Yoshiro Otomo

NaLnF4 : Yb3 + , Er3 + ( Ln : Y , Gd , La ) : Efficient Green‐Emitting Infrared‐Excited Phosphors

Hexagonal was found to be an efficient green‐emitting phosphor with infrared excitation. It was prepared by firing a mixture of and coprecipitated at 630°C in an argon atmosphere. The optimum firing condition of was revealed to lie in the region where (a) the decomposition reaction is complete, (b) liquid and hexagonal are coexistent, and (c) the phase transition of from hexagonal to cubic does not occur. When pumped by a Si‐doped diode, properly prepared is 4 ~ 5 times as bright as the commercially available .

Electron Paramagnetic Resonance Studies of the ZnS‐A and ‐B Centers

Two photosensitive electron paramagnetic resonance signals A and B are found in self‐activated ZnS phosphors of polycrystalline form. Both these signals appear at 77°K when illuminated with uv light, and can be quenched with visible light of longer wavelength. The center responsible for the A signal is a hole trap and is found to be the luminescent center of the self‐activated emission. The atomic structure of this center is concluded to be an associate of zinc‐ion vacancy and a coactivator ion at one of the nearest possible sites. The center responsible for the B signal is an electron trap. A simple sulfur vacancy is proposed to be the structure of this center. In one case, the A signal was traced using a crude single crystal. Owing to the crudeness of the crystal, the result is not complete, but is found to be sufficient enough to substantiate the accuracy of the powder pattern analysis. Also described in this report are the results of investigating the effects of oxygen incorporated into ZnS by both the electron paramagnetic resonance and the thermoluminescence techniques. One of the observed effects is that the incorporation of oxygen leads to formation of self‐activated luminescent centers whose coactivator ions are not at the nearest possible sites.

Satellite Lines Due to Ion-Pairs in the Luminescence Spectra of Y2O2S:Eu3+

In the luminescence spectra of the 5 D 0 → 7 F 1 transition of Y 2 O 2 S:Eu 3+ , satellite lines separated from the main lines by several cm -1 were observed. Under the excitation by 365 mµ radiation, the intensity of the main line increases linearly with the concentration of Eu 3+ , whereas that of the satellite lines increases as the 1.36 th power of the concentration. When Gd 3+ is codoped in Y 2 O 2 S:Eu 3+ keeping the concentration of Eu 3+ constant, the intensity of the satellite lines relative to the main line increases with the concentration of Gd 3+ . It is concluded that the satellite lines originate from the splitting and shift of the crystalline-field components resulting from a slight lattice distortion around a pair of Eu 3+ ions or that of an Eu 3+ ion and a Gd 3+ ion which occupy two nearest cation sites.