Role of defect states in persistent luminescence materials

Abstract

The Eu 2+ doped alkaline earth aluminates, MAl 2O 4:Eu 2+ (M = Ca and Sr) co-doped with selected R 3+ ions are efficient new persistent luminescence materials. The detailed mechanisms of persistent luminescence are not yet known. The importance of the defects to induce persistent luminescence was studied here by EPR, Mössbauer, thermoluminescence (TL) and persistent luminescence measurements. The EPR results show that even the non-doped material, CaAl 2O 4, contains trapped electrons, probably in anion vacancies. Similar EPR properties are shown by the Eu 2+ doped and R 3+ co-doped materials. Other paramagnetic defects are present, too. The Mössbauer results indicated complex distribution of the Eu 2+ ions in the CaAl 2O 4 host. Different R 3+ ions affect the thermoluminescence and persistent luminescence properties of the CaAl 2O 4:Eu 2+, R 3+ materials in a very different manner, from enhancing to total suppression.