ISSN 0030-400X, Optics and Spectroscopy, 2008, Vol. 104, No. 3, pp. 366–373. © Pleiades Publishing, Ltd., 2008. Original Russian Text © O.V. Rzhevskaya, D.A. Spasskiœ, V.N. Kolobanov, V.V. Mikhaœlin, L.L. Nagornaya, I.A. Tupitsina, B.I. Zadneprovskiœ, 2008, published in Optika i Spektroskopiya, 2008, Vol. 104, No. 3, pp. 415–422. 366 INTRODUCTION Cadmium tungstate (CdWO 4 ) is a promising scintil- lation material for X-ray tomography, detection of slow neutrons, and dosimetry [1–3]. The large effective atomic number (z eff = 61.2) and, correspondingly, high density (7.99 g/cm 3 ) provide effective scintillation detection even when a crystal is physically small [2]. The luminescence spectrum of this compound is a wide band in the visible spectral range (λ max ~ 500 nm) and its luminescence decay time is sufficiently short (about 10 μs) for operation in intense X-ray fluxes [1]. In addi- tion, CdWO 4 has advantages over other scintillators with respect to the content of radionuclides and is char- acterized by a high specific light yield (~38% of the corresponding value for NaI–Tl) [2]. With all this, the optical properties of cadmium tungstate in the funda- mental-absorption region have been studied insuffi- ciently. Only recently first theoretical calculations of the density of electron states of the valence and conduc- tion bands of CdWO 4 have been performed [4, 5]. In this paper, the reflection spectra of a high-quality pure CdWO 4 crystal were investigated taking into account the anisotropy of its structure. The problem of optimization of the luminescence properties of this crystal remains urgent. It is known that doping of another representative of tungstates, PbWO 4 , with molybdenum leads to a significant increase in the specific light yield at room temperature [6]. However, for cadmium tungstate doped with molybdenum, an insignificant decrease in the intensity of low-temperature intrinsic luminescence was previ- ously found [7]. In this study, we performed compara- tive investigations of the luminescence properties of a high-quality pure CdWO 4 crystal and a CdWO 4 :Mo crystal doped with molybdenum in different concentra- tions at temperatures of 10 and 300 K. The effect of the molybdenum impurity on the intrinsic luminescence of CdWO 4 was found, and the role of the impurity in the formation of new luminescence centers was investi- gated. The features of the formation of the intrinsic and impurity luminescence excitation spectra of CdWO 4 and CdWO 4 :Mo in the fundamental-absorption region in the temperature range of 10–300 K are considered. EXPERIMENTAL Measurements of the luminescence excitation spec- tra and reflection spectra of CdWO 4 in the energy range 3.7–30 eV, as well as the luminescence spectra upon vacuum UV (VUV) excitation, were performed in the temperature range of 10–300 K, using synchrotron radiation, at the SUPERLUMI system, located in the channel of the DORIS III positron storage ring (DESY, Hamburg) [8]. Synchrotron radiation is most effective and convenient for VUV investigations, since it has an intense continuous emission spectrum in the VUV region, high degree of linear polarization, and a tempo- Optical and Luminescence Properties of CdWO 4 and CdWO 4 :Mo Single Crystals O. V. Rzhevskaya a , D. A. Spasskiœ a , V. N. Kolobanov b , V. V. Mikhaœlin b , L. L. Nagornaya c , I. A. Tupitsina c , and B. I. Zadneprovskiœ d a Skobel’tsyn Research Institute of Nuclear Physics, Moscow State University, Moscow, 119992 Russia b Moscow State University, Moscow, 119992 Russia c Institute for Single Crystals, National Academy of Sciences of Ukraine, Kharkov, 61001 Ukraine d All-Russia Research Institute for Synthesis of Mineral Raw Materials, Aleksandrov, Vladimir oblast, 601600 Russia e-mail: deris2002@mail.ru Received July 30, 2007 Abstract—Luminescence properties of a pure CdWO 4 crystal and a CdWO 4 :Mo crystal doped with molybde- num in different concentrations have been investigated. The effect of molybdenum impurity on the intrinsic luminescence of CdWO 4 has been found, and the role of the impurity in the formation of new luminescence centers has been investigated. The features of the formation of the intrinsic and impurity luminescence excita- tion spectra of CdWO 4 and CdWO 4 :Mo crystals in the fundamental-absorption region have been considered. The reflection spectra of the CdWO 4 crystal have been investigated taking into account the crystal structure anisotropy. PACS numbers: 78.55.-m, 78.40.-q DOI: 10.1134/S0030400X08030090 CONDENSED-MATTER SPECTROSCOPY