Highly Efficient Red/Near-Infrared Phosphorescence from Doped Crystals.

Organic red/near-infrared (NIR) room temperature phosphorescence (RTP) materials with low toxicity and facile synthesis are highly sought after, particularly for applications in biotechnology and encryption. However, achieving efficient red/NIR RTP emitters has been challenging due to the weak spin-orbit coupling of organics and the rapid nonradiative decay imposed by the energy gap law. Here we demonstrate highly efficient red/ NIR RTP with boosted quantum yields (Φp) of up to 32.96% through doping the thionated derivatives of phthalimide (PAI) (MTPAI and DTPAI) into PAI crystals. The red-shifted photoluminescence (PL) stems from a combination of the external heavy atom effect and the formation of emissive clusters centered around electron-rich sulfur atoms. Furthermore, the dopants enhance exciton generation efficiency and facilitate energy transfer from smaller PAI units to larger aggregates, leading to dramatically increased Φp. This strategy proves universal, opening possibilities for acquiring long-wavelength RTP with tunable photophysical properties. The doped crystals exhibit promising applications in optical waveguides and encryption paper/ink. This research provides a practical approach to obtaining long-wavelength RTP materials and offers valuable insights into the mechanisms governing host-guest systems.

Lanthanide-Based Probes for Imaging Detection of Enzyme Activities by NIR Luminescence, T1- and ParaCEST MRI.

Applying a single molecular probe to monitor enzymatic activities in multiple, complementary imaging modalities is highly desirable to ascertain detection and to avoid the complexity associated with the use of agents of different chemical entities. We demonstrate here the versatility of lanthanide (Ln3+) complexes with respect to their optical and magnetic properties and their potential for enzymatic detection in NIR luminescence, CEST and T1 MR imaging, controlled by the nature of the Ln3+ ion, while using a unique chelator. Based on X-ray structural, photophysical, and solution NMR investigations of a family of Ln3+ DO3A-pyridine model complexes, we could rationalize the luminescence (Eu3+, Yb3+), CEST (Yb3+) and relaxation (Gd3+) properties and their variations between carbamate and amine derivatives. This allowed the design of L n L G a l 5 ${{{\bf L n L}}_{{\bf G a l}}^{5}}$ probes which undergo enzyme-mediated changes detectable in NIR luminescence, CEST and T1-weighted MRI, respectively governed by variations in their absorption energy, in their exchanging proton pool and in their size, thus relaxation efficacy. We demonstrate that these properties can be exploited for the visualization of ß-galactosidase activity in phantom samples by different imaging modalities: NIR optical imaging, CEST and T1-weighted MRI.

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications.

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability, and adjustable optical properties. NIR-emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) of over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, are summarized, and their recent advancement is assessed. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. Also, the various applications of NIR-emitting metal halides are highlighted and an outlook for the field is provided.

Aromatic Bridged Bis(triphenylamine) Cascade Assembly Achieved Tunable Nanosupramolecular Morphology and NIR Targeted Cell Imaging.

Possessing four cationic pyridium groups, phenyl-bridged bis(triphenylamine) derivatives (G1, G2) were encapsulated by cucurbit[8]uril (CB[8]) at a 1:2 stoichiometry to form the network-like organic two-dimensional nanosheet, which could efficiently enhance the near-infrared (NIR) luminescence and companies with a red-shift from 750 to 810 nm for G1. Benefiting from the supramolecular multivalent interaction, α-cyclodextrin modified hyaluronic acid (HACD) and G1/CB[8] formed nanoparticles to further enhance NIR luminescence behaviors. Compared with the short rigid aromatic bridged bis(triphenylamine) derivative (G2), the supramolecular assembly derived from G1 with long flexible cationic arms gives a larger Stokes shift, which further coassembles with the phosphorescent bromophenylpyridinium derivative/CB[8] pseudorotaxane, leading to efficient phosphorescent resonance energy transfer (PRET). Especially, the nanoparticle showed delayed NIR fluorescence under 308 nm light excitation with an ultralarge Stokes shift up to 502 nm, which was successfully applied in targeted NIR cell imaging.

Subnano Te Cluster in Glass for Efficient Full-Spectrum Conversion.

