Thermoluminescence and Phosphorescence of VUV‐ and X‐Irradiated CaO Monocrystals at Low Temperatures

Abstract

Thermoluminescence (TL) of CaO and CaO-Bi monocrystals VUV-irradiated at 80 K or X-irradiated at 4.2 K is reported. Varying the energy of VUV-irradiation, the TL creation spectra (TLCS) of various peaks are derived. From the analysis of these spectra it is concluded that in the excitation spectrum of CaO indirect transitions may play an important role already from E,,, = 6.5 eV. Long-lived phosphorescence, as well as low-temperature TL peaks at 20, 37, and ~5 0 K of X-irradiated CaO and CaO-Bi monocrystals at LHeT are observed. The observed phosphorescence is interpreted as a tunneling recombination between holes and electrons, trapped, respectively, by cation vacancies (V centers) and unidentified donor centers, thermal destruction of which takes place at -50 K. A3MepeHa TepMOnEOMHHeC4eHuHX (Tn) MOHOKpHCTanJIOB CaO H CaO-Bi, 06JIyYeHHbIX BY@-PanHauHefi A PeHTRHOBCKAMH JIyYaMA IIpH 80 H 4,2 ! & COOTBeTCTBeHHO. n3 aHaJIH3a CIIeKTpOB CO3flaHHII pa3HblX IIAKOB Tfl CJ(eJIaH BbIBOA 0 CyIIJCcTBeHHOfi POJIH HeIIpXMbIX IIepeXOnOB B CaO YXte C Eso3,j = 6,5 ev. GnX 06JIyYeHHbIX IIPH 4,2 K KpHCTailJIOB CaO M CaO-Bi 06HapyXeHbI AO;ITOXH-ByI4aX @Oc@OpeC~eHuHX IIpH 4,6eV H pan HH3KOTeMIIepaTypHbIX IIHKOB T n IIpH 20, 37 H 50K. 06HapyXeHHaX @OC@OpeC~eHuHX HHTepIIpeTHpOBaHa KaK TyHHeJIbHaX peKOM6HHauHOHHaX JIEOMHHeC-UeH4Afl AbIPOK H 3JIeKTpOHOB, 3aXBaYeHHbIX, COOTBCTCTBeHHO, Ha KaTHOHHbIX BaKaHCAXX (V-LICHTPM) H Ha HeHJ(eHTH~HUAp0BaHHbIX flOHOPHbIX UeHTpaX, TepMHqeCKOe pa3pylIIeHAe KOTOPbIX IIpOHcXOAHT n p~ 50 K.

Luminescence and Hole Center Formation by VUV-Radiation in MgO:Al and MgO:Ge Crystals

“…This result con¢rms the conclusion drawn in [7] that the maximum in the TLCS of V OH centers in CaO at E < E ex is due to the indirect transitions below the exciton region.…”

“…1) and CaO (Fig. 2 in [7]), alongside with the obvious similarity of the picture, we can observe an essential di¡erence: in MgO the intensity of the TL peak of V centers at E > E ex decreases slowly with the growth of the excitation energy and has about one half of its maximum value at E < E ex , while the intensity of the main TL peak in CaO at E < E ex is about 10 times as high as at E > E ex . The same di¡erence can be also observed if we compare the TLCS for V OH centers in CaO with theTLCS curves for variousV centers in MgO (see Fig.…”

“…In this case the absorption coe¤cient is still small and the exciting light penetrates deep into the crystal. By measuring a phosphorescence excitation spectrum it was demonstrated in [7] that in this spectral region an e¡ective creation of separated charge carriers takes place. In MgO the situation is di¡erent: the dominant excitation peak at E < E ex is mainly due to the photoionization of oxygen ions near various but not very numerous defects.…”

“…The aim of the present study was to measure the creation spectra of hole centers in Al 3 and OH À doped MgO crystals in VUV spectral region and to compare these spectra with the analogous ones in CaO and MgO. Hole centers and EE in CaO and MgO have been studied earlier [7,8]. To analyze the role of various EE, created by VUV radiation, in the formation of hole centres, we applied the method of thermostimulated luminescence (TL), the high sensitivity of which facilitates the detection of low concentration V centres.…”