Intense Near-infrared Emission Research Articles

Regulating the broadband near-infrared emission of Eu2+-doped Ca3Sc2Si3O12 phosphors through constructing defect for diversified applications

Near-infrared (NIR) emitting phosphors exhibit admirable photophysical performances which enable their promising application in various fields, whereas the development of a broad NIR emitting phosphors with high performance is still a challenge. Herein, series of Ca2.94Sc2-xSi3O12:0.06Eu2+ (Ca3Sc2-xSi3O12:Eu2+) garnet NIR emitting phosphors were designed and the defect engineering was used to regulate the luminescence properties. Upon 520 nm excitation, the resulting phosphors emit intense broad NIR emission peaking at 876 nm arising from Eu2+. Through decreasing Sc3+ content, the defect (i.e. Sc3+ vacancy) was formed and it can efficiently increase the luminescence characteristics of designed compounds, in which Ca3Sc1.9Si3O12:Eu2+ phosphor possess the strongest intensity. Moreover, based on density functional theory, theoretical calculation was performed to verify the existence of Sc3+ vacancy in studied samples. Furthermore, the fluorescence intensity and full-width at half maximum (FWHM) were all dependent on temperature. Through analyzing the temperature-dependent FWHM value, it was found that the maximum absolute and relative sensitivities were 42.61 % and 0.16 % K−1, respectively. Via utilizing the synthesized phosphors as NIR converters, a new NIR light-emitting diode (LED) was packaged and it presented potential applications in food detection, bioimaging, NIR solid-state lighting and night-vision. Our findings proposed an efficient strategy to manipulate the luminescence properties of NIR emitting phosphors via constructing defect so as to realize their vivid applications.

LiGa5O8: Fe3+: A novel and super long near-infrared persistent material

The development of near-infrared persistent materials has become a popular research area owing to their diverse applications. However, the efficient emitters for these materials remains limited. Cr3+ is one of the strongest candidates, since it displays better performance with long duration. Fe3+ is a potential nontoxic alternative although its performance is not as good as Cr3+. In this study, a series of novel Fe3+-activated near-infrared long afterglow phosphors of LiGa5O8 have been prepared. Photoluminescence and persistence luminescence spectroscopy have been collected to investigate its optical properties. Furthermore, the trap characteristics of the samples were systematically analyzed by collecting thermoluminescence signals. The results indicate that there is an intense near-infrared emission centered at 675 nm and a long afterglow duration of more than 28 h for the optimized sample. Trap analysis indicates that oxygen vacancy defects are not the primary reasons for the extraordinarily long afterglow in these samples. Instead, the interaction of other trap types, such as antisite defects, probably contribute to the excellent afterglow properties of the material.

Highly thermally stable SrLaMgTaO6: Cr3+ double-perovskite phosphors for night-vision applications

In this study, a novel thermally stability broad-band near-infrared (NIR) phosphor SrLaMgTaO6 (SLMT): Cr3+ was research, along with investigations into its structure, morphology, PL spectra and crystal field strengths. Additionally, the mechanism of concentration quenching in these samples was investigated, which primarily attributed to electric multipolar interactions notably. Surprisingly, the NIR emission intensity at 423 K remains 80.4 % of its room temperature intensity, which shows its outstanding thermal stability. To comprehend the mechanism behind the exceptional thermal stability of luminescence, a comprehensive analysis in this material was conducted, focusing on factors such as the crystal field strength of the host material and the electron-phonon coupling (EPC) effect. Subsequently, an optimized phosphor coating was applied to a 470 nm LED chip to get a NIR pc-LED device, which was evaluated for its performance. The research demonstrate that SLMT: Cr3+ phosphor is a promising NIR pc-LED.

Strategy of Charge Compensation for High-Performance Ni2+-Activated MgAl2O4 Spinel Near-Infrared Phosphor Synthesis via the Sol-Gel Combustion Method.

