Luminescence in Eu2+-doped Ba2Si5N8:: fluorescence, thermoluminescence, and upconversion

Fluorescence emission was investigated in a series of Ba2-xEuxS5N8 compounds. Two maxima corresponding to the two crystallographic Eu2+ sites are observed. Excitation with intense laser light at 1.047 mum reveals strong fluorescence emission at similar to 600 nm due to two-photon-excitation. In Ba1.89Eu0.11Si5N8 the long lasting luminescence was studied. The emission peaking at about 590 nm has been observed in the dark with the naked eye even 15 min after removal of the activating lamp. This effect is due to the recombination of holes and traps consisting of nitrogen vacancies formed by reducing synthesis conditions. The maximum emission was observed at -7 degreesC. (C) 2000 Elsevier Science Ltd. All rights reserved.