Photoluminescence properties of a hollandite compound K₂Ga₂Sn₆O₁₆

Abstract

A hollandite compound K 2 Ga 2 Sn 6 O 16 (KGSO) has photocatalytic activity, although little is known about the optical properties of the compound. To design a higher quality photocatalyst, studies on its optical properties are required. In this study, a KGSO powder and a SnO 2 (rutile structure) powder were prepared by the sol-gel method. Photoluminescence (PL) and PL excitation spectra of the two powders were measured. To our knowledge, this is the first report of PL from a hollandite compound. It was found that the band gap energy of the KGSO powder is 3.6 eV, the value of which is identical with that of the band gap energy of SnO 2 . This was confirmed by the result of the photoacoustic spectrum of the KGSO. The shapes of the PL excitation spectra of the two powders agreed. Moreover, the PL spectra of the two powders have one broad band around 600 nm. From these results, one can conclude that the mechanism of PL of KGSO is the same as that of SnO 2 . In air with ethanol, however, the time-course of the KGSO powder was different from that of the SnO 2 powder. By adding ethanol vapor in air, the PL intensity of the SnO 2 powder increased, whereas the PL intensity of the KGSO powder remained unchanged. By comparing the PL time-courses of the two powders with those of a commercial rutile TiO 2 powder, it was concluded that the photodesorption of O 2 in air with ethanol occurs on the SnO 2 powder, not on the KGSO powder. This was supported by the results of the inorganic carbon concentrations on the two powders. These results indicate that the behavior of O 2 on the KGSO surface during a photocatalytic oxidation is different from that on the SnO 2 surface during the oxidation. q