A Novel Near-Infrared Ytterbium Complex [Yb(DPPDA)2](DIPEA) with Φ = 0.46% and τobs = 105 μs

The luminescent performances of near-infrared (NIR) lanthanide (Ln) complexes were restricted greatly by vibration quenching of X-H (X = C, N, O) oscillators, which are usually contained in ligands and solvents. Encapsulating Ln³⁺ into a cavity of coordination atoms is a feasible method of alleviating this quenching effect. In this work, a novel ytterbium complex [Yb(DPPDA)₂](DIPEA) coordinated with 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPDA) was synthesized and characterized by FT-IR, ESI-MS and elemental analysis. Under the excitation of 335 nm light, [Yb(DPPDA)₂](DIPEA) showed two emission peaks at 975 and 1011 nm, respectively, which were assigned to the characteristic ²F_5/2 → ²F_7/2 transition of Yb³⁺. Meanwhile, this ytterbium complex exhibited a plausible absolute quantum yield of 0.46% and a luminescent lifetime of 105 μs in CD₃OD solution. In particular, its intrinsic quantum yield was calculated to be 12.5%, and this considerably high value was attributed to the near-zero solvent molecules bound to Yb³⁺ and the absence of X-H oscillators in the first coordination sphere. Based on experimental results, we further proposed that the sensitized luminescence of [Yb(DPPDA)₂](DIPEA) occurred via an internal redox mechanism instead of an energy transfer process.

Enhanced Near-Infrared Emission from Eight-Coordinate vs Nine-Coordinate YbIII Complexes Using 2-(5-Methylpyridin-2-yl)-8-hydroxyquinoline

Enhanced near-infrared (NIR) luminescence from two structurally related heterobinuclear Na^IYb^III eight-cooridnate and heterobinuclear Yb^IIINa^I eight-coordinate (CN = 8) complexes is reported and compared to a nine-coordinate (CN = 9) homoleptic complex. For the heteroleptic complex, [Yb(MPQ₂)(acac)], the Yb^III cation is coordinated to two tridentate 2-(5-methylpyridin-2-yl)-8-quinolinate (MPQ) anions, with a bidentate acetylacetonate (acac) anion completing the coordination sphere. Instead, the heterobinuclear [NaYb(MPQ)₄] complex comprises a total of four anionic MPQ ligands, two of which exhibit κ³-coordination to the Yb^III cation. The remaining two MPQ anions are unidentate toward the lanthanide and form μ₂-bridges via the deprotonated quinolinate oxygens to a bound Na^I cation which is also coordinated to the remaining nitrogen donor atoms. The structural properties of these complexes were evaluated by single-crystal X-ray diffraction (SXRD), continuous shape measure (CShM) analysis, and ¹H NMR spectroscopy using a diamagnetic Lu^III analogue. The corresponding photophysical properties were examined in CH₂Cl₂ solution by using absorption and emission spectroscopy. For both the complexes, characteristic Yb^III emission is observed at ca. 980 nm, with recorded photoluminescence quantum yields (Φ_obs) and NIR luminescence lifetimes (τ_obs) of 2.0% and 14.0 μs vs 1.5% and 11.6 μs for the [NaYb(MPQ)₄] and [Yb(MPQ)₂(acac)] complexes, respectively. Interestingly, the eight-coordinate Yb^III complexes both have higher photoluminescence quantum yields when compared to the homoleptic [Yb(MPQ)₃] complex, which has a reported quantum yield of 1.0% and a NIR lifetime determined herein of 13.3 μs under identical conditions. These results have been rationalized by considering the overall efficiency of the ligand-centered sensitization process (η_sens = Φ_isc × Φ_eet), together with subsequent radiative (k_r) and nonradiative (k_nr) deactivation of the Yb^III cation. Moreover, the efficiency of the intersystem crossing (Φ_isc) and electronic energy transfer (Φ_eet) processes involved in the antennae effect have been quantified for the new complexes using a combination of nanosecond and femtosecond transient absorption techniques and have been compared to our previous results using [Ln(MPQ)₃] complexes with Ln = Yb and Lu.

Holmium(iii) molecular nanomagnets for optical thermometry exploring the luminescence re-absorption effect

