Solvent-Dependent\nUpconversion Luminescent Studies\nof Single and Colloidal Nanoparticles

The routinely employed ensemble and individual luminescent\nnanoparticles\nplay pivotal roles in nanoscience applications. In this study, water-dispersed\nNaYF<sub>4</sub>:Yb, Er, and NaYF<sub>4</sub>:Yb, Er@SiO<sub>2</sub> nanoparticles were synthesized to investigate solvent-dependent\nupconversion emissions. These prepared particles were used to examine\nboth ensemble and single-particle behavior in various solvents, including\ndimethylformamide (DMF), chloroform (CHCl<sub>3</sub>), ethanol (C<sub>2</sub>H<sub>5</sub>OH), acetone (C<sub>3</sub>H<sub>6</sub>O), deuterium\noxide (D<sub>2</sub>O), and water (H<sub>2</sub>O). It has been observed\nthat the matching of vibration frequency of OH groups in water leads\nto a substantial quenching in emission in bulk as well as at single\nparticles, whereas D<sub>2</sub>O has minimal effect on the upconversion\nluminescence. In the case of organic medium, the –CH vibrations\nare responsible for the emission quenching of the upconversion particle.\nIn addition, it is observed that the thin silica shell of thickness\n∼3 nm ± 0.5 nm has little influence on the medium-influenced\nemission quenching. The nature of medium-dependent emission quenching\nis found to be different for particles in an ensemble as well as at\na single-particle level.