Single-Band Upconversion Emission in Lanthanide-Doped KMnF3 Nanocrystals

Highly efficient upconversion luminescence in narrow-bandgap Y2Mo4O15

Lanthanide-doped upconversion (UC) materials have been extensively investigated for their unique capability to convert low-energy excitation into high-energy emission. Contrary to previous reports suggesting that efficient UC luminescence (UCL) is exclusively observed in materials with a wide bandgap, we have discovered in this study that Y2Mo4O15:Yb3+/Tm3+ microcrystals, a narrowband material, exhibit highly efficient UC emission. Remarkably, these microcrystals do not display any four- or five-photon UC emission bands. This particular optical phenomenon is independent of the variation in doping ion concentration, temperature, phonon energy, and excitation power density. Combining theoretical calculations and experimental results, we attribute the vanishing emission bands to the strong interaction between the bandgap of the Y2Mo4O15 host matrix (3.37 eV) and the high-energy levels (1I6 and 1D2) of Tm3+ ions. This interaction can effectively catalyze the UC emission process of Tm3+ ions, which leads to Y2Mo4O15:Yb3+/Tm3+ microcrystals possessing very strong UCL intensity. The brightness of these microcrystals outshines commercial UC NaYF4:Yb3+,Er3+ green phosphors by a factor of 10 and is 1.4 times greater than that of UC NaYF4:Yb3+,Tm3+ blue phosphors. Ultimately, Y2Mo4O15:Yb3+/Tm3+ microcrystals, with their distinctive optical characteristics, are being tailored for sophisticated anti-counterfeiting and information encryption applications.

Upconversion Luminescence through Cooperative and Energy-Transfer Mechanisms in Yb3+ -Metal-Organic Frameworks

Lanthanide-doped metal-organic frameworks (Ln-MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide-based upconversion luminescence in these materials. Here, 1,3,5-benzenetricarboxylic acid (BTC) and trivalent Yb³⁺ ions were used to generate crystalline Yb-BTC MOF 1D-microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb-BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb³⁺ -based upconversion and energy transfer. Yb-BTC MOFs doped with Er³⁺ , Ho³⁺ , Tb³⁺ , and Eu³⁺ ions exhibit both the cooperative luminescence from Yb³⁺ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb³⁺ is observed in the MOFs doped with Tm³⁺ , Pr³⁺ , Sm³⁺ , and Dy³⁺ . The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln-MOFs exhibiting upconversion.

Recent Advances and Challenges in Light Conversion Phosphor Materials for Third-Generation Quantum-Dot-Sensitized Photovoltaics

Photovoltaic (PV) technologies have received tremendous attention for producing clean and renewable energy from the Sun. Third-generation quantum-dot-sensitized solar cells (QDSCs) present promising alternatives to conventional silicon solar cells due to their unique properties such as simplicity in fabrication, lower processing temperature, high flexibility, semitransparent nature, and a theoretical conversion efficiency of up to 44%. However, the light-harvesting QD materials used in these SCs allow for the absorption of a small portion (from 300 to 800 nm) of the solar spectrum due to their narrow band gap. The nonabsorption of UV and near-infrared (NIR) light limits the power conversion efficiency (PCE) of these SCs. Hence, a PV technique that efficiently uses the entire solar spectrum becomes essential. The incorporation of light conversion phosphor materials (LCs) in QDSCs is a promising technology to absorb the whole part of the solar spectrum and enhance the PCE of these SCs. This review presents an overview of the advantages and limitations of QDSCs, different types of lanthanide-based light conversion phosphor materials, their synthesis and light conversion mechanism, and their influence on QDSCs.

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.

Unravelling the benefits of transition-metal-co-doping in lanthanide upconversion nanoparticles

In this review we provide an overview of the current knowledge on lanthanide upconversion materials co-doped with transition metals. We focus on how the co-dopants affect the host lattice and the energy transfer processes.