Near-infrared (NIR) phosphor conversion light-emitting diodes (pc-LEDs) have great application potential as NIR light sources in many fields such as food analysis, night vision illumination, and bioimaging for noninvasive medical diagnosis. In general, phosphors synthesized by a high-temperature solid-phase method have large particle sizes and have to be processed to fine powders by a grinding process, which may introduce surface defects and lower the luminous efficiency. Here, we report a sol-gel sintering method with ammonium nitrate and citric acid as the sacrificing agents to synthesize high purity, nanosized (less than 50 nm) Zr4+/Ni2+ codoped MgAl2O4 spinel NIR phosphors, in which MgAl2O4 spinel is the matrix, Ni2+ is the luminous center, and Zr4+ acts as the charge compensator. We systematically characterized the crystal structures and NIR luminescence properties of the Ni2+-doped MgAl2O4 and the Zr4+/Ni2+ codoped MgAl2O4. Under 390 nm light excitation, the emission spectrum of the Ni2+-doped MgAl2O4 phosphor covers 900-1600 nm, the half-peak width is 251 nm, and the peak position is located at 1230 nm. We demonstrated that by incorporating small amounts of Zr4+ as the charge compensator, the NIR emission intensity of the Zr4+/Ni2+ codoped MgAl2O4 nanosized phosphor was doubled over that of the Ni2+-doped MgAl2O4 phosphor. The optimal content of the charge compensator was 2 mol %. More importantly, the inclusion of Zr4+ led to a NIR phosphor with improved thermal stability in luminous properties, and the luminous intensity measured at 100 °C was 33.83% of that measured at room temperature (20 °C). This study demonstrates that NIR phosphor nanomaterials with high-purity and enhanced optical properties can be designed and synthesized through the charge compensation strategy by a sol-gel sintering method.

An efficient and thermally stable source with Cr3+ near-infrared luminescence for non-destructive testing applications

The quest for efficient and heat-resistant near-infrared (NIR) phosphors to create advanced smart NIR lighting sources continues to pose a significant challenge. This study introduces a new fluoride phosphor, Cr3+-doped Cs2NaScF6, wherein the Cs2NaScF6 host provides a weak crystal field suitable for Cr3+ doping. This arrangement allows the production of a broad NIR emission peaking at 797 nm, coupled with a notable internal quantum efficiency of 90.8 % when excited by 446 nm blue light. Meanwhile, due to the relatively mild electron-phonon coupling effect and a high activation energy within this phosphor, the overall NIR emission intensity at 150 °C sustains 81.8 % of its level at room temperature. This highlights exceptional thermal stability in photoluminescence performance. Combining the Cs2NaScF6:Cr3+ phosphor with a commercially available blue InGaN chip to construct a NIR light-emitting diode (LED) device, which exhibits efficient and stable NIR emission, making it suitable for non-destructive testing applications. These findings affirm that the Cs2NaScF6:Cr3+ phosphor can function as a promising candidate to fabricate high-performance device for NIR spectroscopy application.

Construction of novel Ag(0)-containing silver nanoclusters by regulating auxiliary phosphine ligands.

Controlled synthesis of metal clusters through minor changes in surface ligands holds significant interest because the corresponding entities serve as ideal models for investigating the ligand environment's stereochemical and electronic contributions that impact the corresponding structures and properties of metal clusters. In this work, we obtained two Ag(0)-containing nanoclusters (Ag17 and Ag32) with near-infrared emissions by regulating phosphine auxiliary ligands. Ag17 and Ag32 bear similar shells wherein Ag17 features a trigonal bipyramid Ag5 kernel while Ag32 has a bi-icosahedral interpenetrating an Ag20 kernel. Ag17 and Ag32 showed a near-infrared emission (NIR) of around 830 nm. Benefiting from the rigid structure, Ag17 displayed a more intense near-infrared emission than Ag32. This work provides new insight into the construction of novel superatomic silver nanoclusters by regulating phosphine ligands.

Incorporation of Eu3+ in ZnGa2O4:Ni2+ for improved NIR persistent luminescence located in second transparency window

