Near-infrared Spectral Region Research Articles

Lithium cadmium phosphate glasses doped Sm3+ as a host material for near-IR laser applications

Abstract Sm2O3 doped Lithium Cadmium Phosphate (LCP) glasses are synthesized by a classical melting method, and their molecular structures are investigated by X-ray Diffraction method (XRD). FT-IR spectra, UV–Vis–NIR spectra, and emission spectra of these glasses are collected and analyzed. The emission spectrum of the present glass shows four emission lines at wavelengths of 562 nm, 598 nm, 645 nm, and 706 nm. The dependence of electronic polarizability and optical basicity of the synthesized glasses on the refractive index and bandgap is investigated. Judd-Ofelt theory is used to evaluate oscillator strengths and JO intensity parameters of Sm3+-doped LCP glasses. The emission and absorption cross-sections of the 562 nm line, which is originated from 6P3/2 → 6F5/2 transition, are calculated. Other emission spectral lines (598 nm, 645 nm, and 706 nm) couldn't be originated from transitions to the ground level. This is due to the weakness of the absorption transitions in this spectral region, i.e., 550 nm–900 nm. The most probable suggestion that these lines are originated from the transitions 4G9/2 → 6F1/2, 4G9/2 → 6F5/2, and 6P3/2 → 6F11/2. Emission and absorption cross-sections of some transitions in the Near-infrared spectral region are evaluated. Laser gain of the 1.1 μm and 1.2 μm emission lines are obtained, where a positive gain is observed at population factors (P) ≥ 0.6 .

Mass-specific light absorption coefficients of mineral particles in aqueous suspension for the ultraviolet to near-infrared radiation spectral region (200-2500 nm).

Light absorption by in-water suspended natural particles in the near-infrared radiation (NIR; 780-3000 nm) region has received little attention. Minerogenic matter is thought to be one source for NIR light absorption in aquatic environments. Here, mass-specific particulate light absorption coefficients of several particulate single minerals and mineral samples for the spectral range of 200-2500 nm are presented. The current methodology allows very sensitive measurements of particle suspension with a detection limit of about 2×10-6m2g-1 for the mass-specific absorption coefficient. Except for one, all mineral materials examined possessed significant light absorption throughout the full spectral range considered. The spectra revealed absorption features of specific elements (like iron) and from water structures (H2O, O-H bonds) in the mineral or crystal structure that have been known from reflectance measurements of minerals. The specific absorption in the NIR was as high as 0.02m2g-1 for laterite earths samples, but also below the detection limit for a steatite sample in a narrow spectral region (1600-1800 nm). The specific absorption by mineral particles in the NIR was, hence, highly variable from strong absorbing black minerals (magnetite) to low absorbing white clays. The information in the absorption coefficient spectrum can be used not only to identify specific mineral in natural particle assemblages but also to quantify their contribution to total particulate absorption in the NIR.

KCs Molecular Bands in the Visible Region

We measured light absorption of potassium and cesium mixed vapors at temperatures 360–660°C in the visible spectral region 380–780 nm. By comparison with the absorption of pure potassium or cesium vapors, we concluded that the spectral phenomena observed in the mixture peaking at 539 nm, 562 nm (and 700 nm) are new KCs molecular bands. Quantum mechanical calculations of the KCs molecular bands in the visible and near-infrared spectral region were performed using available theoretical potential curves for the KCs molecule. Using these calculations, we identified the three observed molecular bands as 31Π–X, 41Σ+–X, and 11Π–X electronic transitions of KCs molecule, respectively.

