Photoluminescence investigation of energy up-conversion in KY1−xErxF4

Using a CW argon-ion laser operating at 488 nm and a pulsed 532 nm laser, we find up-conversion of Er3+ energy in KY1−xErxF4. Among three samples with x=0.1, 0.05, and x=0.0005 that show energy up-conversion, x=0.1 and 0.05 samples were confirmed to have up-conversion caused by energy transfer. By measuring temporal dependence of the photoluminescence (PL) we show that, with energy transfer, 4S3/2 state is up-converted into 2H(2)9/2 and 2P3/2 state by taking energy from other ions in 4F9/2 state. The incident laser power dependence of the up-converted PL intensity indicates that the up-converted states have mutual annihilation at high density via energy transfer.