Near-infrared Optical Properties Research Articles

Near-infrared optical properties of Cs2KScF6:Cr3+ phosphor for high-power light-emitting diodes

The recent years have witnessed a great leap for near-infrared (NIR) spectroscopy technology in multifunctional application fields. In this study, a double-perovskite structured Cr3+-doped Cs2KScF6 fluoride NIR phosphor with peak location at 778 nm and full-width at half maximum (FWHM) of 95 nm was synthesized by a co-precipitation method. The integral emission intensity at 423 K retains 70 % of that at room temperature (RT), showing good luminescent thermal stability. Combining the obtained phosphor in an NIR phosphor converted light-emitting diode (NIR pc-LED) device, the output power and photoelectric conversion efficiency can reach 72.28 mW and 6.83 % at 320 mA. By virtue of the good optical performance, clear structural images of different fruits were visualized by using the NIR pc-LED as light source, suggesting the potential of Cs2KScF6:Cr3+ phosphor to be used in high-power LED devices.

Dehydro[12]- and [18]annulene-Fused Ball-Shaped Ruthenium Complex Oligomers: Synthesis, Aromatic/Antiaromatic Effect, and Symmetry for Near-Infrared Optical Properties.

The appropriate arrangement of near-infrared (NIR) chromophores allows for the modification of the peak wavelength in the NIR region and efficient use of NIR light. However, the preparation of novel NIR chromophores using simple procedures remains a formidable challenge. Herein, we report the synthesis of ball-shaped ruthenium complex oligomers. The metal complexes can be synthesized in a single step and interact strongly with NIR light. Alkyne-substituted low-symmetry ball-shaped ruthenium complexes were synthesized and subjected to Eglinton coupling to obtain dehydro[12] and [18]annulene-fused dimers and trimers. Fine-tuning of the reaction conditions led to the selective synthesis of the target oligomers. NMR spectroscopy confirmed that the 18π-aromatic and 12π-antiaromatic properties of the annulene influenced the ruthenium complex chromophore, and magnetic circular dichroism spectroscopy showed changes in the electronic structure of their excited state owing to molecular-symmetry differences. The absorption coefficient in the NIR region of the absorption spectra of the oligomers increased significantly, supporting the efficient use of light by oligomerization. The formation of oligomers using ball-shaped metal complexes is a simple and effective strategy for controlling NIR optical properties.

Visualization Materials Using Silicon-Based Optical Nanodisks (ViSiON) for Enhanced NIR Imaging in Ophthalmology.

ViSiON (visualization materials composed of silicon-based optical nanodisks) is presented, which offers a unique optical combination of near-infrared (NIR) optical properties and biodegradability. Initially, numerical simulations are conducted to calculate the total extinction and scattering effects of ViSiON by the diameter-to-thickness ratio, predicting precise control over its scattering properties in the NIR region. A top-down patterning technique is employed to synthesize ViSiON with accurate diameter and thickness control. ViSiON with a 50nm thickness exhibits scattering properties over 400 times higher than that of 30nm, rendering it suitable as a contrast agent for optical coherence tomography (OCT), especially in ophthalmic applications. Furthermore, ViSiON possesses inherent biodegradability in media, with ≈95% degradation occurring after 48 h, and the degradation rate can be finely tuned based on the quantity of protein coating applied to the surface. Subsequently, the OCT imaging capability is validated even within vessels smaller than 300µm, simulating retinal vasculature using a retinal phantom. Then, using an ex ovo chick embryo model, it is demonstrated that ViSiON enhances the strength of protein membranes by 6.17 times, thereby presenting the potential for ViSiON as an OCT imaging probe capable of diagnosing retinal diseases.

Engineering Band Gap of Ternary Ag2TexS1−x Quantum Dots for Solution-Processed Near-Infrared Photodetectors

Silver-based chalcogenide semiconductors exhibit low toxicity and near-infrared optical properties and are therefore extensively employed in the field of solar cells, photodetectors, and biological probes. Here, we report a facile mixture precursor hot-injection colloidal route to prepare Ag2TexS1−x ternary quantum dots (QDs) with tunable photoluminescence (PL) emissions from 950 nm to 1600 nm via alloying band gap engineering. As a proof-of-concept application, the Ag2TexS1−x QDs-based near-infrared photodetector (PD) was fabricated via solution-processes to explore their photoelectric properties. The ICP-OES results reveal the relationship between the compositions of the precursor and the samples, which is consistent with Vegard’s equation. Alloying broadened the absorption spectrum and narrowed the band gap of the Ag2S QDs. The UPS results demonstrate the energy band alignment of the Ag2Te0.53S0.47 QDs. The solution-processed Ag2TexS1−x QD-based PD exhibited a photoresponse to 1350 nm illumination. With an applied voltage of 0.5 V, the specific detectivity is 0.91 × 1010 Jones and the responsivity is 0.48 mA/W. The PD maintained a stable response under multiple optical switching cycles, with a rise time of 2.11 s and a fall time of 1.04 s, which indicate excellent optoelectronic performance.