Broadband near-infrared (NIR) photonic materials have wide applications. Although extensive studies on rare-earth, transition-metal, and even semiconductor-activated materials have enabled the development of a rich NIR material pool, developing broadband and efficient photonic candidates covering the NIR I and II regions from 750 to 1500 nm has been met with limited success. Here, it is reported that a subnano Te cluster with a characteristic configuration different from that of the ion state may fill the aforementioned gap. Further, a strategy is proposed for the in situ generation and stabilization of Te clusters by tuning the cluster evolution in glass. A novel active photonic glass embedded with a Te cluster is fabricated; it exhibits intense and broadband short-wave NIR luminescence with a central wavelength at 1030 nm and a bandwidth exceeding 330 nm. Interestingly, the glass exhibited a full visible-spectrum conversion ability from 300 to 800 nm. The application of this unique broadband excitation feature for night vision and tissue penetration is demonstrated using a smartphone as the excitation source. These findings demonstrate a fundamental principle of cluster design in glass for creating new properties and provide a new direction for developing novel cluster-derived functional composite materials.

Ln(III) Complexes Embedded in Biocompatible PLGA Nanoparticles as Potential Vis-to-NIR Optical Probes.

In this contribution, we present the spectroscopic study of two NIR emitting hydrophobic heteroleptic (R,R)-YbL1(tta) and (R,R)-NdL1(tta) complexes (with tta = 2-thenoyltrifluoroacetonate and L1 = N,N'-bis(2-(8-hydroxyquinolinate)methylidene)-1,2-(R,R or S,S)-cyclohexanediamine), both in methanol solution and embedded in water dispersible and biocompatible poly lactic-co-glycolic acid (PLGA) nanoparticles. Thanks to their absorption properties in a wide range of wavelengths extending from the UV up to the blue and green visible regions, the emission of these complexes can be effectively sensitized using visible radiation, which is much less harmful to tissues and skin than the UV one. The encapsulation of the two Ln(III)-based complexes in PLGA allows us to preserve their nature, making them stable in water and to test their cytotoxicity on two different cell lines, with the aim of using them in the future as potential bioimaging optical probes.

Thermosensitive visible-light-excited visible-/NIR-luminescent complexes with lanthanide sensitized by the π-electronic system through intramolecular H-bonding.

Visible-luminescent lanthanide (LnL) complexes with a highly planar tetradentate ligand were successfully developed for a visible-light solid-state excitation system. L was designed by using two 2-hydroxy-3-(2-pyridinyl)-benzaldehyde molecules bridged by ethylenediamine, which was then coordinated to a series of Ln ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Yb). From the measurement of single-crystal X-ray analysis of EuL, two phenolic O atoms and two imine N atoms in L were coordinated to the Eu ion, and each π-electronic system took coplanar with the edged-pyridine moiety through an intramolecular hydrogen bond. The enol group on the phenolic skeleton changed to the keto form, and the pyridine was protonated. Thus, intramolecular proton transfer occurred in L after the complexation. Other complexes take isostructure. The space group is P-1, and the c-axis shrinks with decreasing temperature without a phase transition in EuL. The yellow color caused by the planar structure of L can sensitize ff emission by visible light, and the luminescence color of each complex depends on central Ln ions. Furthermore, a phosphorescence band also appeared at rt with ff emission in LnL. Drastic temperature dependence of luminescence was clarified quantitatively.

Studies into exfoliation and coating of Egyptian blue in methanol for application to the detection of latent fingermarks.

We have recently demonstrated that coated exfoliated Egyptian blue powder is effective for detecting latent fingermarks on a range of highly-patterned non-porous and semi-porous surfaces. In this extension of that work, we present our studies into an alternative approach to prepare exfoliated Egyptian blue coated with cetrimonium bromide and Tween® 20 using a simpler technique. The quality of the latent fingermarks developed with these exfoliated powders and the commercial powder were compared in acomprehensive study. Depletion series of natural fingermarks from a wide range of donors (12 males and females) deposited on non-porous (glass slides) and semi-porous (Australian banknotes) surfaces were used in this study. Enhancement in the performance of the coated exfoliated particles compared to the commercial powder was observed, particularly in the case of aged fingermarks and polymer banknotes as challenging substrates.

Boltzmann- and Non-Boltzmann-Based Thermometers in the First, Second and Third Biological Windows for the SrF2:Yb3+, Ho3+ Nanocrystals Under 980, 940 and 915 nm Excitations.

