OPTICAL ABSORPTION INTENSITIES AND QUANTUM COUNTER ACTION OF ER3+ IN YTTRIUM GALLIUM GARNET

The intensities of optical absorption spectra of Er3+ in single crystals of yttrium gallium garnet at 700°K have been shown to fit Judd's theory of 4f-4f transitions with the following parameters: T2 = 1·44 × 10-21 s, T4 = 1·12 × 10-21 s, T6 = 1·42 × 10-21 s. These have been used to estimate Einstein coefficients useful in a discussion of the quantum efficiency of the fluorescence from the 4S3/2 state, and the efficiency of infra-red quantum counter action in the material. For pure spontaneous radiation an efficiency of 71% for transitions to the 4I15/2 ground state is expected. The quantum efficiency has also been directly measured and a value of 12% was obtained. This is lower owing to competing phonon processes. Using the experimental value for the quantum efficiency, and the above values of T, a theoretical photon gain for quantum counter action of 0·55 × 10-8 has been calculated.