Tunable NIR Research Articles

A Class of Heptaphyrins with NIR Absorption Modulated by Metal Coordination and Nucleophilic Substitution.

The intensive interest in expanded porphyrins can be attributed to their appealing photoelectric and coordination behavior. In this work, an N-confused heptaphyrin 1 was synthesized by an acid-catalyzed [3+4] condensation reaction. The introduction of an N-confused pyrrolic unit into the heptaphyrin macrocycle led to the formation of a figure-eight-like conformation with nonsymmetrical "NNNN" and "NNNC" coordination cavities employable for bimetallic coordination. As a result, chelation of 1 with Zn(II) and Cu(II) afforded mono-Zn(II) complex 2 and bis-Cu(II) complex 3, respectively, with the metal atoms exhibiting distorted square-planar geometries. In complex 3, an oxygen atom is attached to the α-C atom of N-confused pyrrole D, and thus the N and C atoms of ring D participate in coordination within the two cavities. Interestingly, treatment of 1 with Cs2CO3 in MeOH resulted in regioselective substitution of all the seven para-F atoms in the meso-C6F5 groups as well as the α-H of ring D by eight methoxy moieties. Complex 3 displays a red-shifted absorption band edge of ca. 2200 nm, compared to that of ca. 1600 nm observed for 1. This work provides an example of incorporating an N-confused pyrrole to construct expanded porphyrins with distinctive coordination behavior and tunable NIR absorption.

Tunable ultra-broadband multi-band NIR emission in Bi-doped aluminogermanate glasses and fibers via controllable Al2O3 content for broadband amplifiers

The tunable ultra-broadband multi-band NIR emission of Bi-doped germanate glass and fiber can be achieved via constructing various glass local network environments with steerable Al2O3 content and show potential applications in broadband amplifiers.

An interfacial host-guest inclusion complex regulated supramolecular nanocomposite hydrogel showing tunable mechanical strength, self-healing, strain sensitivity and NIR responsiveness.

The development of supramolecular nanocomposite hydrogels with good mechanical properties and multifunctional characteristics remains challenging. The reinforced role of interfacial weak interactions is important for the mechanical properties of nanocomposite hydrogels. Here, a dynamic host-guest inclusion complex from the host molecule CB[7] and guest units was employed to prepare Fe3O4 hybrid supramolecular nanocomposite hydrogels. The results show that the as-obtained hydrogel with a porous structure was prepared. The CB[7]-modified Fe3O4 (Fe3O4@CB[7]) nanoparticles severed as a cross-linker for fabricating the hydrogel's network. By changing the Fe3O4@CB[7] content, their tensile stress ranged from 0.102 to 0.403 MPa and their compression stress ranged (70% compression strain) from 0.059 to 0.775 MPa. By changing the guest units, their tensile stress ranged from 0.3 MPa to 0.403 MPa. The self-healing efficiency of the hydrogels was 99% after 48 h at room temperature. The as-obtained hydrogels with strain sensitivity can be applied for detecting the movement of an elbow and finger. The supramolecular hydrogel exhibits NIR responsiveness, self-healing, injectability, tunable mechanical strength and conductive ability, and can be used in flexible electronics.

From Ancient Blue Pigment to Unconventional NIR Phosphor: A Thermal-Stable Near-Infrared I/II Broadband Emission from Ca1-xSrxCuSi4O10 Solid Solution.

Phosphors used in NIR spectroscopy require broadband emission, high external quantum yield, good ability, as well as a tunable spectral range to meet the detection criteria. Two-dimensional copper silicates MCuSi4O10 (M = Ca, Sr, Ba) play an important part in ancient art and technology as synthetic blue pigments. In the recent years, these compounds were reported to show a broad near-infrared emission when excited in the visible region. Inspired by the tunable structure of MCuSi4O10, a series of broadband phosphors Ca1-xSrxCuSi4O10 were designed for realizing continuously tunable NIR emission by a modulated Cu2+ crystal field environment. The emission maximum exhibits a red shift from 915 to 950 nm and the integral intensity enhances as the Sr2+ content varies in the range of 0-0.50, which is led by the lattice expansion and the following weakened crystal field splitting on tetrahedral-coordinated Cu2+. Compared to CaCuSi4O10, the optimized sample Ca0.5Sr0.5CuSi4O10 shows enhanced NIR emission by about 2.0-fold. It exhibits quite a high external quantum efficiency covering the NIR-I and -II regions (λmax = 950 nm, fwhm = 135 nm, EQE = 26.3%) with a strong absorption efficiency (74.7%) and a long excited-state lifetime (134 μs). These solid-solution phosphors (x = 0.0-0.5) show excellent thermal stability and maintain over 50% of the RT intensity at 200 °C. The optimized phosphor was encapsulated with red-light chips to fabricate NIR pc-LED and put into night-vision application. These good properties make these Cu2+-activated NIR phosphors appealing for multiple applications such as nondestructive testing, night version, lasers, and luminescent solar concentrators.

