TSL and EPR studies of SrBPO5 doped with CeO2and co-doped with CeO2 and Sm2O3

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO₅ samples doped with CeO₂ and co-doped with CeO₂ and Sm₂O₃. On gamma-irradiation at room temperature, BO₃ ^2–, O₂ ^– and O^– radicals were produced. It was seen that the O^– radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O^– radical ions results in transfer of recombination energy to the impurity centre Ce³⁺ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce³⁺ to Sm³⁺ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work.     

Separation of uranium from solid (U,Pu, Ag) oxide analytical waste: effect of batch size and nitric acid molarity

This work presents the investigation of some commercially available and commonly used Si₃N₄ foils prepared with LPCVD technique. The density and the stoichiometry of these films were determined by Rutherford backscattering spectroscopy and profilometry, while the study of impurities was achieved with particle induced X-ray emission method. It was found that the density of the studied Si₃N₄ films is significantly less (~2.71 g cm^?3), while the stoichiometry is close to the values of the bulk material. The results were verified by measuring the ion energy loss through the films by scanning transmission ion microscopy.     

Self-assembled structures of hydroxyapatite in the biomimetic coating on a bioinert ceramic substrate

The tribological properties of alumina ceramic are excellent due in part to a high wettability because of the hydrophilic surface and fluid film lubrication that minimizes the adhesive wear. Such surfaces are further modified with bioactive glass/ceramic coating to promote direct bone apposition in orthopedic applications. The present communication reports the biomimetic coating of calcium hydroxyapatite (HAp) on dense (2-3% porosity) alumina (alpha-Al(2)O(3)) substrate (1cmx1cmx0.5cm), at 37 degrees C. After a total period of 6 days immersion in simulated body fluid (SBF), at 37 degrees C, linear self-assembled porous (pore size: approximately 0.2mum) structures (length: approximately 375.39mum and width: 5-6mum) of HAp were obtained. The phenomenon has been demonstrated by self-assembly and diffusion-limited aggregation (DLA) principles. Structural and compositional characterization of the coating was carried out using SEM with EDX facility, XRD and FT-IR data.     

Rapid synthesis and biological evaluation of 1,4-dihydropyridine derivatives containing a benzothiazolyl moiety

A series of N-(6-methylbenzothiazolyl)-2,3,5,6-tetrasubstituted-4-(aryl)-1,4-dihydropyridines were synthesized by reaction of 2-amino-6-methylbenzothiazole, aromatic aldehyde and active methylene compound in methanol by conventional, as well as, microwave irradiation (solvent free and solid support) methods. The microwave irradiation technique gives better yield and shorter reaction time. Among solid supported microwave irradiation better yields are obtained in acidic alumina as compared to silica, neutral alumina, and basic alumina. All compounds were tested for antibacterial and antifungal activities and results have been compared with standard drugs. Entomological activities were also tested. The results showed that a change in the substitution pattern in 1,4-dihydropyridine derivatives may cause a marked effect on their antimicrobial activity.     

Electron paramagnetic resonance studies in photorefractive crystals I: Hyperfine interaction and photoinduced charge transfer in233U5+ and238U5+ doped LiNbO3

Electron paramagnetic resonance studies were conducted on the photoinduced charge transfer and also hyperfine interaction of U⁵⁺ stabilized in photorefractive matrix LiNbO₃. This work deals with: (i) first observation of hyperfine structure due to²³³U (I=5/2) in its pentavalent state at octahedral sites and comparison with other possible site symmetries, (ii) photoinduced charge transfer as observable by EPR and its relevance to photorefractive behaviour of LiNbO₃. The effect of chemical bonding on the hyperfine interaction of 5f ¹ configuration was also studied by converting the existing literature data on²³⁵U⁵⁺ to that of²³³U⁵⁺ by standard methods. This suggests that progressive substitution of oxygen by F⁻, in the series UO ₆ ⁷⁻ , (UO₅F)⁶⁻ and (UO₄F₂)⁵⁻ drastically decreases the hyperfine coupling constantA _∥, along the local distortion axis. This trend is explained as being due to the absence of ligand ion along the distortion axis at U⁵⁺ site in trigonal LiNbO₃. The effects of illumination by copper vapor laser (CVL) on the intensity of the U⁵⁺ signal was studied in the 10–300K region. The kinetics of decay and restoration of U⁵⁺ was also studied between 10–100K range. The decay kinetics was found to obey double exponential. The reduction of concentration of U⁵⁺ with CVL-illumination and its restoration in the absence of light show that pentavalent uranium takes part in the photorefractive effects in LiNbO₃.     

