Thermodynamic Model for BiPO4(cr) and Bi(OH)3(am) Solubility in the Aqueous Na+–H+–\mathrm{H}_{2}\mathrm{PO}_{4}^{-}–\mathrm{HPO}_{4}^{2-}–\mathrm{PO}_{4}^{3-}–OH−–Cl−–H2O System

Prior to this study no data for the solubility product of BiPO₄(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO₄(cr) was studied at 23±2?°C from both the over- and under-saturation directions as functions of a wide range in time (6–309 days), pH values (0–15), and phosphate concentrations (reaching as high as 1.0 mol?kg^?1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in <6 days. The data were interpreted using the SIT model. These extensive data provided a solubility product value for BiPO₄(cr) and an upper limit value for the formation of BiPO₄(aq). Because the aqueous system in this study involved relatively high concentrations of chloride, reliable values for the complexation constants of Bi with chloride were required to accurately interpret the solubility data. Therefore as a part of this investigation, existing Bi–Cl data were critically reviewed and used to obtain values of equilibrium constants for various Bi–Cl complexes at zero ionic strength along with the values for various SIT ion interaction parameters. Predictions based on these thermodynamic quantities agreed closely with our experimental data, the chloride concentrations of which ranged as high as 0.7 mol?kg^?1. The study showed that BiPO₄(cr) is stable at pH values <9.0. At pH values >9.0, Bi(OH)₃(am) is the solubility controlling phase. Reliable values for the Bi(OH)₃(am) solubility reactions involving Bi(OH)₃(aq) and $\mathrm{Bi}(\mathrm{OH})_{4}^{-}$ and the formation constants of these aqueous species are also reported.     

Inter-conversion of Tb3+ and Tb4+ states and its fluorescence properties in MO–Al2O3: Tb (M = Mg,Ca, Sr,Ba) phosphor materials

Terbium ion doped MO–Al₂O₃ (M = Mg, Ca, Sr and Ba) series phosphors have been synthesized through combustion technique and their luminescence properties have been studied and compared. Terbium ion in different phosphors has shown different fluorescence properties due to the presence of different ratios of Tb³⁺ and Tb⁴⁺ states in different samples. The UV/Visible absorption and XPS techniques have been used to probe the existence of Tb³⁺ and Tb⁴⁺ states. The host sensitive 4f–5d and the charge transfer transitions enabled the use of terbium ion as an indicator of the structure.     

NIR to visible upconversion in Er/Yb co-doped CaYAl3O7 phosphor obtained by solution combustion process

Using the combustion synthesis, CaYAl₃O₇:Er³⁺ phosphor powders co-doped with Yb³⁺ have been prepared at low temperatures (550 °C) in a few minutes. Formation of the compound was confirmed by X-ray powder diffraction. Near-infrared to visible upconversion fluorescence emission in the Er³⁺ doped CaYAl₃O₇ phosphor powder has been observed. The effect of co-doping with triply ionized ytterbium in the CaYAl₃O₇:Er³⁺ phosphor has been studied and the process involved is discussed.     

Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1-20 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 30-60 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature (T_C) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting P-E hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (ΔE) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.     

Study of Sm-doped ZnO samples sintered in a nitrogen atmosphere and deposited on n-Si(1 0 0) by evaporation technique

The samarium doping zinc oxide (Zn_1-xSm_xO) with (x=0.0, 0.04, 0.05 and 0.17) polycrystalline thin films have been deposited on n-Si(1 0 0) substrate using thermal evaporation technique. Ceramic targets for deposition were prepared by the standard solid-state reaction method and sintered in nitrogen atmospheres. X-ray diffraction and scanning electron microscopy analyses show that the bulk and films features reveal wurtzite crystal structure with a preferential (1 0 1) crystallographic orientation and grows as hexagonal shape grains. According to the results of the Hall effect measurements, all the films show p-type conductivity, possibly a result of nitrogen incorporation into the Sm-doped ZnO samples. Magnetic measurements show that ferromagnetic behavior depends on the Sm³⁺ concentration. For a film with lower Sm₂O₃ contents (x=0.04), a phenomenon of paramagnetism has been observed. While, with further increase of Sm³⁺ contents (x=0.05) the ferromagnetic behavior has been observed at room temperature. However, at higher doping content of Sm³⁺, the ferromagnetic behavior was suppressed. The decrease of ferromagnetism with increasing doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Zn_1-xSm_xO films.     

N-Iodosaccharin (NISac): a new reusable catalyst for formal [2+4] cycloaddition of imines and enones

The first example of N-iodosaccharin (NISac)-catalyzed step, pot and atom economic synthesis of 1,3-oxazines via formal [2+4] cycloaddition of imines and enones has been reported. No by-product formation, operational simplicity, ambient temperature and high yields (85-95%) are the salient features of the present synthetic protocol. After isolation of the product, the catalyst NISac can be easily recovered and reused without any loss of efficiency.     

Rotation Structure in the Ultraviolet Bands of SnF

Rotation structure of (0,0) bands of the (C-X)_3/2 and (G-X)_3/2 systems of SnF molecule has been photographed in the third order of a 10.6 meter concave grating spectrograph. The rotation constants, as determined from the analysis, have been reported to be:-     

Synthesis of Nanosized Silicon Carbide Through Non-Transferred Arc Thermal Plasma

A thermal plasma system was used for the preparation of nanosized SiC powder. First SiC was synthesized by solid-state reaction using waste silicon and activated carbon powders and then plasma processing was carried out to form nanosized SiC. Phase and structural analysis was carried out by X-ray diffraction which confirmed the formation of SiC in both cases. Plasma treatment did not show any kind of change in structure and phase of SiC; except little free silicon. Morphological investigation showed the formation of 20–30 nm spherical SiC particles after plasma treatment which was initially 1–5 μm. It was found that DC current played an important role in the reduction of particle size. It was proposed that nanosized SiC was formed due to the dissociation of grains from their grain boundary due to strong plasma gas stream.     

Thermal,physicochemical and spectroscopic studies on some novel organic complexes obtained by green synthesis

Journal of Thermal Analysis and Calorimetry - The solid–liquid equilibrium phase diagram and thermochemical studies on two binary organic systems involving N-methylurea (MU) with...     

Lasing without population inversion in molecules

We have described here the physical basis for lasing without population inversion (LWOPI). This type of amplification is obtained basically by two mechanisms: (i) one is based on atomic interference and (ii) the other is based on Fano-type interference. We have shown here, in H₂ molecules, amplification without population inversion is feasible by considering both the mechanisms.