Abstract
Transparent oxyfluoride glass–ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0–2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF4 NCs with a size ranging 9–30 nm were obtained after heat treatments at Tg + 20–80 °C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF4 nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass–ceramics clearly shows that Er3+ and Yb3+ ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.
Highlights
The develop of transparent rare-earth (RE3+)-doped oxyfluoride glass–ceramics (GCs) in which the nanocrystals (NCs) are homogeneously distributed in a glass matrix have gained increasing attention for their application in more efficient photonic devices for energy and optics
The crystallization mechanism of different fluoride phases, such as LaF3, NaLaF4, KaLaF4 among others [7,16,17,18] in aluminosilicate glasses occurs via phase separation with the formation of droplets enriched in Si, F, La, Y- or Lu
The glass matrix gets depleted of crystal formers and a viscous barrier made of network formers, mainly SiO2, surround the NCs
Summary
The develop of transparent rare-earth (RE3+)-doped oxyfluoride glass–ceramics (GCs) in which the nanocrystals (NCs) are homogeneously distributed in a glass matrix have gained increasing attention for their application in more efficient photonic devices for energy and optics. This kind of materials combines the incorporation of active rare-earth (RE3+) ions into low phonon energy fluoride crystals (300–450 cm−1) and the good thermal stability and high mechanical and chemical properties of an aluminosilicate glass matrix [1,2,3]. Oxyfluoride GCs can be obtained after careful control of the crystallization process of the precursor glass using adequate heat treatments. The former barrier avoids further crystal growth, limiting the NCs size to the nanometric scale
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