Synthesis and up-conversion luminescence of Ho3+ and Yb3+ co-doped La7P3O18 phosphors

Ho 3+ and Yb 3+ co-doped La 7 P 3 O 18 up-conversion phosphors were prepared by a high-temperature solid-state process. XRD results reveal that the samples are mixtures of monoclinic structure La 7 P 3 O 18 crystals with P 21/ n space group and minor LaPO 4 crystals. UV—Vis DRS results indicate that La 7 P 3 O 18 crystal is an indirect semiconductor with an optical band gap of 4.10 eV. After 980 nm laser excitation, the Ho 3+ and Yb 3+ co-doped La 7 P 3 O 18 phosphors show the characteristic blue (486 nm), green (550 nm), and red (661 nm) luminescence peaks of Ho 3+ ions. The peak at 661 nm dominates in the up-conversion luminescence spectra of samples. Meanwhile, with the increase of Ho 3+ and Yb 3+ doping content, the up-conversion luminescence intensity increases first and then decreases. By increasing the doping contents of Ho 3+ and Yb 3+ up to 1 at.% and 10 at.%, respectively, concentration quenching may appear by an electric quadrupole– electric quadrupole interaction process. The pumping power dependence of luminescence indicates that the green and red emissions of samples are excited by a two-photon absorption process. The color coordinates of Ho 3+ and Yb 3+ co-doped La 7 P 3 O 18 crystals locate in the orange—red region.