Probing the nature of upconversion nanocrystals: instrumentation matters

Abstract

Probing the nature of nanocrystalline materials such as the surface state, crystal structure, morphology, composition, optical and magnetic characteristics is a crucial step in understanding their chemical and physical performance and in exploring their potential applications. Upconversion nanocrystals have recently attracted remarkable interest due to their unique nonlinear optical properties capable of converting incident near-infrared photons to visible and even ultraviolet emissions. These optical nanomaterials also hold great promise for a broad range of applications spanning from biolabeling to optoelectronic devices. In this review, we overview the instrumentation techniques commonly utilized for the characterization of upconversion nanocrystals. A considerable emphasis is placed on the analytical tools for probing the optical properties of the luminescent nanocrystals. The advantages and limitations of each analytical technique are compared in an effort to provide a general guideline, allowing optimal conditions to be employed for the characterization of such nanocrystals. Parallel efforts are devoted to new strategies that utilize a combination of advanced emerging tools to characterize such nanosized phosphors.

Phase angle encoded upconversion luminescent nanocrystals for multiplexing applications

“…Due to the nature of sequential discrete absorption of two or more excitation photons, the upconversion luminescence kinetics following a short pulse Please do not adjust margins Please do not adjust margins excitation typically features a delayed maximum in the time trace rather than immediate decay, reflecting both rise and decay behavior (Fig. 1b) 37,38 . Such luminescence kinetics can generally fit adequately to the following equation [39][40][41] : ,…”

A Rationally Designed Upconversion Nanoprobe for in Vivo Detection of Hydroxyl Radical

“…[28][29][30][31][32][33][34][35][36][37][38] UCNPs are promising energy donors for luminescence resonance energy transfer (LRET)-based fluorescence probes, in which a specific target recognizing moiety acts as the energy acceptor and quenches the luminescence of UCNPs. The target-induced recovery of UCNPs luminescence can provide turn-on signals, with the sensitivity predominantly dependent on the quenching efficiency.…”

Polyaniline-coated upconversion nanoparticles with upconverting luminescent and photothermal conversion properties for photothermal cancer therapy

“…31 Thus, lanthanidebased upconversion nanoparticles (UCNPs) have special optical characteristics, such as sharp emission lines, large anti-Stokes shifts of several hundred nanometers, and the absence of autofluorescence in biosamples. [32][33][34][35][36][37][38] Therefore, UCNPs have been recently used as building blocks in the construction of multimodal contrast agents for imagingguided therapy. [39][40][41][42][43][44][45] In the current study, upconversion nanoparticles (UCNPs) were first prepared by a typical solvothermal method.…”