Synthesis and photothermal conversion properties of sandwich N-fused porphyrin rhodium-μ-dichloride dimer complexes: π-extended analog of pentamethylcyclopentadienyl dirhodium(III)-μ-dichloride dimer

Anionic cyclopentadienyl (Cp) and its pentamethyl-substituted derivative (Cp*) serve as crucial ligands for creating stable π-coordinated materials, including catalysts. From a structural perspective, the π-extended analog of Cp, known as an N-fused porphyrin (NFP), is recognized as an intriguing 18π aromatic chromophore, offering near-infrared (NIR) optical properties that can be fine-tuned through metal complexation. When coordinated with rhodium at the central NFP core, it forms a sandwich binuclear rhodium(III) complex along with terminal and bridging chloride ligands, denoted as Rh-1, and its bromo derivative, Rh-1-Br. In contrast to the bis-NFP complex of iron(II) reported previously by our team, both Rh-1 and Rh-1-Br complexes exhibit strong NIR optical properties and narrow HOMO-LUMO energy gaps, attributed to minimal orbital interactions between the two co-facial NFP ligands. Leveraging these NIR absorption properties, we assessed the photothermal conversion properties of Rh-1 and ligand 1, revealing high conversion efficiency. This suggests their potential application as photothermal agents for use in photothermal therapy.

Growth and near-infrared optical properties of Nd3+-doped KGd0.1Lu0.9(WO4)2 crystal

In this paper, x at.% Nd3+: KGd0.1Lu0.9-x(WO4)2 (x = 1, 2, 3, 4, 5) crystals were grown by the top seed solution growth method (TSSG). The crystal structure was analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), and the crystal structure data was obtained by Rietveld refinement. The absorption spectra, near-infrared emission spectra and fluorescence decay curves of Nd3+ ions in the crystal were measured at indoor temperature. According to Judd-Ofelt theory, the spectral intensity parameters Ω2, Ω4 and Ω6 are calculated. When the doping concentration is 3 at.%, Ω2 is the largest, which is 3.84 × 10−20 cm2, while the spectral mass factor is the lowest, which is 0.3734. The absorption and emission cross-section are calculated by combining the absorption spectrum and emission spectrum, and the maximum calculated result of emission cross-section is 1.35 × 10−19 cm2. The results show that Nd3+: KGd0.1Lu0.9(WO4)2 crystals has great application potential in the 1.0 µm field.

Self-referenced dual-near-infrared emission-based sensor platform for the ultrasensitive discrimination of D2O and H2O

Due to its chemical and physical similarities, the ultrasensitive discrimination of D2O in the presence of H2O remains a practical challenge. In this study, we present an approach to utilize the near-infrared (NIR) optical properties of H2O. Specifically, the absorption coefficient of H2O at approximately 980 nm, which is derived from the second overtone of the O–H stretching mode of H2O, exhibits a notable distinction from that of D2O. To this end, we construct and optimize a dual-NIR emissive lanthanide-doped nanoprobe with a strong emission intensity at 980 nm. In addition, to enhance the reliability of the proposed sensor platform, we introduce a self-referenced signal at 865 nm, which shows a stable signal intensity in both H2O and D2O. Our self-referenced dual-NIR emission-based sensor platform successfully discriminates between D2O and H2O and shows ultrasensitive discrimination capabilities with a limit of detection of 0.17 nM, which has the highest sensitivity among that of previously reported D2O sensors.

Prediction of soluble solids content using near-infrared spectra and optical properties of intact apple and pulp applying PLSR and CNN

