Plasmonic Enhanced Emissions from Cubic NaYF₄:Yb:Er/Tm Nanophosphors

Abstract

A metal shell was used in this study to provide significant enhancement of the up-converted emission from cubic NaYF4 nanoparticles, creating a valuable composite material for labeling in biology and other applications – use of the cubic form of the material obviates the need to undertake a high temperature transformation to the naturally more efficient hexagonal phase. The NaYF4 matrix contained ytterbium sensitizer and an Erbium (Er) or Thulium (Tm) activator. The particle sizes of the as-synthesized nanoparticles were in the range of 20–40 nm with a gold shell thickness of 4–8 nm. The gold shell was macroscopically amorphous. The synthesis method was based on a citrate chelation. In this approach, we exploited the ability of the citrate ion to act as a reductant and stabilizer. Confining the citrate ion reductant on the nanophosphor surface rather than in the solution was critical to the gold shell formation. The plasmonic shell enhanced the up-conversion emission of Tm from visible and near-infrared regions by up to a factor of 8, in addition to imparting a visible color arising from the plasmon absorption of the gold shell. The up-conversion enhancement observed with Tm and Er were different for similar gold coverages, with local crystal field changes as a possible route to enhance up-conversion emission from high symmetry structural hosts. These novel up-converting nanophosphor particles combine the phosphor and features of a gold shell, providing a unique platform for many biological imaging and labeling applications.

Recent Progress on Plasmon-Enhanced Fluorescence

“…It is reported that the luminescenceenhanced effect from Ln-doped NPs situated near noble metal nanostructures is generally attributed to the local enhanced EM field related with the excitation of SPR in the metal nanostructures [111,112], which under favorable circumstances can increase the sample's absorption and emission cross-sections. Recently, the enhancement of lanthanide-based UC and DC luminescence were experimentally observed simultaneously on metal nanodiskinsulator-metal (MIM) nanostructure fabricated via a nanotransfer printing method [113].…”

Large Upconversion Enhancement in the “Islands” Au–Ag Alloy/NaYF4: Yb3+, Tm3+/Er3+ Composite Films, and Fingerprint Identification

“…In previous literatures, various gold or silver nanostructures have been utilized to amplify the UCL signals of the well-known NaYF 4 : Yb 3+ , Tm 3+ (Er 3+ ) UCNPs, and the enhancement factor of the overall UCL strength usually varies from several to several ten times, which is much lower than the theoretical prediction. [ 31,40 ] It should be highlighted that Chou and co-workers [ 41 ] recently prepared a periodic structure of gold by the nanoimprint technique, on which the overall UCL intensity of NaYF 4 : Yb 3+ , Er 3+ wileyonlinelibrary.com © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim was improved more than 100 times. However, the equipment for preparing the structure is expensive and complicated, thus the result is diffi cult to be popularized.…”

Upconversion Nanoparticle-Based Nanocomposites

“…(ii) Metallic nanoparticles are attached or self-assembled onto the surface of lanthanide-doped fluoride, oxide, or vanadate upconversion nanoparticles [147,148,152,[158][159][160][161]. (iii) core/shell structures of metallic/silica/UCNPs, UCNPs/ silica/metallic, metallic/UCNPs, and UCNPs/metallic [150,151,162,163].…”