Fabrication and characterization of TiO2 nanoparticles conjugated luminescence upconversion nanoparticles

Abstract

TiO2 nanoparticles conjugated luminescence upconversion (TiO2-UC) nanocomposites have been fabricated by covalently linking of carboxyl-functionalized TiO2 and amino-functionalized NaYF4:Yb3+,Er3+,Ce3+ upconversion nanoparticles (UCNP) in the presence of N,N'–dicyclohexylcarbodiimide (DCC) /4-dimethylaminopyridine (DMAP) coupling reagents. The carboxyl-functionalized TiO2 nanoparticles and amino-functionalized UCNPs have been synthesized by hydrothermal method with 5±2 and 55±10 nm in diameter, respectively. In the synthesis of UCNPs, the percentage of stabilizing agent (polyethyleneimine, PEI), the mole ratios of NaCl/NH4F and the co-doping ratio of Ce3+ ion have been found to be a significant effect on their size and morphology. Size, morphology, conjugation as well as photo-physical properties of all synthesized nanomaterials have been characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. UCNPs and TiO2-UCnanocomposites exhibit strong green luminescence at room temperature under 980 nm excitation leaded the emissions at 440, 520, 540 and 658 nm, representing 2H9/2 → 4 I15/2, 2H11/2→4 I15/2, 4 S3/2→4 I15/2 and 4 F→4 I15/2 transitions, respectively. The water dispersible luminescence nanocomposites having NIR light utilizing ability are promising for efficient light harvesting and/or bio-imaging applications.