Synthesis and photoluminescence properties of nanostructured mullite/α-Al2O3

Abstract

Phase transformation of a-Al 2 O 3 to mullite was observed by correlated X-ray diffraction and low-temperature (7 K) time-and energyresolved photoluminescence methods. The aluminosilicate solids with different Si:Al ratios were prepared after thermal treatment (1400°C) of ultraporous alumina (UPA) monoliths impregnated with vapour of silica precursors at room temperature. The initial dispersion of Si is homogeneous on a size-scale of 5 nm raw UPA fibres, which grow in size during the thermal treatment stage up to $50-100 nm. Three phases were resolved in the considered SiO 2 /Al 2 O 3 system: silica, a-Al 2 O 3 and their interaction product 2:1 mullite (2Al 2 O 3 :SiO 2 ). The 2:1 mullite mass increases and a-Al 2 O 3 mass decreases with an increase of the initial silica content. At the SiO 2 content in the initial system above 20 mol.%, the phase transformation to 2:1 mullite is complete and no a-Al 2 O 3 was observed. No mullite phases with either lower or higher Si content were observed. The fundamental absorption onset energy 7.55 eV of 2:1 mullite was measured.

Tunable white light emission by variation of composition and defects of electrospun Al2O3–SiO2 nanofibers

“…On the other hand, the 3A1 2 O 3 ·2SiO 2 (3:2) mullite components first increase with more Al addition; once excessive amounts of Al were added to the sample, the 2A1 2 O 3 ∙1SiO 2 (2:1) mullite components formed. It is know from previous work [ 38 , 40 ] that the 3:2 mullites possess a wide band gap in the range of 3.95–5.5 eV, which can be of benefit to the intersystem radiative crossing for ≡Si(Al)–O–C∙=O. However, the 2:1 mullites have a wide band gap of 7.7 ± 0.2 eV, which is too wide for our case.…”

Characterization by Photoluminescence and Raman Spectroscopy of the Oxide Scales Grown on the PM2000 at High Temperatures

“…33,34 The orange emission is less commonly reported and its origin, although not fully understood, seems to involve interstitial oxygen ions (Oi), [35][36][37] the luminescence, providing a strong absorption between 6 eV and 7 eV. 38,39 Because of a high sensitivity, the luminescence method is capable of observing traces of metal ions. 40,41 Optical properties of oxide solids are also in°uenced by metal ions (extrinsic defects), which can appear in quantities below 0.1 wt.%.…”

Effect of temperature on the reaction sintering of mechanically activated ZrSiO4–Al2O3 mixture

“…Mullite is an important ceramic and has attracted considerable attention due to its high melting point, chemical stability, low thermal expansion, high creep and thermal shock resistance, attractive bending strength at high temperatures, resistance to abrasion and good electrical resistivity [1,2]. However, low fracture toughness and difficulty in sintering limits its widespread usage [3].…”