Luminescence of SrY 2 O 4 :Eu 3+ associated with defects
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SrY2O4:Eu3þ phosphors were synthesized by both the solid-state reaction method and the sol-gel method, and their photoluminescence in vacuum ultraviolet (VUV) and the ultraviolet (UV) region were evaluated. The excitation spectra of SrY2O4:Eu3þ phosphors prepared by solid-state reaction show another excitation band centered at 324 nm except for the charge-transfer bands (CTB) of Eu3þ when monitored at 610 nm, and a blue emission band around 406 nm is observed when excited at 324 nm, which could be associated with defects. Both the excitation and emission bands mentioned above disappear when the samples were prepared by the sol-gel method. SrY1.98O4:0.02Eu3þ phosphors synthesized by the sol-gel method exhibit a higher emission intensity under 147 nm excitation compared with solid-state reaction technology. The main reason could be that the samples prepared by the solution-based route have more regular and uniform morphologies.
I. INTRODUCTION
Phosphors are an essential component in emerging technology in lighting and display devices.1 Currently, there is a demand for the development of new phosphors that can be excited under ultraviolet (UV) and vacuum ultraviolet (VUV).2,3 Therefore, it is imperative to explore new luminescent materials suitable for display and lighting devices and to carry out basic research on phosphors. SrY2O4 belongs to CaFe2O4-related structures, and there are three types of cation sites in the SrY2O4 structure: Sr, Y(1), and Y(2).4,5 When the SrY2O4:Eu3þ samples were prepared at high temperature, it was possible for Eu3þ to substitute all cation sites simultaneously.6 So far, the studies on SrY2O4:Eu3þ phosphor are mainly focused on the Eu3þ ions occupying sites in SrY2O4 under UV excitation4,5,7,8 and the VUV luminescence properties.6,9 Although many studies indicate emission from multiple Eu3þ centers, there does not appear to be general agreement on the assignment of the sites.6 Nevertheless, it has been reported that the charge transfer bands (CTB) of Eu3þ are located between 200 and 300 nm in almost all the references on SrY2O4:Eu3þ except for Xu et al.,7 in which the band of 300–350 nm in excitation spectrum is assigned to the CTB of Eu3þ at Sr2þ sites. But this band was not reported in Park et al.,4 Fu et al.,5 or Fu et al.8 In addition, a new excitation band centered at 295 nm and an emission band around 470 nm, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0283
2120
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 11, Nov 2010 Downloaded: 25 Jun 2014
which have a relationship with oxygen deficiency, were detected when the SrY2O4:Eu3þ sample was prepared in a reducing atmosphere.4 To sum up, considering such differences in the literature, it is necessary to further clarify the attribution of the excitation band in the excitation spectrum. The sol-gel synthesis method was also adopted. The VUV-UV spectroscopic properties of SrY2O4:Eu3þ phosphors prepared by both solid-state reaction and the sol-gel method were investigated. II
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