Synthesis and up-conversion luminescence of Er3+ and Yb3+ co-doped La14W8O45 phosphors

Pure phase orthorhombic Er3+ and Yb3+ co-doped La14W8O45 up-conversion luminescent materials were successfully prepared by the hydrothermal method combined with calcination treatment. The structures, morphology, and optical properties of the samples were analyzed by X-ray powder diffractometer (XRD), scanning electron microscope (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and up-conversion photoluminescence spectroscopy (UPL) with a 980 nm laser. XRD results indicated that the obtained samples are single-phase orthorhombic Er3+ and Yb3+ co-doped La14W8O45 crystals. SEM results showed that the prepared sample exhibits an irregular and melted polyhedral-like morphology with agglomeration in submicron size of particles approximately 50–200 nm. UV–vis DRS results revealed that the La14W8O45 crystal is a direct semiconductor with an optical band gap of 3.84 eV. The prepared Er3+ and Yb3+ co-doped La14W8O45 crystals exhibit strong up-conversion emission peaks at about 526 nm, 548 nm, and 660 nm under 980 nm laser excitation. The intensity of up-conversion luminescence is affected by the Er3+ doping concentration, and concentration quenching will be observed due to the cross-relaxation (CR) process when the Er3+ doping content is above 1%. The pumping power dependence of the luminescence indicated that the up-conversion emissions of samples are excited by a two-photon absorption process. The color coordinates of the samples are located in the green light region.