Browsing by Author "P.V. Ramakrishna"

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Enhanced up-conversion and temperature-sensing behaviour of Er3+ and Yb3+ co-doped Y2Ti2O7 by incorporation of Li+ ions
(2014) B.P. Singh; A.K. Parchur; R.S. Ningthoujam; P.V. Ramakrishna; S. Singh; P. Singh; S.B. Rai; R. Maalej
Y2Ti2O7: Er3+/Yb3+ (EYYTO) phosphors co-doped with Li+ ions were synthesized by a conventional solid-state ceramic method. X-ray diffraction studies show that all the Li+ co-doped EYYTO samples are highly crystalline in nature with pyrochlore face centred cubic structure. X-ray photon spectroscopy studies reveal that the incorporation of Li+ ions creates the defects and/or vacancies associated with the sample surface. The effect of Li+ ions on the photoluminescence up-conversion intensity of EYYTO was studied in detail. The up-conversion study under ∼976 nm excitation for different concentrations of Li+ ions showed that the green and red band intensities were significantly enhanced. The 2 at% Li+ ion co-doped EYYTO samples showed nearly 15- and 8-fold enhancements in green and red band up-converted intensities compared to Li+ ion free EYYTO. The process involved in the up-conversion emission was evaluated in detail by pump power dependence, the energy level diagram, and decay analysis. The incorporation of Li+ ions modified the crystal field around the Er3+ ions, thus improving the up-conversion intensity. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was evaluated using the fluorescence intensity ratio technique. Appreciable temperature sensitivity was obtained using the synthesized phosphor material, indicating its applicability as a high-temperature-sensing probe. The maximum sensitivity was found to be 0.0067 K-1 at 363 K. © the Partner Organisations 2014.
Improved photo-luminescence behaviour of Eu3+ activated CaMoO4 nanoparticles via Zn2+ incorporation
(Royal Society of Chemistry, 2015) B.P. Singh; Maheshwary; P.V. Ramakrishna; Saurabh Singh; V.K. Sonu; Santosh Singh; P. Singh; A. Bahadur; R.A. Singh; S.B. Rai
Zn2+ (0, 2, 5, 7 and 10 at%) co-doped CaMoO4:2Eu3+ nanophosphors have been synthesized via the polyol method using ethylene glycol (EG) as both capping agent and reaction medium at 150°C. From XRD analysis, all 900°C annealed Zn co-doped CaMoO4:Eu3+ nanophosphors have a tetragonal scheelite phase. Some extra phase evolution has been observed for the as-prepared Zn doped samples. The intensity and crystallinity of XRD patterns increase as heat treatment increases to 900°C. The valence states of the involved compositions (Zn co-doped CaMoO4:Eu) were investigated by X-ray photoelectron spectroscopy (XPS) and it was found that Ca, Mo, Eu and Zn are in their +2, +6, +3 and +2 oxidation states, respectively. TG-DSC studies of the as-prepared samples corroborate their thermal stability. A TEM (Transmission electron microscopy) study reveals that the particles have spherical morphology. Photoluminescence studies have been carried out under ∼266, and 395 nm excitation wavelengths. Zn co-doping in the CaMoO4:Eu matrix produces a high distortion and modifies the crystal field around the Eu3+ ion and improves the PL intensity. CIE co-ordinates of the 900°C annealed 10 at% Zn co-doped CaMoO4:Eu sample under 266 nm excitation is x = 0.64 and y = 0.35, which are close to the standard of NTSC (x = 0.67 and y = 0.33). These investigations reveal that Zn co-doped CaMoO4:Eu3+ nano-materials can be used as potential red emitting phosphors, an area which is a bottleneck in the development of low cost LEDs. © The Royal Society of Chemistry.