Cationic site engineering enables tunable NIR-emitting chromium-activated double perovskite niobates with thermal stability

NIR emitters have grown in popularity due to their non-destructive and non-contact properties in composition analysis. However, developing a tunable NIR emitter with good thermal stability remains difficult. Herein, we propose a cationic site engineering strategy to fulfill a tunable NIR emitting A2InNbO6:Cr3+ (A = Ca, Sr, Ba) phosphor with thermal stability. The double perovskite phosphors were synthesized via a conventional high-temperature solid-state method. The phase purity and surface morphology of A2InNbO6:Cr3+ were investigated by employing X-ray diffraction and Scanning Electronic Microscopy. The band structure and density of the state of A2InNbO6:Cr3+ were calculated based on the density functional theory. The photoluminescence spectra of A2InNbO6:Cr3+ span gradually from the NIR-I window to the NIR-II window with A site modulation. Moreover, the thermal stability of A2InNbO6:Cr3+ increases from 21.43% to 50.24% via cationic site engineering. The Huang–Rhys factor (S) and activation energy were further analyzed to understand the improved thermal stability. Finally, the optimal phosphor was fabricated into a NIR emitting LED and showed its advantages in the application. The work demonstrates another pathway to rationally design a tunable NIR emitter with thermal stability.

Near-infrared emission of Cr3+ in five-coordinated field

Cr3+-activated NIR phosphors have received increasing attention due to their versatile applications. Cr3+ generally shows tunable NIR emission by occupying a six-coordinated field (Oh). Herein, we discover broadband NIR emission of Cr3+ at the five-coordinated field in the phosphors BaXP2O7:Cr3+ (X = Mg/Zn) for the first time. The five-coordinated [MgO5] (D3h) or [ZnO5] (C4v) site provides a quasi-octahedral field. The symmetry of D3h and C4v fields is lower than that of Oh, thus leading to further splitting of the energy levels and generating the broadband NIR emission from 700 to 1100 nm. This work breaks through the traditional limitation of NIR luminescence of Cr3+ in the six-coordinated field and opens a new window to explore novel NIR phosphors of Cr3+ in five-fold coordination.

Thermally stable and tunable broadband near-infrared emission from NIR-I to NIR-II in Bi-doped germanate glass for smart light sources

Bi-doped germanate glasses are reported as all-inorganic tunable broadband NIR LED devices (gc-LEDs) operating in both NIR-I and NIR-II regions with potential applications in night vision, bio-imaging, and rapid analysis of food quality.

Tunable near-infrared piezochromic luminescence by effective substituent modification of D–A structures

Tunable NIR piezochromic luminescence was achieved by the substitute modification of D–A structures. More than 200 nm red-shifted emission is realized under high pressure, while the unsubstituted TPAM is blue-shifted during the compression process.

Synthesis and coordination of a dipyrrin appended N-confused porphyrin

A hexapyrrane P6 with a terminal N-confused pyrrole was synthesized by acid-catalyzed [3+3] condensation followed by oxidation with DDQ, which did not afford the expected N-confused hexaphyrin. In stead, a rearranged product, i.e., [Formula: see text]-dipyrrin appended N-confused porphyrin 1 was obtained in a yield of 46%. Chelation of 1 with Pt(II) afforded the peripheral complex 1-Pt, which was further coordinated with Rh(I) in the cavity to afford the corresponding bimetallic complex 1-Pt-Rh. Both 1-Pt and 1-Pt-Rh exhibit split Soret-like bands and noticeable Q-like bands tailing to the NIR region up to ca. 1200 nm. Single crystal X-ray diffraction analyses of 1 and 1-Pt revealed that the peripheral coordination of Pt(II) slightly modifies the interplanar angle between the porphyrin macrocycle and the dipyrrin unit, which may modulate the absorption spectra. The results of this work compose an interesting example of synthesizing porphyrinoids appended with conjugated peripheral chains by the oxidative ring closure reaction of an oligopyrrane containing a terminal N-confused pyrrole, and such compounds may be used for both inner and peripheral coordination to afford complexes with tunable NIR absorption.