Enhancing upconversion of manganese through spatial control of energy migration for multi-level anti-counterfeiting

The upconversion of manganese (Mn²⁺) exhibits a green light output with a much longer lifetime than that of lanthanide ions, showing great potential in the frontier applications like information security and anti-counterfeiting. Mn²⁺ can be activated by energy migration upconversion. However, there exists serious quenching interactions between Mn²⁺ and the lanthanides at the core-shell interfacial area, which would markedly reduce the role of Tm³⁺ as a ladder to facilitate the up-transition and subsequently limit the upconversion of Mn²⁺. Here, we propose a mechanistic strategy to enhance the upconversion luminescence of Mn²⁺ by spatial control of energy migration among Gd sublattice through introducing an additional migratory NaGdF₄ interlayer within the commonly used core-shell nanostructure. This design can not only isolate the interfacial quenching interactions between the sensitized core and luminescent shell, but also allow an efficient channel for energy transport, resulting in enhanced upconversion of Mn²⁺. Moreover, the relatively long lifetime of Mn²⁺ (around 32.861 ms) provides new possibilities to utilize the temporal characteristic for the frontier application of multi-level anti-counterfeiting through combining the time-gating technology.

Expanding the Toolbox of Upconversion Nanoparticles for In Vivo Optogenetics and Neuromodulation

Optogenetics is an optical technique that exploits visible light for selective neuromodulation with spatio-temporal precision. Despite enormous effort, the effective stimulation of targeted neurons, which are located in deeper structures of the nervous system, by visible light, remains a technical challenge. Compared to visible light, near-infrared illumination offers a higher depth of tissue penetration owing to a lower degree of light attenuation. Herein, an overview of advances in developing new modalities for neural circuitry modulation utilizing upconversion-nanoparticle-mediated optogenetics is presented. These developments have led to minimally invasive optical stimulation and inhibition of neurons with substantially improved selectivity, sensitivity, and spatial resolution. The focus is to provide a comprehensive review of the mechanistic basis for evaluating upconversion parameters, which will be useful in designing, executing, and reporting optogenetic experiments.

Ultrabright single-band red upconversion luminescence in highly transparent fluorosilicate glass ceramics containing KMnF3 perovskite nanocrystals

With a specially designed composition, highly transparent Yb³⁺/Er³⁺-doped fluorosilicate glass ceramic (GC) containing KMnF₃ perovskite nanocrystals (NCs) is obtained for the first time. The rare-earth ions are preferentially accumulated in regions embedded with KMnF₃ NCs; as a result, a remarkably enhanced (by an order of magnitude) single-band red upconversion luminescence (UCL) is achieved. Absolute quantum efficiency of the red UCL, which cannot be measured in previous GCs owing to insufficiency, reaches as high as 0.10%±0.02% in the GC sample reported in this Letter. This value is even higher than that of the well-known multiband emitting β-NaYF₄:Er³⁺/Yb³⁺ NCs and widely recognized GCs containing NaYF₄:Yb³⁺/Er³⁺NCs.

Effect of Mn2+ on Upconversion Emission, Thermal Sensing and Optical Heater Behavior of Yb3+ - Er3+ Codoped NaGdF4 Nanophosphors

In thiswork, we investigate the influence of Mn2+ on the emission color, thermal sensing and optical heater behavior of NaGdF4: Yb/Er nanophosphors, which the nanoparticles were synthesized by a hydrothermal method using oleic acid as both a stabilizing and a chelating agent. The morphology and crystal size of upconversion nano particles (UCNPs) can be effectively controlled through the addition of Mn2+ dopant contents in NaGdF4: Yb/Er system. Moreover, an enhancement in overall UCL spectra of Mn2+ doped UCNPs for NaGdF4 host compared to the UCNPs is observed, which results from a closed back-energy transfer between Er3+ and Mn2+ ions (4S3/2 (Er3+) → 4T1 (Mn2+) → 4F9/2 (Er3+)). The temperature sensitivity of NaGdF4:Yb3+/Er3+ doping with Mn2+ based on thermally coupled levels (2H11/2 and 4S3/2) of Er3+ is similar to that particles without Mn2+ in the 303-548 K range. And the maximum sensitivity is 0.0043 K-1 at 523 K for NaGdF4:Yb3+/Er3+/Mn2+. Interestingly, the NaGdF4:Yb3+/Er3+/Mn2+ shows preferable optical heating behavior, which is reaching a large value of 50 K. These results indicate that inducing of Mn2+ ions in NaGdF4:Yb3+/Er3+ nanophosphors has potential in colorful display, temperature sensor.

