Effect of Microstructure on Photo-Induced Current Characteristics of Eu²⁺-Doped SrAl₂O₄

Research interest is active in Eu²⁺/Dy³-doped SrAl₂O₄ phosphors, and the photocurrent characteristics of Eu²⁺-doped SrAl₂O₄ without Dy³⁺ was investigated extensively. However, it exhibits a low photocurrent of ~1 μA owing to high resistance. In this study, the changes in a photo-induced current with grain size were examined. The effect of the processing methods on the microstructure and photocurrent characteristics of Eu²⁺-doped SrAl₂O₄ phosphors was investigated. (Sr_0.99Eu_0.01)Al₂O₄ powders were synthesized using a conventional solid-state method and calcined at 1350 °C under a 3% H₂/(Ar + H₂) reducing gas atmosphere. Sample pellets were fabricated as conventional and hot-press-sintered bodies at 1400 °C. A thin film of the sample was deposited on an alumina substrate by radio-frequency magnetron sputtering. Scanning electron microscopy revealed that the hot-press-sintered body has larger grains than the conventionally sintered body. The photo-induced current of the hot-press-sintered body at 400 lx was ~100 and ~1000 times higher than those of the conventionally sintered body and thin film, respectively. Impedance analysis confirmed that this dramatic increase in the photo-induced current is closely related to the increase in the grain size and crystallinity of the sample. This study verifies the applicability of Eu²⁺-doped SrAl₂O₄ as both a phosphor and photosensor.