AbstractIt is well known that near‐infrared (NIR) persistent phosphors have rather low absorption coefficients of biological tissues for NIR light. However, recent research shows that the phosphors emitting NIR lights in second NIR (NIR‐II, 1000–1350 nm) and third (NIR‐III, 1500–1800 nm) biological window have advantages over that in NIR‐I (650–900 nm). Although ZnGa2O4:Ni2+ outputs NIR emission and afterglow locatedin NIR‐II, the weak signal significant limits its application. In this work, persistent luminescent phosphors of ZnGa2O4:xNi2+, yEu3+ (x = 0–0.013, y = 0.01–0.06) (termed as ZEGN) were synthesized via a traditional high‐temperature solid‐state reaction, which feature a broad emission band in the NIR‐II window. The phosphors exhibit a broad NIR emission at about 1300 nm after ultraviolet (UV) or orange–red lights excitation, arising from the 3T2(3F) → 3A2(3F) transition of Ni2+. However, incorporation of Eu3+ ions, the NIR emission intensity significantly increases with the increase of Ni2+ ion concentration, reaching the maximum by 18 times at x = 0.005. Removing the light source, the sample still outputs intense NIR afterglow and red afterglow that can last over 500 s. It is noteworthy that the red afterglow of Eu3+ shows a dramatically decrease but the NIR afterglow increases with increasing the Ni2+ ion concentration, because of energy transfer. Under the excitation of 282‐nm UV light, the ZGEN sample exhibits a good thermal stability. The phosphor offers a promising application in biological imaging due to broadband NIR‐II light and afterglow.

Optical behaviors of Mn4+-modified cubic type ZnTiO3:Eu3+ nanocrystals: Application in optical thermometers based on fluorescence intensity ratio and lifetime

Cubic type ZnTiO3 nanophosphors were fabricated by using hydrothermal method. The photoluminescence behaviors of Eu3+/Mn4+ co-doped ZnTiO3 crystals and Mn4+-modified ZnTiO3:Eu3+ crystals were investigated. The red and near-infrared emissions assigned to Eu3+ and Mn4+ were observed at the excitation wavelength of 465 nm for Eu3+/Mn4+ co-doped ZnTiO3 crystals and Mn4+ modified ZnTiO3:Eu3+ crystals. Eu3+/Mn4+ co-doped ZnTiO3 crystals revealed the most intense near-infrared emission assigned to Mn4+. For Mn4+-modified ZnTiO3:Eu3+ crystals, the red emissions assigned to Mn4+ revealed an obvious enhancement with the concentration of Mn4+ increasing from 0.01 mol% to 0.1 mol%, and then revealed a concentration quenching behavior at the Mn4+ concentration of 0.5 mol% and 1 mol%. Under 465 nm excitation wavelength, the emission assigned to 2Eg → 4A2g of Mn4+ in ZnTiO3 revealed stronger temperature dependence compared with that assigned to 5D0 → 7F2 transition of Eu3+. Based on the fluorescence intensity ratio between Eu3+ and Mn4+, the maximum relative sensitivity of 3.15 %/K at 305 K for the 0.05 mol% Mn4+ modified ZnTiO3:Eu3+ was achieved, which was higher than that of 2.9 %/K for Eu3+/Mn4+ co-doping ZnTiO3 nanocrystals. Based on the lifetime of the emission of Mn4+, the highest relative sensitivity of 1.4 %/K was obtained in the 0.05 mol% Mn4+ modified ZnTiO3:Eu3+, which was lower than that based on fluorescence intensity ratio. It indicated that the surface modification by transition metals should improve the temperatures sensing performance and had potential applications in optical thermometers.

Egyptian Blue/gold nanocomposite supramarbles, a platform for IR emission enhancement

Nanotechnology manufacturing requires a unique skillset and access to that technology is not yet within the reach of many small businesses and startups. What if a specialty product could be offered as pellets or marbles, and this new platform enabled uniform nano-coatings readily handled by off the shelf standard manufacturing technologies? The platform – a supramarble (SM) – introduced in this work is a crosslinked polymer core with a coating (or corona) of hydrophobic micro- and nanoparticles. A photoactive 2-D nanoparticulate pigment, Egyptian Blue (EB) has gained tremendous popularity in sensing applications recently due to its intense near-infrared emission at ∼900 nm. Gold nanoparticles (AuNPs) have been reported to modify the spontaneous emission of other adjacent fluorophores in a remarkable way. By combining near-infrared emitting EB microparticles and AuNP decorated fumed silica (Au-FS) NPs as the corona of an SM, significant (4-fold) fluorescence enhancement is demonstrated in this work. A maximum in fluorescent intensity was shown at 70 wt% EB and 30 wt% Au-FS composite coating. The 4-fold enhancement was attributed to AuNPs’ generation of a localized electric field synergistically interacting with the fluorescent emission of EB. The influence of Au-FS on the original, intrinsic fluorescent emission wavelength of EB (∼900 nm) was also investigated.

