Under the excitation of 980 nm diode laser, intense green emission （5F4＋5S2–5I8） of Ho3＋ was observed in Ho3＋ and Yb3＋ co-doped cubic Y2O3. The doping concentration and laser power dependence of the upconverted emission were studied. The decay curves of 5F4＋5S2 emission of Ho3＋ under the excitation of 355 nm pulse laser were measured to investigate the energy transfer process between Ho3＋ and Yb3＋. The results indicated that two-photon process was responsible for the upconversion （UC） emission. The Ho3＋ concentration of 0.04 mol.% and the Yb3＋ concentration of 5 mol.% were determined to be the best value for the strongest Ho3＋ emission under the excitation of 980 nm light. The cross-relaxation between two neighboring Ho3＋ ions and the back energy transfer from Ho3＋ to Yb3＋ were important factors for determin- ing the optimal doping concentration. This material was a promising candidate for the application in biomedical fluorescent labels for the intense green emission upon excitation of near-infrared （NIR） light.
In order to obtain a single-host-white-light phosphor, a series of Bal.8 -x-y-zSrwLi0.4xCexEuyMnzSi04 （BSLS：Ce3＋,Eu2＋, Mn2＋） powder samples were synthesized via high temperature solid-state reaction. The structure and photoluminescence properties were investigated. Under ultraviolet excitation, the emission spectra contained three bands： the 370-470 nm blue band, the 470-570 nm green band and the 570-700 nm red band, which arose from the 5d---4f transitions of Ce3＋ and Eu2＋, and the 4TI---6A1 transition of Mn2＋, respectively. The excitation spectra of the emissions of Ce3＋ and Mn2＋ ions showed the energy transfer from Ce3＋ to Mn2＋. White light emission was obtained from the tri-doped samples of appropriate doping concentration under 31 0-360 nm excitation.
We constructed an effective one-electron Hamiltonian by using the 4f/5d energies and eigenvectors obtained from the first-principles calculation with the relativistic self-consistent discrete variational Slater software package （DV-Xα）. From the effective Hamiltonian, we obtained the crystal-field and spin-orbit interaction parameters for the 4f and 5d electrons of lanthanide ions （Ce^3＋, Pr^3＋, Nd^3＋ and Eu^3＋） doped in YPO4, and these parameters were used to calculate the 4fN-4fN- 15d transition. Comparison with experiments shows that the obtained parameters are reasonable and the excitation spectra can be well predicted.
