Revisiting the optimized doping ratio in core/shell nanostructured upconversion particles

Abstract

The development of rare-earth doped upconversion nanoparticles (RE-UCNPs) in various applications is fuelling the demand for nanoparticles with highly enhanced upconversion luminescence (UCL). Although the core/shell structure is proved to enhance the UCL effectively, there is still plenty of room to further improve the UCL by optimizing the doping ratio of the materials. In this article, a general strategy is demonstrated to achieve highly-enhanced visible UCL in core/shell nanostructured NaREF by increasing the doping ratio of Yb in the core region. The energy transfer from RE-UCNPs to surface quenching sites through Yb-Yb energy migration is demonstrated to be the main reason for restricting the doping ratio of Yb. Notable UCL enhancement (ca. 15 times) of core/shell structured α-NaYF:Yb,Er@CaF nanoparticles is observed by increasing the concentration of Yb to 98 mol%. The highly-enhanced visible UCL signal is used to guide the lymphatic vessel resection with the naked eye.

Advances in highly doped upconversion nanoparticles

“…Adapted with permission from ref. 47 Copyright (2017) Royal Society of Chemistry. f Schematic of the experimental configuration for capturing upconversion luminescence of NaYF 4 :Yb 3+ ,Tm 3+ nanocrystals using a suspended-core microstructured optical-fibre dip sensor.…”

“…Chen et al reported that highly Yb 3+ -doped sub-10 nm cubic phase (α-) NaYF 4 :Yb 3+ ,Tm 3+ nanocrystals display a 43 times emission enhancement at NIR wavelengths compared to the conventional 20% Yb 3+ -doped one 46 . With an inert shell coating, the α-NaYbF 4 :2%Er 3+ @CaF 2 UCNPs display a 15-fold enhancement in visible light emission (Figure 2e ) 47 . Using an inert CaF 2 shell, heavy doping of Yb 3+ ions in the ultra-small α-NaYF 4 :Yb 3+ ,Tm 3+ and α-NaYbF 4 :Tb 3 + nanoparticles was found to dramatically enhance the upconversion emission for high-contrast bioimaging 48 – 51 .…”

Controlling the non-linear emission of upconversion nanoparticles to enhance super-resolution imaging performance

“…Despite the possible limiting factor of concentration quenching, 19 significant improvements in brightness compared to the common Y-based UCNPs have been reported. 17,24,27,28 Given the above advances in UCNP design and synthesis, the question arises whether there are consequential improvements that can be made to super-resolution imaging performance. For example, changes in the Yb/Tm composition ratio are expected to affect excitation and depletion rates and the efficiency of cross-relaxation mechanisms, leading to variations in the non-linear emission characteristics of the excited nanoparticles.…”

Temperature Sensing in the Short-Wave Infrared Spectral Region Using Core-Shell NaGdF4:Yb3+, Ho3+, Er3+@NaYF4 Nanothermometers

“…These mainly affect the sensitizer Yb 3+ [ 53 , 54 ] and therefore suppress the activator emission. It has previously been shown that the quenching of luminescence in the VIS and NIR regions could be prevented by using core-shell or complex core-multi-shell structures [ 55 , 56 , 57 ]. In this study, we examined the influence of NaYF 4 inert shell on the luminescence intensity in SWIR and the thermal sensing sensitivity of Yb 3+ , Ho 3+ , Er 3+ tri-doped NaGdF 4 NPs.…”