Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy

Abstract

Lanthanide-doped glasses and crystals are attractive for laser applications because the metastable energy levels of the trivalent lanthanide ions facilitate the establishment of population inversion and amplified stimulated emission at relatively low pump power. At the nanometre scale, lanthanide-doped upconversion nanoparticles (UCNPs) can now be made with precisely controlled phase, dimension and doping level. When excited in the near-infrared, these UCNPs emit stable, bright visible luminescence at a variety of selectable wavelengths, with single-nanoparticle sensitivity, which makes them suitable for advanced luminescence microscopy applications. Here we show that UCNPs doped with high concentrations of thulium ions (Tm), excited at a wavelength of 980 nanometres, can readily establish a population inversion on their intermediate metastable H level: the reduced inter-emitter distance at high Tm doping concentration leads to intense cross-relaxation, inducing a photon-avalanche-like effect that rapidly populates the metastable H level, resulting in population inversion relative to the H ground level within a single nanoparticle. As a result, illumination by a laser at 808 nanometres, matching the upconversion band of the H → H transition, can trigger amplified stimulated emission to discharge the H intermediate level, so that the upconversion pathway to generate blue luminescence can be optically inhibited. We harness these properties to realize low-power super-resolution stimulated emission depletion (STED) microscopy and achieve nanometre-scale optical resolution (nanoscopy), imaging single UCNPs; the resolution is 28 nanometres, that is, 1/36th of the wavelength. These engineered nanocrystals offer saturation intensity two orders of magnitude lower than those of fluorescent probes currently employed in stimulated emission depletion microscopy, suggesting a new way of alleviating the square-root law that typically limits the resolution that can be practically achieved by such techniques.

Photon Upconversion Kinetic Nanosystems and Their Optical Response

“…Liu et al. reported that the blue upconversion emission at 455 nm of Tm 3 + ions in UCNPs doped with high concentrations of thulium ions, excited at a wavelength of 980 nm, can be optically inhibited by a laser at 808 nm . Interestingly, in an independent work we observed similar optical inhibition of the 455‐nm emission band of Tm 3 + ions (excited at 975 nm) by the addition of an 810‐nm laser irradiation in high Tm 3 + ‐doped UCNPs .…”

Rare Earth Ion‐Doped CsPbBr3 Nanocrystals

“…

and thus abundant PL emissions covering ultraviolet, visible light, as well as infrared region. [13,14] Recently, some reports demonstrated that colloidal CsPbX 3 NCs with Mn 2+ doping exhibited dual-color emission, validating the facile doping in perovskites due to their nonrigid structures. [13,14] Recently, some reports demonstrated that colloidal CsPbX 3 NCs with Mn 2+ doping exhibited dual-color emission, validating the facile doping in perovskites due to their nonrigid structures.

…”

Weakening thermal quenching to enhance luminescence of Er3+ doped β‐NaYF4 nanocrystals via acid‐treatment

“…Even after more than several decades of extensive search, rare earth (RE) ions‐doped luminescent nanocrystals (NCs) continue to intrigue research due to its irreplaceable advantages, such as various emission bands and decay lifetime, absence of on‐off blinking and photo‐bleaching, deep excitation penetration, no overlap with cellular autofluorescence, as well as low toxicity, etc . Hence, RE ions‐doped NCs present very broad applications in three‐dimensional display, fluorescence microscopy, nanoscale sensor, security inks, solid state laser, solar cells, and biomedical fields, etc . Among the RE ions‐doped NCs, fluoride compounds with general formula NaReF 4 (Re: Y, Gd, Lu or Sc) because of owning low phonon energy and high chemical stability, have gained more attention .…”