NIR-I-Responsive Single-Band Upconversion Emission through Energy Migration in Core-Shell-Shell Nanostructures.

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations.

Enhancing red upconversion emission in NaErF4@NaYF4 core-shell nanoparticles by introducing Yb3+ ions as energy trapping centers

Effect of A-site cations on the broadband-sensitive upconversion of AZrO3:Er3+,Ni2+ (A = Ca, Sr, Ba) phosphors

Highly stable green and red up-conversion of LiYF4:Yb3+,Ho3+ for potential application in fluorescent labeling

Crystalline-structure-dependent green and red upconversion emissions of Er 3+–Yb 3+–Li + codoped TiO 2

Numerous endeavors have been undertaken to gain enhanced upconversion luminescence via surface plasmon resonance (SPR) generated by specially designed nanostructures of noble metals (e.g., Au, Ag). However, the SPR response of these metals is usually weak in the ultraviolet (UV) region because of their intrinsic electronic configurations; thus, only green and red upconversion emissions can undergo significant plasmonic enhancement yet without selectivity, while an efficient approach to selectively enhancing the blue upconversion luminescence has been lacking. Herein, by integrating the pronounced UV SPR of silica‐coated indium nanocrystals (InNCs) with blue‐emission upconversion nanoparticles (UCNPs) of NaYbF4:Tm, an up to tenfold selective luminescence enhancement at 450 nm is obtained upon 980 nm laser excitation. Precise manipulation of the silica shell thickness suggests an optimal working distance of 3 nm between InNCs and UCNPs. This study has, for the first time, realized selective blue upconversion luminescence enhancement by using an inexpensive, non‐noble metal material, which will not only enrich the fundamental investigations of SPR‐enhanced upconversion emission, but also widen the applications of blue light‐emitting nanomaterials, for example, in therapeutics.

Photon upconversion (UC) is one kind of anti-Stokes shift process, which generally requires a combination of two or more low-energy photons to produce one high-energy photon. However, another inter...

Red upconversion (UC) emission at 626 nm is obtained from a LiNbO(3) crystal codoped with Er(3+) and Eu(3+) under 800 nm femtosecond laser excitation. Energy transfer from ((2)H(11/2,),(4) S(3/2)) levels of Er(3+), which are excited by excited state absorption, to (5)D(1) of Eu(3+) followed by rapidly relaxing to (5)D(0) nonradiatively leads to this red UC emission. The energy transfer efficiency and Er-Eu transfer microparameter of approximately 30% is obtained in LiNbO(3):Er(3+)(1.0 mol%),Eu(3+)(0.1 mol%). These initial experimental results indicate that the red UC emission can be obtained from Er(3+)/Eu(3+) codoped system under diode laser excitation.

Enhancement of the red upconversion luminescence in NaYF4:Yb3+, Er3+ nanoparticles by the transition metal ions doping

Control of red upconversion emission in Er3+–Yb3+– Fe3+ tri–doped biphasic calcium phosphate

Excitation of Ho3+ and Yb3+ co-doped lanthanum silicate and lanthanum zirconate nanoparticles with 980 nm diode laser light gave a red and green glow, respectively, observable by naked eye. Spectroscopic investigations on these materials revealed green (540 nm), red (660 nm), and near-infrared (750 nm) upconversion emissions with the green to red ratio varying with the matrix type and the dopant ion (Yb3+) concentration. The emission was predominantly red for Ho3+:Yb3+ (1:3) in lanthanum silicate nanoparticles, while it was predominantly green for Ho3+:Yb3+ (1:7) in lanthanum zirconate nanoparticles. A mechanism involving cross-relaxations and energy back transfer has been proposed to explain the observed behavior. The predominance of red emission has been attributed to a strong quenching of Ho3+ green emitting level mainly by energy back transfer from Ho3+ to Yb3+ on the basis of the near-infrared (NIR) emission spectral analysis.

Intense visible upconversion and energy transfer in Ho3+/Yb3+ codoped tellurite glasses for potential fiber laser

Optical thermometry through green and red upconversion emissions in Er3+/Yb3+/Li+:ZrO2 nanocrystals

Upconversion nanoparticles (UCNPs) doped with lanthanide ions that possess ladder-like energy levels can give out multiple emissions at specific ultra-violet or visible wavelengths irrespective of excitation light. However, precisely controlling energy migration processes between different energy levels of the same lanthanide ion to generate switchable emissions remains elusive. Herein, a novel dumbbell-shaped UCNP is reported with upconverted red emission switched to green emission when excitation wavelength changed from 980 to 808 nm. The sensitizer Yb ions are doped with activator Er ions and energy modulator Mn ions in NaYF4 core nanocrystal coated with an inner NaYF4 :Yb shell to generate red emission after harvesting 980 nm excitation light, while an outer NaNdF4 :Yb shell is coated to form a dumbbell shape to generate green emission upon 808 nm excitation. Such specially designed UCNPs with switchable green and red emissions are further explored for imaging of latent fingerprint and detection of explosive residues in the fingerprint simultaneously. This work suggests a novel research interest in fine-tuning of upconversion emissions through precisely controlling energy migration processes of the same lanthanide activator ion. Furthermore, use of these nanoparticles in other applications such as simultaneous dual-color imaging or orthogonal bidirectional photoactivation can be explored.

Upconverting CeO2: Yb3+/Tm3+ hollow nanospheres for photo-thermal sterilization and deep-tissue imaging in the first biological window