Enhanced optical temperature sensing and upconversion emissions based on the Mn2+ codoped NaGdF4:Yb3+,Ho3+ nanophosphor

In this study, to explore new phosphors for temperature sensing with high detection sensitivity, Yb³⁺/Ho³⁺/Mn²⁺ doped hexagonal NaGdF₄ nanoparticles were designed.

Preparation and Evaluation of Multifunctional Autofluorescent Magnetic Nanoparticle-Based Drug Delivery Systems Against Mammary Cancer

The Fe₃O₄@C@NaYF₄:Yb,Er nanocarriers of multifunction were synthesized. The mitoxantrone was selected as model drug, and these nanoparticles have high drug loading (0.63 mg/mg). The temperature of Fe₃O₄@C@NaYF₄:Yb,Er in water reached 60°C with 808 nm irritation (2.5 W/cm²). The cumulative release of these nano drug carriers significantly increased because of the increase in temperature, and the 4T1 cell growth inhibition rates were 59.15%, almost 2.25-fold higher than mitoxantrone group (p <0.05). Because the nanoparticles had autofluorescence under 808 nm irritation, the nanocarriers could be traced in both in vitro and in vivo studies. Based on magnetic field, the fluorescence signal of these nano drug carriers could be observed at tumor region during 2-9 h in vivo study. The nanocarriers with magnetic and 808 nm laser group, tumor growth inhibition rate achieved almost 83.14%. These nanoparticles are an outstanding potential carrier for antitumor drugs, which can improve curative effect for tumor while reducing toxicity.

Confining Excitation Energy in Er3+ -Sensitized Upconversion Nanocrystals through Tm3+ -Mediated Transient Energy Trapping

A new class of lanthanide-doped upconversion nanoparticles are presented that are without Yb³⁺ or Nd³⁺ sensitizers in the host lattice. In erbium-enriched core-shell NaErF₄ :Tm (0.5 mol %)@NaYF₄ nanoparticles, a high degree of energy migration between Er³⁺ ions occurs to suppress the effect of concentration quenching upon surface coating. Unlike the conventional Yb³⁺ -Er³⁺ system, the Er³⁺ ion can serve as both the sensitizer and activator to enable an effective upconversion process. Importantly, an appropriate doping of Tm³⁺ has been demonstrated to further enhance upconversion luminescence through energy trapping. This endows the resultant nanoparticles with bright red (about 700-fold enhancement) and near-infrared luminescence that is achievable under multiple excitation wavelengths. This is a fundamental new pathway to mitigate the concentration quenching effect, thus offering a convenient method for red-emitting upconversion nanoprobes for biological applications.

Regulating angiogenesis with light-inducible AntimiRs

The inhibition of microRNAs (miRs) in a spatiotemporally defined manner by an exogenous trigger would help to specifically target the biological activity and avoid off-target effects. Novel antimiRs directed against miR-92a can be activated by irradiation (see scheme; 3'-UTR=3'-untranslated region) In this way miR-92a is inhibited, the miR-92a target integrin α5 is derepressed, and angiogenesis of endothelial cells is enhanced.

Rare-Earth nanoparticles with enhanced upconversion emission and suppressed rare-Earth-ion leakage

Upconversion emissions from rare-earth nanoparticles have attracted much interest as potential biolabels, for which small particle size and high emission intensity are both desired. Herein we report a facile way to achieve NaYF(4):Yb,Er@CaF(2) nanoparticles (NPs) with a small size (10-13 nm) and highly enhanced (ca. 300 times) upconversion emission compared with the pristine NPs. The CaF(2) shell protects the rare-earth ions from leaking, when the nanoparticles are exposed to buffer solution, and ensures biological safety for the potential bioprobe applications. With the upconversion emission from NaYF(4):Yb,Er@CaF(2) NPs, HeLa cells were imaged with low background interference.