Photochromic properties in Eu 3+ doped Sr 2 SnO 4

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Photochromic properties in Eu3+ doped Sr2SnO4 Sunao Kamimura1 Hiroshi Yamada1,2 and Chao-Nan Xu 1,2,3 Interdisciplinary Graduate School of Engineering Science, Kyushu University, Fukuoka 816-8580, Japan 2 National Institute of Advanced Industrial Science and Technology (AIST), Saga 841-0052, Japan 3 International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Fukuoka 819-0395, Japan 1

ABSTRACT We report the photochromism (PC) in Eu3+ doped Sr2SnO4. The Sr2SnO4:Eu3+ is sensitive to UV light (λ < 350 nm) and turns to purple color. When visible light (λ  400-700 nm) is irradiated, the colored Sr2SnO4:Eu3+ is bleached. From the results of absorption spectrum, Sr vacancies in the host lattice and charge transfer transition between Eu3+-O2- is responsible for PC process of Sr2SnO4:Eu3+. INTRODUCTION In general, perovskite oxides show various functional properties such as switchable polarization, piezoelectricity, pyroelectricity, and non-linear dielectric behavior [1]. These properties are indispensable for application in electric and optical devices such as non-volatile memories, thermoelectric modules, sensors, microactuators, infrared detectors, microwave phase filters, and so on [1-3]. Despite the diverse function of perovskite oxides, photochromic (PC) properties had been little known until in 1970s Faughnan reported transition-metal doped SrTiO3 [4], which turns to black color by visible light irradiation and the black color is bleached by heating. Here PC is a reversible change in color of materials under light irradiation, and it has application that include rewritable copy papers, smart windows, optical filters and photoswitchs [5,6]. Especially, inorganic PC materials are expected as the high density optical memory devices with small semiconductor laser diodes due to their excellent thermal stability and chemical resistance [7]. Although some inorganic oxides, such as WO3, MoO3, TiO2 and BaMgSiO4, display PC performance [8-11], perovskite oxides which exhibit PC are very attractive because they can be used as multi-functional materials. Recently, rare-earth doped Sr2SnO4, which belongs to the layered perovskite-related structure with space group Pbnb, lattice parameters a = 5.735, b = 12.587, c = 5.728 Å and V = 413.55 Å3 [12], has attracted attention due to showing various optical properties, such as photoluminescence, mechanoluminescence, upconversion [13,14]. In this paper, we report PC performance in Eu3+ doped Sr2SnO4. The Sr2SnO4:Eu3+ shows a colorless before light irradiation and then, after UV light (λ < 350 nm) irradiation, it turns to be purple color. After visible light (λ  400-700 nm) irradiation, the colored Sr2SnO4:Eu3+ is bleached. The PC process for Sr2SnO4:Eu3+ is discussed in accordance with their absorption properties and crystal structure. EXPERIMENTAL The Sr2SnO4:Eu3+ powders were synthesized by a solid reaction process as follows. The starting materials of ultrafine powder of SrCO3, Eu2O3, SnO2 were weighted according to the

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chemical stoichiometry of Sr1.995Eu0.005SnO4

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