Bright green up-conversion luminescence of LaNbO4: Nd3+/Yb3+/Ho3+ phosphors under 808 nm and 980 nm excitations and the effects of dopant concentration

LaNbO4: Nd3+/Yb3+/Ho3+ phosphors with various concentrations of Nd3+, Yb3+ and Ho3+ were prepared by a traditional high temperature solid-state reaction method. The crystal structure of the as-prepared samples was characterized by X-ray diffraction (XRD) and the results showed that monoclinic LaNbO4 samples were obtained. Green and red up-conversion (UC) emissions of Ho3+ were observed under the excitations of 808 nm and 980 nm. Concentration dependent studies indicated that Nd3+ and Yb3+ played different roles in the UC emissions of Ho3+ under different wavelength excitations. The same optimal concentrations of Yb3+ and Ho3+ ions were obtained when excited by 808 nm and 980 nm lasers. The UC luminescence mechanisms under different excitation sources were discussed by detecting the UC luminescence intensity related to the laser pumped power density. The energy transfer efficiencies from Nd3+ to Yb3+ and Yb3+ to Ho3+ were confirmed via lifetime measurement. By comparing with the commercial green NaYF4: Er3+/Yb3+ UC luminescence phosphor, the UC luminescence performance of Ho3+ doped sample was evaluated. The results showed that LaNbO4: Nd3+/Yb3+/Ho3+ phosphors had excellent green UC luminescence properties under both 808 nm and 980 nm excitations.