Modification of luminescence spectra of CaF2:Eu2+.

CaF2:Eu(2+) is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid-state lighting (SSL), and down-conversion for solar cells. However, emission of CaF2:Eu(2+) is around 424 nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue - 450 nm, green - 540 nm or red - 610 nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF2:Eu(2+) to meet these requirements using co-dopants. A Ca0.49 Sr0.50 Eu0.01 F2 phosphor showing better colour coordinates and having an emission maximum around 440 nm was discovered during these studies.

Luminescence and energy transfer in Ce3+, Mn2+- doped K2AEP2O7 (AE = Ca, Sr) phosphor.

Pyrophosphates K2AEP2O7 (AE = Ca, Sr) prepared by the classical solid-state technique and activated with Ce(3+) are described. Intense emission was observed in K2AEP2O7 (AE = Ca, Sr). The effect of Mn(2+) co-doping was studied. The broad emission peak of Mn(2+) was observed at 534 nm in K2 rP2O7:Ce(3+) and at 539 nm in K2CaP2O7:Ce(3+), Mn(2+). Mn(2+) emission was greatly enhanced by addition of the sensitizer Ce(3+) due to efficient energy transfer from Ce(3+) to Mn(2+).

Luminescence in Li2BaP2O7.

The photo-, thermo- and optically stimulated luminescence in Li2BaP2O7 activated with Eu(2+) /Cu(+) are reported. Strong thermoluminescence, which is about two times greater than LiF-TLD 100 was observed in the Eu(2+) -activated sample. It also exhibited optically stimulated luminescence sensitivity of ~20% that of commercial Al2O3:C phosphor.

Wet-chemical preparation of Ce3+-activated K2LaX5 (X = Cl, Br or I) phosphors.

There has been a renewed interest in Ce(3+) -activated halide phosphors due to applications as scintillation detectors, especially for positron emission tomography. For K(2) LaCl(5), the light yield increases and the energy resolution (FWHM) improves with increasing Ce(3+) doping. K(2) LaX(5) compounds are also important as laser hosts for the mid-IR range. K(2) LaCl(5):Nd crystals show bright mid-IR luminescence, which makes them a candidate for IR laser materials. Efficient emission in the IR range has also been reported in K(2) LaCl(5):U(3+). A one-step, wet chemical process for preparing Ce(3+)-activated K(2) LaCl(5) phosphor is described. Intense luminescence of Ce(3+) can be observed in the as-prepared powders without any heat treatment. The availability of such powders opens up several exciting possibilities, such as growing single crystals without going to the high temperatures required for melting the constituent chlorides, or even obtaining processed, transparent, Ce(3+)-activated materials without taking recourse to crystal growth.

Luminescence studies of decomposition of ceric sulfate.

Literature results on the decomposition products of ceric sulfate are inconsistent. A group of researchers claim that ceric sulfate decomposed to ceric oxide without going through a cerous phase at any stage, while the results of the other group show that cerous sulfate is formed as an intermediate phase. Most of these studies used DTA/TGA, XRD and IR techniques. Cerous compounds can also be detected by the characteristic luminescence of Ce(3+). Using such techniques we show that the thermal decomposition of both monoclinic and ßCe(SO(4) )(2) · 4H(2) O in air at 500°C leads to the formation of cerous sulphate. Use of various atmospheres (air/N(2) /vacuum) and temperature profiles for the decomposition by the different researchers may be responsible for the discrepancies between literature results.

Modulatory effect of distillate of Ocimum sanctum leaf extract (Tulsi) on human lymphocytes against genotoxicants.

