Phase Transformations upon Formation of Transparent Lithium Alumosilicate Glass-Ceramics Nucleated by Yttrium Niobates

Phase transformations in the lithium aluminosilicate glass nucleated by a mixture of yttrium and niobium oxides and doped with cobalt ions were studied for the development of multifunctional transparent glass-ceramics. Initial glass and glass-ceramics obtained by isothermal heat-treatments at 700–900 °C contain YNbO4 nanocrystals with the distorted tetragonal structure. In samples heated at 1000 °C and above, the monoclinic features are observed. High-temperature X-ray diffraction technique clarifies the mechanism of the monoclinic yttrium orthoniobate formation, which occurs not upon high-temperature heat-treatments above 900 °C but at cooling the glass-ceramics after such heat-treatments, when YNbO4 nanocrystals with tetragonal structure undergo the second-order transformation at ~550 °C. Lithium aluminosilicate solid solutions (ss) with β-quartz structure are the main crystalline phase of glass-ceramics prepared in the temperature range of 800–1000 °C. These structural transformations are confirmed by Raman spectroscopy and illustrated by SEM study. The absorption spectrum of the material changes only with crystallization of the β-quartz ss due to entering the Co2+ ions into this phase mainly in octahedral coordination, substituting for Li+ ions. At the crystallization temperature of 1000 °C, the Co2+ coordination in the β-quartz solid solutions changes to tetrahedral one. Transparent glass-ceramics have a thermal expansion coefficient of about 10 × 10−7 K−1

Structural transformations and spectroscopic properties of Ni-doped magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2 for broadband near-IR light emission

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Transparent glass-ceramics based on Co2+-doped γ-GaxAl2−xO3 spinel nanocrystals for passive Q-switching of Er lasers

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ZnO – Yb2_2O3_3 composite optical ceramics: Synthesis, structure and spectral-luminescent properties

International audienceZinc oxide optical ceramics containing 0 – 2 wt% ytterbium are prepared byuniaxial hot pressing of commercial oxides at 1150 and 1180 °C. The ceramics have themain crystalline phase of hexagonal wurtzite-type ZnO. Ytterbium ions do not enter theZnO crystals but form a cubic sesquioxide phase of Yb2O3 located at the ZnO grainboundaries. Yb acts as an inhibitor for the ZnO grain growth. The ceramics exhibittransmittance up to 60% in the visible. Their transmission in the infrared is determinedby the free charge carrier absorption. The Yb3+ ions are found in C2 and C3i sites in Yb2O3crystals. Under X-ray excitation, the ceramics exhibit intense luminescence bands in theblue (near-band-edge emission) and green (defect emission) whose positions, intensitiesand decay times depend on the Yb content. Yb2O3 causes a redistribution of luminescenceintensity in favor of the near-band-edge emission and fastens the emission decay

Transparent materials based on semiconducting ZnO: glass-ceramics and optical ceramics doped with rare-earth and transition-metal ions

International audienceThe structure of multiphase transparent glass-ceramics prepared from glasses by controlled crystallization and of optical ceramics prepared by uniaxial recrystallization hot pressing are compared. Glass-ceramics and ceramics were doped with rare-earth (RE) and transition metal (TM) ions.In the course of the glass-ceramics development, regions of structural inhomogeneity enriched in ZnO are formed in the initial glass. Their composition depends on the type and concentration of the TM and RE ion and determines the difference in phase assemblage of glass-ceramics. In opticalceramics, cobalt ion enter the structure of ZnO and form the CoO phase. RE ions do not enter the structure of ZnO crystals, but are located on their surface and form the RE2O3 phase. ZnO optical ceramics doped with cobalt and RE ions should also be considered as multiphase materials

Synthesis, structure and spectroscopy of Fe2+:MgAl2O4 transparent ceramics and glass-ceramics

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