Soluble solids content (SSC) is one of the most important internal quality attributes of fruit and could be predicted using near-infrared (NIR) spectra and optical properties. Partial least squares regression (PLSR) is a conventional regression method in SSC prediction. In recent years, deep learning methods represented by convolutional neural network (CNN) was suggested to be implied in spectral analysis. However, researchers are inevitably facing problems with regard to the selection of spectral pretreatment methods and the evaluation of the performance of the chosen regression. This study employed PLSR and CNN regression to predict SSC of apple based on the collected diffuse reflectance spectra of intact apple, total reflectance and total transmittance spectra of apple pulp, and the calculated optical property spectra, i.e., absorption coefficient and reduced scattering coefficient spectra of apple pulp. Five different spectral pretreatment methods were exerted on these spectra. Results showed that at a given regression (PLSR or CNN), the built models based on the diffuse reflectance spectra of intact apple had the best SSC prediction, and the built models based on pulp’s reduced scattering coefficient spectra had the poorest prediction performance. The best prediction performance was achieved by PLSR models using Savitzky-Golay with multiple scattering correction (Rp = 0.96, RMSEP = 0.54 %) and CNN regressions using Savitzky-Golay with standard normal variational transformation (Rp = 0.95, RMSEP = 0.59 %), respectively. Additionally, when the unknown original spectra were used for modeling, CNN had a better performance compared to PLSR, indicating the outstanding preponderance of CNN in spectral analysis. This study provides an effective reference for the selection of chemometric method based on NIR spectra.

Near-Infrared Optical Properties of Thiol-Passivated Substoichiometric WO3–x Nanodots Studied by Magnetic Circular Dichroism (MCD) Spectroscopy

We report a facile method to synthesize oxygen-deficient tungsten oxide (WO3–x) nanodots passivated by thiols. Addition of thiolated amino acid glutathione (GSH) or penicillamine (Pen) into ethanolic WCl6 solution gives blue WO3–x nanodot dispersion with the absorption maximum of ∼900 nm; however, complete isolation of the as-synthesized products based on precipitation–redispersion cycles makes them insoluble in any solvent. We then adopt water-based ultrafiltration for purification. Interestingly, after ultrafiltration, the optical absorption is significantly modified, having a broad peak at 1300–1500 nm with a shoulder at ∼950 nm. Magnetic circular dichroism (MCD) investigations reveal that (i) the near-infrared (NIR) absorption peak (at ∼900 nm) observed in the as-synthesized products arises from localized surface plasmon resonance, giving a derivative-like MCD response, and (ii) the shoulder observed at ∼950 nm in the ultrafiltrated products is due to the excitation to a polaronic state, giving a single-peaked MCD signal. The results suggest that the plasmonic state in the WO3–x nanodots is easily and significantly modulated by the synthesis/environmental conditions, and thus, care should be taken to account appropriately for the NIR spectroscopic properties.

Synthesis of Bioctacene-Incorporated Nanographene with Near-Infrared Chiroptical Properties.

We report the synthesis of a hexabenzoperihexacene (HBPH) with two incorporated octacene substructures, which was unambiguously characterized by single-crystal X-ray analysis. The theoretical isomerization barrier of the (P,P)-/(P,M)-forms was estimated to be 38.4 kcal mol-1 , and resolution was achieved by chiral HPLC. Notably, the enantiomers exhibited opposite circular dichroism responses up to the near-infrared (NIR) region (830 nm) with a high gabs value of 0.017 at 616 nm. Moreover, HBPH demonstrated NIR emission with a maximum at 798 nm and an absolute PLQY of 41 %. The excited-state photophysical properties of HBPH were investigated by ultrafast transient absorption spectroscopy, revealing an intriguing feature that was attributed to the rotational and/or conformational dynamics of HBPH after excitation. These results provide new insight into the design of chiral nanographene with NIR optical properties for potential chiroptical applications.

Synthesis of Bioctacene‐Incorporated Nanographene with Near‐Infrared Chiroptical Properties

AbstractWe report the synthesis of a hexabenzoperihexacene (HBPH) with two incorporated octacene substructures, which was unambiguously characterized by single‐crystal X‐ray analysis. The theoretical isomerization barrier of the (P,P)‐/(P,M)‐forms was estimated to be 38.4 kcal mol−1, and resolution was achieved by chiral HPLC. Notably, the enantiomers exhibited opposite circular dichroism responses up to the near‐infrared (NIR) region (830 nm) with a high gabs value of 0.017 at 616 nm. Moreover, HBPH demonstrated NIR emission with a maximum at 798 nm and an absolute PLQY of 41 %. The excited‐state photophysical properties of HBPH were investigated by ultrafast transient absorption spectroscopy, revealing an intriguing feature that was attributed to the rotational and/or conformational dynamics of HBPH after excitation. These results provide new insight into the design of chiral nanographene with NIR optical properties for potential chiroptical applications.

