Luminescence Studies in Ca(PO₃)₂:Eu³⁺ Glass by Laser-Induced Fluorescence Line-Narrowing Technique. I. Optical Transition Mechanism of the ⁵D₀−⁷F₀ Line

Abstract

Fluorescence spectra have been measured in Ca(PO₃)₂:Eu³⁺ at 77 K under dye laser excitation at various energies within the absorption lines due to the transitions ⁷F₀, ⁷F₁−⁵D₀, ⁵D₁. It has been found that the ⁵D₀−⁷F₀ transition probability and the mean energy of the three ⁵D₀−⁷F₁ lines are linearly correlated with the energy of the ⁵D₀−⁷F₀ line, and also that this energy is quadratically correlated with the transition energy between ⁵D₀ and the lowest level of ⁷F₁. These results are interpreted in terms that the spreads of these energies and the transition probability are due to the site-to-site variation in the second-order crystal-field parameter. Further, the forbidden ⁵D₀−⁷F₀ transition is concluded to be allowed by the borrowing of the intensity from the ⁵D₀−⁷F₂ (M_J=0) line through the J-mixing. Using polarization characteristics of fluorescence, whether the lines are due to the electric or magnetic dipole transition is determined and the Stark levels of the ⁷F₁ and ⁵D₁ manifolds are assigned. It is also shown that the point symmetry of the Eu³⁺ site is C_2V or C₂.