OBJECTIVE: To study the modulatory effect of distillate of Ocimum sanctum (traditionally known as Tulsi) leaf extract (DTLE) on genotoxicants. METHODS: In the present investigation, we studied the antigenotoxic and anticlastogenic effect of distillate of Tulsi leaf extract on (i) human polymorphonuclear leukocytes by evaluating the DNA strand break without metabolic activation against mitomycin C (MMC) and hexavalent chromium (Cr+6) and (ii) human peripheral lymphocytes (in vitro) with or without metabolic activation against mitomycin C (MMC), hexavalent chromium (Cr+6) and B[a]P by evaluating chromosomal aberration (CA) and micronucleus assay (MN). Three different doses of DTLE, 50 microL/mL, 100 microL/mL, and 200 microL/mL were selected on the basis of cytotoxicity assay and used for studying DNA strand break, chromosomal aberration and micronucleus emergence. The following positive controls were used for inducing genotoxicity and clastogenicity: MMC (0.29 micromol/L) for DNA strand break, chromosomal aberration and 0.51 micromol/L for micronucleus assay; Potassium dichromate (Cr+6) 600 micromol/L for DNA strand break and 5 micromol/L for chromosomal aberration and micronucleus assay; Benzo[a]pyrene (30 micromol/L) for chromosomal aberration and 40 micromol/L for micronucleus assay. The active ingredients present in the distillate of Tulsi leaf extract were identified by HPLC and LC-MS. RESULTS: Mitomycin C (MMC) and hexavalent chromium (Cr+6) induced statistically significant DNA strand break of respectively 69% and 71% (P<0.001) as revealed by fluorometric analysis of DNA unwinding. Furthermore, the damage could be protected with DTLE (50 microL/mL, 100 microL/mL, and 200 microL/mL) on simultaneous treatment. Chromosomal aberration and micronucleus formation induced by MMC, Cr+6 and B[a]P were significantly protected (P<0.001) by DTLE with and without metabolic activation. CONCLUSION: Distillate of Tulsi leaf extract possesses antioxidants contributed mainly by eugenol, luteolin and apigenin as identified by LC-MS. These active ingredients may have the protective effect against genotoxicants.

Role of neuropeptide Y in the regulation of gonadotropin releasing hormone system in the forebrain of Clarias batrachus (Linn.): immunocytochemistry and high performance liquid chromatography-electrospray ionization-mass spectrometric analysis.

Although the importance of neuropeptide Y (NPY) in the regulation of gonadotropin releasing hormone (GnRH) and reproduction has been highlighted in recent years, the neuroanatomical substrate within which these substances might interact has not been fully elucidated. Present work was undertaken with a view to define the anatomical-physiological correlates underlying the role exercised by NPY in the regulation of GnRH in the forebrain of the teleost Clarias batrachus. Application of double immunocytochemistry revealed close associations as well as colocalizations of the two peptides in the olfactory receptor neurons (ORNs), olfactory nerve fibers and their terminals in the glomeruli, ganglion cells of nervus terminalis, medial olfactory tract, fibers in the area ventralis telencephali/pars supracommissuralis and cells as well as fibers in the pituitary. NPY containing axons were found to terminate in the vicinity of GnRH cells in the pituitary with light as well as electron microscopy. Double immunoelectron microscopy demonstrated gold particles for NPY and GnRH colocalized on the membrane and in dense core of the secretory granules in the cells distributed in all components of the pituitary gland. To assess the physiological implication of these observations, NPY was injected via the intracranial route and the response of GnRH immunoreactive system was evaluated by relative quantitative morphometry as well as high performance liquid chromatography (HPLC) analysis. Two hours following NPY (20 ng/g body weight) administration, a dramatic increase was observed in the GnRH immunoreactivity in the ORNs, in the fibers of the olfactory bulb (163%) and medial olfactory tract (351%). High performance liquid chromatography-electrospray ionization-mass spectrometric analysis confirmed the immunocytochemical data. Significant rise in the salmon GnRH (sGnRH)-like peptide content was observed in the olfactory organ (194.23%), olfactory bulb (146.64%), telencephalon+preoptic area (214.10%) and the pituitary (136.72%) of the NPY-treated fish. However, GnRH in the hypothalamus was below detection limit in the control as well as NPY-treated fish. Present results suggest the involvement of NPY in the up-regulation of sGnRH containing system at different level of neuraxis extending from the olfactory epithelium to the pituitary in the forebrain of C. batrachus.