Influence of Alkali Metal Ions on the Structural and Spectroscopic Properties of Sm3+-Doped Silicate Glasses

In the present work, the influence of alkali ions (Li, Na, K) on the structural and spectroscopic properties of silica glasses doped with Sm3+ was investigated. Infrared and Raman spectroscopy techniques were used to investigate the structural properties of the alkali silicate glasses. The optical absorption showed bands characteristic of Sm3+ ions in alkali silicate glasses, and this was investigated. The Judd–Ofelt theory was applied to evaluate the phenomenological intensity parameters (Ω2, Ω4, and Ω6) of the optical absorption measurements. The multi-channel visible and near infrared emission transitions originating from the 4G5/2-emitting state of the Sm3+ in alkali silicate glasses with a maximum phonon energy of ~1050 cm−1 were investigated. From the evaluated Judd–Ofelt parameters, radiative parameters such as spontaneous emission probabilities, radiative lifetimes, branching ratios, and stimulated emission cross-sections were calculated. The recorded luminescence spectra regions revealed intense green, orange, red, and near-infrared emission bands, providing new traces for developing tunable laser and optoelectronic devices.

Tetracyanobuta-1,3-diene (TCBD)-appended pyrrolopyrrole aza-BODIPYs as a panchromatic chromophore based on the push-pull strategy

Pyrrolopyrrole aza-BODIPY (PPAB), a dimeric BODIPY analogue containing a pyrrolopyrrole structure at the center, exhibits intense far-red and near-infrared (NIR) absorption and emission. Herein, tetracyanobuta-1,3-diene-appended PPABs (TCBD-PPABs) were synthesized by post-modification based on a [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethylene. Owing to the redshift of the PPAB absorption in the NIR region and the emergence of the intramolecular charge-transfer band in the visible region, TCBD-PPABs exhibit panchromatic absorption in the visible/NIR regions.

A Lipid Droplet-Specific NIR Fluorescent Probe with a Large Stokes Shift for In Vivo Visualization of Polarity in Contrast-Induced Acute Kidney Injury.

The research on lipid droplets (LDs) has attracted great attention in the field of biomedical science in recent years. LD malfunction is found to be associated with the development of acute kidney injury (AKI). To monitor this biological process and explain related pathological behavior, the development of excellent LD fluorescent probes with a polarity-sensitive character would provide a desirable strategy. Herein, we designed a new polarity-susceptible fluorescent probe named LD-B with LD targetability, which exhibits very weak fluorescence in highly polar solvents based on the twisted intramolecular charge transfer effect but enhanced fluorescence in low polar environments, enabling us to visualize polarity alteration. The probe LD-B also possesses the merits of intense near-infrared (NIR) emission, good photostability, large Stokes shift, low toxicity, faster metabolic rate, and wash-free ability; thereby, it would contribute to efficient LD fluorescence visualization application. Using LD-B via confocal laser scanning fluorescence imaging and a small-animal imaging system in vivo, we first manifested a prominent rise of LD polarity in contrast-induced AKI (CI-AKI), not only at the cellular level but also in animals in vivo. Furthermore, the in vivo studies suggest that LD-B could accumulate in the kidney. In addition, the normal cell lines (including kidney cells) exhibiting a greater polarity of LDs than the cancer cells have been demonstrated systemically. Altogether, our work presents an effective approach for the medical diagnosis of LDs related to CI-AKI and identification of potential therapeutic markers.

NIR enhancement induced by refractive index differences between noble metal particles and nanocrystals in glass-ceramics

The use of optically active ions doped into photonic media containing noble metals is an intriguing area of photoluminescence (PL) research. In this paper, we present a new approach using nickel ions doped into photonic glass ceramics (GCs) containing Au metal NCs. We exploit the unique PL properties of Ni2+ embedded in ZnAl2O4 nanocrystals (NCs). Under the same conditions, the Au-ZAO duplex samples exhibit 2–3 times higher near-infrared (NIR) emission intensity and higher absorption intensity compared to the samples without Au metal. We provide direct evidence of energy harvesting around NCs through numerical simulations. The significant NIR PL properties of Ni2+ in Au-ZAO GCs can be explained by the significant dielectric coefficient difference between the Au metal, the surrounding medium, and the ZAO NCs. Furthermore, the intense and broad emission spectra of our samples cover the entire second biological NIR region, which makes them particularly useful for biomedical applications.

