Determination of the refractive index of BaY2F8:Er3+ (0.5 mol% to 30 mol%) in the 300 nm to 1800 nm range by ellipsometry; a record-breaking upconversion material

Abstract This work reports the ellipsometric study of trivalent erbium (Er3+) doped monocrystalline barium yttrium fluoride (BaY2F8), which has recently been shown to be one of the best photon upconversion (UC) materials available. This spans the BaY2F8 applications in a large range of wavelengths, from ultraviolet (UV) to near-infrared (NIR). We detail the optical properties of BaY2F8: Er3+ (0.5 mol%, 10 mol%, and 30 mol%), measured via variable angle spectroscopic ellipsometry over a spectral range from 300 nm to 1800 nm, reporting for the first time the indices of refraction for BaY2F8:Er3+. The upconversion external photoluminescence quantum yield (ePLQY) of the BaY2F8:Er3+ samples have also been studied by exciting at [ J G ] λ = 1588 n m λ = 1493 nm. The highest ePLQY of BaY2F8 was found for the largest dopant concentration 30 mol% Er3+ reaching the value of [JG]1.07% ± 0.12%, at an irradiance of 9.512 × 10 − 2 W/cm23.62% ± 0.01%, at an irradiance of (6.23 ± 0.45) × 10 − 2 W/cm2. The refractive index ( λ = 589.3 nm) was determined to be 1.4808 ± 0.014 for 0.5 mol%, 1.4980 ± 0.003 for 10 mol%, and 1.5022 ± 0.006 for 30 mol%. Increasing Er3+ doping concentration increased the refractive index. All samples decreased monotonically with increasing wavelength. The Brewster angle of BaY2F8:Er3+ is observed to be ≈ 56 ∘ , whilst the Abbe number of the samples was found to be as high as 124.62. These findings provide valuable insight into the optical properties of BaY2F8:Er3+ in the wide range of frequencies that is has proven useful.