Synthesis,characterization and studies of radiative properties on Eu3+-doped ZnAl2O4

Eu³⁺-doped ZnAl₂O₄ phosphors were successfully synthesized in air atmosphere at 900 °C. The phosphors were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermally stimulated luminescence (TSL) and photoluminescence (PL) techniques. The average particle size of the system as determined from SEM was found to be 100–150 nm (for samples annealed at 900 °C). PL spectra of the doped phosphors showed emission peaks corresponding to Eu³⁺ ions. Lifetime studies revealed Eu³⁺ ions to be in two different sites. The asymmetric ratio (I₆₁₆/I₅₉₂) was observed to be about 3.75. This suggested that Eu³⁺ ion entered the host mainly substituting Al³⁺ site distorting the local environment and is partly located on surface of the phosphors. A prominent glow peak at 430 K was observed in the TSL of γ-irradiated Eu³⁺-doped ZnAl₂O₄ phosphors. Trap parameters for this peak have been determined and the probable mechanism for the glow peak is proposed. CIE chromaticity coordinates for the system were evaluated. It was observed that, the system could be employed as a potential red emitting phosphor. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. The PL intensity of the as prepared phosphors was 63% of that of the commercial phosphor. Apart from this, various radiative properties such as the Judd–Ofelt intensity parameters, spontaneous emission probabilities, luminescence branching ratios, radiative lifetimes and quantum efficiency were evaluated for the system.     

Photoinduced changes in photorefractive PVA films doped with Cr3+ and VO2+: EPR and PAS investigations

In order to understand the mechanism of optical image storage in photorefractive polyvinyl alcohol (PVA) films, photo-EPR and photoacoustic spectral investigations were carried out on PVA films doped with Cr³⁺ and VO²⁺. The EPR spectrum of Cr³⁺ has shown reduction in intensity onin situ illumination with copper vapor laser (CVL). The decay and recovery of Cr³⁺ signal, with and without CVL illumination respectively, was monitored at different temperatures in 10–300 K region. These were found to obey a double exponential, with one time constant independent of temperature, and the other showing significant temperature dependence. From Τ(T), activation energy for the charge carrier transport in one of the processes was estimated to be 0.016 eV. The PA spectra showed shift towards lower wavelength side on consecutive runs. On the other hand, VO²⁺ doped PVA film has not shown any significant changes in intensity on laser illumination. These observations suggest (i) interaction of PVA matrix with excited Cr³⁺ and (ii) predominant non-radiative relaxation in VO²⁺: PVA system with no change in the oxidation state.     

TSL and EPR studies of SrBPO5 doped with CeO2 and co-doped with CeO2 and Sm2O3

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO₅ samples doped with CeO₂ and co-doped with CeO₂ and Sm₂O₃. On gamma-irradiation at room temperature, BO₃ ^2–, O₂ ^– and O^– radicals were produced. It was seen that the O^– radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O^– radical ions results in transfer of recombination energy to the impurity centre Ce³⁺ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce³⁺ to Sm³⁺ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work.     

Studies on ultrasonic velocity and electrical conductivity of samarium soaps in non-aqueous medium

Summary The ultrasonic velocity of solutions of samarium soaps in non-aqueous medium has been measured at a constant temperature and the results have been used to evaluate the various acoustic parameters. The pre-micellar association and the formation of micelles in samarium soap solutions have been determined by conductometric measurements. The molar conductance at infinite dilution, degree of ionisation and ionisation constant have been evaluated. The results show that samarium soaps behave as weak electrolyte in dilute solutions.

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Untersuchungen zur Ultraschallgeschwindigkeit und elektrischen Leitfähigkeit von Samarium-Seifen in nichtwäßrigem Medium

Zusammenfassung Die Ultraschallgeschwindigkeit in Lösungen von Samarium-Seifen in nichtwäßrigem Medium wurde bei konstanter Temperatur gemessen, und die Ergebnisse wurden zur Auswertung verschiedener akustischer Parameter genutzt. Die vormicellare Assoziation und die Ausbildung von Micellen in Samarium-Seifen-Lösungen wurden mittels konduktometrische Messungen bestimmt. Die molare Leitfähigkeit bei unendlicher Verdünnung, der Ionisierungsgrad und die Ionisationskonstante wurden ermittelt. Die Ergebnisse zeigen, daß sich Samarium-Seifen in verdünnten Lösungen als schwache Elektrolyte verhalten.

     

Effect of Temperature on Micellization and Thermodynamic Behavior of Gadolinium Alkanoates in Nonaqueous Media

The conductometric measurements were employed to determine the critical micellar concentration (CMC), degree of dissociation and dissociation constant of dilute solutions of Gadolinium decanoate and dodecanoate in benzene and methanol mixture (7:3 v/v). The results show that the Gadolinium alkanoates behave as moderate electrolyte below the CMC. The various thermodynamic parameters were also evaluated for both dissociation and association process.