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In this paper we report for the first time synthesis of Eu3+-doped transparent glass-ceramics ( TGC) with BaBi2Ta2O9 ( BBT) as the major crystal phase using the glass system SiO2-K2O-BaO-Bi2O3-Ta2O5 by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat-treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE- SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass-ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu3+ was observed due to incorporation of Eu3+ ions into the low-phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (εr), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency. [ABSTRACT FROM AUTHOR]

Precursor glasses for the ferroelectric barium bismuth titanate ( BaBi4 Ti4 O15) ( BBiT) have been prepared by the melt-quench technique in the SiO2- K2 O- BaO- Bi2 O3- TiO2 ( SKBBT) glass system with and without Eu2 O3 doping. BBiT glass-ceramic ( GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction ( XRD), electron microscopy ( FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200-400 nm and TEM images show 10-20 nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm−1. The activation energy of crystallization ( Ec) varies from 295 to 307 kJ/mol. The dielectric constants (εr) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat-treated GCs show higher εr values, in the range 25-55, compared to the precursor glasses (20-37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5D0 → 7F2 transition. An intense 466 nm excitation band corresponding to the 7F0 → 5D2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8-5.1 GPa) and fracture toughness (1.8-3.5 MPam0.5) values obtained in the GCs are high and suitable for structural applications. [ABSTRACT FROM AUTHOR]

The precursor glass in the ZnO- Al2 O3- B2 O3- SiO2 ( ZABS) system doped with Eu2 O3 was prepared by the melt-quench technique. The transparent willemite, Zn2 SiO4 ( ZS) glass-ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat-treatment time was examined by X-ray diffraction ( XRD) and field-emission scanning electron microscopy ( FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18-70 nm whereas the grain size observed in FESEM is 50-250 nm. The refractive index value is decreased with increase in heat-treatment time which is caused by the partial replacement of ZnO4 units of ZS nanocrystals by AlO4 units due to generation of vacancies. Fourier transform infrared ( FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass-ceramics compared with its precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7Fj ( j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass-ceramic nanocomposites is enhanced up to 17-fold with the process of heat treatment. This enhancement is caused by partitioning of Eu3+ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass-ceramic nanocomposites are expected to find potential applications in solid-state red lasers, phosphors, and optical display systems. [ABSTRACT FROM AUTHOR]

The glass-ceramics containing a rarely achievable nanocrystalline SrII NbIV O3 phase in the 53.75 SiO2-18.25 K2 O-9 Bi2 O3-9 SrO-9 Nb2 O5-0.5 CeO2-0.5 Eu2 O3 (mol%) glass system were prepared by the melt-quench technique followed by a two-stage controlled heat treatment. The unusual oxidation state of Nb in SrII NbIV O3 crystal is 4+ and upon heat treatment of the samples at lower temperature of 500°C for several hours, the glass composition and chemical environment around Nb ions played a key role for the formation of SrII NbIV O3 in the glass-ceramics. The microstructure of the glass-ceramics was studied using TEM and FESEM. The TEM images advocate 10-40 nm crystallite size of SrII NbIV O3. FTIR study confirms that all the samples consist of SiO4, BiO3, BiO6, and NbO6 structural units. The refractive index at different wavelengths was found to vary in the range 1.7105-1.7905 and increase with increase in heat-treatment time. The luminescence spectra of Eu3+-doped glass and glass-ceramics were recorded at 465 nm excitation wavelength and the luminescence intensity is found to be increased with heat-treatment time due to increase in crystallinity. The high intensity ratio of 5D0→7F2 to 5D0→7F1 indicates that the Eu3+-doped nanocrystalline SrII NbIV O3 glass-ceramics are promising candidate materials as red-light source. [ABSTRACT FROM AUTHOR]

Bismuth titanate ( Bi4Ti3O12) ( BiT), glass is prepared by the melt-quench technique in the SiO2- K2O- Bi2O3- TiO2 ( SKBT) system doping with Eu2O3 and transparent BiT glass-ceramics ( GC) is derived from it by controlled heat-treatment at 500°C by varying duration. The structural properties of the heat-treated GC are investigated using X-ray diffraction ( XRD), electron microscopy [Field emission scanning electron microscopy ( FE-SEM), transmission electron microscopy ( TEM)], and fourier transform infrared reflectance spectroscopy. FE-SEM and TEM images show the formation of polycrystalline spherical particles of 100-200 nm with 10-15 nm crystallites after heat-treatment. A significant increase in εr value (from 20 to 35) was observed with increase in heat-treatment time. The transmission losses of GC which happened with heat-treatment time are due to Rayleigh scattering exhibited by nanocrystallites of BiT. The excitation spectra have been recorded by monitoring emission at 612 nm corresponding to the 5D0 → 7F2 transition and an intense 467 nm excitation band corresponding to the 7F0 → 5D2 has been observed. Emission spectra were recorded by exciting the glass samples at 467 nm. It is observed that with increase in heat-treatment time, the intensity of red emission at 612 nm increases by 8-fold, which has happened due to the occupancy of Eu3+ ions in the low phonon energy crystal sites of BiT. [ABSTRACT FROM AUTHOR]

