Irradiated Phosphor Research Articles

Preparation, luminescence and defect studies of Eu 2+-activated strontium hexa-aluminate phosphor prepared via combustion method

Preparation of Eu 2+ ions activated strontium hexa-aluminate phosphor using the combustion method is described. An efficient phosphor can be prepared by this method at reaction temperatures as low as 500 °C in a few minutes. Powder X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscope analysis were used to characterize the as prepared product and the optical properties were studied by photoluminescence (PL) spectra. Thermally stimulated luminescence studies also have been carried out on SrAl 12O 19:Eu 2+ phosphor. The TSL glow curve is broad and indicates two dominant peaks at 206 and 345 °C. Defect centres formed in irradiated phosphor have been studied using the technique of electron spin resonance. One of the centres is characterized by an isotropic g-value of 2.0055 and is assigned to a F + centre. The two annealing stages of F + centre in the region 125–230 and 340–390 °C appear to correlate with the release of carriers resulting in TSL peaks at 206 and 345 °C, respectively.

Electron-beam-induced charging of phosphors for low voltage display applications

Shifts of the surface potential were measured for several commercial phosphors by monitoring secondary and Auger electron spectra during electron beam irradiation at energies between 0.5 and 5 keV. The insulating phosphors charge strongly negative above 2 keV, whereas the conductive ones do not. This charging behavior is exaggerated after prolonged beam exposure. Measurements using two coincident electron beams to control the surface potential demonstrate that aging-enhanced surface charging decreases the phosphor cathodoluminescence. The dependence of the phosphor surface potential on the voltage applied to the metal plate on which they are deposited was also determined. These data suggest the presence of substantial space charge in the phosphors, even at low electron beam energies where no beam-induced shifts of the surface potentials are seen. We suggest that the electric fields due to these near-surface space charge regions are crucial in altering secondary emission and in establishing a steady state charge balance in the case where no currents can flow from the irradiated phosphor surface to the conductive backplane.

Digital radiography — a review of detector design

The last decade has seen a steady expansion in the use of digital imaging techniques in medicine, X-ray film radiographs may be digitised using a laser scanner or TV camera. Image intensifier-TV systems may readily be adapted to a digital role by capturing TV frames. Scintillators coupled to photomultiplier tubes or photodiodes have been used in line or spot scanning configurations where scatter rejection is high. A relatively recent development is the use of photostimulable phosphors, in which image information is extracted by laser scanning of the irradiated phosphor. Finally, imaging is an important part of radiotherapy treatment planning, where localisation and verification of X-ray treatment beams is required.

Spatial intensity distributions of vacuum ultraviolet photon beams measured by thermoluminescent image films

The thermoluminescent phosphor, calcium sulfate activated by manganese, was found to be a suitable material for imaging films to record the spatial distributions and reflections of vacuum ultraviolet (vuv) photon beams used for high-resolution photoelectron spectrometers. He I 584 Å photons radiated in a microwave discharge tube were collimated through capillary tubes, and the phosphor films were placed at the position of the photoionization chamber. When the irradiated phosphor films were heated up to 200 °C in a darkroom, faint green glow images were observable on the phosphor films and these images were recorded by photographic films. When the films were placed 118 mm from the exit of the collimating capillary tube, the photon beam images were almost circular, about 4.5 mm in diameter. The photon distribution in the collimated beam was interpreted with the aid of computer simulation. The experimental results revealed that the reflections of vuv photons at planes of various kinds were almost specular if the surface was clean and smooth and the glancing angles were small.

Photoluminescence and absorption spectra of various common TL phosphors—Interpretation of TL mechanisms

Photoluminescence and absorption spectra of TL phosphors TLD-100, CaF 2:Dy, CaSO 4:Dy (0.05% wt),CaSO 4:Tm (0.05% wt) and Mg 2SiO 4:Tb have been measured. The absorption spectra are typical of RE 2+ in rare earth doped irradiated phosphors. On heating RE 2+ → RE 3+ and emission from the excited states of RE 3+ is observed.

Development of a new highly sensitive LiF thermoluminescence dosimeter and its applications

New highly sensitive phosphors of LiF-TLD were prepared for use in a low dose measurement. The phosphor was doped with three kinds of impurities which are Cu, Mg, and P, Si or B ion. Sensitivity of these phosphors doped with the third dopant was higher than that of TLD-600 LiF and, especially, the sensitivity of LiF(Mg, Cu, P) phosphor was about 23 times that of TLD-600 LiF, and nearly equal to Mg 2SiO 4(Tb) and CaSO 4(Tm) phosphors. The thermoluminescence response to the dose increases sublinearly in the dose range of 1000 rad and more, but increases linearly in the dose range of 1000 rad and less. Tribothermoluminescence intensity increases with the vibrating period, and the maximum intensity is equivalent to about 300 mrad, but when the irradiated phosphor was heated up to about 270°C or less for evaluating the dose, the dose evaluation was scarcely affected. Application of this new phosphor to environmental radiation dosimeter and medical radiation dosimeter is discussed.

The thermoluminescent properties of lithium borate activated by silver.

To determine the effect of various impurities on the thermoluminescent properties of lithium borate, 60 phosphors were initially prepared which were individually doped with three different concentrations of manganese, cobalt, magnesium silver or one of 15 rare earth elements. Silver and manganese were the only impurities which showed a significant enhancement of thermoluminescence; all others had no effect on lithium borate. The silver activated phosphors exhibited glow curves consisting of peaks at 100° and 175°C, and emission spectra consisting of two broad peaks in the ultraviolet at 290 and 365 nm. The high temperature peak of Li2B4O7: Ag showed good stability at room temperature when stored in the dark; however, considerable fading occurred when the irradiated phosphor was exposed to fluorescent lighting. Lithium borate activated with silver showed a tendency to absorb less moisture from the air than did Li2B4O7: Mn. Because of the high atomic number of silver, the calculated energy response of Li2B4O7: Ag was found to be critically dependent upon the activator concentration at concentrations greater than 0.1 M %. The most favorable theoretical energy response occurs at a concentration of about 0.1 M %. The ultraviolet emission spectrum of Li2B4O7: Ag represents a considerable improvement over the yellow-orange spectrum of Li2B4O7: Mn, with respect to detector efficiency and to infrared blackbody interference. Combined with the proper detection system, Li2B4O7: Ag should be useful for detecting lower radiation exposures than is currently possible with Li Mn, without sacrificing a favorable energy response.

The radiothermoluminescence of (ZnS:CdS:Ag:Ni:Co) phosphors irradiated with beta-rays

The radiothermoluminescence characteristics have been studied for a number of (ZnS:CdS::Ag:Ni:Co) phosphors, with various cobalt impurity contents, after exposure to90Sr beta-rays at room temperature. Thermoluminescent spectra show a peak wavelength of 7000 A, which remains unchanged with increase in cobalt concentration. Thermoluminescence curves exhibit a single well-defined peak appearing at temperatures far above room temperature. This peak shifts to lower temperatures with increasing cobalt content. The relation between thermoluminescence response and dose is linear over the dose range of 1 to 500 rads. Thermoluminescence measurements made after storing the irradiated phosphor for 48 hours in dark have revealed an information loss of 4% over this storage period. The radiothermoluminescence characteristics, storage capacity and storage stability of these sulphide phosphors compete reasonably with those of lithium fluoride over the dose range of 1 rad to 500 rads.