Infrared to Visible Upconversion of Er3+ Doped in a Chloride Matrix

Efficient infrared-to-visible upconversion is achieved in the YCl3-ErCl3-PbCl2-KCl phosphor system. Under 1.52 µm laser diode (LD) excitation, a specimen containing 20 mol% Er3+ dopant emitted bright green luminescence, and the fluorescence lines at 410 nm, 550 nm and 660 nm reached the respective intensities of 48, 20 and 9 times those of conventional Er3+-doped fluoride. A strong upconversion fluorescence at 496 nm due to the 4F7/2-4I15/2 transition is observed in the chloride phosphor under 0.972 µm LD excitation. This is ascribed to the direct two-step excitation process which occurs when multiphonon relaxation is suppressed in the chlorides.