Spectrally determination of temperature based on the lanthanide-doped nanocrystals (NCs) is a vital strategy to noninvasively measure the temperature in practical applications. Here, we synthesized a series of SrF2:Yb3+/Ho3+ NCs and simultaneously observed the efficient visible upconversion luminescence (UCL) and near-infrared (NIR) downconversion luminescence (DCL) under 980, 940 and 915 nm excitations. Subsequently, these NCs were further utilized for thermometers based on the Boltzmann (thermally coupled levels, TCLs) and non-Boltzmann (non-thermally coupled levels, NTCLs) of Ho3+ ions in the first (~ 650 nm), second (~ 1012 nm) and third (~ 2020 nm) biological windows (BW-I, BW-II and BW-III) under tri-wavelength excitations. The thermometric parameters including the relative sensitivity ([Formula: see text]) and temperature uncertainty ([Formula: see text]) are quantitatively determined on the I648/I541 (BW-I), I1186/I1012 (BW-II), and I1950/I2020 (BW-III) transitions of Ho3+ ions in the temperature range of 303-573 K. Comparative experimental results demonstrated that the thermometer has superior performances.

Upconverting NIR-to-NIR LuVO4:Nd3+/Yb3+ Nanophosphors for High-Sensitivity Optical Thermometry.

Accurate contactless thermometry is required in many rapidly developing modern applications such as biomedicine, micro- and nanoelectronics, and integrated optics. Ratiometric luminescence thermal sensing attracts a lot of attention due to its robustness toward systematic errors. Herein, a phonon-assisted upconversion in LuVO4:Nd3+/Yb3+ nanophosphors was successfully applied for temperature measurements within the 323-873 K range via the luminescence intensity ratio technique. Dual-activating samples were obtained by codoping and mixing single-doped nanopowders. The effect of the type of dispersion system and the Yb3+ doping concentration was studied in terms of thermometric performances. The relative thermal sensitivity reached a value of 2.6% K-1, while the best temperature resolution was 0.2 K. The presented findings show the way to enhance the thermometric characteristics of contactless optical sensors.

A turn-on NIR fluorescence sensor for gossypol based on Yb-based metal-organic framework.

The development of analytical method for selective and sensitive detection of gossypol (Gsp), an extraction from the cotton plants, is important but still challenging in food safety and medical field. Herein, we reported a turn-on near infrared (NIR) fluorescence detection strategy for Gsp based on a metal-organic framework (MOF), QBA-Yb, which was prepared from 4,4'-(quinolone-5, 8-diyl) benzoate with Yb(NO3)3·5H2O by solvothermal synthesis. The Gsp acted as another "antenna" to sensitize the luminescence of Yb3+, leading to the turn-on NIR emission upon 467 nm excitation. As Gsp concentration increased, the NIR emission at 973 nm enhanced gradually, thus enabling highly sensitive Gsp detection in a turn-on way. The experiment and theoretical calculation results revealed the presence of strong hydrogen bonds between Gsp molecules and the MOF skeleton. The developed QBA-Yb probe showed excellent characteristics for detection of Gsp molecules, accompanied by wide linear range (5-160 µg/mL), low detection limit (0.65 µg/mL) and short response time (within 10 min). We have further demonstrated that the QBA-Yb probe was successfully applied for the determination of Gsp in real samples of cottonseeds.

Switchable up and down-conversion luminescent properties of Nd(III)-nanopaper for visible and near-infrared anti-counterfeiting.

A series of lanthanide-based nanopaper (Nd-nanopaper) was synthesized via a neodymium organic framework (Nd-MOFs)-grafted TEMPO-oxidized cellulose nanofibrils (tCNF) using a solvothermal reaction. Not using the traditional down-conversion visible emissions of anti-counterfeiting techniques, this Nd-nanopaper achieved down-conversion near-infrared (NIR) and up-conversion visible emissions. The down-conversion luminescent property of these Nd-nanopapers exhibited characteristic NIR luminescence (λEm = 1080 nm) of Nd3+ ions with 311 nm excitation, undergoing an "antenna" effect. In contrast, the up-conversion visible light emission (λEm =450 nm) of Nd-nanopaper was detected under 580 nm excitation. The mechanism of up-conversion fluorescence was ascribed to excited-state absorption and energy transfer up-conversion. Interestingly, Nd-nanopaper induced both up and down-conversions for visible and NIR emissions that were completely devoid of the interference from fluorescent brighteners and background fluorescence. These switchable up and down-conversion fluorescent Nd-nanopapers with visible and NIR dual emissions or dual channels could be applied in high level anti-counterfeiting applications.

DNA Intercalating Near-Infrared Luminescent Lanthanide Complexes Containing Dipyrido[3,2-a:2',3'-c]phenazine (dppz) Ligands: Synthesis, Crystal Structures, Stability, Luminescence Properties and CT-DNA Interaction.

