抄録
Absorption and excitation spectra associated with the 4f-4f transitions of Eu3+ ions in CaWO4:Eu, Na, NaEu(WO4)2 and KEu(WO4)2 were studied at low temperatures. Vibronic transitions are observed as bands with fine structure composed of sharp lines. The observed vibronic spectra were compared with the k=0 phonon spectra of CaWO4. Fairly good agreement is found between the both spectra, and the existence of a distinct gap in the spectra is noted. The intensity of the vibronic transition associated with 7F0→5D1 transition is weaker by one order of magnitude than those associated with 7F0→5D0 and 5D2 transitions. These results are well interpreted by use of Judd and Ofelt’s theory. Namely, the 7F0→5D0 and 5D2 vibronic transitions are allowed by the first-order electric-dipole, while the 7F0→5D1 vibronic transition is only allowed by the second-order electric-dipole and first-order magnetic-dipole.