Coordination complexes of lanthanide(3+) ions can combine Single-Molecule Magnetism (SMM) with thermally modulated luminescence applicable in optical thermometry. We report an innovative approach towards high performance SMM-based optical thermometers which explores tunable anisotropy and the luminescence re-absorption effect of HoIII complexes. Our concept is shown in dinuclear cyanido-bridged molecules, {[HoIII(4-pyridone)4(H2O)2][MIII(CN)6]}·nH2O (M = Co, 1; Rh, 2; Ir, 3) and their magnetically diluted analogues, {[HoIII x YIII 1-x (4-pyridone)4(H2O)2][MIII(CN)6]}·nH2O (M = Co, x = 0.11, 1@Y; Rh, x = 0.12, 2@Y; Ir, x = 0.10, 3@Y). They are built of pentagonal bipyramidal HoIII complexes revealing the zero-dc-field SMM effect. Experimental studies and the ab initio calculations indicate an Orbach magnetic relaxation with energy barriers varying from 89.8 to 86.7 and 78.7 cm-1 K for 1, 2, and 3, respectively. 1-3 also differ in the strength of quantum tunnelling of magnetization which is suppressed by hyperfine interactions, and, further, by the magnetic dilution. The YIII-based dilution governs the optical properties as 1-3 exhibit poor emission due to the dominant re-absorption from HoIII while 1@Y-3@Y show room-temperature blue emission of 4-pyridone. Within ligand emission bands, the sharp re-absorption lines of the HoIII electronic transitions were observed. Their strong thermal variation was used in achieving highly sensitive ratiometric optical thermometers whose good performance ranges, lying between 25 and 205 K, are adjustable by using hexacyanidometallates. This work shows that HoIII complexes are great prerequisites for advanced opto-magnetic systems linking slow magnetic relaxation with unique optical thermometry exploiting a luminescence re-absorption phenomenon.

Enhanced near-infrared luminescence in Ln2Cd2 (Ln = Nd, Yb) heterotetranuclear complexes

Due to the effect of the combination of the rigid structure and synergistic interactions of two ligands on energy transfer, the Cd–Ln complexes show excellent NIR luminescence properties with the QYs reaching 0.34% for Nd³⁺ and 2.13% for Yb³⁺.

Efficient Ytterbium Near-Infrared Luminophore Based on a Nondeuterated Ligand

A novel molecular ytterbium complex is reported with a new tetradentate ligand based on the 2,2'-bipyridine-6,6'-dicarboxylic acid scaffold. The photophysical properties are investigated, especially with respect to near-infrared luminescence. The ytterbium complex shows a rather high absolute luminescence quantum yield of Φ = 3.0% and a luminescence lifetime of τ_obs = 72 μs at room temperature in CD₃OD solution.

Near-infrared emissive Er(iii) and Yb(iii) molecular nanomagnets in metal–organic chains functionalized by octacyanidometallates(iv)

Photoluminescent single-molecule magnets are formed in lanthanide(pyrazine N,N′-dioxide) chains with octacyanidometallate(iv) coordination branches playing a crucial role in sensitized NIR emission.

Synthesis and photoluminescence properties of europium(III) complexes sensitized with β-diketonato and N, N-donors ancillary ligands

Synthesis of three new europium(III) complexes with 1,3-[bis(4-methoxyphenyl)]propane-1,3-dionato (HBMPD) ligand and ancillary ligands such as 2,2'-biquinoline (biq) or neocuproine (neo) has been reported in this report. The synthesized complexes were characterized by IR (infrared), ¹H and ¹³C NMR (nuclear magnetic resonance) spectroscopy, CHN (carbon, hydrogen and nitrogen) elemental analysis, XRD (X-ray diffraction), TGA (thermogravimetric analysis) and photoluminescence (PL) spectroscopy. The emission spectra of europium(III) complexes displayed both the low intensity ⁵D_1-3→⁷F_0-3 transitions in 410-560nm blue-green region and high intensity characteristic ⁵D₀→⁷F_0-3 transitions in 575-640nm orange-red region correspond to the emission of ancillary ligands and europium ion respectively, which can lead to white luminescence due to integration of blue, green and red color emissions. The photoluminescence investigations indicate that the absorbed energy of the HBMPD ligand transferred to the central europium(III) ion in an efficient manner, which clearly explained by antenna effect. The excellent results of thermal behavior and photophysical properties like luminescence spectra, CIE (Commission Internationale Eclairage) chromaticity coordinates, luminescence decay curves and high quantum efficiency of the complexes make them a promising component of the white light-emitting diodes in display devices.

Bright Photon Upconversion on Composite Organic Lanthanide Molecules through Localized Thermal Radiation

Converting low-energy photons via thermal radiation can be a potential approach for utilizing infrared (IR) photons to improve photovoltaic efficiency. Lanthanide-containing materials have achieved great progress in IR-to-visible photon upconversion (UC). Herein, we first report bright photon, tunable wavelength UC through localized thermal radiation at the molecular scale with low excitation power density (<10 W/cm²) realized on lanthanide complexes of perfluorinated organic ligands. This is enabled by engineering the pathways of nonradiative de-excitation and energy transfer in a composite of ytterbium and terbium perfluoroimidodiphosphinates. The IR-excited thermal UC and wavelength control is realized through the terbium activators sensitized by the ytterbium sensitizers having high luminescence efficiency. The metallic molecular composite thus can be a potential energy material in the use of the IR solar spectrum for thermal photovoltaic applications.