Double‐Site Occupation Triggered Broadband and Tunable NIR‐I and NIR‐II Luminescence in AlNbO4:Cr3+ Phosphors

AbstractNear‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) are desired for optoelectronic and biomedical applications, while the development of target broadband NIR phosphors still remains a significant challenge. Herein, a kind of Cr3+‐doped AlNbO4 phosphors with a broad NIR emission ranging from 650 to 1400 nm under 450 nm excitation are reported. A giant red‐shift emission peak from 866 to 1020 nm together with broadened full width at half‐maximum of 320 nm is achieved simply by varying the doped Cr3+ concentrations. Structural and spectroscopy analysis demonstrate that a concentration‐dependent site‐occupation of Cr3+ emitters in different Al3+ sites is responsible for the tunable NIR luminescence. The as‐fabricated NIR pc‐LED based on optimized AlNbO4:Cr3+ phosphor exhibits great potential in night‐vision applications. This work provides a novel design principle on the Cr3+‐doped AlNbO4 phosphor with tunable broadband luminescence from NIR‐I to NIR‐II, and these materials can be employed in NIR spectroscopy applications.

Enlarging the Stokes Shift by Weakening the π-Conjugation of Cyanines for High Signal-to-Noise Ratiometric Imaging.

The signal-to-noise ratio (SNR) is one of the key features of a fluorescent probe and one that often defines its potential utility for in vivo labeling and analyte detection applications. Here, it is reported that introducing a pyridine group into traditional cyanine-7 dyes in an asymmetric manner provides a series of tunable NIR fluorescent dyes (Cy-Mu-7) characterized by enhanced Stokes shifts (≈230nm) compared to the parent cyanine 7 dye (<25nm). The observed Stokes shift increase is ascribed to symmetry breaking of the Cy-Mu-7 core and a reduction in the extent of conjugation. The fluorescence signals of the Cy-Mu-7 dyes are enhanced upon confinement within the hydrophobic cavity of albumin or via spontaneous encapsulation within micelles in aqueous media. Utilizing the Cy-Mu-7, ultra-fast in vivo kidney labeling in mice is realized, and it is found that the liver injury will aggravate the burden of kidney by monitoring the fluorescence intensity ratio of kidney to liver. In addition, Cy-Mu-7 could be used as efficient chemiluminescence resonance energy transfer acceptor for the reaction between H2 O2 and bisoxalate. The potential utility of Cy-Mu-7 is illustrated via direct monitoring fluctuations in endogenous H2 O2 levels in a mouse model to mimic emergency room trauma.

Enhancement and broadening of near infrared photoluminescence in Ag2X (X= S, Se) quantum dots via Cd doping for mini light-emitting diodes towads non-invasive bioimaging

Exploring excellent near infrared-II (NIR-II) emitting materials is desirable for the advancement of high quality bioimaging, in virtue of the lower scattering, deep penetration and high sensitive of biological components in the second optical transmission window. Colloidal Ag2X (X = S, Se) nanocrystals exhibit tunable NIR photoluminescence in the second NIR region. However, the lack of highly efficient broadband NIR emitting Ag2X (X = S, Se) nanocrystals limits their spectroscopy applications. Herein, cadmium (Cd) doped Ag2X (X = S, Se) nanocrystals were prepared through a facile hydrothermal method at room temperature. The NIR luminescence was efficiently enhanced through controllable doping a little amount of Cd ions into the Ag2X (X = S, Se) quantum dots (QDs). Simultaneously, the great broadening of NIR emission was achieved in the Cd doped Ag2Se QDs, and the maximum full width at half maximum could reach up to 530 nm. Following the general principles of photoluminescence light-emitting diode (LED) devices, the fabricated NIR mini LEDs) light sources based on Cd doped Ag2Se QDs exhibited broadband NIR electroluminescence and superior optoelectronic stability, and were successfully employed for clear vessel imaging. The works proves the feasibility of NIR mini LEDs in non-invasive bioimaging, and paves way for the miniaturized broadband NIR light sources.

