Dispersible Tm 3+ ‐Doped Nanoparticles that Exhibit Strong 1.47 μm Photoluminescence

A general procedure is described for the synthesis and conversion of dispersible core/shell LaF 3 :Tm/LaF 3 nanoparticles to highly dispersible thulium‐doped lanthanum disilicate nanoparticles (La 2 Si 2 O 7 :Tm) with an average diameter of 7 nm that show emission at a wavelength of 1.47 μm. Measurement of the citrate‐stabilized precursor nanoparticles in a KBr pellet shows a 1.47 μm emission with an effective lifetime of only 3 μs 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 Stöber method, followed by baking at 900 °C for 12 h to convert the LaF 3 matrix to La 2 Si 2 O 7 . Excitation with a 785 nm continuous wave (CW) diode laser results in the luminescence of the 3 H 4 – 3 F 4 transition at 1.47 μm with an effective lifetime of 56 μs 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 3 H 4 level.