Weakening heat accumulation behavior caused by femtosecond pulses for high-performance antireflection micro-nano porous structures

Multi-scale porous micro-nano structures can exhibit perfect broadband antireflection performances on material surface and have essential importance in optical and optoelectronic devices. However, heat accumulation between the subsequent laser pulses increases the temperature of the material substrate and eventually changes micro-nano structures, affecting the antireflection performance. In this study, a strategy for preparing antireflection structures was proposed by weakening the heat accumulation behavior of femtosecond pulses on materials, and the proposed strategy was experimentally demonstrated. This strategy can tune the multi-scale porosity properties of the surface structure by cooling the material substrate under high-repetition-rate laser irradiation. Thus, comprehensively improved antireflection performances can be realized over ultraviolet to near-infrared spectral regions. When the pulse repetition rate is 150 kHz, the average reflectance of the silicon and Cu surfaces is 3.50% and 3.82%, respectively. The reduction rate of the reflectance on silicon and Cu surfaces reaches 25.21% and 19.75%, respectively. More importantly, the processing speed increased three times by increasing the pulse repetition rate. The presented strategy opens a novel and convenient route for the preparation of multi-scale porous micro-nano structures for various types of structural absorbing materials.

Laboratory-based spectral data acquisition of roof materials

ABSTRACT Roof characteristics such as material type and their properties information are essential to integrating urban agriculture (UA), rainwater harvesting systems (RWHS), and energy systems on roofs. Roof materials can be identified from their spectral signatures. However, this identification requires a priori knowledge of the materials’ spectral characteristics. The main perspective of this work is the future use of spectral data for roof classification. A common practice in mapping materials is the use of spectral libraries. In this regard, this work describes a novel framework for laboratory-based spectral data acquisition. The reflectance data of common, recently introduced (plastics and metals), and representative roof materials from the Mediterranean region were obtained. Data acquisition was conducted in a laboratory under controlled conditions using a high-spatial-resolution (HSR) sensor, which is usually used for airborne surveys. Large variations in the spectral reflectance data were observed due to the composition of the roof material. Flat spectral signatures were found for fibre cement, concrete, gravels and some metals, especially from the near-infrared (NIR) spectral region. Colour and surface finish greatly influence the visible (VIS) spectral range. It was confirmed that the view angle did not modify the spectral shapes. A collection of 39 spectral data of roof materials (ceramics, concrete, fibre cement, metals, plastics, paints, stone, and wood) were compiled into a spectral library that is available online.

Photosensitive highly Er/Yb co-doped phosphosilicate optical fibers for continuous-wave single-frequency fiber laser applications

Highly Er/Yb co-doped phosphosilicate fibers with low optical losses were fabricated by the MCVD method, utilizing an all-gas-phase deposition technique developed “in house.” Important characteristics such as photodarkening and photosensitivity of these fibers were thoroughly investigated. An almost negligible impact of photodarkening-induced losses (no more than 1 dB/m) was discovered in the near-infrared spectral region. The photosensitivity of hydrogen-loaded fiber samples was studied using excimer laser irradiation at a wavelength of 193 nm. A photoinduced refractive index value of 1 × 10 − 3 at the total UV irradiation exposure dose of 550 J / c m 2 was achieved. A single-frequency laser with a Fabry–Perot short cavity was designed by inscribing highly reflective ( R > --> 99.9 % ) and partially reflective ( R = 94.3 % ) fiber Bragg gratings directly in the Er/Yb co-doped phosphosilicate fiber core. The laser showed stable CW output emitting with a narrow peak centered at 1551.5 nm in the absence of any signs of Y b 3 + parasite lasing in a wavelength range from 1000 to 1100 nm.

Solar transparent radiators based on in-plane worm-like assemblies of metal nanoparticles

Windows with solar heating capacity can facilitate the indoors–outdoors thermal balance and improve the thermal energy efficiency of buildings, thus reducing the energy consumption in winter; however, their development has been hindered by the narrow light absorption and limited transparency of photothermal materials. In this study, transparent solar thermal surfaces on window glazing are constructed by the in-plane linear assembly of thermoplasmonics under a hierarchical electrostatic field. First results with gold nanoparticles (Au NPs) demonstrated that the hierarchical electrostatic field induced the random generation and chain growth of NP oligomers to yield controlled in-plane nanoassemblies. The linear morphology of these nanoassemblies enhanced the local electric field along the NP chains and caused additional plasmon absorption in the near-infrared spectral region, thereby improving the photothermal conversion effect without sacrificing the transparency. The solar thermal surface with Au NP assemblies increased the window glazing temperature by up to 9.8 °C under natural solar irradiation, while maintaining a high visible transmittance (>65%). The temperature increment was within the ballpark of the highest reported values and satisfied the standard requirements for thermal insulation of buildings in cold climates. This work extends new applications of linear nanoassemblies in solar energy harvesting and related energy conversion technologies.