Effect of crystallinity on optical properties of PEEK prepreg tapes for laser-assisted automated fiber placement

Laser-assisted automated fiber placement (L-AFP) is an efficient additive manufacturing process to fabricate complex thermoplastic composite parts. The optical properties of prepreg tapes are crucial factors affecting heating efficiency and uniformity during the L-AFP process. Here, we investigate the effect of crystallinity of Polyetheretherketone (PEEK) on the near-infrared optical properties of prepreg tapes reinforced with transparent glass fiber (GF) or opaque carbon fiber (CF). PEEK films, GF/PEEK and CF/PEEK prepregs with different crystallinities were prepared by controlling the cooling rate. Spectrophotometric results show that the reflectance of 25–200 μm PEEK films increases with crystallinity. Moreover, the dependency of reflectance on crystallinity increases with thickness. This is because there are more layers of crystal structures within the highly crystalline thick film compared to the thin film, resulting in multi-layer reflection and resultant higher reflectance. Similarly, the reflectance of GF/PEEK prepreg increases with the crystallinity due to the high transmittance of glass fibers and multi-layer reflection, which increases the temperature in the shadow region by up to 100 °C during the L-AFP process. However, similar to the thin film, the crystallinity has a negligible effect on the reflectance of CF/PEEK prepreg due to the opacity of carbon fiber and less crystallite reflection.

Tunable ultrafast near-infrared nonlinear optical properties of Eu3+ and silver nanoparticles doped alkali borate glasses

Achieving strong optical nonlinearities in vitreous nanocomposites is imperative for the advancement of futuristic telecommunication and photonic technologies. In this regard the borate materials (vitreous) are deemed to be important and currently available commercial hosts. In the current work, we demonstrate the tuning of the third-order nonlinear optical (NLO) attributes of borate-based glass samples doped with metal nanoparticles (NPs) and rare earth ions through annealing process. The NLO attributes, such as nonlinear optical absorption and refraction have been analysed by the sensitive Z-scan approach in the open and closed aperture configurations, respectively. The NLO features were examined in the near-infrared spectral region using ultrafast laser pulses fired at a high repetition rate from a Ti: sapphire laser oscillator. The open aperture data unveiled the existence of two-photon absorption whilst closed aperture indicated the occurrence of self-focusing nonlinear refraction. The NLO coefficients improved with heat treatment duration but the nonlinear absorption coefficient reduced at longer heat treatment schedules. The enhancement in the NLO coefficients is ascribed to the local field enriched by metallic silver NPs in the proximity of the rare earth ions when high-energy laser pulses irradiate the hosts. The results suggest the glasses routed with rare earth ions and metallic silver NPs annealed for 40 hrs at 450 °C are beneficial for optical communication and nonlinear photonic device applications, including optical limiting functionalities.

Yb3+, Er3+: CeF3 crystals: Growth, first-principles simulation, and near-infrared optical properties

Yb3+, Er3+: CeF3 crystals were successfully grown via Bridgman-Stockbarger technique, and their structure and physicochemical properties were characterized and analyzed. The results have shown that the maximum phonon vibrational frequency of the crystals is 391 cm−1. Under 980 nm excitation, Yb3+ ions doping can effectively improve the luminescence intensity at 1550 nm. The maximum luminescence intensity was achieved at the Yb3+ ion concentration of 3 at.%. The energy transfers, concentration quenching mechanisms and the factors affecting the fluorescence decay time were investigated in detail. The band gap structure, density of states and charge distribution of Yb3+, Er3+: CeF3 crystals were studied in depth by first principles simulation. This work proves that Yb3+, Er3+: CeF3 crystals have great potential for the near-infrared laser applications.

Growth, first-principles simulations and near-infrared optical properties of rare earth (Nd3+, Er3+)-doped CeF3 crystals for laser applications

Growth, first-principles simulations and near-infrared optical properties of rare earth (Nd3+, Er3+)-doped CeF3 crystals for laser applications

Enhanced near-infrared femtosecond nonlinear optical properties in zinc borate glasses activated with Er2O3

Several advanced materials have been investigated for nonlinear optical device applications. However, oxide glasses are competing materials in contrast to those advanced materials due to ease of preparation in three dimensions with diverse shapes along with flexibility in choosing the composition which is essential to tune the nonlinear optical features for specific applications. Doping rare-earth ions is one of the methods used to tune the nonlinear optical features of glass specimens, and it has been explored extensively in recent years. Using femtosecond laser pulses, the effect of Er2O3 concentration on nonlinear optical characteristics such as nonlinear absorption, nonlinear refraction, and optical limiting qualities was investigated using the Z-scan approach. The dual photon absorption and self‒focusing refraction nonlinear magnitudes are improved as the function of Er2O3 content owing to the formation of non‒bridging oxygens and enhancement in polarizability of glasses while the optical limiting features were decreased. These nonlinear absorptions and optical limiting results endorse the high Er2O3 loaded glasses are beneficial for nonlinear photonic devices functioning in the near-infrared regions.