The Eu3+-doped novel precursor glass in the K2 O- SiO2- SrO- Bi2 O3- Ta2 O5 system was prepared using the melt-quench technique. The transparent SrBi2 Ta2 O9 ( SBT) glass-ceramic nanocomposites were derived from this glass using a controlled crystallization process. The formation of SBT crystal phase, size, and morphology with increase in heat-treatment time was examined using X-ray diffraction, field emission scanning electron microscopy, and fourier transform infrared transmission spectroscopy. Vicker's hardness study indicates marked improvement of hardness in the glass-ceramics compared to precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7 F j ( j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 467 nm. These spectra reveal that the Eu3+ ions are gradually entering into the SBT nanocrystals present in the glass-ceramics. This study indicates that the incorporation of Eu3+ ions into SBT crystal lattice enhances the photoluminescence performance of the glass-ceramics by two-fold. It is believed that this work would generate significant impact in the exploration of SBT glass-ceramic nanocomposites. [ABSTRACT FROM AUTHOR]

The Eu3+-doped novel precursor glass in the K2 O- SiO2- SrO- Bi2 O3- Ta2 O5 system was prepared using the melt-quench technique. The transparent SrBi2 Ta2 O9 ( SBT) glass-ceramic nanocomposites were derived from this glass using a controlled crystallization process. The formation of SBT crystal phase, size, and morphology with increase in heat-treatment time was examined using X-ray diffraction, field emission scanning electron microscopy, and fourier transform infrared transmission spectroscopy. Vicker's hardness study indicates marked improvement of hardness in the glass-ceramics compared to precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7 F j ( j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 467 nm. These spectra reveal that the Eu3+ ions are gradually entering into the SBT nanocrystals present in the glass-ceramics. This study indicates that the incorporation of Eu3+ ions into SBT crystal lattice enhances the photoluminescence performance of the glass-ceramics by two-fold. It is believed that this work would generate significant impact in the exploration of SBT glass-ceramic nanocomposites. [ABSTRACT FROM AUTHOR]

An Eu3+-doped novel mother glass in the K2O-SiO2-Y2O3-Al2O3 (KSYA) system was prepared by the melt-quench technique. The transparent Y3Al5O12 (YAG) glass-ceramics were derived from this glass by a controlled crystallization process. The formation of YAG crystal phase, size and morphology with the progression of heat treatment was examined by X-ray diffraction (XRD), transmission electron microscopy, field-emission scanning electron microscopy, and Fourier transformed infrared reflectance spectroscopy. The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range of 35-45 nm. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7F j ( j=0, 1, 2, 3, and 4) and its excitation spectra show a charge transfer band around 280 nm. From these emissions, the site symmetry in the vicinity of Eu3+ ions has been found to be Cs or lower than Cs in the nanoglass-ceramics. Absorption and fluorescence spectra reveal that the Eu3+ ions are entering into the YAG nanocrystals of the glass-ceramics. The present study indicates that the incorporation of Eu3+ ions into the YAG crystal lattice enhance the fluorescence performance of the nanoglass-ceramics. We believe that this work would generate new avenues in the exploration of YAG nanoglass-ceramics in particular and other glass-ceramics of very high-temperature melting crystals in general. [ABSTRACT FROM AUTHOR]

We report here the processing and properties of transparent glass and glass–ceramic nanocomposites in the Li2O–Ta2O5–SiO2–Al2O3 system in the presence of Eu2O3 as luminescent probe. The formation of the LiTaO3 crystal phase, the crystallite size, and the morphology with the progression of heat treatment have been examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformed infrared reflectance spectroscopy measurements. The crystallite sizes obtained from XRD and TEM are found to increase with heat-treatment time and vary in the range of 2–20 nm. The measured photoluminescence spectra exhibit emission transitions of 5D0,1→7F j ( j=0, 1, 2, 3, and 4) of Eu3+ ions. From the nature of the emission transitions, the site symmetry in the vicinity of Eu3+ ions has been found to be near C3v in the glass–ceramic nanocomposites. An inverse correlation has been observed between the asymmetric ratio ( IED/ IMD) of Eu3+ ions and the dielectric constant (ℇr), with an increase in the heat-treatment time of glass, which is caused by the dipole–dipole interaction. [ABSTRACT FROM AUTHOR]

The glass-ceramics containing a rarely achievable nanocrystalline SrII NbIV O3 phase in the 53.75 SiO2-18.25 K2 O-9 Bi2 O3-9 SrO-9 Nb2 O5-0.5 CeO2-0.5 Eu2 O3 (mol%) glass system were prepared by the melt-quench technique followed by a two-stage controlled heat treatment. The unusual oxidation state of Nb in SrII NbIV O3 crystal is 4+ and upon heat treatment of the samples at lower temperature of 500°C for several hours, the glass composition and chemical environment around Nb ions played a key role for the formation of SrII NbIV O3 in the glass-ceramics. The microstructure of the glass-ceramics was studied using TEM and FESEM. The TEM images advocate 10-40 nm crystallite size of SrII NbIV O3. FTIR study confirms that all the samples consist of SiO4, BiO3, BiO6, and NbO6 structural units. The refractive index at different wavelengths was found to vary in the range 1.7105-1.7905 and increase with increase in heat-treatment time. The luminescence spectra of Eu3+-doped glass and glass-ceramics were recorded at 465 nm excitation wavelength and the luminescence intensity is found to be increased with heat-treatment time due to increase in crystallinity. The high intensity ratio of 5D0→7F2 to 5D0→7F1 indicates that the Eu3+-doped nanocrystalline SrII NbIV O3 glass-ceramics are promising candidate materials as red-light source. [ABSTRACT FROM AUTHOR]