Papers by Keyword: Luminescence

Abstract: Lead arsenate glasses containing different concentrations of CuO ranging from 0 to 1.5 mol% (in steps of 0.3 mol%) were prepared by melt quenching method. Further, samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and differential scanning calorimetric analysis (DSC). A number of studies viz., optical absorption, luminescence and FTIR spectra also have been carried out on these glasses. XRD and SEM studies have confirmed that the prepared samples are of amorphous in nature. DSC results indicate the more structural degree of disorder for glass containing 1.5 mol% of CuO. From the IR spectra, it is observed that the intensity of bands due to ν₁, ν₂, ν₃ and ν₄ and vibrations of AsO₃ group seems to be decreasing with shifting of the metacentres towards slightly higher wavenumber. The optical absorption and luminescence studies have indicated that copper exist in both the valence states viz., Cu⁺ and Cu²⁺. Finally the analyses of all results indicate that there will be growing degree of structural disorder with increase in the content of CuO. Keywords: Arsenate glasses, copper oxidation, optical absorption, luminescence

Abstract: In this paper, Stöber silica particles were decorated with polyethyleneimine and silver nanoparticles and Eu-polyoxometalates were grafted on the surface of polyethyleneimine/silica spheres. The hybrid SiO₂/Eu-polyoxometalates/Ag particles were characterized by IR, UVvis, luminescent spectra, scanning electron microscopy, transmission electron microscope, and cyclic voltammetry (CV), respectively. The hybrid particles show the bright red emission under UV light which can be observed by naked eyes. The luminescent properties of particles have been investigated which show that Ag nanoparticles have an influences on the luminescence of europium ions. The electrochemical activities of SiO₂/Eu-polyoxometalates/Ag particles have been demonstrated by CV measurement. The catalytic results indicate that the hybrid particles show the catalytic properties in the oxidation of styrene and benzaldehyde is the main product of the reaction.

Abstract: A new red phosphor Ca₃SiO₄Cl₂:Sm³⁺ has been synthesized and its luminescent properties have been investigated. The X-ray powder diffraction (XRD) was measured for studying the host structure. The excitation and emission spectra were measured at room temperature. The effect of Sm³⁺ ion content on the luminescent intensity and concentration quenching mechanism were studied. The results suggest that this phosphor maybe a good candidate of red phosphor for near UV-based white LED.

Abstract: In this work, a series of novel bipolar copolymers containing 8-hydroxyquinoline aluminum (Alq₃) and carbazole had been synthesized by copolymerization of Alq₃ complex monomer and N-vinylcarbazole (NVK), and the luminescence properties of the copolymers were investigated by UV-vis and fluorescence spectra. The results showed that energy can transfer effectively from carbazole group to Alq₃. Furthermore, energy transfer process and luminescence mechanism of the bipolar copolymers were discussed.

Abstract: Organic light-emitting diodes (OLEDs) were fabricated containing guest molecule of Tris (8-hydroxyquinoline) aluminum (Alq₃) blend with host molecules of N,N-diphenyl-N,N-bis (3-methylphenyl)-1,1-biphenyl-4,4-diamine (TPD) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) small molecules. Optical, photoluminescence (PL) and electroluminescence (EL) properties were investigated with respect to blend systems. The obtained optical energy gap and PL intensity in the blend systems increased due to the transfer of high energy from the host to guest molecules. Luminance and current efficiency were enhanced for blended OLEDs as compared to that of pure Alq₃, related to high exiton recombination in guest caused by high injection and accumulation of charge carrier.

Abstract: The luminescence of rare earth composite micelles was measured in different polarity. The polarity of complexes was changed with the molar ratios of block copolymers, trivalent europium (Eu (III)) ions and 1,10-phenanthroline (Phen). When 4-vinyl pyridine (4VP) coordinated with central ions Eu (III), the improved asymmetry of composite micelles resulted in higher polarity. The higher polarity strengthened the ability of electron transition, which improved the luminescence of complexes. When Phen participated in coordination, the polarity was improved further. The strongest luminescence of complexes could be obtained by changing the molar ratios of block copolymers, Eu (III) ions and Phen.

Abstract: The organic ligand sulfosalicylic acid (SSA) which was selected as molecular bridge for sensitization of terbium ions was modified by thionyl chloride (SOCl₂) and 3-ammonium propyl triethoxy silane (APTES) to obtain the hybrid precursor SSA-Si. Then the solution of Tb (NO₃)₃ was added in the presence of tetraethylorthosilicate (TEOS). The binary lanthanide organic/inorganic hybrid material was obtained. The ternary hybrid material was obtained by adding the solution of Tb (NO₃)₃ and polyurethane. We investigated the thermal stability and luminescence properties of hybrids and found that the ternary hybrid materials exhibit better thermal stability and stronger emission intensity. Furthermore, compared with the binary mesoporous material Tb-(SSA-Si)₃, the ternary mesoporous material Tb-(SSA-Si)₃-PU exhibits the characteristic emission of the Tb³⁺ ion with a higher luminescence intensity, suggesting that the introduction of polymer polyurethane into the mesoporous matrix is of benefit for the sensitization of Tb³⁺ luminescence, by replacing H₂O groups that can quench the luminescence of Tb³⁺ ion.

Abstract: Visible luminescence of Pr³⁺ ions in bismuth borate glasses doped with difference concentration of Pr₂O₃ have been studies. The glasses of composition 30Bi₂O₃ : (70-x)B₂O₃ : xPr₂O₃ (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) were prepared by the melt quenching technique. The spectral properties were investigated using the absorption and emission measurement. These glasses have shown emission and excitation bands in visible region. The emission band of Pr³⁺ doped glass centered at 600 nm (¹D₂ ³H₄), 642 nm (³P₀ ³F₂) and 704 nm (³P₀ ³F₃) have been observed with 469 nm (³H₄ ³P₁) excitation wavelength. The excitation band revealed centered at 447, 469 and 482 nm corresponding to the ³H₄ ³P₂, ³P₁ and ³P₀ transitions, respectively.

Abstract: In this research present the results of the analysis of Sm³⁺ ions doped bismuth borate glasses. Optical measurements such as absorption, excitation and emission profiles have been carried out. Glasses with the chemical compositions (50-x)B₂O₃50Bi₂O₃xSm₂O₃ (x = 0.0, 0.5, 1.0, 1.5, 2.50 and 2.5 mol%) were prepared using a conventional melt-quenching method. The emission spectrum of Sm³⁺ doped bismuth borate glasses has shown the emission transitions of to ⁴G_5/2⁶H _5/2 (563 nm), ⁴G_5/2⁶H _7/2 (598 nm), ⁴G_5/2⁶H_9/2 (644 nm). Energy level schemes relating to the emission mechanisms involved in Sm³⁺ glasses have been given.

Abstract: The strong yellow upconversion (UC) light emission has been observed in Ho³⁺/Yb³⁺ co-doped La₂(WO₄)₃ phosphor under the excitation of 980 nm diode laser. The phosphors were synthesized by the traditional solid-state reaction method. The phrase structures of the samples were characterized by X-ray diffraction (XRD). The doping concentration of Yb³⁺ was determined to be 20mol% for the strongest yellow emission. Then, the dependence of UC emission intensity on excitation power density showed that the green and red UC emissions are involved in two-photon process. The possible UC mechanisms for the strong yellow emission were also investigated.