By controlling the reactant ratios, hydrothermal time, hydrothermal temperatures, p H values of the prepared solutions, and the concentrations of K3C6H5O7·2H2O, 1 mol% Eu3+ doped cubic phase of K5Gd9F32 and/or orthorhombic phase of Gd F3 micro/nanocrystals have been synthesized based on a hydrothermal method. For comparison, the sample was also synthesized by a co-precipitation method. The samples were characterized by X-ray diffraction(XRD) patterns, field emission scanning electron microscopy(FE-SEM) images, energy-dispersive spectroscopy(EDS) spectra, and photoluminescence(PL) excitation and emission spectra. By host Gd3+ sensitizing, the Eu3+ presents relatively strong emissions. The energy transfers from host Gd3+ to doping Eu3+ are observed in all the samples and the energy transfer plays an important role in the emission of Eu3+. Acting as a probe, the Eu3+ presents its distinct optical properties in the samples. By controlling the reactant ratios, hydrothermal time, hydrothermal temperatures, p H values ​​of the prepared solutions, and concentrations of K3C6H5O7 · 2H2O, 1 mol% Eu3 + doped cubic phase of K5Gd9F32 and / or orthorhombic phase of Gd F3 micro / nanocrystals have been synthesized based on a hydrothermal method. For comparison, the sample was also synthesized by a co-precipitation method. The samples were characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FE- By energy transfer from host Gd3 + to doping Eu3 + are observed in all the samples and the energy transfer plays an important role in the emission of Eu3 +. Acting as a probe, the Eu3 + presents its distinct optical properties in the samples.