New Infrared Materials Incorporating Non-Radiative Energy Transfer

Abstract

ABSTRACT We apply a recently developed model for non-radiative energy transfer in correlated systems to recently published data on energy transfer in garnets. We show that even in well-studied materials in which the analysis of the data appears straight forward, subtle deviations from theory and difficulty in quantitatively evaluating interaction parameters may be due to a non-random distribution of donors and acceptors in the crystal. 1. INTRCDUCTIOSf The development of new solid-state infrared lasers to substitute for Nd:YAG for industrial, academic and military applications is continuing. In particular, one method to develop materials with enhanced efficien­ cies and new wavelengths is to codope the materials with acceptors (ions to absorb the pump radiation) and donors (ions to emit the laser radiation) and to rely on Foerster-Dexter non-radiative energy transfer for the interaction of the donors and acceptors. Both Nd:Cr:GSGG (with an output wavelength of 1.06 microns) and Er:YAG (with an output wavelength of 2.94 microns) have a non-radiative energy transfer step in the flow of their energy from pump input to the las ing output. The rate of trasnfer is proportional to ]/r6 where r is the distance between a donor and an acceptor.We consider in this paper the development of laser materials in which donors and acceptors are micro­ scopically paired or correlated within the lasing material. A theoretical expression is derived for the rate of energy transfer as a function of the degree of correlation between donors and acceptors in the crystal. Methods to achieve such correlation, based on ion-site size mismatch (two doped ions will locate next to each other to relieve lattice strain) are described. Experimental evidence for such correlation in luminescent materials, including Nd:Cr:GSGG and Nd:Ce:YAG will be detailed.