Structural induced tunable NIR luminescence of (Y,Lu)3(Mg,Al)2(Al,Si)3O12: Cr3+ phosphors

Garnet-type (Y,Lu)3(Mg,Al)2(Al,Si)3O12: Cr3+ compounds were successfully synthesized by high-temperature solid-phase reaction method. Starting from Y3Al5O12, Mg2+-Si4+ pairs were used to replace Al(1)3+-Al(2)3+ in octahedral and tetrahedral site, respectively, and then Y3+ was substituted by Lu3+ in dodecahedra of Y3(MgAl)(Al2Si)O12: Cr3+. Narrow-band to broad-band tunable NIR luminescence was achieved by ionic substitution at different polyhedral positions. The peak emission wavelength can be tuned from 705 to 770 nm, and the full width at half maximum (FWHM) can be extended from 27 to 160 nm. The results indicate that Y3(MgAl)(Al2Si)O12: 0.06Cr3+ is a promising NIR material. Under the excitation of blue light, the peak wavelength of Y3(MgAl)(Al2Si)O12: 0.06Cr3+ is about 760 nm with a FWHM of ∼160 nm and an IQE of 64%. Furthermore, the luminescence intensity at 150 °C remains at 84.2% of that at room temperature. Additionally, packaging performance was studied to evaluate its practical application in LEDs.

Application of NIR Spectral Standardization Based on Principal Component Score Evaluation in Wheat Flour Crude Protein Model Sharing

In order to explore spectral standardization methods for spectra collected by different NIR spectrometers, to reduce spectral differences, and to realize model sharing among different instruments, the crude protein content of 154 wheat flour samples was measured using one grating and three Fabry-Perot tunable filter NIR spectrometers in wavelength. At the same wavelength range and wavelength interval, three algorithms, namely, direct standardization (DS), piecewise direct standardization (PDS), and simple linear regression direct standardization (SLRDS), were used to standardize spectra collected by different instruments from the same samples. Spectral standardization error rate (SSER), principal component score error rate (PCSER), and other indicators were employed to analyze the spectral differences between the master and the target spectra, and the effect of model sharing was evaluated using parameters including prediction correlation coefficient (Rp), root mean square error of prediction (RMSEP), and relative prediction deviation (RPD). The results show the following: (1) The difference between spectra can be quantitatively evaluated through analyzing SSER and PCSER. (2) After standardization by the three algorithms, the spectral difference between the three target and the master spectrometers is significantly reduced and the prediction effect of the master model is greatly improved. (3) Among the three algorithms, DS algorithm had the smallest error rate in standardizing spectra from three target spectrometers. After standardization by the DS algorithm, the master model had the best effect. Its prediction accuracy was greatly improved compared with that before standardization. (4) The standard model established based on the S450 spectrometer can be applied to the same spectrometer as the N500 spectrometer with the same resolution and different wavelength ranges, so as to achieve model sharing. Therefore, DS, PDS, and SLRDS algorithms can effectively reduce the spectral differences between different instruments and realize the sharing of NIR calibration models for wheat flour crude protein measurement.

Spectral engineering and thermometric performance of LiIn(Si2-xGex)O6: Cr3+ phosphor for multi-mode NIR thermometry

Exploring the phosphors with tunable NIR emission to realize versatile application is highly desired while remains a challenging. Herein, we show that the composition modification of Si/Ge ratio in LiIn(Si2-xGex)O6: Cr3+ could lead to a precise tuning of Cr3+ emission wavelength in 840–900 nm range with significant emission enhancement. The spectral engineering is quantitatively analyzed on the base of structural variation and crystal fielding parameters, revealing that the PL tuning is originated from reducing crystal field by Ge4+-induced lattice expansion. It is found that the strong temperature-dependence of Cr3+ emission enables it to read the temperature in three ways: variation of peak wavelength, fluorescence intensity and decay lifetime variation. All modes exhibit good linear response with R2 > 0.99 in range of 293–473 K. The ability to absorb and emit in NIR-I biological window allows it to be used as a thermometer in deep tissue temperature sensing and imaging. All results indicate that this phosphor is of great potential in NIR thermometry application.

Novel broadband near-infrared emitting phosphor LiGe2(PO4)3:Cr3+ with tuning and enhancement of NIR emission by codoping Sb5+

A highly efficient novel broadband NIR emission peaking at 814 nm with a large full width at half maximum (FWHM) of 170 nm was realized in novel LiGe2(PO4)3:Cr3+ (LGP:Cr3+) with internal quantum efficiency about 90% (IQE). An innovative strategy of Sb5+ codoped phosphor (LGP:Cr3+,Sb5+) led to the increases in the luminescence intensity and thermal stability. Moreover, tunable NIR emission from 814 to 743 nm was achieved which can be ascribed to the attenuation of electron-phonon coupling with increasing Sb5+-concentration. The output powers of phosphor-converted lighting emitting diodes (pc-LEDs) by combining 460 nm chips with LGP:0.01Cr3+ and LGP:0.05Cr3+,0.05Sb5+ phosphors reached 34.68 mW @ 300 mA and 40.36 mW @ 250 mA, respectively. Our results prove that the codoped strategy can provides a new idea for research on tunable NIR phosphors.

