Cooperative upconversion and energy transfer of new high Er3+- and Yb3+-Er3+-doped phosphate glasses

Systematic studies of cooperative upconversion and Yb3+-Er3+ energy transfer in newly developed phosphate glasses were performed by a rate-equation formalism. The cooperative-upconversion coefficients of the I-4(13/2) level for different Er3+ concentrations were determined from the luminescence-decay curves for high pump intensities. A small cooperative-upconversion coefficient of 1.1 x 10(-18) cm(3)/s was obtained for a high Er3+ concentration of 4 x 10(20) ions/cm(3), Yb3+-Er3+ energy-transfer coefficients for an Er3+ concentration of 2 x 10(20) ions/cm(3) codoped with different Yb3+ concentrations were calculated fi om the lifetime measurements of the F-2(5/2) level of Yb3+ ions. For Er3+ codoped with an Yb3+ concentration of 6 x 10(20) ions/cm(3), an energy-transfer coefficient of 1.1 x 10(-16) cm(3)/s and an energy-transfer efficiency higher than 95% were determined from our measurements under weak excitation. The cooperative-upconversion coefficients of Yb3+-Er3+-doped samples were found to be consistent with that of an Er3+-doped sample with the same Er3+ concentration. The weak cooperative-upconversion effect of high Er3+ concentrations and efficient Yb3+-Er3+ energy transfer indicate that these newly developed Er3+- and Yb3+-Er3+-doped phosphate glasses are excellent for active device applications. (C) 2000 Optical Society of America [S0740-3224(00)01804-X]. OCIS codes: 500.6280, 160.5690, 250.4480.