Radiation-induced defects in Pr3+-activated LiYF4 laser host

Rare earth doped fluorides have been used in laser applications. Not much is known about the effect of ionizing radiation on the lasing and other properties of fluorides. Therefore, in recent years much attention has been paid to the study of radiation-induced defects in laser materials, as they affect the optical and stimulated emission properties. The defect formation by gamma-ray irradiation in Pr3+ activated LiYF4, powder prepared by melt method, have been studied by thermoluminescence and electron spin resonance techniques and are reported in this paper. It is shown that LiYF4:Pr3+ is sensitive to gamma-ray radiation. Characterization of this laser material using ESR and photoluminescence techniques is also described

Correlated ESR, PL and TL studies on K3Na(SO4)(2): Eu thermoluminescence dosimetry phosphor

Strong thermoluminescence (TL) was observed in K3Na(SO4)(2):Eu phosphor in the Eu doped K2SO4-Na2SO4 system. The defect centres formed in this TL phosphor are studied using the technique of electron spin resonance. Two glow peaks at 423 and 475 K are observed in K3Na(SO4)(2):Eu phosphor prepared by the melt method. The peak 475 K is shown to be at least thrice as sensitive as the conventional CaSO4: Dy phosphor used in the TL dosimetry of ionizing radiations. Two centres, assigned to SO4- and SO3-, are observed at room temperature in the melt prepared phosphor. Step annealing measurements showed a connection between these centres and the observed TL glow peaks. Three TL glow peaks at 360, 423 and 453 K are observed in the K3Na(SO4)(2):Eu phosphor prepared by the evaporation method. A SOS centre and two different SO4- centres are observed in this phosphor. TL and photoluminescence emission spectra indicate that the europium ion is in the divalent state in K3Na(SO4)(2):Eu phosphor. (C) 2001

Correlated ESR, PL and TL studies on Sr-5(PO4)(3)Cl : Eu thermoluminescence dosimetry phosphor

Electron spin resonance (ESR), thermoluminescence and photoluminescence studies in Eu2+ activated Sr-5(PO4)(3)Cl phosphor are reported in this paper. The Sr-5(PO4)(3)Cl:Eu2+ phosphor is twice as sensitive as the conventional CaSO4:Dy phosphor used in thermoluminescence dosimetry of ionizing radiations. It has a linear response, simple glow curve, emission peaking at 456 nm. The defect centers formed in the Sr-5(PO4)(3)Cl:Eu2+ phosphor are studied by using the technique of ESR. A dominant TL glow peak at 430 K with a smaller shoulder at 410K is observed in the phosphor. ESR studies indicate the presence at three centers at room temperature. Step annealing measurements show a connection between one of the centers and the dominant glow peak at 430 K. The 430 K TL peak is well correlated with center I, which is tentatively identified as (PO4)(2-) radical. (c) 200

Luminescent studies of impurity doped SrS phosphors

SrS phosphors activated with Ce and Dy ions were prepared by solid-state diffusion method. Photoluminescent study was carried out on SrS : Ce, SrS : Dy and SrS : Dy, Ce. Thermoluminescence and electron spin resonance studies were also carried out on SrS : Dy phosphor. The thermoluminescence glow curve shows a peak at around 142degreesC. Irradiated SrS : Dy exhibits an ESR line due to a defect centre. Thermal annealing behaviour indicates that this centre correlates with the TL peak at 142degreesC. The centre is characterized by an isotropic g-value of 2.0039 and is assigned to a F+ centre

Radiation effect on the luminescence of LiYF4 : Er3+

Luminescence and also the effects of ionising radiation on luminescence have been investigated in LiYF4:Er. The defects created by ionising radiation are studied by means of Thermally Stimulated Luminescence (TSL) and Electron Spin Resonance (ESR). TSL studies indicate a prominent glow peak at 386-412 K, whose position is found to depend on the radiation dose. Two defect centres, tentatively assigned to F-centres, are observed at room temperature. Step annealing measurements suggest a connection between these centres and the TSL glow peak. Photoluminescence studies indicate considerable reduction in emission intensity which appears to arise from the distortion of the lattice around the Er3+ ion caused by the defect centres. An explanation of the observations is suggested on the basis of impurity ion-defect centre formation. (C) 199

Structural and spectroscopic characterizations of a new near-UV-converting cyan-emitting RbBaScSi3O9:Eu2+ phosphor with robust thermal performance

To facilitate the next generation of White Light Emitting Diodes (WLEDs) with higher color rendering and warm lighting, the development of inorganic phosphor for efficient conversion of photons from blue/near-UV light to other visible wavelengths is essential. In this regard, we demonstrate a systematic, cost effective, solution-processable, easily scalable and fully controllable synthesis of a series of RbBaScSi3O9:xEu(2+) (x = 0.2, 0.5, 2, 5, 7), a new cyan emitting scandium silicate based phosphor with 79% internal quantum efficiency under n-UV excitation with robust thermal performance. The concept as well as the methodology of using a ``Mineral Inspired Approach'' emerges as a new blueprint for the rational design of novel phosphor for phosphor converted WLEDs. The structural refinement, electronic structural calculation using ``Density Functional Theory'', characteristic photoluminescence study, lifetime measurement as well as the thermal quenching properties of the phosphor has been investigated in detail. Owing to the highly efficient cyan emission at lambda(max) similar to 492 nm a full-width at half-maximum of 63 cm(-1) that shows only very low thermal quenching (89.28% relative to the PL intensity at 150 degrees C with respect to that of measured at room temperature), reflects the great potential for the industrial application of this particular phosphor. (C) 2017 Elsevier B.V. All rights reserved

Synthesis, photoluminescence and Judd-Ofelt parameters of LiNa3P2O7:Eu3+ orthorhombic microstructures

We report, for the first time, the photoluminescence properties of Eu3+-doped LiNa3P2O7 phosphor, synthesized by a facile solid-state reaction method in air atmosphere. The crystal structure and phase purity of the phosphors were analyzed by X-ray diffraction analysis. Orthorhombic structural morphology was identified by scanning electron microscopy. The phosphate groups in the phosphor were confirmed by Fourier transform infrared analysis. Bandgap of the phosphor was calculated from the diffuse reflectance spectra data using Kubelka-Munk function. Under 395-nm UV excitation, the phosphors show signs of emitting red color due to the D-5(0) -> F-7(2) transition. In accordance with Judd-Ofelt theory, spectroscopic parameters such as oscillator intensity parameter Omega(t) (t = 2), spontaneous emission probabilities, fluorescence branching ratios and radiative lifetimes were calculated and analyzed for the first time in this system

Effect of particle size in the TL response of natural quartz sensitized by high dose of gamma radiation and heat-treatments

This work investigates the effect of particle size in the thermoluminescence (TL) response of a quartz crystal that was initially crushed and classified into ten size fractions between 38 μm and 5 mm. Aliquots of each size fraction were sensitized with a dose of 25 kGy of γ rays and heat-treatments at 400 °C. TL glow curves of sensitized and non-sensitized samples were recorded as a function of different test-doses of γ rays. For the non-sensitized samples, the TL peak near 325 °C increases with the decrease in particle size. In the case of sensitized samples, a strong TL peak near 300 °C increases with the increase in particle size up to mean grain size equal to 304 μm. Above 304 μm, an abrupt reduction in the TL intensity is noticed for the sensitized peak. These effects are discussed in relation to the specific surface area of quartz particles and the intensity of the electron paramagnetic resonance signal of the E'1 center induced by the sensitization process