Lowest 4f-to-5d and Charge-Transfer Transitions of Rare-Earth Ions in LaPO₄and Related Host-Lattices

In order to study the high energy optical transitions i.e., 4f-to-5d (f-d) and charge-transfer (CT) spectra of trivalent rare earth (4f n -series, lanthanide) ions in crystal lattices, the luminescence excitation spectra of the series ions in LaPO 4 host lattices are measured in the vacuum ultraviolet (VUV)-ultraviolet (UV) spectral region of 120–350 nm, and the CT-excitation spectra of Y 2 O 2 S and La 2 O 2 S are measured in a UV region. The f-d and CT bands are observed for the most 4f n -series ions in which the predicted transition energies are lower than the host lattice absorption edge, that is, the f-d bands for Ce 3+ , Pr 3+ , Sm 3+ , Tb 3+ and Dy 3+ , and the CT band for Nd 3+ , Sm 3+ , Eu 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ and Yb 3+ . The energies of these observed peaks of f-d and CT bands agree fairly well with the values calculated by the method proposed in our previous report. The relationship between the energies of the CT transition and the absorption edge in various host lattices is discussed.