Facile Enhancement of Upconversion Luminescence by Localized Surface Plasmon Resonance(LSPR) Effect with Metal Nanoparticles

Upconversion material that convert infrared light into visible and ultraviolet photon are capable of a broad range application such as deep tissue bio-imaging, security labelling and anti-counterfeit, etc. Lanthanide-doped sodium yttrium fluoride (NaYF₄) upconversion nanoparticles (UCNP) are one of the most efficient UCNPs. However, the practical application of upconverting materials is limited owing to their extremely weak and narrow band absorption. Moreover, it is still a great challenge to short-wave infrared photon (such as 1550 nm) to visible since photon should be 3-pumped for visible region emission which hamper itself to a wide variety of applications. To solve this problem, we applied the localized surface plasmon resonance (LSPR) effect of indium tin oxide (ITO) NPs to enhance the 1550 nm absorbance of NaYF₄:Er³⁺ NPs. We have synthesized core-shell NaYF₄:Er³⁺@NaYF₄ NPs with particles size distribution of 15 nm via co-precipitation synthesis method. Synthesized 7 nm particle sized ITO NPs (Sn 10 mol% doped) exhibit intense LSPR effect in the range of 1400 to 1800 nm that perfectly overlap with 1550 nm excitation of Er³⁺ ions. We characterized upconversion efficiency of NaYF₄:Er³⁺@NaYF₄ UCNPs with ITO NPs mixture solution with 1550 nm laser (10 mWcm^-1).