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 λ=1493 nm. The highest ePLQY of BaY2F8 was found for the largest dopant concentration 30 mol% Er3+ reaching the value of 3.62% ± 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.
Highlights
Fluoride compounds doped with rare-earth (RE) ions are attractive for optical applications as they exhibit low phonon energies and optical transparency over a broad spectral range [1,2,3,4,5]
The obtained photoluminescence spectra, and the determined external photoluminescence quantum yield (ePLQY) of the BaY2F8 samples for the corresponding Er3+ doping concentrations, measured under [JG]λ = 1588 nmλ = 1493 nm excitation, are compared (Fig. 1b [JG]and to Fig. 1[JG]ce). [JG]It is generally more common to measure the photoluminescence quantum yields (PLQY) for the transition 4I11/2→4I15/2, as this accounts for approximately 97% of UC emission [59], and including higher photon emission in the calculation would increase PLQY only fractionally
The excitation wavelength λ = 1493 nm was selected as the absorption coefficient of BaY2F8:Er3+ is known to reach its highest peak centred at 1493 nm [37,60]
Summary
Fluoride compounds doped with rare-earth (RE) ions are attractive for optical applications as they exhibit low phonon energies and optical transparency over a broad spectral range [1,2,3,4,5]. UC materials have received increasing attention in recent years for a huge variety of applications, for example, in microscopy and multimodal in vivo imaging [22,23], medical photodynamic therapy for cancer treatment [24], theranostics [25,26], dye lasers [27], optical thermometry [28], thermal sensors [29,30], and for the enhancement of photovoltaic (PV) devices [19,21] This last application makes use of a large range of wavelengths, and requires high photoluminescence quantum yields (PLQY) at low irradiance. To the best of our knowledge, this paper describes for the first time the spectral index of refraction (n) in the 300 nm–1800 nm range, the extinction coefficient (k), the Brewster angle (θB), and the Abbe number (νD) of BaY2F8, measured for three different Er3+ doping concentrations (0.5 mol%, 10 mol%, and 30 mol%)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
