Papers by Keyword: Luminescence

Abstract: Praseodymium doped KNbO₃ (KNbO₃:Pr) phosphors were synthesized by a facile solgel combustion method. Phase evolution, particle size and luminescent properties of the powders synthesized at various temperatures were investigated. Single-phase KNbO₃:Pr nanoscale particles were obtained at 600°C by directly crystallizing from amorphous precursors. The particle size of KNbO₃:Pr powders can be well controlled by varying the heat treatment temperature. Under the excitation of 450 nm, KNbO₃:Pr phosphors showed the well-known Pr³⁺ emissions associated with the 4f inter-level electronic transitions in Pr³⁺ ions.

Abstract: CdSiO₃: Mn²⁺, Er³⁺ long-lasting phosphor was prepared by the conventional high temperature solid-state method. Effects of the concentration of Mn²⁺ and Er³⁺ on the luminescent properties of phosphor CdSiO₃: Mn²⁺, Er³⁺ were investigated by means of photoluminescence (PL) spectra and the afterglow intensity decay curves. It was found that when the Mn²⁺ and Er³⁺ dopant-concentrations were 0.2 mol% and 0.8 mol% of Cd²⁺ ions in CdSiO₃, respectively, the luminescence of phosphor prepared had better luminescent property and longer afterglow time. The phosphorescence for it could be seen with the naked eye for more than 60 min in the dark after the removal of the 254 nm UV light. Role of Er³⁺ co-doped into CdSiO₃: Mn²⁺ matrix was discussed in this paper.

Abstract: The paper presents some results of study based on applications of ZnS core shell quantum dots (QDs) doped with Cu. Keeping the luminous properties in focus we synthesized the core shell QDs by chemical precipitation route, resulting in formation of core@shell QDs with ZnS core doped with copper and ZnS shell on it, i.e. [ZnS:Cu@Zn. We focus the application of these particles in field of OLEDs (AMOLED) to address the performance deficiencies like varying brightness of the different wavelength emitting LEDs, called Green Window problem. Efforts have been done to address the problems by synthesizing highly luminescent green emitting copper doped ZnS, core@shell QDs. Further a monolayer of core shell quantum dots was deposited on ITO by spin coating for analyzing the photometric properties of the QDs.

Abstract: Nowadays, luminescence dating technique has become one of the unique tools for paleoclimatic studies. A lot of progress has been made in terms of understanding the phenomenon of luminescence, development of methodology for luminescence dating and its application. Still there are several directions which require better understanding and refinement. This brief review article focuses on the different aspects of luminescence dating, covering basic theory behind luminescence and luminescence dating, procedural aspects, complications and issues of luminescence dating and future perspective.

Abstract: Luminescence is "cold light", light from other sources of energy, which can take place at normal and lower temperatures. There are several varieties of luminescence, each named according to what the source of energy is, or what the trigger for the luminescence is. Luminescence is a collective term for different phenomena where a substance emits light without being strongly heated, i.e., the emission is not simply thermal radiation. This definition is also reflected by the term "cold light".

Abstract: Well-crystallized SrWO₄ mesocrystals with different shapes including flower-like sphere, bundle, peanut, dumbbell, and notched sphere were controllably synthesized via a simple microwave-assisted precipitation method. X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) measurements were used to characterize these mesocrystals. XRD patterns indicate that the SrWO₄ mesocrystals present a scheelite-type tetragonal structure. FESEM and HRTEM micrographs showed different shapes for the SrWO₄ mesocrystals. The molar ratio of [WO₄^2-] to [Sr²⁺] was found to play an important role in the morphological controlling of the resulting SrWO₄ mesocrystals. With the increase of the molar ratio, the shape of the SrWO₄ mesocrystals changed from flower-like sphere assembled with nanorods to notched sphere with intermediate peanut and dumbbell shapes. PL spectra measurements showed that the luminescence properties of the SrWO₄ mesocrystals strongly relied on its shapes.

Abstract: A novel series of copolymers containing fluorene units are synthesized by Sonogashira coupling reaction in mild condition. Benzene, naphthalene and anthracene are co-polymerized with ethynylfluorene, respectively. The structures are confirmed by NMR, Mass, Elemental analysis and GPC. The polymers have good thermal properties with glass-transition temperature of 90-155°C(Tg), and they have bandgaps from 2.21-2.77 eV. The results of photoluminescence in solid state show that introduction of huge chromophore could effectively suppress the formation of aggregates and excimers which typically cause red-shifted or new emission.

Abstract: Eu²⁺-doped Ba₃La (PO₄)₃ phosphors were synthesized by solid-state reaction method. The X-ray diffraction (XRD) results showed that the obtained phosphors were cubic phase. The structure of Ba₃La (PO₄)₃ doped slight Eu²⁺ does not changed. Ba₃La_1-x(PO₄)₃:xEu²⁺ phosphor can be excited by UV-visible light, which emits intensely blue light with broadband peaked at about 466 nm. The relative PL intensity increases with Eu²⁺-concentration increasing until a maximum intensity is reached, at about x=0.015mol. According to the Dexters theory, it was found that the major mechanism for concentration quenching as a result of dipole-dipole (d-d) interaction.

Abstract: We report on 0.93 eV luminescence observed in multicrystalline silicon. The spectral line is close to the well known D3 one, but its properties are different. The new feature shows a remarkable intensity at room temperature, exceeding the intensity of the band to band radiative transition. Moreover, it appears as a single line in the entire temperature range 10-300K, in contrast to the D3, which is usually accompanied by D4. Cathodoluminescence (CL) and electron beam induced current (EBIC) micrographs revealed that the centers causing 0.93 eV emission are irregularly distributed along certain grain boundaries. Electron backscattering diffraction examination showed that the 0.93 eV luminescence appears at grain boundaries characterized by a lattice rotation around a <344> axis. The EBIC contrast at those irregularities indicates strong total recombination. Based on an analysis of the temperature dependence of the CL intensity and the EBIC contrast we obtained an activation energy of about 120 meV.

Abstract: We present an overview on generation of direct gap photo- and electroluminescence in Ge bulk wafers, Ge thin films deposited on Si, and Ge p-i-n diodes prepared on Si substrates. We analyzed the emission in a spectral range from 0.45 eV to 0.95 eV, covering the radiation caused by direct gap transitions, the indirect one, and also the luminescence related to transition on dislocations. The temperature and excitation level strongly influence the intensities of direct and indirect photoluminescence in bulk samples. As it could be expected, high temperature and excitation favour the generation of direct gap luminescence. Intrinsic bulk Ge shows a quadratic dependence of the direct gap luminescence on the excitation and a sub-quadratic one for the indirect. The photoluminescence spectra taken from intrinsic Ge on Si layers show features related to dislocations. There are two spectral regions associated with dislocation recombination. At room temperature one is at around 0.45 eV and the other at 0.72 eV. We found strong direct gap radiation from the Ge p-i-n diodes with intrinsic, highly dislocated active area (dislocation density of about 10⁸-10¹⁰ cm^-2). There is a threshold current density of 8 kA/cm², at which the direct band luminescence becomes a super-quadratic. The dependence of the radiation intensity on the excitation is governed by a power law with exponent of 1.7 before reaching that threshold and 4.5 after exceeding it. Above the threshold the dislocation radiation shows similar dependence on the excitation as the direct band luminescence.