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

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.

Luminescent thermometry based on Er3+/Yb3+ co-doped yttrium niobate with high NIR emission and NIR-to-visible upconversion quantum yields

Design of a bi-functional NaScF4: Yb3+/Er3+ nanoparticles for deep-tissue bioimaging and optical thermometry through Mn2+ doping

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

Enhanced red up-conversion of β-NaYF4:Er3+,Tm3+ microcrystals for bio-imaging applications

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

Under a 980 nm laser pumping, quenching of green upconversion (UC) emission accompanied with enhancement of red UC emission observed was dominated by the energy back-transfer (EBT) process in Er(3+) and Yb(3+) co-doped PbTiO(3), BaTiO(3), and SrTiO(3) polycrystalline powders. The efficiency of the EBT process depends not only on Yb(3+) concentration but also on level match of the doped Er(3+) and Yb(3+) ions caused by the crystal fields with different symmetries. Our UC emission spectra and X-ray diffraction confirm that the centrosymmetric crystal field arising from reducing tetragonality causes level match of transition (4)S3/2-->I13/2 of Er(3+) and (2)F7/2-->(2)F5/2 of Yb(3+). This level match is responsible for enhancing red UC emission.

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

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

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

In the last few years, huge progress has been made in the development of remote optical thermometry strategies, due to their non-contact, high-sensitivity and fast measurement characteristics, which are especially important for various industrial and bio-applications. For these purposes, lanthanide-doped particles seem to be the most promising luminescence thermometers. In this study, Tm3+/Yb3+:Na3GdV2O8 (NGVO) phosphors were prepared using a sol-gel method. Under 980 nm excitation, the upconversion (UC) and down-shifting (DS) emission spectra are composed of two visible emission bands arising from the Tm3+ transitions 1G4 → 3H6 (475 nm) and 1G4 → 3F4 (651 nm), a strong emission at 800 nm (3H4 → 3H6) in the first biological window and emission in the third biological window at 1625 nm (3F4 → 3H6), respectively. Accordingly, the luminescence intensity ratio (LIR) between the Tm3+ LIR1 (800/475) and LIR2 (1625/475) transitions demonstrates excellent relative sensing sensitivity values (4.2% K-1-2% K-1) and low-temperature uncertainties (0.4 K-0.5 K) over a wide temperature sensing range of 300 K to 565 K, which are remarkably better than those of many other luminescence thermometers. This phosphor exhibits strong NIR emission at low excitation density, meaning that it has potential uses in deep tissue imaging, optical signal amplification and other fields. The results indicate that Tm3+/Yb3+:NGVO is an ideal candidate for thermometers and particularly for biological applications.

Laser induced thermal effect on upconversion luminescence and temperature-dependent upconversion mechanism in Ho3+/Yb3+-codoped Gd2(WO4)3 phosphor

Upconversion emission of Yb, Er co-doped Bi4Ti3O12 (Bi4Ti3O12: Yb, Er) inverse opal photonic crystals was investigated. Strong green (548 nm) and red (660 nm) upconversion emission bands were observed under a 980 nm excitation at room temperature. The results showed that the intensity of upconversion emission bands can be tuned by controlling the structure of the inverse opal. Significant suppression of the green or red upconversion emission was obtained if the photonic band gap overlaps with the Er3+ ions emission band, resulting in color tunable up-conversion photonic crystals with applications in solid-state color displays.

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.

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.