Dual near infrared emission in Ag2Se quantum dots via Pb doping for broadband mini light-emitting diodes.

Dual emission almost covering the entire NIR-II region with the maximum full width at half maximum of 542 nm was achieved by doping small amounts of Pb ions into Ag2Se quantum dots, which to the best of our knowledge has not been realized for continuous tunable dual NIR emission in Ag-based QDs. The fabricated broadband NIR mini light-emitting diodes based on the Pb-doped Ag2Se QDs exhibit potential applications for highly sensitive and multispectral non-invasive imaging and NIR lighting.

Simultaneous Broadening and Enhancement of Cr3+ Photoluminescence in LiIn2 SbO6 by Chemical Unit Cosubstitution: Night-Vision and Near-Infrared Spectroscopy Detection Applications.

Near-infrared (NIR)-emitting phosphor materials have been extensively developed for optoelectronic and biomedical applications. Although Cr3+ -activated phosphors have been widely reported, it is challenging to achieve ultra-broad and tunable NIR emission. Here, a new ultra-broadband NIR-emitting LiIn2 SbO6 :Cr3+ phosphor with emission peak at 965 nm and a full-width at half maximum of 217 nm is reported. Controllable emission tuning from 965 to 892 nm is achieved by chemical unit cosubstitution of [Zn2+ -Zn2+ ] for [Li+ -In3+ ], which can be ascribed to the upshift of 4 T2g energy level due to the strengthened crystal field. Moreover, the emission is greatly enhanced, and the FWHM reaches 235 nm. The as-prepared luminescent tunable NIR-emitting phosphors have demonstrated the potential in night-vision and NIR spectroscopy techniques. This work proves the feasibility of chemical unit cosubstitution strategy in emission tuning of Cr3+ -doped phosphors, which can stimulate further studies on the emission-tunable NIR-emitting phosphor materials.

Simultaneous Broadening and Enhancement of Cr3+Photoluminescence in LiIn2SbO6by Chemical Unit Cosubstitution: Night‐Vision and Near‐Infrared Spectroscopy Detection Applications

AbstractNear‐infrared (NIR)‐emitting phosphor materials have been extensively developed for optoelectronic and biomedical applications. Although Cr3+‐activated phosphors have been widely reported, it is challenging to achieve ultra‐broad and tunable NIR emission. Here, a new ultra‐broadband NIR‐emitting LiIn2SbO6:Cr3+phosphor with emission peak at 965 nm and a full‐width at half maximum of 217 nm is reported. Controllable emission tuning from 965 to 892 nm is achieved by chemical unit cosubstitution of [Zn2+–Zn2+] for [Li+–In3+], which can be ascribed to the upshift of4T2genergy level due to the strengthened crystal field. Moreover, the emission is greatly enhanced, and the FWHM reaches 235 nm. The as‐prepared luminescent tunable NIR‐emitting phosphors have demonstrated the potential in night‐vision and NIR spectroscopy techniques. This work proves the feasibility of chemical unit cosubstitution strategy in emission tuning of Cr3+‐doped phosphors, which can stimulate further studies on the emission‐tunable NIR‐emitting phosphor materials.

Li/Na substitution and Yb3+ co-doping enabling tunable near-infrared emission in LiIn2SbO6:Cr3+ phosphors for light-emitting diodes

SummaryNear-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) has great potential in non-invasive detection, while the discovery of tunable broadband NIR phosphor still remains a challenge. Here, we report that Cr3+-activated LiIn2SbO6 exhibits a broad emission band ranging from 780 to 1400 nm with a full width at half maximum (FWHM) of 225 nm upon 492 nm excitation. The emission peaks are tuned from 970 to 1020 nm together with considerable broadening of FWHM (∼285 nm) via Li/Na substitution. Depending on Yb3+ co-doping, a stronger NIR fluorescence peak of Yb3+ appears with improved thermal resistance, which is ascribed to efficient energy transfer from Cr3+ to Yb3+. An NIR pc-LED package has been finally designed and demonstrated a remarkable ability to penetrate pork tissues (∼2 cm) so that the insertion depth of a needle can be observed, indicating that the phosphor can be applied in non-destructive monitoring.