New perspective in degradation mechanism of SrTiO 3 :Pr,Al,Ga phosphors
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Jo¨rg Weber Institute for Applied Physics-Semiconductor Physics, TUI-Dresden, Dresden D-01062, Germany (Received 3 February 2004; accepted 2 June 2004)
Under prolonged electron-beam exposure, perovskite-structured SrTiO3:Pr,Al,Ga (STO) phosphor can be easily reduced due to oxygen loss. In particular, it is well known that dissociative H2O molecules are well adsorbed on reduced STO surfaces. The hydroxyl species produced by such dissociative adsorption of H2O strongly decompose organic compounds chemisorbed on the surface from vacuum ambient used in display devices into carbon species due to the photocatalytic properties of STO. Consequently, it is very likely that this mechanism attributes to the larger amounts of carbon adsorption by electron-stimulated chemical reactions on the STO phosphor surface than other phosphors. I. INTRODUCTION
Recently, vacuum fluorescent displays (VFDs) have been investigated for application as display devices for dashboards in cars and cockpits in airplanes, placing severe demands for screen brightness.1 Above all, under these applications, to maintain the adjusted initial color coordinate and such high brightness, the phosphor particles are irradiated for a long time under a high anode current. If any of the selected red, green, and blue (RGB) phosphors tailored for the VFDs suffer from this environment, the light output will decrease, resulting in a color coordinate shift in the display over its lifetime.2 Thus for applications where high current density of electron beam is used, such as in VFDs, the degradation behavior is expected to be a major selection criterion for the phosphor.3 Satisfying these requirements, VFD manufacturers have selected phosphors that are already known and reported in literature.4 However, among the RGB phosphors for the VFDs, (Zn,Cd)S:Ag,Cl currently used as the red-emitting phosphor needs to be substituted by other oxide phosphors in the near future due to instability of the host lattice, such as sulfide and Cd-containing material.5–7 Thus, the development of new red-emitting phosphors with high efficiency is urgently needed for low voltage display applications. In 1996, a new red-emitting phosphor, SrTiO3:Pr3+ was successfully developed by adding Al and/or Ga, which offers the high low voltage cathodoluminescence (CL) efficiency a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0337 2694
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 9, Sep 2004 Downloaded: 14 Mar 2015
and excellent color purity.8–10 SrTiO3:Pr,Al,Ga (STO) phosphor-based low voltage display devices, however, have exhibited short lifetimes. The characteristics of these drawbacks include rapid degradation of low voltage CL of phosphors. Even though there have been several reports on these properties, there is no clear-cut understanding yet.11–13 Thus, in this study, we propose a new mechanism which can provide explict understanding as to the rapid degradation of low voltage CL. II. EXPERIMENTAL A. Synthesis of phosphors
The SrTiO
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