Solvent-Dependent Upconversion Luminescent Studies of Single and Colloidal Nanoparticles

The routinely employed ensemble and individual luminescent nanoparticles play pivotal roles in nanoscience applications. In this study, water-dispersed NaYF4:Yb, Er, and NaYF4:Yb, Er@SiO2 nanoparticles were synthesized to investigate solvent-dependent upconversion emissions. These prepared particles were used to examine both ensemble and single-particle behavior in various solvents, including dimethylformamide (DMF), chloroform (CHCl3), ethanol (C2H5OH), acetone (C3H6O), deuterium oxide (D2O), and water (H2O). It has been observed that the matching of vibration frequency of OH groups in water leads to a substantial quenching in emission in bulk as well as at single particles, whereas D2O has minimal effect on the upconversion luminescence. In the case of organic medium, the –CH vibrations are responsible for the emission quenching of the upconversion particle. In addition, it is observed that the thin silica shell of thickness ∼3 nm ± 0.5 nm has little influence on the medium-influenced emission quenching. The nature of medium-dependent emission quenching is found to be different for particles in an ensemble as well as at a single-particle level.