An efficient strategy of charge compensation for Ni2+-activated SrTiO3 perovskite near-infrared phosphor toward optical imaging illumination

Near-infrared (NIR) light sources have great potential in applications such as optical imaging, non-destructive medical diagnosis, and non-visual lighting. Ni2+ activated phosphors as a class of newly discovered NIR emitting material shows broadband luminescent properties that covers NIR-II (1000–1600 nm) region which is relatively transparent and less scattering in tissues. However, it has shortcomings, such as low luminous efficiency and poor thermal stability that need to be improved. Here, we report the synthesis of new Ni2+-activated SrTiO3 perovskite-based broadband NIR phosphor by high-temperature solid-state reaction method, with M5+ (M = Ta, Sb, Nb, P) as the co-doping agent to compensate charges. By charge compensation, the new composition significantly improved the NIR emission intensity by 12 folds, increased the luminescence quantum efficiency from 7.9% to 19.7%, and improved the resistance to thermal quenching. We studied the synergistic effect of charge compensation on the luminescence performance of NIR phosphor by experimental and simulation approaches. We showed that co-doping of charge compensator improved NIR phosphors by eliminating electronic defects and introducing defect or distortion to lattice octahedra. We further demonstrate that NIR pc-LED can be made by packaging the optimized NIR phosphor with a UV LED chip. Its potential application in the field of optical imaging was discussed.

A Feasible Strategy for a Highly Efficient Thermally Activated Delayed Fluorescence Emitter Over 900 nm Based on Phenalenone Derivatives.

Near-infrared (NIR) organic light-emitting diodes (OLEDs) suffer from the low external electroluminescence (EL) quantum efficiency (EQE), which is a critical obstacle for potential applications. Herein, 1-oxo-1-phenalene-2,3-dicarbonitrile (OPDC) is employed as an electron-withdrawing aromatic ring, and by incorporating with triphenylamine (TPA) and biphenylphenylamine (BBPA) donors, two novel NIR emitters with thermally activated delayed fluorescence (TADF) characteristics, namely OPDC-DTPA and OPDC-DBBPA, are first developed and compared in parallel. Intense NIR emission peaks at 962 and 1003 nm are observed in their pure films, respectively. Contributed by the local excited (LE) characteristics in the triplet (T1 ) state in synergy with the charge transfer (CT) characteristics for the singlet (S1 ) state to activate TADF emission, the solution processable doped NIR OLEDs based on OPDC-DTPA and OPDC-DBBPA yield EL peaks at 834 and 906 nm, accompanied with maximum EQEs of 0.457 and 0.103 %, respectively, representing the state-of-the-art EL performances in the TADF emitter-based NIR-OLEDs in the similar EL emission regions so far. This work manifests a simple and effective strategy for the development of NIR TADF emitters with long wavelength and efficiency synchronously.

Structure, morphology, photonconversion and energy transfer characteristics of Er3+/Yb3+:BaYF5 nanocrystals synthesized by hydrothermal method for photovoltaics

