Highly efficient upconversion in Er3+ doped BaY2F8 single crystals: dependence of quantum yield on excitation wavelength and thickness

This manuscript presents a study of the upconversion (UC) in barium yttrium fluoride (BaY2F8) single crystal doped with trivalent erbium ions (Er3+) under excitation of the I-4(13/2) level at three different wavelengths: 1493 nm, 1524 nm and 1556 nm. The resulting UC emission at around 980 nm has been investigated and it has been found that a thickness optimization is required to reach high quantum yield values, otherwise limited by self-absorption losses. The highest external photoluminescence quantum yield (ePLQY) measured in this study was 12.1 +/- 1.2 % for a BaY2F8:30at% Er3+ sample of thickness 1.75 +/- 0.01 mm, while the highest internal photoluminescence quantum yield (iPLQY) of 14.6 +/- 1.5 % was measured in a BaY2F8:20at% Er3+ sample with a thickness of 0.49 +/- 0.01 mm. Both values were obtained under excitation at 1493 nm and an irradiance of 7.0 +/- 0.7 Wcm(-2). The reported iPLQY and ePLQY values are among the highest achieved for monochromatic excitation. Finally, the losses due to self-absorption were estimated in order to evaluate the maximum iPLQY achievable by the upconverter material. The estimated iPLQY limit values were similar to 19%, similar to 25% and similar to 30%, for 10%, 20% and 30% Er3+ doping level, respectively. (C) 2015 Optical Society of America