CIE coordinates of the sample doped with 1 at.% Ho<sup>3+</sup> were [0.27, 0.53] and [0.30, 0.69], under the excitation of 363 nm and 448 nm light, respectively). The possibility of its application as laser diode lighting was reported. Under the excitation of 450 nm blue laser, the sample doped with 0.5 at.% Ho<sup>3+</sup> had the best performance: the saturated luminous flux, lumen efficiency, and the luminescence saturation power densities were 800 lm, 57.7 lm/W, and 17.6 W/mm<sup>2</sup>, respectively. Furthermore, the materials have high thermal conductivity and mechanical strength due to their host of rare-earth sesquioxide. Thus, Ho:Y<sub>2</sub>O<sub>3</sub> transparent ceramics are expected to be a promising candidate for green-light-emitting devices for solid-state lighting, such as laser diode lighting.
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