Spark plasma sintering and optical properties of Tm3+ and Tm3+ /Yb3+ doped NaLaF4 transparent glass-ceramics

Tm3+ doped oxyfluoride glass-ceramics (GCs) containing NaLaF4 nanocrystals (NCs) have been obtained by spark plasma sintering (SPS). First, the precursor glasses were melted and then milled and sieved to a suitable particle size. Glass powder pellets were sintered by spark plasma sintering under vacuum conditions. The SPS processing parameters (temperature, pressure, and holding time) were optimized to obtain transparent glass-ceramics. The times of SPS processing are considerably shorter compared with those for the preparation of these GCs by conventional thermal treatment. All glass-ceramics contain nanocrystals of the β- NaLaF4 phase with an average crystal size of 20 nm, but the more highly doped samples (2Tm3+ and 0.5Tm3+/2Yb3+) show evidence of the presence of another phase corresponding with α-NaLaF4. The luminescence properties of the near infrared (NIR) emissions of Tm3+ for different concentrations reveal the presence of concentration quenching of the 3H4 and 3F4 levels. The analysis of the decay from the 3H4 level with increasing concentration is consistent with a dipole-dipole quenching process assisted by energy migration, whereas the self-quenching of the 3F4→3H6 emission can be attributed to fast diffusion. Energy transfer between Yb3+ and Tm3+ ions is confirmed by the NIR and upconverted (UC) emissions after Yb3+ excitation at 975 nm. No UC emission is observed under 791 nm excitation of Tm3+ ions.Funding from MICINN under project PID2020–115419 GB-C-21/C-22/AEI/10.13039/501100011033 is acknowledged. This paper is part of the dissemination activities of project FunGlass. This project has received funding from the European Union´s Horizon 2020 research and innovation program under grant agreement No 739566

Er/Yb co-doped LiYF4 transparent oxyfluoride glass-ceramics with up-conversion optical properties

Transparent oxyfluoride glass-ceramics doped with rare earth ions (RE3+) are promising materials for photoluminescence up- and down-conversion. In this study, glass compositions within the system 40SiO2–25Al2O3–18Li2O–7LiF–10YF3 (mol.%) doped with ErF3 and codoped with ErF3/YbF3 were prepared by melt-quenching method and subjected to thermal treatment at temperatures above glass transition (Tg + 35 °C) for long dwell times to obtain the corresponding glass-ceramics. The formation of LiYF4 and LiAlSiO4 nanocrystals was confirmed by XRD analysis after thermal treatment at 540 °C for 20 h. The increase in the treatment time up to 80 h resulted in the enhancement of the UC luminescence yield and the decrease of the Red to Green ratio (R/G) emission intensity. Due to the nano-sized crystals, the glass-ceramic products were transparent (%T) in near-infrared (NIR) and visible spectral region with %T remaining approximately 85% and 75%, respectively, after 20 h treatment. However, the visible window transparency reduced, with %T dropping to around 50% after 80 h due to the increase in crystal size and crystalline fraction. The influence of Yb3+ co-doping on the up-conversion (UC) luminescence has been investigated in the glass-ceramics and compared to the parent glasses, confirming that Yb3+ ions were also a key factor for facilitating up-conversion via energy transfer (ET), leading to a greater luminescence yield than for Er3+ single doped glass-ceramics and tuning of R/G intensities.This work was supported by a part of the European Union’s Horizon 2020 research and innovation program [grant number 739566]; the MICINN [grant number PID2020-115419GBC-21/C-22/AEI/10.13039/501100011033]; and the project VEGA 1/0476/22

KLaF4:Nd3+ doped transparent glass-ceramics processed by spark plasma sintering

[EN] Transparent oxyfluoride glass-ceramics (GCs) containing KLaF4 nanocrystals (NCs) doped with Nd3+ were prepared by Spark Plasma Sintering (SPS). Glass powder pellets were sintered under a vacuum atmosphere, optimizing the processing parameters such as particle size, pressure, temperature, and holding time to obtain full densification. Transparency decreased when decreasing the particle size due to higher carbon contamination from the die. The alpha-KLaF4 crystalline phase was identified by X-ray diffraction (XRD) and its average crystal size was 10-20 nm. High-resolution transmission electron microscopy (HR-TEM) confirmed the presence of KLaF4 nanocrystals with incorporated Nd3+ ions. Low-temperature site-selective emission and excitation spectra of Nd3+ ions confirmed that alpha-KLaF(4 )was the predominant polymorph, although a minor presence of beta- KLaF4 was also demonstrated.This work was supported by MINECO under Projects MAT2017-87035-C2-1-P/-2-P (AEI/FEDER, UE) , PID2020-115419GB-C-21/C-22 and Basque Country Government PIBA2018-24. AAC also thanks the scholarships of the Federal Agency for the Support and Improvement of Higher Education (CAPES) , contract #99999.002598/2015-09. This paper is part of the dissemination activities of project FunGlass. This project has received funding from the European Unions Horizon 2020 research and innovation program under grant agreement No 739566