Photodetachment and Electron Dynamics in 1-Butyl-1-methyl-pyrrolidinium Dicyanamide.

The ultrafast transient absorption spectrum of 1-butyl-1-methyl-pyrrolidinium dicyanamide, [Pyr1,4+][DCA-], was measured in the visible and near-infrared (IR) spectral regions. Excitation of the liquid at 4.6 eV created initially delocalized and highly reactive electrons that either geminately recombined (69%) or localized onto a cavity with a time constant of ∼300 fs. Electron localization was reflected in the evolution of the TA spectrum and the time-dependent loss of reactivity with a dichloromethane quencher. The delocalized initial state and spectrum of the free electrons were consistent with computational predictions by Xu and Margulis [ J. Phys. Chem. B, 2015, 119, 532-542] on excess electrons in [Pyr1,4+][DCA-]. The computational study considered two possible localization mechanisms for excess electrons, localization on ions, and localization on cavities. In the case of photogenerated electron-hole pairs, the results presented here demonstrate localization to cavities as the dominant channel. Following localization onto a cavity, the free electrons underwent solvation and loss of reactivity with the quencher with rates that slowed in time. The dynamics were similar to an analogous prior study on the related liquid [Pyr1,x+][NTf2-]. One significant difference was the larger yield of free electrons from photoexcitation of [Pyr1,4+][DCA-]. This was found to primarily reflect more efficient localization onto cavities rather than a slower geminate recombination rate.

Optically Tunable Tin Oxide-Coated Hollow Gold-Silver Nanorattles for Use in Solar-Driven Applications.

Core@shell metal nanoparticles have emerged as promising photocatalysts because of their strong and tunable plasmonic properties; however, marked improvements in photocatalytic efficiency are needed if these materials are to be widely used in practical applications. Accordingly, the design of new and functional light-responsive nanostructures remains a central focus of nanomaterial research. To this end, we report the synthesis of nanorattles comprising hollow gold–silver nanoshells encapsulated within vacuous tin oxide shells of adjustable thicknesses (∼10 and ∼30 nm for the two examples prepared in this initial report). These composite nanorattles exhibited broad tunable optical extinctions ranging from ultraviolet to near-infrared spectral regions (i.e., 300–745 nm). Zeta potential measurements showed a large negative surface charge of approximately −35 mV, which afforded colloidal stability to the nanorattles in aqueous solution. We also characterized the nanorattles structurally and compositionally using scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Futhermore, finite-difference time-domain simulation and photoluminescence properties of the composited nanoparticles were investigated. Collectively, these studies indicate that our tin oxide-coated hollow gold–silver nanorattles are promising candidates for use in solar-driven applications.

CuSx hole transport layer for PbS quantum dot solar cell

Lead sulfide (PbS) colloidal quantum dot solar cells (CQDSCs) are emerging photovoltaic technology due to their outstanding light-harvesting ability in the visible and near-infrared spectral region, long-term air stability, multiple exciton generation and solution processability. However, PbS CQDSCs have been limited by the unsatisfactory carrier collection in the CQD films. Band alignment engineering using p-type hole transport layer (HTL) was proved to efficiently promote the carrier collection in cells with both planar and ordered bulky heterojunctional (OBH) structures. Nevertheless, seeking for proper p-type materials suitable for the PbS CQDSCs is still an open question. Herein, we reported a new p-type metal-organic material, CuSx, could act as HTL of PbS CQDSCs with OBH structure. The CuSx possesses a Fermi level EF (−5.02 eV), shallower valence band energy (−5.48 eV) and conduction band energy (−3.19 eV), inducing a proper band alignment at the PbS light-harvesting layer/CuSx interface. This not only enhanced hole extraction proved by the increase of short-circuit current density (Jsc) from 19.12 to 22.33 mA/cm2, but also blocked back electron demonstrated by the extended carrier lifetime. Consequently, cells with CuSx HTL generated a power conversion efficiency of 5.2%, leading to a PCE increase of 13% compared with that of reference HTL-free cell (4.6%). Our work introduced a promoting CuSx hole extraction material which shows great potential application in quantum-dot-based devices suffering from the insufficient carrier collection.

