Lowest 4f-to-5d and charge-transfer transitions of rare-earth ions in LaPO4 and 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 LaPO4 host lattices are measured in the vacuum ultraviolet (VUV)-ultraviolet (UV) spectral region of 120-350 nm, and the CT-excitation spectra of Y2O2S and La2O2S 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 Ce3+, Pr3+, Sm3+, Tb3+ and Dy3+, and the CT band for Nd3+, SM3+, Eu3+, Dy3+, Ho3+, Er3+, Tm3+ and Yb3+. 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.