Y-89 static and -MAS NMR, and Al-27-MAS NMR in green phosphor, Tb-doped Y3Al5O12 and luminous characteristics

Luminous properties of a green phosphor, Tb-doped Y3Al5O12, have been studi ed by Y-89 (nuclear spin 1/2)-static and -magic angle spinning (MAS) NMR an d Al-27 (nuclear spin 5/2)-MAS NMR. In pure Y3Al5O12, a sharp signal at 239 ppm was observed in Y-89-MAS NMR spectrum, which was expected from a powde r pattern due to 8O-coordinated Y in D-2 symmetry in Y-89-static NMR spectr um. In the Al-27-MAS NMR spectrum of Y3Al5O12, two typical signals were obs erved, i.e., a sharp signal at 0 ppm due to 60-coordinated Al in the octahe dral site and a characteristic signal due to 4O-coordinated Al in the tetra hedral site. These Y-89 and Al-27 signals became broader in Tb-Y3Al5O12 wit h increasing in content of the doped Tb. In addition to the main peak at 23 9 ppm, furthermore, extra peaks appeared in the bottom of the main peak in Y-89-MAS NMR; these were assigned to the second nearest to the fifth neares t neighboring Y (Y-2 to Y-5) atoms to Tb atom substituted in the site of Y atom. Shifts of these Y atoms were reasonably explained by a pseudocontact shift via a paramagnetic Tb3+ ion. Incorporation of Tb3+ ions caused a larg e reduction in Y-89 nuclear spin-lattice relaxation time from 4000s (pure Y 3Al5O12) to several hundred seconds (3% Tb-Y3Al5O12) as well. The line-broa dening of the signals was mainly dominated by the dipole-dipole interaction mechanism between the Al or Y resonating nucleus and a Tb3+ ion. The signals of Y atoms in the sites where either one of the nearest neighbo ring Y-1 atoms was replaced by Tb atom were not detected because of the lar ge line-broadening. The stronger brightness was obtained in the specimens which showed the much broader linewidth in Al-27-MAS signals and in Y-89-static NMR signals unde r the same Tb content. So we concluded that the homogeneous distribution of Tb3+ ions in Tb-Y3Al5O12 plays a key role for the higher brightness in the green phosphor as in the red phosphor.