Lanthanide doped nanocrystalline fluoride optical materials have been explored for diverse applications in the solar energy harvesting, industry, medical, forensic and biological fields because of high photoluminescence quantum yield and low phonon energy. In this manuscript, Er3+/Yb3+:BaYF5 nanocrystals were synthesized by hydrothermal process. These nanocrystals were investigated through X-ray diffraction (XRD), SEM/TEM, Raman, quantum yield, photoluminescence upconversion (UC) and downconversion (DC) studies. XRD patterns exhibited the cubic phase and no phase deviation with the addition of Er3+ and Yb3+ ions. The TEM images illustrate the cubic-like morphologies of the obtained nanocrystals. Raman spectrum unveils the characteristic vibrational bands with an intense band at 498 cm−1, which is considered the phonon energy of the BaYF5 matrix. Under 488 nm excitation, the near infrared (NIR) emission of Er3+ increases up to 5 mol% and then decreases for a 10 mol% doped sample. Photoluminescence DC quantum yield of Er3+/Yb3+:BaYF5 sample is measured by using integrating sphere in the visible region under 488 nm (Xe flash lamp) excitation, is 4.25%. Under 900 nm laser excitation, intense NIR emissions at 978 and 1550 nm corresponding to Yb3+ (2F5/2 → 2F7/2) and Er3+ (4I13/2 → 4I15/2) ions, respectively, were observed. With the increase of Yb3+ concentration, the NIR emissions of both Er3+ and Yb3+ increase to 5 mol% and then decrease to 10 mol%. The strength of green UC emission of Er3+ decreases with increase of Er3+ concentration, whereas it enhances with the rise of Yb3+ concentration under 980 nm laser excitation. Two-photon UC process is confirmed as the slopes of the green, and red intensities are 2 and 2. These nanocrystals exhibit intense UC and DC emissions under 980 nm and 480 nm, respectively, which can be suitable for improving the efficiency of solar cells.

Nd-doped NASICON-type nanophosphors for near-infrared excitation and emission

ABSTRACT Neodymium-doped phosphates, (Nd1-x Gd x )0.33Zr2(PO4)3 (0 ≤ x ≤ 1), were synthesized by co-precipitation. (Nd1-x Gd x )0.33Zr2(PO4)3 was obtained as a single-phase and was confirmed to be a NASICON-type structure consisting of a three-dimensional network of PO4 tetrahedra sharing corners with ZrO6 octahedra. The particle size of the (Nd1-x Gd x )0.33Zr2(PO4)3 samples was in the nanoscale, which is suitable for in vivo optical imaging. The (Nd1-x Gd x )0.33Zr2(PO4)3 samples showed characteristic luminescence corresponding to the f – f transitions of Nd3+. The highest emission intensity at 1072 nm with excitation at 824 nm was observed for (Nd0.75Gd0.25)0.33Zr2(PO4)3, which was 4.5 times higher than that of Nd0.33Zr2(PO4)3. The near-infrared (NIR) emission intensity of this nanophosphor was significantly higher than that of indocyanine green, which is actually used as an in vivo optical probe reagent.

Efficient Near-Infrared Luminescence of Self-Assembled Platinum(II) Complexes: From Fundamentals to Applications.

ConspectusDesigning bright and efficient near-infrared (NIR) emitters has drawn much attention due to numerous applications ranging from biological imaging, medical therapy, optical communication, and night-vision devices. However, polyatomic organic and organometallic molecules with energy gaps close to the deep red and NIR regime are subject to dominant nonradiative internal conversion (IC) processes, which drastically reduces the emission intensity and exciton diffusion length of organic materials and hence hampers the optoelectronic performances. To suppress nonradiative IC rates, we suggested two complementary approaches to solve the issues: exciton delocalization and molecular deuteration. First, exciton delocalization efficiently suppresses the molecular reorganization energy through partitioning to all aggregated molecules. According to the IC theory together with the effect of exciton delocalization, the simulated nonradiative rates with the energy gap ΔE = 104 cm-1 decrease by around 104 fold when the exciton delocalization length equals 5 (promoting vibronic frequency ωl = 1500 cm-1). Second, molecular deuterations reduce Franck-Condon vibrational overlaps and vibrational frequencies of promoting modes, which decreases IC rates by 1 order of magnitude in comparison to the rates of nondeuterated molecules under ΔE of 104 cm-1. Although deuteration of molecules has long been attempted to increase emission intensity, the results have been mixed. Here, we provide a robust derivation of the IC theory to demonstrate its validity, especially to emission in the NIR region.The concepts are experimentally verified by the strategic design and synthesis of a class of square-planar Pt(II) complexes, which form crystalline aggregates in vapor deposited thin films. The packing geometries are well characterized by the grazing angle X-ray diffraction (GIXD), showing domino-like packing arrangements with the short ππ separation of 3.4-3.7 Å. Upon photoexcitation, such closely packed assemblies exhibit intense NIR emission maximized in the 740-970 nm region through metal-metal-to-ligand charge transfer (MMLCT) transition with unprecedented photoluminescent quantum yield (PLQY) of 8-82%. To validate the existence of exciton delocalization, we applied time-resolved step-scan Fourier transform UV-vis spectroscopy to probe the exciton delocalization length of Pt(II) aggregates, which is 5-9 molecules (2.1-4.5 nm) assuming that excitons mainly delocalized along the direction of ππ stacking. According to the dependence of delocalization length vs simulated IC rates, we verify that the observed delocalization lengths contribute to the high NIR PLQY of the aggregated Pt(II) complexes. To probe the isotope effect, both partially and completely deuterated Pt(II) complexes were synthesized. For the case of the 970 nm Pt(II) emitter, the vapor deposited films of per-deuterated Pt(II) complexes exhibit the same emission peak as that of the nondeuterated one, whereas PLQY increases ∼50%. To put the fundamental studies into practice, organic light-emitting diodes (OLEDs) were fabricated with a variety of NIR Pt(II) complexes as the emitting layer, showing the outstanding external quantum efficiencies (EQEs) of 2-25% and the remarkable radiances 10-40 W sr-1 m-2 at 740-1002 nm. The prominent device performances not only successfully prove our designed concept but also reach a new milestone for highly efficient NIR OLED devices.This Account thus summarizes our approaches about how to boost the efficiency of the NIR emission of organic molecules from an in-depth fundamental basis, i.e., molecular design, photophysical characterization, and device fabrication. The concept of the exciton delocalization and molecular deuteration may also be applicable to a single molecular system to achieve efficient NIR radiance, which is worth further investigation in the future.

