Effects of surroundings on upconversion luminescent properties of rare earth luminescence centers

Abstract

A special core/shell/shell structured NaYF₄/NaYF₄:Yb³⁺,Er³⁺/NaYF₄ (CSS) nanocrystal was designed to ensure each luminescence center in the emitting shell had the same surroundings. The nanocrystal includes a support core NaYF₄ nanoparticle in the center coated by a thin emitting shell NaYF₄:Yb³⁺,Er³⁺ and another NaYF₄ shell with adjustable thickness as the outer shielding shell. The green upconversion fluorescence intensity I_g(d) of the CSS nanoparticles shows an exponential relationship with the thickness d of the shielding shell. When d decreased to 0, I_g(0) was ~356 times smaller than I_g(∞) due to the drastic fluorescence quenching of the rare earth luminescence centers by the surroundings. Our experimental results indicate that ~90% of the severe effect of the surroundings can be eliminated by coating with a ~4 nm-thick NaYF₄ shielding shell.