Synthesis and Characterization of Oxygen Doped ZnTe for Powder Phosphor Application
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V. Valdna Tallinn Technical University, 19086 Tallinn, Estonia (Received 22 December 2004; accepted 31 May 2005)
The synthesis of efficient ZnTe powder phosphors is very difficult due to its high moisture sensitivity and chemical instability during processing. In this study, an efficient ZnTe:O powder phosphor for x-ray imaging application was successfully synthesized by vacuum firing ZnTe powder prepared from ZnTe bulk crystals ball-milled in an O2 atmosphere. The phosphors were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, photoluminescence, and cathodoluminescence (CL) measurements and found to exhibit a luminescent efficiency three times that of ZnTe:O prepared by ZnO doping. The ZnTe:O samples exhibited a deep red emission centered at 680 nm and a CL decay time of 1.1s.
I. INTRODUCTION
As one of the most efficient and versatile phosphors, with application in cathode ray tubes and electroluminescent devices, doped ZnS has been widely used for many years to produce blue to red light. Intense green and red luminescence has also been achieved in doped ZnSe.1 ZnSe:Cu,Cl is a red emitting (650 nm) scintillator with the highest known x-ray conversion efficiency. However, ZnSe is not suitable for multi-wavelength anomalous dispersion (MAD) studies because the atomic absorption edge of the Se atom interferes with some biological cells. As the counterpart of ZnS and ZnSe, ZnTe can avoid this problem and can potentially achieve efficiencies comparable to ZnSe.2 The objective of this research is to synthesize ZnTe powder phosphor materials that can be screened for large-area (20 × 20 cm) x-ray imaging screens and match the spectral sensitivity of convenional red sensitive charge coupled device (CCD) detectors, which has a quantum efficiency that peaks near ∼700 nm. However, unlike ZnS and ZnSe, high-efficiency ZnTe phosphors are very difficult to synthesize in powder form, probably due to their high moisture sensitivity and chemical instability during synthesis. Thus, most of the recent research on ZnTe has been focused on the synthesis of pure or doped ZnTe films for electro-optic applia)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0299 2510
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 9, Sep 2005 Downloaded: 14 Mar 2015
cations. Bulk ZnTe crystals can be synthesized by meltor vapor-phase techniques.3–6 Also, ZnTe thin films have been fabricated by epitaxial growth techniques.7–10 However, little work has been reported on the synthesis of efficient luminescent ZnTe for powder phosphor applications. The photoluminescence of doped ZnTe has been widely reported,3,4,8–18 with effective dopants including oxygen,3,11–17 copper,4,18 ytterbium,9 arsenic,10 etc. However, no emission of suitable intensity and spectral properties for phosphor applications was reported. In 1962, Dietz et al. reported a broad red emission centered at ∼660 nm from vapor-grown ZnTe bulk crystals measured at 20 K.11 From additional investigations on m
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