Effect of Nd3+ Doping on Structural, Near-Infrared, and Cathodoluminescent Properties for Cadmium Tantalate Phosphors

Cd1-xTa2O6:xNd3+ (x=0.5, 1.5, 3, 5, 7, and 10 mol%) phosphor series were fabricated by conventional solid state method at 1100 °C for 17 hours. The samples of cadmium tantalate were investigated by structural (XRD, SEM) and spectroscopic (CL, PL) analyses. In XRD results, the symmetry of CdTa2O6 phase with orthorhombic columbite structure was confirmed between 0.5 and 10 mol% Nd3+ doping concentrations. SEM analysis of the grains revealed round and shapeless morphology while grain sizes ranged from submicron to several microns. The emission spectra of Cd1-xTa2O6:xNd3+ (x=0.5, 1.5, 3, 5, 7 and 10 mol%) phosphor series recorded with the transitions of 4F3/2→4I9/2 and 4F3/2→4I11/2. Among these transitions, the transition 4F3/2→4I9/2 (at 889 nm) has a high near-infrared emission intensity, which can be attributed to the laser potential of the phosphor. The NIR emission of the phosphor increased with increasing concentration of Nd3+ up to 5 mol% and then declined because of concentration quenching phenomenon. The CL emission peak at about 450 nm found in all samples is related to the intrinsic emission of the cadmium tantalate host. In addition, Nd3+ doped phosphors exhibited the 4F3/2→4I9/2 transition of Nd3+ and defect-related CL emissions at 670 nm. Decreasing crystallinity with increasing Nd3+ concentration caused a decrease in host emission intensity at 450 nm.

Broadband downconversion in Eu2+,3+/Yb3+ doped calcium aluminosilicate glasses for solar cells applications

Novel Eu2+,3+/Yb3+ co-doping calcium aluminosilicate glasses prepared under a vacuum atmosphere were developed and characterized from the spectroscopic point of view, as a potential spectral converter for application in solar cells. The emission of near-infrared photons by downconversion due to cooperative energy transfer (ET) from Eu2+ and Eu3+ to Yb3+ in these glasses was reported. Absorption, excitation, emission, and fluorescence decay measurements were performed to examine the ET processes. The occurrence of cooperative energy transfer from Eu2+ and/or Eu3+ to Yb3+ ions was discussed in detail. The obtained samples have high efficiency and broad absorption in the ultraviolet and visible regions. Under 325 nm excitation, the samples achieve intense near-infrared emission, which increases with Yb2O3 concentration (0 < Yb2O3 < 1.38 mol. %). The energy transfer efficiency from Eu2+,3+ to Yb3+ was evaluated, and a maximum efficiency of ∼85% was obtained (Yb2O3 = 1.38 mol. %).