Energy Transfer and Population of ~4S_(3/2) and ~4F_(9/2) Erbium Levels in Er~(3+):Na_(0.4)Y_(0.6)F_(2.2) Laser Crystals under Direct and Upconversion Selective IR Excitation

摘要

Energy transfer processes in Er~(3+):Na_(0.4)Y_(0.6)F_(2.2) laser crystals under selective laser diode pumping have been studied theoretically and experimentally. Concentration and pump power dependences of the intensity of luminescence from the ~4S_(3/2) and ~4F_(9/2) levels are investigated. It is shown, that under LD excitation at ~4I_(11/2) level (λ_(exc) = 975 nm) and certain conditions of pumping and erbium concentration the ~4F_(9/2) level is populated due to complicated excitation pathway including ESA from ~4I_(11/2) and ~4I_(13/2) levels and upconversion energy transfer steps, while relaxation from the ~4S_(3/2) level is ineffective for population of the ~4F_(9/2) level. The relative intensity of red (~4F_(9/2) level) and green (~4S_(3/2) level) luminescence can be controlled by means of excitation power, doping concentration and temperature.