Huge enhancement of upconversion luminescence by dye/Nd³⁺ sensitization of quenching-shield sandwich structured upconversion nanocrystals under 808 nm excitation

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) have shown potential applications in diverse fields. However, their upconversion luminescence (UCL) intensity and excitation wavelength range are limited by the weak and narrowband absorption of lanthanide ions. Herein, we introduce and validate a strategy to largely increase the absorptivity and upconversion luminescence intensity under 808 nm excitation by broadband dye-sensitized quenching-shield sandwich structured upconversion nanocrystals NaLuF:Gd,Yb,Tm@NaLuF:Gd,Yb@NaNdF:Yb. The dye molecules anchored on the surface of the UCNPs serve as an antenna which can broadly and strongly harvest NIR light. The Nd facilitates the energy transfer and photon upconversion of the lanthanide activator at a biocompatible excitation wavelength (around 800 nm) with a significant increase in penetration ability and minimizes the overheating problem associated with conventional 980 nm excitation. The quenching-shield sandwich structure can greatly eliminate the deleterious cross-relaxation pathway between the activator and sensitizer. This approach combines the merits of the use of Nd as a sensitizer, a quenching-shield sandwich structure and the "antenna" effect, leading to a tremendous enhancement of UCL under excitation at 808 nm. These well-designed UCNPs excited at 808 nm with improved optical performances will outperform conventional UCNPs excited at 980 nm and play an important role in the development of luminescent probes for future biological and medical applications.

Lanthanide-based inorganic–organic hybrid materials for photon-upconversion

“…68 Later, NaLuF 4 :Gd,Yb,Tm/ NaLuF 4 :Gd,Yb/NaNdF 4 :Yb NPs sensitized with IR-820 were reported. 69 In these studies, Nd 3+ was incorporated into the outermost inorganic shell and the activator ions were doped in the inner core. The intermediate layer between the core and the Fig.…”

Sub-20 nm Core–Shell–Shell Nanoparticles for Bright Upconversion and Enhanced Förster Resonant Energy Transfer

“…22 Other works have investigated FRET coupling and related energy transfer through active core and active shell strategies, 35 passivating shell effects, 32 and sensitization via dye antennas. [36][37][38] Further when UCNPs are coupled to a fluorescent dye via FRET, the upconversion quantum yield (UCQY) of the system has been shown to improve by nearly an order of magnitude. 23 Together, these studies inform design considerations for bright upconversion in a small nanoparticle for FRET: a passivating inert shell, a high concentration of Yb 3+ , a tuned Er 3+ concentration, and efficient coupling to a FRET acceptor.…”

Large enhanced photocatalytic activity of g-C3N4 by fabrication of a nanocomposite with introducing upconversion nanocrystal and Ag nanoparticles

“…The UCNPs of NaLuF 4 :Gd,Yb,Tm@NaLuF 4 :Gd,Yb were first synthesized through a thermal decomposition method. 33 A layer of amorphous SiO 2 as the media shell was generated outside the UCNPs via a reverse microemulsion method. 34 Ag NPs generated by the reduction of AgNO 3 using sodium citrate as the reductant were immobilized on the surface of the SiO 2 shell through a chemical affinity towards primary amines.…”

“…The NaLuF 4 :Gd,Yb,Tm nanoparticles were prepared using a method similar to our previous report with slight modifications. 33 Typically, 2 mmol of CF 3 COONa, 0.555 mmol of Lu(CF 3 COO) 3 , 0.24 mmol of Gd(CF 3 COO) 3 , 0.2 mmol of Yb(CF 3 COO) 3 and 0.005 mmol of Tm(CF 3 COO) 3 were added to a mixture of OA (6 mL) and ODE (6 mL) in a three-necked flask at room temperature. The solution was pre-degassed for 30 min with vigorous magnetic stirring and then heated to 110 °C under vacuum for 30 min to remove water and oxygen.…”