SENSITIZED PHOTON AVALANCHE

This paper discusses the principle and the results of analytical and n umerical modelling of sensitized photon avalanche. In this process cro ss-relaxation necessary to feed a reservoir level of an active ion is sensitized by another ion which is able to transfer back the accepted excitation to the reservoir level. Models taking into account the loca l variation of the pump intensity of real systems from the distributio n in the incident pump beam or due to absorption are presented. This m odelling shows that sensitized photon avalanche could be an efficient upconversion process for visible emission under infrared pump excitati on for systems where other processes are not operative or have very lo w efficiencies. This model gives a good description of the available d ata for Yb3+-sensitized photon avalanche of Pr3+ ions under infrared-p ump excitation. Criteria for selection of other active systems are pre sented. (C) 1998 Elsevier Science B.V. All rights reserved.