Bedside hyperspectral imaging for the evaluation of microcirculatory alterations in perioperative intensive care medicine: a study protocol for an observational clinical pilot study (HySpI-ICU)

IntroductionNormalisation of macrocirculatory parameters during resuscitation therapy does not guarantee the restoration of microcirculatory perfusion in critical illness due to haemodynamic incoherence. Persistent microcirculatory abnormalities are associated with severity of...

Meat freshness revealed by visible to near-infrared spectroscopy and principal component analysis

Increasing concerns about adulterated meat encouraged industry looking for new non-invasive methods for rapid accurate meat quality assessment. Main meat chromophores (myoglobin, oxy-myoglobin, fat, water, collagen) are characterized by close comparable absorption in visible to near-infrared (NIR) spectral region. Therefore, structural and compositional variations in meat may lead to relative differences in the absorption of light. Utilizing typical fiber-optic probes and integrating sphere, a degradation of pork samples freshness was observed at room temperature referring to the relative changes in absorbance of main meat chromophores. The application of principal component analysis (PCA) used for examination of measured absorbance spectra revealed more detailed sub-stages of freshness, which are not observed by the conventional analysis of the reflectance spectra. The results show a great potential of the combined application of optical-NIR spectroscopy with complementary use of PCA approach for assessing meat quality and monitoring relative absorbance alternation of oxymyoglobin and myoglobin in visible, and fat, water, collagen in NIR spectral ranges.

Visible-to-near-infrared organic photodiodes with performance comparable to commercial silicon-based detectors

Photodetection in the visible and near-infrared (NIR) spectral regions offers a wide range of applications, such as image arrays of high pixel density and artificial intelligence. In this work, broadband organic photodiodes (OPDs) are developed with performance comparable to that of crystalline silicon-based commercial devices. Through the strategy of combining an NIR-absorbing non-fullerene acceptor and a thick junction, the resulting devices show significantly improved performance parameters, with a suppressed dark current density of 0.35 nA/cm2, an enhanced spectral response covering 300–1000 nm, and external quantum efficiency over 60% el/ph. Owing to the low dark current noise and high responsivity to NIR wavelengths, an unexpectedly high specific detectivity of 5.1 × 1013 Jones at 930 nm is obtained together with a linear dynamic range of 157 dB and a −3 dB cutoff frequency of 4.5 kHz. These results reveal that the NIR OPD has great potential for 2D and 3D imaging applications with a high frame rate and multiple band selection.

Tunable Polarization Gratings Based on Nematic Liquid Crystal Mixtures Photoaligned with Azo Polymer-Coated Substrates

Liquid crystal polarization gratings are of great interest for optical communications as elements performing beam steering, splitting, multiplexing or beam combining. Material birefringence, cell thickness or a period of the liquid crystal director pattern influence, among other features, spectroscopic and electro-optical characteristics of fabricated devices, determining thus their functionality and applicability. Here, we report on liquid crystal polarization gratings that allow for complete maximization of the first-order diffraction efficiency (resulting in total elimination of the zeroth-order diffraction) for any wavelength of an incident beam from green to the near-infrared spectral region by applying a low electric voltage. The gratings with periods as small as 10 μm were obtained by holographic exposure of the cell substrates coated with light-sensitive azo polymer alignment layers, and then filled with three different liquid crystal mixtures. The influence of gold nanoparticle dopants in the liquid crystalline mixtures on spectroscopic and electro-optical properties of the devices is presented. Moreover, on the basis of the measured transmittance spectra of the fabricated gratings, the unknown birefringence of liquid crystal mixtures as well as their effective birefringence due to molecular reorientation in the electric field in the visible and near IR region were determined.