Numerical evaluation of an optically switchable photovoltaic glazing system for passive daylighting control and energy-efficient building design

Adaptive control of solar heat gain and visible light transmission through windows is perceived to be a potential measure for enhancing energy conservation and visual comfort in buildings. In this study, a novel versatile window, named Building Integrated Photovoltaic (BIPV) smart window, was proposed to offer simultaneous improvement of daylighting control, on-site electricity generation and building energy efficiency, compared to traditional BIPV windows with static optical properties. The key components of the proposed system include an optically switchable thermotropic layer made of Hydroxypropyl Cellulose (HPC) hydrogel, crystalline-silicon photovoltaic cells, clear glass and low-emissivity (low-e) glass covers. The thermotropic layer can respond to heat by autonomously changing its visible and near-infrared optical properties, with which the amount of solar radiation into building spaces can be manipulated and thus the risks of excessive solar heating and illumination can be prevented. Apart from excellent solar modulation, the BIPV smart window can collect a proportion of the light scattered from the thermotropic layer and concentrate it onto the integrated PV cells for extra electricity generation. An innovative methodology has been proposed to predict the optical, thermal and electrical properties of the BIPV smart window under varying ambient conditions. Numerical simulations have been carried out in EnergyPlus to predict the window's performance when it is applied to an office-type environment in the climate of Nottingham, the UK. The influence of different window design scenarios, in terms of Window-to-Wall Ratio (WWR), orientation and transition temperature, has been investigated. It was found that using the BIPV smart window can achieve an annual energy saving of 36.6% but also a more comfortable indoor luminous environment, compared to the counterpart BIPV window (with no thermotropic layer integrated), when installed in the south-oriented office with a WWR of 25%.

Revealing the vibronic coupling effects in the size-dependent optical properties of cycloparaphenylene dications

We explain the visible and near-infrared optical properties of low-lying singlet excited states (S and S) of [5]-, [7]- and [9]cycloparaphenylene dications (CPPs). A narrow energy gap (<150 cm) separates these states at the Franck–Condon point of the individual molecule. The energy gap increases upon increasing the molecular size. Consequently, [5]CPP possesses highly overlapping S and S absorption bands. The overlap between these bands decreases and the resulting composite spectrum appears broader, particularly for [9]CPP. Theoretical spectra generated using quantum wavepacket calculations within the linear vibronic coupling approach match well with the experiment. Our findings reveal near-degenerate S and S minima, highlighting the relevance of both these states while assigning experimental fluorescence emission properties of CPPs.

Near-infrared switching between slow and fast light in the metal nanoparticles-graphene nanodisks-quantum dots hybrid systems

Graphene-based nanocomposites have recently attracted much interest due to the unique properties of graphene plasmons paving the way to promising potential applications. We study the near-infrared linear optical properties of the metal nanoparticle-graphene nanodisk- quantum dot hybrid system by numerically solving the equation of motion for the density matrix elements that describe the dynamics of the system where the quantum dot is modeled as a three-level atomic system of Λ configuration interacting with a weak probe field and strong control field. We obtain a strong switching between slow and fast light near resonance can be controlled by the distances between the components of the system, the size of metal nanoparticle as well as the Rabi frequency of the control field. Moreover, the proposed hybrid plasmonic system shows a significant amplification without population inversion can be effectively monitored by strength of the control field. Thus, we think that the metal nanoparticle-graphene nanodisk- quantum dot hybrid system has potential applications in communication, sensing, imaging, signal processing and optoelectronics devices.

Two Selective Sites Control of Cr3+‐Doped ABO4 Phosphors for Tuning Ultra‐Broadband Near‐Infrared Photoluminescence and Multi‐Applications

AbstractAchieving ultra‐broadband and tunable photoluminescence of near‐infrared (NIR) emitting phosphors is a key challenge for realizing its multi‐applications. Here, a series of new ABO4:Cr3+`(A3+ = Ga, Sc, In; B5+ = Ta, Nb) NIR‐emitting phosphors with unprecedented tunable photoluminescence based on crystallographic site engineering and crystal field regulation is reported. Large spectral tuning from NIR‐I to NIR‐II is realized with the peak position varying from 825 to 1025 nm, by cation substitution with decreasing crystal field strength. Broadened full‐width at half maximum from 125 to 231 nm can be tailored by controlling the occupancy of Cr3+ on two different sites. Potential multi‐applications of the tunable NIR emitting phosphors are proposed and validated in NIR spectroscopy detection, night vision, penetrating biology tissue, and so on. This work demonstrates that crystallographic site engineering can effectively tune the NIR optical properties of Cr3+‐doped phosphor materials for multi‐photoelectric applications.