Dispersible Tm3+-doped nanoparticles that exhibit strong 1.47 μm photoluminescence

A general procedure is described for the synthesis and conversion of dispersible core/shell LaF3:Tm/LaF3 nanoparticles to highly dispersible thulium-doped lanthanum disilicate nanoparticles (La2Si2O7:Tm) with an average diameter of 7 nm that show emission at a wavelength of 1.47 mu m. Measurement of the citrate-stabilized precursor nanoparticles in a KBr pellet shows a 1.47 mu m emission with an effective lifetime of only 3 mu s and an estimated quantum yield of << 1 %. However, significant improvements to the emission properties are obtained by forming a ca. 1 nm thick silica shell around the nanoparticles via a modified Stober method, followed by baking at 900 degrees C for 12 h to convert the LaF3 matrix to La2Si2O7. Excitation with a 785 nm continuous wave (CW) diode laser results in the luminescence of the H-3(4)-F-3(4) transition at 1.47 mu m with an effective lifetime of 56 mu s and an estimated quantum yield of 4 %. High-resolution measurements at 77 K are carried out in order to improve the resolution of the crystal-field splitting observed from the H-3(4) level.