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Several bands of fast emission (τ < 2 ns) have been observed in the spectral region of 1.6-6.0 eV in K 2 SO 4 , Rb 2 SO 4 , Cs 2 SO 4 , CaSO 4 , SrSO 4 and BaSO 4 under irradiation by single electron pulses (300 keV, 3 ns, 80 A/cm 2 ) at 80 K. In K 2 SO 4 , Cs 2 SO 4 and BaSO 4 , the photoexcitation of fast emission starts at 14-15 eV. At a crystal heating the intensity of fast emission bands decreases, while the intensity of a structureless intraband luminescence increases (especially at hν > 6 eV). On the basis of our experimental data and band structure calculations, we interpret the observed fast emissions as elecron transitions between the subbands of a split valence band. There are manifestations of the cationic states, superimposed on the states from an oxygen-sulphur medium subband, in the excitation spectra of fast emissions.1 Introduction In addition to impurity luminescence and the luminescence of free or self-trapped excitons, data on two new types of intrinsic emission in several wide-gap crystals was accumulated in the last decades. These two emissions are the so-called intraband luminescence (IBL) and crossluminescence. The IBL arises under irradiation due to the transitions of hot electrons (electron IBL) and hot holes (hole IBL) between the levels of the conduction band or the valence band of a crystal, respectively [1, 2]. The IBL is a fast, continuous and temperature-independent emission in a wide region with a structureless spectrum. The crossluminescence is connected with the radiative transitions of the holes, formed by irradiation in a cation outermost-core band, to the upper anion valence band [3,4]. This emission is also known as Auger-free or core-valence luminescence. The present study is devoted to the fast emissions that can be detected in metal sulphates in addition to IBL and crossluminescence.Several bands of fast (τ < 2 ns) emission have been observed in K 2 SO 4 under irradiation by single nanosecond electron pulses [5]. The threshold exciting photon energy of 15 eV has been detected in the excitation spectra for the most intense emission bands at 5.8 and 3.8 eV. Taking into account the band structure calculations of K 2 SO 4 [6], these fast emissions have been ascribed to the electron transitions between subbands of a splitted valence band [5]. The investigation of the nature of fast emissions and the conditions of their excitation in various metal sulphates has much potential for yielding important information about the structure of a valence band. Therefore, our efforts are aimed at the search for fast emissions and the measuring of the excitation spectra for these emissions in Me 2 SO 4 (Me: Na, K, KLi, Rb, NH 4 ) and MeSO 4 (Me: Ca, Sr, Ba) systems.

. Da:f~l'k /3, 480/00 Almaty, Ka=akhstan .. 'The emission spectra have been measured in the range of 1.6 -9.0eV under irradiation of wide-gap oxides by single electron pulses (3 ns, 300 kV). A fast ( r < 3 ns) continuous and temperature-independent emission, connected mainly with the transitions of hot holes between the levels of the valence band of oxides, can be separated in these spectra at 300 600 K, when the inertial emissions (5-7 eV) of localized excitations undergo a strong thermal quenching. It is suggested that a drastic decrease of the intensity of this so-called hole intraband luminescence (IBL) in a shortwavelength spectral region is caused by the lowering of the density of states at the edges of the valence band and, therefore, supplies information on the width of an anion valence band £, .. The drastic decrease of the IBL intensity takes place at 6.4-8.6eV in BaMgAiw017• SrAI204, MgAI407, MgO and BeO, that agrees satisfactorily with the values of £,. in these systems obtained by other methods.