Nuclear Instruments and Methods in Physics Research A 486 (2002) 367–373 Study of optical and luminescent properties of some inorganic scintillators in the fundamental absorption region V.V. Mikhailin*, A.N. Belsky, I.A. Kamenskikh, V.N. Kolobanov, P.A. Orekhanov, I.N. Shpinkov, D.A. Spassky, A.N. Vasil’ev Synchrotron Radiation Laboratory, Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow 119899, Russia Abstract The relaxation of electronic excitations in scintillating crystals is discussed in terms of recombination of correlated and stochastic electronic excitations. The effects of impurities and excitation density on the intrinsic luminescence yield in the fundamental absorption range and luminescence spectra are analyzed. r 2002 Elsevier Science B.V. All rights reserved. PACS: 78.60; 29.40.M Keywords: Energy relaxation; Vacuum ultraviolet region; Correlated electronic excitations 1. Introduction For most applications high scintillation yield is one of the main priorities in the choice of a specific material, that is why different stages of energy conversion and relaxation were under scrutiny in many papers. The present revival of interest towards tungstate crystals was triggered by the application of PbWO 4 in high-energy physics, which seems to be an exception since the yield in this case is not the key issue due to extreme high energy of incident particles. However, radiation hardness and reproducibility of scintillation prop- erties addressed the problems of the energy transfer in this case as well. This paper is intended to illustrate what type of information essential for the application of scintillating crystals in their working range (high-energy photons or particles) can be derived from their studies in the vacuum ultraviolet (VUV) region. Probably, the first tungstate crystal studied in any detail was CaWO 4 , which has been applied for the conversion of X-rays to visible light for more than 100 years. In Ref. [1] it was shown that CaWO 4 had a constant luminescence energy yield in the X-ray region (providing a scintillation response proportional to the energy of the incident photons or particles); however, in the VUV region its luminescence yield was oscillating (Fig. 1). From the first glance the yield in the X-rays appears as an average over the VUV range. The reason for that was investigated in Refs. [2–4]. The main results useful for the present discussion can be summarized as follows. *Corresponding author. Physics Department, Synchrotron Radiation Laboratory, Moscow State University, Vorob’evy Gory, 117234 Moscow, Russia. Tel.: +7-95-9393169; fax: +7- 95-9392991. E-mail address: mikh@opts.phys.msu.ru (V.V. Mikhailin). 0168-9002/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0168-9002(02)00735-0