We have studied the photoluminescence of calcite crystals. In the blue region of the photoluminescence spectrum of calcite crystals obtained from Siberia (Russia) and from Saaremaa Island (Estonia), three strongly overlapping luminescence bands due to intrinsic defects are observed. Luminescence due to impurities in the crystals are hardly detectable. The experimentally measured time dependence of the luminescence intensity for the indicated luminescence bands is compared with the dependences obtained as a result of a calculation based on a proposed model for the luminescence center. Better agreement between experiment and calculation is achieved if the model of the luminescence center includes a metastable level with electron ejection energy of 4 meV; the characteristic time for the radiative transition is 1.3 nsec. Studying the time dependence of the luminescence at different wavelengths within the indicated bands allows us to conclude that the photoluminescence (three bands) is due to one type of luminescence center.Introduction. Calcite is of interest for geology because it can be used for luminescent dating of various specimens. In nature, calcite is encountered within both biological and geological specimens, and so the possibilities for its use in dating are quite broad. Up to now, the thermoluminescence method has been used for dating using calcite [1,2]. At the same time, the optically stimulated luminescence method has been successfully used for some minerals (for example, quartz and feldspar) [3].In this work, we have studied the short-wavelength portion of the luminescence spectrum of calcite in order to refine the mechanism of luminescence in calcite and to expand the possibilities for using this compound in luminescent dating. Most researchers (see, for example, [3][4][5][6][7][8]) believe that luminescence of undoped calcite is observed in the blue region of the spectrum (400-450 nm). But in [6,7], it is suggested that the luminescence bands at wavelengths of 520 nm, 575 nm, and 640-660 nm are also not associated with impurities. The luminescence of undoped calcite has not been sufficiently studied, and different researchers have presented different spectra for it. This may be due to the fact that the luminescence originates from different intrinsic defects in the calcite and also the fact that the spectrum of the relatively weak luminescence of intrinsic defects is distorted by the luminescence of poorly studied impurities. For example, according to the data in [9], in the 400-500 nm region of the spectrum, we may encounter luminescence bands that can be attributed to Eu 2+ impurity. All the indicated luminescence bands are quite weak compared with the luminescence due to Mn 2+ impurity, the luminescence of which more or less masks the bands due to intrinsic defects [4]. The luminescence of Mn 2+ impurity with maximum at about 590-620 nm has been studied more completely.The experiment. The calcite crystals were placed into a cryostat, which made it possible to make the measurements both at 293 K a...

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The effect of IR irradiation on the shape of the individual luminescence band of ZnS=Cu phosphors was investigated in [1][2][3][4]. In this paper we use this effect to determine the structure of the luminescence centers and the mechanism of IR quenching.There are two different explanations of the change in the shape of the individual luminescence band due to IR light. According to the first, some of the energy of the iR quanta is transferred directly [2], or by means of optical electrons [3], to the luminescence centers (optical electrons are electrons which are released by the IR light and have excess energy in comparison with the equilibrium electrons [3]). This excess energy, which brings some of the centers into a nonequilibrium state, is the reason for the indicated effect. According to the second viewpoint [4], the effect is due to the redistribution of holes between different energetically close activator levels by the IR light, i.e., to the nonelementary nature of the luminescence band itself.We think that these two essentially different modes of action of iR emission can be distinguished by the rate of restoration of the initial shape of the luminescence band after the IR light is turned off. In the first case the shape of the luminescence band will be restored in the time required for dissipation of the excess energy of the luminescence center or the optically released carrier. This time will not exceed i0 -9 sec [5, 6]. In the second case the restoration of the initial distribution of holes among the different activator levels after alteration by IR light will be brought about by recombination transitions to these levels. The time for restoration of the shape of the luminescence band will be close to the time required to restore the total intensity of the band itself and, hence, will be very large.We investigated ZnS=Cu and ZnS CdS=Cu phosphors with an activator (copper) content of 10 -4 and 2.10 -4 g per g of the host substance.The phosphors were prepared by the method described in [7] and were kindly presented to us by K. Piir. Some of these specimens were investigated earlier [8].The phosphors were excited by a SVD-120A mercury lamp. The ZnS = Cu phosphors were excited by the 365 n_m line and the mixed ZnS (60 mole %) CdS = Cu phosphors were excited by the 436 nm line.For measurements of the IR quenching and its relaxation in relation to the wavelength of the phosphor luminescence we used a UM-2 monochromator and anFEU-17A or FEU-27 photomultiplier.The quenching long-wave light was isolated by another UM-2 monochromator from the light flux of a 300 W projection lamp.The iR luminescence quenching factor #(~, t) as a function of the energy ~ of the luminescence quanta and the time t after removal of the long-wave radiation was calculated from the formula ~ (~, t) -A/(~, t)Io (~)The intensity of the luminescence due to the short-wave exciting light I0(~) and its reduction AI(e, t) due to the long-wave light were determined separately for each spectral region.The investigated phosphors were contained in...