Sensitization, energy transfer and infra-red emission decay modulation in Yb3+-doped NaYF4 nanoparticles with visible light through a perfluoroanthraquinone chromophore

Infra-red emission (980 nm) of sub 10 nm Yb3+-doped NaYF4 nanoparticles has been sensitized through the excitation of 2-hydroxyperfluoroanthraquinone chromophore (1,2,3,4,5,6,7-heptafluro-8-hydroxyanthracene-9,10-dione) functionalizing the nanoparticle surface. The sensitization is achieved with a broad range of visible light excitation (400-600 nm). The overall near infra-red (NIR) emission intensity of Yb3+ ions is increased by a factor 300 as a result of the broad and strong absorption of the chromophore compared with ytterbium's intrinsic absorption. Besides the Yb3+ NIR emission, the hybrid composite shows organic chromophore-based visible emission in the orange-red region of the spectrum. We observe the energy migration process from the sensitized Yb3+ ions at the surface to those in the core of the particle using time-resolved optical spectroscopy. This highlights that the local environments for emitting Yb3+ ions at the surface and center of the nanoparticle are not identical, which causes important differences in the NIR emission dynamics. Based on the understanding of these processes, we suggest a simple strategy to control and modulate the decay time of the functionalized Yb3+-doped nanoparticles over a relatively large range by changing physical or chemical parameters in this model system.

Optical Features of Efficient Europium(III) Complexes with β-Diketonato and Auxiliary Ligands and Mechanistic Investigation of Energy Transfer Process

Two new europium (III) complexes have been synthesized with 1,3-[bis(4-methoxyphenyl)]propane-1,3-dionato (HBMPD) as main ligand and 2,2'-bipyridyl (bipy) or 1,10-phenanthroline (phen) as an auxiliary ligand. The main ligand HBMPD has been synthesized by ecofriendly microwave approach and complexes by solution precipitation method. The resulting materials are characterized by IR, (1)H-NMR, elemental analysis, X-ray diffraction, UV-visible and TG-DTG techniques. The photoluminescence (PL) spectroscopy depicts the detail analysis of photophysical properties of the complexes, their results show that the ligand interact with Eu (III) ion which act as antenna and transfers the absorbed energy to the central europium(III) ion via sensitization process efficiently. As a consequence of this interaction, these materials exhibit excellent luminescent intensity, long decay time (τ), high quantum efficiency (η) and Judd-Ofelt intensity parameter (Ω2). The CIE coordinates fall under the deep red region, matching well with the NTSC (National Television Standard Committee) standard. Hence, these highly efficient optical materials can be used as a red component in organic light emitting diodes (OLEDs) and full color flat panel displays.

NIR luminescence of a series of benzoyltrifluoroacetone erbium complexes

A series of five benzoyltrifluoroacetone Er(iii) complexes with various azacyclo-auxiliary ligands exhibit unique NIR luminescence and may be potential materials in optical amplifiers.

Visible-Range Sensitization of Er(3+)-Based Infrared Emission from Perfluorinated 2-Acylphenoxide Complexes

Five new fully fluorinated acylphenoxide ligands, which are aromatic analogues of β-diketonates, provide visible photosensitization of the Er(3+4)I13/2 → (4)I15/2 emission at ∼1540 nm (of interest for telecommunications) via the "antenna effect", as observed in Cs[ErL4] compounds. Depending on the chemical functionalization, the excitation wavelength can be tuned in the 400-650 nm range. Decay times for the solids are in the range of 7-16 μs, proving that the complexes can be of interest for a number of optoelectronic and photonic applications.

Organo-erbium systems for optical amplification at telecommunications wavelengths

Modern telecommunications rely on the transmission and manipulation of optical signals. Optical amplification plays a vital part in this technology, as all components in a real telecommunications system produce some loss. The two main issues with present amplifiers, which rely on erbium ions in a glass matrix, are the difficulty in integration onto a single substrate and the need of high pump power densities to produce gain. Here we show a potential organic optical amplifier material that demonstrates population inversion when pumped from above using low-power visible light. This system is integrated into an organic light-emitting diode demonstrating that electrical pumping can be achieved. This opens the possibility of direct electrically driven optical amplifiers and optical circuits. Our results provide an alternative approach to producing low-cost integrated optics that is compatible with existing silicon photonics and a different route to an effective integrated optics technology.

Anion-dependent self-assembly of near-infrared luminescent 24- and 32-metal Cd-Ln complexes with drum-like architectures

Two series of 4d-4f clusters [Ln8Cd24L12(OAc)48] and [Ln6Cd18L9Cl8(10)(OAc)28(26)] (Ln = Nd, Gd, Er, and Yb) with novel drum-like structures were prepared using a flexible Schiff base ligand. Their NIR luminescence properties were determined.