Selective enhancement of red emission from upconversion nanoparticles via surface plasmon-coupled emission

Abstract

Upconversion nanoparticle and gold nanorod heteronanostructures spaced by a polyelectrolyte are prepared by a layer-by-layer assembly process to enhance red emission.

Tuning Plasmonic Enhancement of Single Nanocrystal Upconversion Luminescence by Varying Gold Nanorod Diameter

“…An intense red emission band around 660 nm and a very weak green emission band ≈550 nm could be identified in the spectrum as shown in Figure d, which were attributed to the 4 F 9/2 → 4 I 15/2 and the 2 H 11/2, 4 S 3/2 → 4 I 15/2 transitions of Er 3+ ion (Figure e), respectively. Many previous studies on the plasmonic enhancement UCL of Yb 3+ and Er 3+ coactivated hexagonal NaYF 4 nanocrystals have indicated that the enhancement factor was not equal for green and red emissions but varied strongly with different characteristics of plasmonic structures . Furthermore, a fraction of red UCL in Yb 3+ /Er 3+ codoped NaYF 4 nanocrystals originates from the excited state nonradiative relaxation of the green UCL ( 4 S 3/2 level) .…”

“…This localization results in the near‐field enhancement by orders of magnitude and can be used to greatly promote photochemical reactions and amplify the luminescence from nearby optical emitters as extensively demonstrated in plasmonic‐enhanced fluorescence of semiconductor quantum dots and dye molecules . This strategy has also been extended to enhance the UCL of UCNPs with metallic nanoparticles, structured metallic surfaces, metal shell architectures, and metallic tip …”

“…For Au nanorods with diameter larger than 30 nm, extinction is dominated by scattering, making them favorable for applications in metal‐enhanced fluorescence and bioimaging, and so forth, whereas for smaller Au nanorods, absorption mainly contributes to extinction, which makes them suitable for photothermal therapy with a high photon‐to‐heat conversion efficiency . Recent reports also demonstrated the plasmonic enhancement UCL of UCNPs by single or assembly Au nanorods . However, the diameters of Au nanorods used in these works are all below 30 nm, and therefore the enhancement efficiency of these Au nanorods will be reduced due to the photon‐to‐heat conversion loss.…”

Enhancement of Upconverted Fluorescence by Interference Layers

“…There have been two main strategies to enhance the upconversion efficiency, which is either by modifying the upconverting materials or by tailoring the electromagnetic field with plasmonic nanostructures close to the UCNP's surface, improving its absorption (more than 100×) and/or emission (up to 20×) . Previous investigations involve UCNPs in close proximity to metallic nanostructures and nanoarrays, such as nanospheres, nanorods, nanoparticle islands, nanocrescents, gold pillars, disk‐coupled dots‐on‐pillar arrays, nanocavity arrays, and nanocaps . In these ensemble studies, increased emission of up to 300‐fold was observed by Zhang et al Direct evidence of plasmonic‐enhanced upconversion luminescence has been provided at the single particle level, where one UCNP is coupled to an individual plasmonic nanostructure or coated with noble metals offering fluorescence enhancements of up to 48‐fold .…”

A proposal and a theoretical analysis of an enhanced surface plasmon coupled emission structure for single molecule detection

“…Therefore, detection of a biological sample is difficult when the excitation volume is very limited as in for SMD so that the number of fluorophores that radiate is less. The pursuit of increasing the SPCE light intensity is an active area of research [14][15][16][17][18][19]. Two approaches are usually used to increase the SPCE light intensity: First, by increasing the radiation of the fluorophores, and second, by increasing the coupling of the radiation of the fluorophores to SPCE.…”