Influence of Surface Coating on Structural and Photoluminescent Properties of CaMoO_4:Pr Nanoparticles

摘要

CaMoO_4:Pr(core), CaMoO_4:Pr@CaMoO_4 (core/shell) and CaMoO_4:Pr@CaMoO_4@SiO_2 (core/shell/shell) nanoparticles were synthesized using polyol method. X-ray diffraction (XRD), thermogravimatric analysis (TGA), UV-vis absorption, optical band gap energy analysis, Fourier transform infrared (FTIR), FT-Raman and photoluminescence (PL) spectroscopy were employed to investigate the structural and optical properties of the synthesized core and core/shell nanoparticles. The results of the XRD indicate that the obtained core, core/shell and core/shell/shell nanoparticles crystallized well at ~150 °C in ethylene glycol (EG) under urea hydrolysis. The growth of the CaMoO_4 and SiO_2 shell (~12 nm) around the CaMoO_4:Pr core nanoparticles resulted in an increase of the average size of the nanopaticles as well as in a broadening of their size distribution. These nanoparticles can be well-dispersed in distilled water to form clear colloidal solutions. The photoluminescence spectra of core, core/shell and core/shell/shell nanoparticles show the characteristic charge transfer emission band of MoO_4~(2-) (533 nm) and Pr~(3+) 4f~2→4f~2, with multiple strong ~3H_4→~3P_2, ~1D_2→~3H_4 and ~3P_0→~3F_2 transitions located at ~490, 605 and 652 nm, respectively. The emission intensity of the CaMoO_4:Pr@CaMoO_4 core/shell and CaMoO_4:Pr@CaMoO_4@SiO_2 core/shell/shell nanoparticles increased ~4.5 and 1.7 times,respectively, with respect to those of CaMoO_4:Pr core nanoparticles. This indicates that a significant amount of nonradiative centers existing on the surface of CaMoO_4:Pr@CaMoO_4 core/shell nanoparticles can be eliminated by the shielding effect of CaMoO_4 shells.