Efficient sub-15 nm cubic-phase core/shell upconversion nanoparticles as reporters for ensemble and single particle studies

Abstract

A set of sub-15 nm ytterbium-enriched α-NaYbF4:Er3+@CaF2 core/shell upconversion nanoparticles have been developed for both ensemble- and single particle-level imaging studies, presenting a high quantum yield of 0.77% at a low saturation power density of 110 W cm−2.

Dopant ion concentration-dependent upconversion luminescence of cubic SrF2:Yb3+,Er3+ nanocrystals prepared by a fluorolytic sol–gel method

“…Also, previously reported cubic UC-host matrices such as α-NaYF 4 , CaF 2 , SrF 2 , and α-NaYbF 4 exhibit a strong red emission. 19,23,35,[50][51][52] Moreover, the evolution of the 855 nm and 806 nm bands upon increasing χ Yb differ from the behaviour commonly observed for hexagonal β-NaYF 4 UCNC. High amounts of Yb 3+ are known to elevate surface quenching, i.e., the migration of the excitation energy to quenching sites at the surface via multiple Yb 3+ -ions.…”

“…Also, previously reported cubic UC-host matrices such as α-NaYF 4 , CaF 2 , SrF 2 , and α-NaYbF 4 exhibit a strong red emission. 19,23,35,50–52…”

Enhanced two-step two-frequency upconversion luminescence in a core/shell/shell nanostructure

“…Guo et al 39 demonstrated that enhanced emission intensity in GdVO 4 :Yb/Er nanoparticles doped with Lu 3+ , Y 3+ and PO 4 3− ions was realized by 980 & 1550 nm excitation. However, TSTF UCNPs often surfer from low luminescent efficiency [42][43][44] , attributing to the concentration quenching and surface defects [45][46][47][48][49][50] , which partly restrict the further applications in 3-D display. For enhancing UCL efficiency, many approaches, such as doping sensitizer, fabricating core/shell structures, changing the hosts are widely studied [51][52][53][54] .…”

“…Many excellent studies on TSTF UCNPs have been reported. [42][43][44] attributed to concentration quenching and surface defects, [45][46][47][48][49][50] which partly restrict further applications in the 3-D display. To enhance UCL efficiency, many approaches, such as doping sensitizers, fabricating core/shell structures, and changing the hosts, have been widely studied.…”

Excitation Laser Power and Temperature-Dependent Luminescence of Optically Trapped Upconversion Particles

“…However, the higher spatial-resolution requirements of the measurements in semiconductors and biological cells demand investigation at a single-particle level. − The major challenge while carrying out single-particle emission measurements is the requirement of 10 5 –10 6 W cm –2 excitation intensity as compared to 1–100 W cm –2 for bulk or ensemble samples. Recently, it has been demonstrated that core–shell architectures can lower the excitation intensity required for single-particle emission. − Optical arresting, wherein the gradient force created via focusing a Gaussian laser excitation beam through a high numerical aperture microscope objective balances the photon scattering force along the light propagation direction, is an ideal noncontact approach to optically arrest single upconversion particles for further studies. , The mechanism and potential of the technique have already been demonstrated in the case of nanoparticles (quantum dots, metallic nanoparticles, upconversion particles), biological cells, bacteria, etc. − The investigation of optically trapped particles facilitates the understanding of physical phenomena at a single-particle level and allows the development of efficient optical single-particle probes. ,, This single-particle spectrometry is expected to provide microstructure-dependent spectroscopic characteristics compared to ensemble studies. − …”