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Photochromic materials have attracted increasing interests as optical switchers and erasable optical memory media. Here, we report on a novel reversible colorless-cyan photochromic powder material Sr3YNa(PO4)3F:Eu 2+ . The photochromic properties including coloring and bleaching are characterized by reflectance spectra after the powder is irradiated by different wavelength light for different irradiation times or thermal treatment. The results turn out that it can be colored by short wavelength light (200-320 nm) and bleached by longer wavelength light (320-800 nm) or thermal treatment at 240 °C. The optimal doping concentration of Eu 2+ is determined to be about 0.5 mol%. It shows high fatigue resistance in photochromism performance. Electrons in 4f ground levels excited by short wavelength irradiation to higher 5d states of Eu 2+ and then captured by traps are responsible for the coloring process. Correspondingly, the releasing of trapped electrons from two kinds of traps with different depths causes the initially fast and later slow bleaching processes. The critical role of charge carrier motions between two different traps is discussed. The colorless-cyan photochromism can be explained semi-quantitatively on the basis of obtained results. A tentative model was proposed to illustrate the PC mechanism.

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A novel blue-emitting phosphor Na 2 ZnGeO 4 and a novel green-emitting phosphor Na 2 ZnGeO 4 :Mn 2+ have been newly developed via high-temperature solid-state reaction. The crystal structure of Na 2 ZnGeO 4 has been identified. Energy transfer from Na 2 ZnGeO 4 host to Mn 2+ ions was affirmed. Undoped and Mn 2+ -doped Na 2 ZnGeO 4 phosphors exhibit blue and green long persistent luminescence (LPL) with persistent duration more than 40 min and 4 h, respectively. The traps created in host lattice were clarified. The LPL mechanism in Na 2 Zn-GeO 4 and Na 2 ZnGeO 4: Mn 2+ was discussed briefly. This investigation provides two new and efficient long persistent phosphors (LPPs).J. Ballato-contributing editor Manuscript No. 35621.