Studies of defects inYVO(4): Pb2+, Eu3+ red phosphor material

Doubly doped YVO4:Ph2+, Eu3+ red phosphor materials with fixed Eu3+ concentration (5 mol%) and varying Pb2+ concentration were prepared via a self-propagating (combustion) synthesis. This consisted of bringing a saturated aqueous solution of the desired metal salts and a suitable organic fuel to the boil, until the mixture ignited and a self-sustaining and rather fast combustion reaction initiated, resulting in dry, amorphous or usually crystalline fine particles of the desired material. The formation of crystalline vanadates was confirmed by X-ray diffraction. A strong emission line at 619 nm due to the (5) D-0 --> F-7(2) transition in the red region was observed. Defects, created by gamma radiation, were studied by means of photoluminescence, thermally stimulated luminescence (TSL) and electron spin resonance. Photoluminescence studies display considerable reduction in emission intensity which appears to arise due to the formation of defect centres after irradiation. The defect centres formed in the present system are tentatively assigned to F+ centres and step annealing measurements suggest a connection between these centres and the TSL glow peak

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

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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

LUMINESCENCE OF AGGREGATE COLOR-CENTERS IN KF

Complex F-aggregate centers were studied in pure and Li+-doped KF, by means of optical excitation. Three new emission bands in the near infrared region were revealed. Among them, the luminescence at 1040 nm was identified as the emission of F3 defects because of its excitation, its peak position and its enhancement under irradiation at room temperature with F light. The luminescences at 950 and at 1250 nm were too weak and could not be unambiguously identified. However, they are probably due to complex F-aggregate centers, like F4 defects