Tuning the energy migration and new insights into the mechanism of upconversion

Fluorescent Nanoparticles for Super-Resolution Imaging

Super-resolution imaging techniques that overcome the diffraction limit of light have gained wide popularity for visualizing cellular structures with nanometric resolution. Following the pace of hardware developments, the availability of new fluorescent probes with superior properties is becoming ever more important. In this context, fluorescent nanoparticles (NPs) have attracted increasing attention as bright and photostable probes that address many shortcomings of traditional fluorescent probes. The use of NPs for super-resolution imaging is a recent development and this provides the focus for the current review. We give an overview of different super-resolution methods and discuss their demands on the properties of fluorescent NPs. We then review in detail the features, strengths, and weaknesses of each NP class to support these applications and provide examples from their utilization in various biological systems. Moreover, we provide an outlook on the future of the field and opportunities in material science for the development of probes for multiplexed subcellular imaging with nanometric resolution.

Bismuth(III)-Doped NaYbF4:Tm3+ Fluorides with Highly Efficient Upconversion Emission under Low Irradiance

Concentration quenching of upconversion (UC) luminescence (UCL) is a common phenomenon in rare-earth-doped materials that seriously restricts the concentration of the activator and sensitizer and withholds their UC emissions and quantum yields. In particular, it remains a tremendous challenge to develop one novel strategy based on the introduction of trivalent bismuth (Bi³⁺) ions to exceed the typical thulium (Tm³⁺) ion concentration and reach high-efficiency UC under low illumination. In this work, the Tm³⁺ accommodation capacity can be increased from 2.0 to 8.0 mol % in NaYbF₄:Tm³⁺ materials with the assistance of Bi³⁺ ions, which maintains strong UC emissions with large absolute UC quantum yields under low illumination. Specifically, the total upconversion quantum yield (UCQY) of the as-obtained Na(Tm_0.08Yb_0.60Bi_0.32)F₄ (8Tm60Yb32Bi) sample can reach as high as 1.45% upon continuous-wave (CW) laser excitation at 40 W cm^-2. Strikingly, the total UCQY still remains at a high level (0.41%) even though the CW power density decreases to 1.5 W cm^-2. Moreover, the intrinsic mechanism of the breakthrough in the threshold of concentration quenching of UCL by Bi³⁺ ions was also fully explored. These advances in enhancing UC emissions and UCQYs under a low pump power density offer exciting opportunities for important photonic applications.

Lanthanide upconversion luminescence at the nanoscale: fundamentals and optical properties

Upconversion photoluminescence is a nonlinear effect where multiple lower energy excitation photons produce higher energy emission photons. This fundamentally interesting process has many applications in biomedical imaging, light source and display technology, and solar energy harvesting. In this review we discuss the underlying physical principles and their modelling using rate equations. We discuss how the understanding of photophysical processes enabled a strategic influence over the optical properties of upconversion especially in rationally designed materials. We subsequently present an overview of recent experimental strategies to control and optimize the optical properties of upconversion nanoparticles, focussing on their emission spectral properties and brightness.

Improved sensitization efficiency in Er3+ ions and SnO2 nanocrystals co-doped silica thin films

High performance near-infrared luminous using broadband UV pumping.