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.