In order to create near-infrared (NIR) luminescent lanthanide complexes suitable for DNA-interaction, novel lanthanide dppz complexes with general formula [Ln(NO3)3(dppz)2] (Ln = Nd3+, Er3+ and Yb3+; dppz = dipyrido[3,2-a:2',3'-c]phenazine) were synthesized, characterized and their luminescence properties were investigated. In addition, analogous compounds with other lanthanide ions (Ln = Ce3+, Pr3+, Sm3+, Eu3+, Tb3+, Dy3+, Ho3+, Tm3+, Lu3+) were prepared. All complexes were characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction analysis of the complexes (Ln = La3+, Ce3+, Pr3+, Nd3+, Eu3+, Er3+, Yb3+, Lu3+) showed that the lanthanide's first coordination sphere can be described as a bicapped dodecahedron, made up of two bidentate dppz ligands and three bidentate-coordinating nitrate anions. Efficient energy transfer was observed from the dppz ligand to the lanthanide ion (Nd3+, Er3+ and Yb3+), while relatively high luminescence lifetimes were detected for these complexes. In their excitation spectra, the maximum of the strong broad band is located at around 385 nm and this wavelength was further used for excitation of the chosen complexes. In their emission spectra, the following characteristic NIR emission peaks were observed: for a) Nd3+: 4F3/2 → 4I9/2 (870.8 nm), 4F3/2 → 4I11/2 (1052.7 nm) and 4F3/2 → 4I13/2 (1334.5 nm); b) Er3+: 4I13/2 → 4I15/2 (1529.0 nm) c) Yb3+: 2F5/2 → 2F7/2 (977.6 nm). While its low triplet energy level is ideally suited for efficient sensitization of Nd3+ and Er3+, the dppz ligand is considered not favorable as a sensitizer for most of the visible emitting lanthanide ions, due to its low-lying triplet level, which is too low for the accepting levels of most visible emitting lanthanides. Furthermore, the DNA intercalation ability of the [Nd(NO3)3(dppz)2] complex with calf thymus DNA (CT-DNA) was confirmed using fluorescence spectroscopy.

One Nanoscale Zn(II)-Nd(III) Complex With Schiff Base Ligand: NIR Luminescent Sensing of Anions and Nitro Explosives.

One Zn-Nd complex [Zn2Nd4L2(OAc)10(OH)2(CH3OH)2] (1) was synthesized from Schiff base ligand bis(3-methoxysalicylidene)ethylene-1,2-phenylenediamine (H2L). 1 shows nanoscale rectangular structure with sizes of about 0.8 × 1.1 × 2.8 nm. 1 exhibits typical near-infrared luminescence of Nd(III) under the excitation of UV-visible light. Further study shows that the complex displays luminescent response behavior to anions and nitro explosives, especially with high sensitivity to H2 PO 2 - and 2,4,6-trinitrophenol.

Enhancing Singlet Oxygen Generation in Conjugates of Silicon Nanocrystals and Organic Photosensitizers.

Silicon nanocrystals (SiNCs) are regarded as a green and environmentally friendly material when compared with other semiconductor nanocrystals. Ultra-small SiNCs (with the size 4.6-5.2 nm) demonstrate strong UV absorption and photoluminescence in the near infrared (NIR) range with the high photoluminescence quantum yield (PLQY) up to 60%. In contrast to nanoporous silicon, ultra-small SiNCs do not possess an intrinsic ability to generate singlet oxygen (1O2). However, we demonstrate that SiNC-dye conjugates synthesized via microwave assistant hydrosilylation reaction produce 1O2 with moderate quantum yield (ΦΔ) up to 27% in cyclohexane. These interesting results were obtained via measurements of singlet oxygen phosphorescence at 1,270 nm. SiNCs play an important role in the production of singlet oxygen as SiNCs harvest UV and blue radiation and transfer absorbed energy to a triplet state of the attached dyes. It increases the population of the triplet states and leads to the enhancement of the singlet oxygen generation. Simultaneously, the SiNC-dye conjugates demonstrate NIR luminescence with the PLQY up to 22%. Thus, the luminescence behavior and photosensitizing properties of the SiNC-dye conjugates can attract interest as a new multifunctional platform in the field of bio-applications.

Bimodal Nd-Doped LuVO4 Nanoprobes Functionalized with Polyacrilic Acid for X-Ray Computed Tomography and NIR Luminescent Imaging.

