On the nature of optically active centres in selfactivated luminophors of the CaWO4 type |
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Authors: | AM Gurvich VB Gutan BN Meleshkin VV Mikhailin AA Mikhalev MI Tombak |
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Institution: | Institute of Radiology; P.N. Lebedev Physical Institute, Academy of Sciences; State University, Moscow, USSR;Institute of Luminophors, Stavropol, USSR |
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Abstract: | The evidence in favour of the assumption that impurities of V group elements creates defects of the MeO′4 type (centres of luminescence), Me?3 and V?, or WO3 (capture centres) which are responsible for recombination afterglow different from the steady-state luminescence spectral distribution (Me = As, Sb, Nb, Ta; V0 - oxygen vacancy) are presented. These same impurities, and phosphorous, lead to quenching of luminescence observed as afterglow with excitation quanta greater than 6.3 eV. This corresponds to the valued of the energy gap. Experimental data together with results of thermodynamic analysis lead to the conclusion that the luminescence of CaWO4 and of other undoped oxygen containing compounds of transition elements luminophors is caused by direct self-activation connected with ability of these elements to convert spontaneously into a lower valency state and to form variable phases (non-stoichiometric compounds). It is proposed that in case of CaWO4 centres of luminescence are formed by W5+. |
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