Masaaki Tamatani

Luminescence Properties of Rare Earth Ion-Doped Monoclinic Yttrium Sesquioxide.

Monoclinic Y2O3 phosphors doped with Eu3+ or Pr3+ are obtained for the first time by treatments in inductively-coupled thermal plasma. This paper reports the luminescence properties of these phosphor materials. The assumption proposed earlier by the authors, that the emitting levels of Pr3+ in Gd2O3 are determined by the distance between the Pr3+ ion and the surrounding oxygen ligands, is found consistent even when the monoclinic Y2O3:Pr and other oxides are included.

Coloration caused by mechanical stress on rare earth oxysulfides

Abstract Oxysulfide powders of yttrium, gadolinium, terbium and lanthanum display distinctive colors when they are either heavily ball-milled or pressed in a steel die. These colors are due to optical absorption bands in the visible region, peak positions of which obey an empirical rule like the Mollowo-Ivey relation of color centers in alkali halides. The c-axis shrinks in the colored samples. The colors are bleached and the cell constants are restored to the original values by heat treatment up to 450°C. Some distortions, however, still remain in the annealed samples.

Contact electrification phenomena on phosphor particle surfaces

Abstract Contact electrification phenomena are reviewed to understand phosphor powder behavior. The origin of contact electrification is described in terms of the acid–base concept for solid surfaces. Electric charges produced by contact electrification affect phosphor properties. Various examples related to contact electrification are shown: particle surface modification, dispersion in liquids, adhesion strength to a substrate, electrostatic coating, interaction between a phosphor and mercury in a fluorescent lamp, and electron emission ability in a fluorescent lamp.

Gold-activated zinc sulphide phosphors

Over the past few years, phosphors of the gold-activated zinc sulphide type have been developed for use in television tubes. They are now applied for this purpose on a large scale by manufacturers in Japan and, as a result, their luminescence is a familiar feature in homes throughout the world. The scientific and technical background to the development of these products is presented here and their applications are described.

Color centers in rare earth oxysulfide phosphors

Abstract Color centers are found to be induced by mechanical stress on Ln 2 O 2 S powders. They have a significant influence on the practical use of the phosphors. Optical coloration and the Mollwo-Ivey relation suggest that atomically dispersed electron excess centers in the lattice may be responsible for the coloration. From ESR spectra observed in the stressed Y 2 O 2 S, F + centers are considered to be the most probable model, though the signal is absent in La 2 O 2 S.

Preparation of spherical phosphors by thermal‐plasma treatment

Garnet-structured rare-earth oxysulfide and zinc sulfide phosphors were treated by thermal plasma in order to obtain spherically shaped phosphor particles. Although spherical particles of garnet phosphor and rare-earth oxysulfide phosphor were obtained, their luminescence properties were lowered. However, the properties could be partially restored by optimized heat treatment.

30.3: Reduction of Electron‐Beam‐Induced Degradation of ZnS Green Phosphor Coated with Phosphate

Electron-beam-induced luminescence degradation is found to be reduced in ZnS: Cu, Al phosphor coated with a limited low content of phosphate. The behavior of the degradation is correlated with the quantities of SO2 and H2O gases released from the phosphors, analyzed by temperature programmed desorption-mass spectrometry (TPD-MS) and transmission electron microscopy (TEM) observations. We find that the layer coated with the appropriate phosphate content is uniform and continuous, which prevents the surface chemical reactions that cause the degradation.

Development of x-ray detector for multislice CT with 0.5-mm slice thickness and 0.5-second revolution

The purpose of this study is to develop an x-ray detector system for multislice CTs with 0.5 slice thickness and 0.5- second revolution, and to evaluate clinical advantages. The detector adopts a newly developed ceramic scintillator having a high light-output efficiency as well as a high light-transmittance. By employing high precision machining technology to fabricate the detector, it is not necessary to mask the gap from incident x-ray in the longitudinal direction between neighboring cells. The scintillator properties and the geometry of the detector provide a high x-ray-to-light conversion efficiency, and realize a good low-contrast detectability for CTs. The detector structure allows 0.5 mm slice thickness. The afterglow intensity of the scintaillator is less than 0.1 percent at 3 ms, facilitating 1800 views per second for 0.5-second revolution. This detector improves the performance of CT scanners.