Nano materials, development of upconversion nanomaterials for solar energy and other potential applications, synthesis of luminescent materials, coordination complexes synthesis etc.,
FUTURE PROJECTS
Development of upconersion nanomaterials for solar enegy and other potential applications
High-frequency EPR investigation of X-ray storage SrBPO5:Eu phosphor T. Nakamura, T. Takeyama, N. Takahashi, R. Jagannathan, A. Karthikeyani, et al. Journal of Luminescence, 2003 High-frequency EPR (HFEPR) spectra of the SrBPO 5 :Eu with stillwellite structure, which was prepared using EuCl 3 .6H 2 O as a dopant, have been examined in order to clarify the Eu sites in it. They showed an intense doublet at 3.3 T corresponding to g =2.0 as is expected for the 8 S state ions. Also, weak satellites were observed on both sides of the central doublet signal symmetrically. This means that microwave energy at 90 GHz is sufficiently larger than the zero-field splitting. Taking into account the crystal structure of stillwellite and the earlier PL investigation, a single Eu 2+ site was assumed for the HFEPR simulation. As a result, it was found that HFEPR spectrum simulated using g =1.98161, ∣ D ∣=0.130 T and λ =∣ E / D ∣=0.06 reasonably agrees well with the experimental one, supporting that the Eu 2+ occupies the Sr site. The large ∣ D ∣ value small λ value obtained implies that the crystal field surrounding Eu 2+ has a strong axial field with weak rhombic distortion.
Eu2+ luminescence in stillwellite-type SrBPO5 - a new potential X-ray storage phosphor A Karthikeyani, R Jagannathan Journal of Luminescence, 2000 Eu 2+ -doped SrBPO 5 with stillwellite structure has been identified as a new luminescent system which shows intense photostimulated luminescence for UV and X-ray radiations. Various spectral features observed for the new system are very much similar to BaFBr : Eu 2+ , the extensively applied phosphor system in digital radiography. Apart from its potential for application, the unusually low wavelength Eu 2+ emission observed has been explained by the absence of preferred orientation of d-orbital of Eu 2+ as dictated by crystal chemistry of the system.
Structural distortion in (La,Sr)2CuO4 cuprates: An insight using luminescence and EPR probes V.V.S.S Sai Sundar, A Karthikeyani, R Jagannathan Chemical Physics Letters, 1999 We have demonstrated that Eu 3+ luminescence can be successfully employed as a local probe to explore the microscopic symmetry of the cationic sites in the Sr 2+ -substituted lanthanum cuprate superconductor(s). It has been found that Sr 2+ substitution in La 1− x Sr x CuO 4 ( x ∼0.4) does not alter the microscopic symmetry of the cationic site(s). Further, using electron paramagnetic resonance spectroscopy we have demonstrated that the hole centers arising out of Sr 2+ substitution are localized around Cu 2+ site(s).
Melt-quenched KCl:Eu2+ films for photostimulated luminescence applications R. Jagannathan, M. Watanabe, N. Murase, A. Karthikeyani, Y. Kanematsu, et al. Journal of Applied Physics, 1998 Using a conventional melt-quenching method, Eu2+-doped KCl films have been prepared. These films yield intense photostimulated luminescence (PSL) with the stimulated excitation maximum shifting to longer wavelengths as compared to the reports on the single-crystal analog. This will be advantageous for image reading by a He–Ne laser or red-emitting diode lasers when used in the PSL applications. Several types of centers have been found. Further, in the electron paramagnetic resonance spectrum, the hyperfine structure due to the Eu2+ centers has been observed to disappear at low temperatures (∼5 K). This can be attributed to the formation of complexes by the trapping of defect centers at the Eu2+ site(s). Crystallization effects and paramagnetic centers as well as optical properties of these films are discussed.
