Population of higher-energy levels in LiY1-xErxF4(x=0.003/1) crystals under CW IR laser-diode pumping

Steady-state population of 7 lowest excited erbium levels in LiY1-xErxF4 (YLF:Er3+) crystals was studied under up conversion CW InGaAs laser-diode pumping with varied power density. Theoretical and experimental concentration and power dependencies of population of higher-energy radiative levels were obtained. Relative changes in populations of studied levels in YLF:Er3+ crystals were experimentally controlled by visible spectra of steady-state luminescence in the wavelength ranges corresponding to transitions 4S3/2 yields 4I15/2 micrometers and 4F9/2 yields 4I15/2 micrometers . IR-pumped luminescence kinetic curves of higher-energy transitions 4S3/2 yields 4I15/2 and 2H9/2 yields 4I15/2 were recorded. The energy-transfer mechanisms were determined, and the predominant mechanisms responsible for up conversion excitation were elucidated. Microparameters of energy transfer and concentration dependencies of the self-quenching rates and non-linear coupling were obtained on the basis of theoretical and experimental estimates of the rates of intra- and intercenter relaxation processes allowing for statistics of coupling between the impurity centers in the system. The steady-state dependencies of population on the erbium concentration and pumping power density were calculated within the framework of rate balance equations. Good agreement between the theory and experimetnal data was obtained.