title: Highly efficient upconversion in Er³⁺ doped BaY₂F₈ single crystals: dependence of quantum yield on excitation wavelength and thickness.
abstract: 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 4I(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 ∼19%, ∼25% and ∼30%, for 10%, 20% and 30% Er3+ doping level, respectively.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Boccolini
authors.forename: Elena
authors.initials: E
authors.lastname: Favilla
authors.forename: Mauro
authors.initials: M
authors.lastname: Tonelli
authors.forename: Bryce S
authors.initials: BS
authors.lastname: Richards
authors.forename: Robert R
authors.initials: RR
authors.lastname: Thomson