Synthesis and up-conversion photoluminescence properties of NaYF4:Yb3+, Er3+@sSiO2@mSiO2 nanoparticles

• The up-conversion emission intensity of NaYF4:Yb3+, Er3+ after silica coating was significantly enhanced.
• The up-conversion intensity ratio between red emission and green emission was decreased after silica coating.
• The mechanism of up-conversion luminescence and emission intensity change was illuminated.

NaYF4:Yb3+, Er3+ nanoparticles were synthesized through co-precipitation using EDTA as the chelator. The monodisperse core–shell structure NaYF4:Yb3+, Er3+@sSiO2 were synthesized by sol–gel method using TEOS as silica source. The core–shell–shell structure NaYF4:Yb3+, Er3+@sSiO2@mSiO2 were prepared by coating mesoporous silica shell onto NaYF4:Yb3+, Er3+@sSiO2 through hydrolysis of TEOS using CTAB as mesoporous template. Effects of CTAB concentration, TEOS concentration and different addition ways of CTAB were studied. The results show that the NaYF4:Yb3+, Er3+@sSiO2@mSiO2 nanoparticles with uniform amorphous silica and mesoporous silica shell were successfully synthesized. Up-conversion spectra of these nanoparticles were recorded with 980 nm laser excitation under room temperature. There were no changes of the emission centers of nanoparticles before or after silica coating, but the emission intensities of nanoparticles after silica coating were significantly enhanced. Furthermore, the relative intensity ratio between red emission and green emission was decreased after silica coating.