Defect formation in photochromic Ca2SnO4: Al³⁺

Photoluminescence, photochromism and defect formation were analysed in Ca₂SnO₄ doped with 0–20% Al³⁺. Bright cyan luminescence attributed to Sn²⁺ was detected in all samples. Introduction of Al³⁺ in Ca₂SnO₄ led to an enhancement of Sn²⁺ emission by up to 70% in comparison with an undoped sample. After exposure to UV irradiation, two absorbance bands centered at 520 nm and 710 nm and three paramagnetic defects were observed in Al³⁺-doped Ca₂SnO₄ samples. The paramagnetic centers were identified as a hole type and two different Sn³⁺ centers. Electron paramagnetic resonance (EPR) data suggested that one of the Sn³⁺ centers is located in a close proximity of Al³⁺. Analysis of the stability of the absorbance bands and paramagnetic centers revealed that the hole type center is related to the 520 nm absorbance band, and one of the Sn³⁺ centers is associated with the 710 nm band. The effect of Al³⁺ on defect formation in Ca₂SnO₄ was discussed.