Comparison between the optical properties of sol–gel process and solid state reaction derived LiYF4:Eu3+ powders

Sol–gel route has been successfully used to obtain pure LiYF4:Eu3+ powders for the first time to our best knowledge. Fluorine ions were introduced through trifluoroacetic acid as reacting agent which is decomposed under heating treatment and as a result leads to the formation of fluorides. Sintering under F2 reactive atmosphere was performed to prevent any oxidation and insure residual hydroxide elimination. The materials structure was analyzed by means of X-ray diffraction (XRD) while infrared spectroscopy (IR) was carried out to examine the presence of residual organic groups. Laser induced luminescence spectra as well as fluorescence decays of Eu3+ ions were recorded and compared to those of LiYF4:Eu3+ prepared by conventional solid state reaction. In both cases, the results are undoubtedly typical of Eu3+ emitting center embedded in a unique site of D2d symmetry. Nevertheless, the sol–gel derived samples exhibit 5D0 luminescence decays characterized by longer rise times upon 5D2 excitation as well as a larger 5D1/5D0 branching ratio at room temperature or 100 K.