Uniform Nd3+-doped LuVO4 nanophosphors have been synthesized for the first time in literature by using a poliol-based method at 120 °C from Nd3+ and vanadate precursors. After optimizing the Nd doping level, these phosphors present intense luminescence in the near-infrared biological windows. The X-ray attenuation capacity of the optimum nanophosphor has been found to be higher than that of a commercial X-ray computed tomography contrast agent. After surface coating with polyacrylic acid, such nanoparticles present high colloidal stability in physiological pH medium and high cell viability. Because of these properties, the developed Nd3+-doped LuVO4 nanoparticles have potential applications as a bimodal probe for NIR luminescent bioimaging and X-ray computed tomography.

Visualization of Fingermarks Deposits on Untreated Thermal Paper Exploiting the Near Infrared Luminescence.

Thermal paper is widely used as a print medium for different applications but it constitutes a tricky substrate for fingermark visualization. An earlier work (J Forensic Sci 2015;60:1034) reported how to visualize fingermarks on untreated thermal paper by illuminating the item with a UV-A light source. In the present paper, the potential of the near infrared (NIR) luminescence has been tested on thermal paper compared to the mentioned method. A controlled study was carried out utilizing eccrine enriched fingermarks. The promising outcomes obtained were further confirmed by performing a pseudo-operational trial. Data clearly showed that the use of the NIR filter gave better results. Finally, preliminary tests suggested a different mechanism of reaction induced by fingermarks with respect to the one behind the thermal printing. Thus, NIR luminescence represents a refinement to the suite of optical examination processes, including the potential to increase the number of marks recovered in a noncontact, nondestructive way.

Near-Infrared Luminescent Ternary Ag3 SbS3 Quantum Dots by in situ Conversion of Ag Nanocrystals with Sb(C9 H19 COOS)3.

Differently from the normal three single precursor method to produce colloidal ternary quantum dots (QDs), herein ternary Ag3 SbS3 quantum dots (QDs) with efficient near-infrared (NIR) luminescence have been prepared by a new facile in situ conversion of Ag nanocrystals (NCs) with a binary Sb/S organic precursor Sb(C9 H19 COOS)3 under low temperature. The unprecedented construction evolution from Ag NCs to Ag3 SbS3 /Ag hetero-structure and final monodisperse Ag3 SbS3 QDs has been demonstrated. These novel Ag3 SbS3 QDs exhibit efficient NIR emission at ≈1263 nm and possess high colloidal stability.

Near-infrared emissive lanthanide hybridized nanofibrillated cellulose nanopaper as ultraviolet filter.

The lanthanide complexes [Yb(fac)3(H2O)2, Yb(tta)3(H2O)2, Nd(tta)3(H2O)2] functionalized nanofibrillated cellulose (Ln-NFC) nanopapers with near-infrared (NIR) luminescence and high transparency are rapidly fabricated after solvent exchange using a simple suction filtration film-making method. The effects of NFC and lanthanide complexes content on their photophysical properties of Ln-NFC nanopapers and their mechanism of UV filters are fully investigated. With increasing lanthanide complexes content in the Ln-NFC nanopaper, their transmittances are gradually decreased while their NIR luminescences are obviously increased. Yb-fac NFC nanopaper has high UVB block rate at 298 nm, whereas the high UVA block ratio of Ln-tta NFC nanopaper is observed at 345 nm. Ln-NFC nanopapers show a much higher photostability without decomposition under UV irradiation at 365 nm over 5 h. The emission spectra of the Ln-NFC nanopaper process the NIR luminescence of the corresponding lanthanide ions through the efficient triplet-triplet energy transfer process. Ln-NFC nanopapers can bring a brilliant future for UV filters, labeling fields and marking soft materials application.

Phonon Confinement Induced Non-Concomitant Near-Infrared Emission along a Single ZnO Nanowire: Spatial Evolution Study of Phononic and Photonic Properties.

The impact of mixed defects on ZnO phononic and photonic properties at the nanoscale is only now being investigated. Here we report an effective strategy to study the distribution of defects along the growth direction of a single ZnO nanowire (NW), performed qualitatively as well as quantitatively using energy dispersive spectroscopy (EDS), confocal Raman-, and photoluminescence (PL)-mapping technique. A non-concomitant near-infrared (NIR) emission of 1.53 ± 0.01 eV was observed near the bottom region of 2.05 ± 0.05 µm along a single ZnO NW and could be successfully explained by the radiative recombination of shallowly trapped electrons V_O^(**) with deeply trapped holes at V_Zn^''. A linear chain model modified from a phonon confinement model was used to describe the growth of short-range correlations between the mean distance of defects and its evolution with spatial position along the axial growth direction by fitting the E2H mode. Our results are expected to provide new insights into improving the study of the photonic and photonic properties of a single nanowire.