Crystallization and visible–near-infrared luminescence of Bi-doped gehlenite glass

Abstract

Gehlenite glass microspheres, doped with a different concentration of Bi3+ ions (0.5, 1, 3 mol%), were prepared by a combination of solid-state reaction followed by flame synthesis. The prepared glass microspheres were characterized from the point of view of surface morphology, phase composition, thermal and photoluminescence (PL) properties by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and PL spectroscopy. The closer inspection of glass microsphere surface by SEM confirmed a smooth surface. This was further verified by XRD. The basic thermal characteristics of prepared glasses, i.e. Tg (glass transition temperature), Tx (onset of crystallization peak temperature), Tf (temperature of the inflection point of the crystallization peak) and Tp (maximum of crystallization peak temperature), were estimated from the DSC records. High-temperature XRD experiments in the temperature interval range 600–1100°C were also performed. The PL emission properties of prepared glasses and their polycrystalline analogues (glass crystallized at 1000°C for 10 h) were studied in the visible and near-infrared (NIR) spectral range. When excited at 300 nm, the glasses, as well as their polycrystalline analogues, exhibit broad emission in the visible spectral range from 350 to 650 nm centred at about 410–450 nm, corresponding to Bi3+ luminescence centres. The emission intensity of polycrystalline samples was found to be at least 30 times higher than the emission of their glass analogues. In addition, a weak emission band was observed around 775 nm under 300 nm excitation. This band was attributed to the presence of a minor amount of Bi2+ species in prepared samples. In the NIR spectral range, the broad band emission was observed in the spectral range of 1200–1600 nm with the maxima at 1350 nm. The chemistry of Bi and its oxidation state equilibrium in glasses and polycrystalline matrices is discussed in detail.

Silver quasi-nanoparticles: bridging the gap between molecule-like clusters and plasmonic nanoparticles

“…Aluminum MAS NMR experiments were performed on a 500 MHz Bruker AVANCE III spectrometer operating at 130.32 MHz for 27 Al, and equipped with a double resonance 4 mm probe head. X-ray photoelectron spectroscopy (XPS) measurements were carried out on an AXIS Supra electron spectrometer (Kratos Analyical Ltd.) with base vacuum in the analysis chamber in the order of 10 -8 Pa.…”

“…The unexpected detection of Bi 2+ in ZX-Bi-3 sample reveals a chemical reduction of Bi 3+ precursor during the synthesis process. The reduction of Bi 3+ to its lower-valence bismuth ions usually occurs after thermal treatment at a relatively high temperature under anaerobic atmosphere conditions 27 . The low synthesis temperature (50°C) excludes the thermal reduction hypothesis, which is probably due to the in in-situ loading of Bi in presence of metallic alumina in the synthesis, characterized with a very low standard potential (-1.67 V SHE, for Al 3+ /Al at 25°C) in respect to Bi 3+ /Bi (+0.317V SHE at 25°C).…”

Crystallization kinetics of gehlenite glass microspheres

“…The precursor powder with gehlenite composition (50 mol% calcium oxide, 25 mol% aluminium oxide and 25 mol% silicon dioxide) was prepared by solid-state reaction, from high-purity chemicals (SiO 2 ; p.a., Polske odczynniki chemiczne, Gliwice; Al 2 O 3 ; p.a., Centralchem, Bratislava; CaCO 3 (p.a., Centralchem, Bratislava). The details are described in our previous work [9]. From precursor powder, the glass microspheres were prepared by flame synthesis [41,42].…”

“…They found that the photoluminescent properties of Eu 2+ are influenced by the crystal structure of Ca 2 Al 2 SiO 7 , and gehlenite thus has the potential to become a single component luminophore emitting warm white light in the production of white LEDs. Gehlenite doped with Bi 3+ exhibits PL emissions in different spectral regions (visible, deep red and NIR range) indicating the presence of Bi in various oxidation states (Bi 3+ , Bi 2+ and Bi + ) [9].…”