ビスマス (III) 付活硫化カルシウム蛍光体の残光特性と表面改質

抄録

The presented paper investigated the afterglow property and surface modification of Bi³⁺ doped CaS phosphor showing a blue emission which was prepared by reducing Bi³⁺ doped CaSO₄·2H₂O. Especially, the relationship between afterglow intensity and lattice strain, which was formed such as anion vacancy and size of incorporation ion by substitutional incorporation was also noticed. Bi³⁺ doped CaSO₄·2H₂O was synthesized by adding 0.2 mol·dm^-3 (NH₄) 2SO₄ solution into 0.2 mol·dm^-3 CaCL₂ solution including Bi (NO₃)₃. Bi³⁺ doped CaS phosphor was obtained by reducing the CaSO₄·2H₂O in H₂S atmosphere at 900°C for 1-5 hours. The sample was characterized by means of X-ray powder diffraction pattern, infrared absorption spectrum and fluorescence spectrum.
Formation of CaS phosphor was possible by mixing Bi³+ doped CaSO₄·2H₂O and Na2SO₄ as reduction accelerator. Bi³⁺ ion in CaS phosphor was incorporated by substitution of Ca²⁺ ion in the host structure, and the charge compensation was carried out by substitution of Na+ ion. The upper limit of the incorporation of Bi³⁺ ion was 5 × 10^-4 in Bi/Ca atomic ratio. The excitation wavelength was observed at 312 and 419 nm, the emission wavelength of the CaS phosphor excited with 312 nm light was 449 nm and the emission color is blue. The anion vacancy of S^2- ion site was formed by substitution of Ca²⁺ _??_ Na⁺. The lattice strain rose by increasing number of anion vacancy. The afterglow intensity was enhanced with increase of anion vacancy as trapping center, which could be accumulated the excitation energy. On the other hand, stability of the emission and the afterglow intensity of CaS in the humidity were investigated. As this result, it was confirmed that surface modification was effective.