Energy Transfer and Population of ~(4)S_(3/2) and ~(4)F_(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 ~(4)S_(3/2) and ~(4)F_(9/2) levels are investigated. It is shown, that under LD excitation at ~(4)I_(11/2) level ((lambda)_(exc)velence 975 nm) and certain conditions of pumping and erbium concentration the ~(4)F_(9/2) level is populated due to complicated excitation pathway including ESA from ~(4)I_(11/2) and ~(4)I_(13/2) levels and upconversion energy transfer steps, while relaxation from the ~(4)S_(3/2) level is ineffective for population of the ~(4)F_(9/2) level. The relative intensity of red (~(4)F_(9/2) level) and green (~(4)S_(3/2) level) luminescence can be controlled by means of excitation power, doping concentration and temperature.