The spherical KLa(WO_4)_2:5%Eu~(3+) nanocrystals with pure tetragonal structure were synthesized by the hydrothermal method using K_2WO_4·2H_2O and La_2O_3 as the raw materials and oxalic acid as precipitation-template agent at p H = 7 and t = 180 ℃. The structural and optical properties of the products prepared under different conditions were studied systematically by X-ray diffraction(XRD), scanning electron microscopy(SEM), and photoluminescence(PL). The effects of the amount of oxalic acid on the morpho...