Synthesis and Photoluminescence Properties of Novel Red Phosphors for White Light Emitting Diode Applications

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Synthesis and Photoluminescence Properties of Novel Red Phosphors for White Light Emitting Diode Applications

Show simple item record Linda, Francis T Prabhakar Rao, P 2016-02-02T07:15:51Z 2016-02-02T07:15:51Z 2015-08
dc.description Materials Science and Technology Division CSIR - National Institute for Interdisciplinary Science and Technology (NIIST) Thiruvananthapuram en_US
dc.description.abstract Several series of Eu3+ based red emitting phosphor materials were synthesized using solid state reaction route and their properties were characterized. The present studies primarily investigated the photoluminescence properties of Eu3+ in a family of closely related host structure with a general formula Ln3MO7. The results presented in the previous chapters throws light to a basic understanding of the structure, phase formation and the photoluminescence properties of these compounds and their co-relations. The variation in the Eu3+ luminescence properties with different M cations was studied in Gd3-xMO7 (M = Nb, Sb, Ta) system.More ordering in the host lattice and more uniform distribution of Eu3+ ions resulting in the increased emission properties were observed in tantalate system.Influence of various lanthanide ion (Lu, Y, Gd, La) substitutions on the Eu3+ photoluminescence properties in Ln3MO7 host structures was also studied. The difference in emission profiles with different Ln ions demonstrated the influence of long range ordering, coordination of cations and ligand polarizability in the emission probabilities, intensity and quantum efficiency of these phosphor materials. Better luminescence of almost equally competing intensities from all the 4f transitions of Eu3+ was noticed for La3TaO7 system. Photoluminescence properties were further improved in La3TaO7 : Eu3+ phosphors by the incorporation of Ba2+ ions in La3+ site. New red phosphor materials Gd2-xGaTaO7 : xEu3+ exhibiting intense red emissions under UV excitation were prepared. Optimum doping level of Eu3+ in these different host lattices were experimentally determined. Some of the prepared samples exhibited higher emission intensities than the standard Y2O3 : Eu3+ red phosphors. In the present studies, Eu3+ acts as a structural probe determining the coordination and symmetry of the atoms in the host lattice. Results from the photoluminescence studies combined with the powder XRD and Raman spectroscopy investigations helped in the determination of the correct crystal structures and phase formation of the prepared compounds. Thus the controversy regarding the space groups of these compounds could be solved to a great extent. The variation in the space groups with different cation substitutions were discussed. There was only limited understanding regarding the various influential parameters of the photoluminescence properties of phosphor materials. From the given studies, the dependence of photoluminescence properties on the crystal structure and ordering of the host lattice, site symmetries, polarizability of the ions, distortions around the activator ion, uniformity in the activator distribution, concentration of the activator ion etc. were explained. Although the presented work does not directly evidence any application, the materials developed in the studies can be used for lighting applications together with other components for LED lighting. All the prepared samples were well excitable under near UV radiation. La3TaO7 : 0.15Eu3+ phosphor with high efficiency and intense orange red emissions can be used as a potential red component for the realization of white light with better color rendering properties. Gd2GaTaO7 : Eu3+, Bi2+ red phosphors give good color purity matching to NTSC standards of red. Some of these compounds exhibited higher emission intensities than the standard Y2O3 : Eu3+ red phosphors. However thermal stability and electrical output using these compounds should be studied further before applications. Based on the studies in the closely related Ln3MO7 structures, some ideas on selecting better host lattice for improved luminescence properties could be drawn. Analyzing the CTB position and the number of emission splits, a general understanding on the doping sites can be obtained. These results could be helpful for phosphor designs in other host systems also, for enhanced emission intensity and efficiency. en_US
dc.description.sponsorship Cochin University of Science & Technology en_US
dc.language.iso en en_US
dc.publisher Cochin University Of Science And Technology en_US
dc.subject Phosphors en_US
dc.subject Photoluminescence properties en_US
dc.subject Gd3-xMO7 : Eu3+ (M = Nb, Sb, Ta) red phosphors en_US
dc.subject Ln3-xTaO7 : Eu3+ (La, Lu, Y, Gd) red phosphors en_US
dc.subject La3TaO7 : Eu3+ red phosphors en_US
dc.subject Cationic modifications en_US
dc.subject Gd2GaTaO7 : Eu3+, Bi2+ en_US
dc.title Synthesis and Photoluminescence Properties of Novel Red Phosphors for White Light Emitting Diode Applications en_US
dc.type Thesis en_US

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