Impact of spectroscopic information on total column water vapor retrieval in the near-infrared spectral region

Water vapor is an important greenhouse gas. The atmospheric water vapor content is monitored by remote methods, which require accurate spectroscopic information about H2O absorption line parameters. The problems of accuracy of accounting the selective water vapor absorption in the simulation of atmospheric transfer of solar radiation are considered in this work. The atmospheric spectra are simulated using different versions of spectroscopic databases of H2O absorption line parameters and compared with the solar spectra measured by a ground-based Fourier transform spectrometer. The total column (TC) water vapor is retrieved from the solar spectra measured. The effect of the differences in absorption line parameters in modern spectroscopic databases on the results of retrieval of the TC water vapor from high-resolution spectra is estimated.

Photothermally active nanoparticles as a promising tool for eliminating bacteria and biofilms

Bacterial contamination is a severe issue that affects medical devices, hospital tools and surfaces. When microorganisms adhere to a surface (e.g., medical devices or implants) they can develop into a biofilm, thereby becoming more resistant to conventional biocides and disinfectants. Nanoparticles can be used as an antibacterial agent in medical instruments or as a protective coating in implantable devices. In particular, attention is being drawn to photothermally active nanoparticles that are capable of converting absorbed light into heat. These nanoparticles can efficiently eradicate bacteria and biofilms upon light activation (predominantly near the infrared to near-infrared spectral region) due a rapid and pronounced local temperature increase. By using this approach new, protective, antibacterial surfaces and materials can be developed that can be remotely activated on demand. In this review, we summarize the state-of-the art regarding the application of various photothermally active nanoparticles and their corresponding nanocomposites for the light-triggered eradication of bacteria and biofilms.

Lanthanide-Doped Near-Infrared Nanoparticles for Biophotonics.

Light in the near-infrared (NIR) spectral region is increasingly utilized in bioapplications, providing deeper penetration in biological tissues owing to the lower absorption and scattering in comparison with light in the visible range. Lanthanide-doped luminescent nanoparticles with excitation and/or emission in the NIR range have recently attracted tremendous attention as one of the prime candidates for noninvasive biological applications due to their unique optical properties, such as large Stokes shift, spectrally sharp luminescence emissions, long luminescence lifetimes, and excellent photostability. Herein, recent advances of lanthanide-doped nanoparticles with NIR upconversion or downshifting luminescence and their uses in cutting-edge biophotonic applications are presented. A set of efficient strategies for overcoming the fundamental limit of low luminescence brightness of lanthanide-doped nanoparticles is introduced. An in-depth literature review of their state-of-art biophotonics applications is also included, showing their superiority for high-resolution imaging, single-nanoparticle-level detection, and efficacy for tissue-penetrating diagnostics and therapeutics.

Studying the Structural, Morphological, Optical, and Electrical Properties of CdS/PbS Thin Films for Photovoltaic Applications

The cadmium sulfide (CdS) and lead sulfide (PbS) materials have been chosen in order to boost solar energy conversion from ultraviolet region to the near-infrared (NIR) spectral region. These materials belonging to the II–VI group have suitable direct band gaps and in solar energy conversion. CdS and PbS layers are used as window and absorber materials, respectively, in solar cells. This paper presents structural, morphological, and optical properties of PbS and CdS thin films prepared by chemical spray pyrolysis at different temperatures as well as its photovoltaic performance. The X-ray diffraction results show the PbS films have cubic structure and CdS films have hexagonal structure. FESEM measurements reveal the films have homogeneous surfaces with spherical particles. Optical analyses exhibit the optical band gap redshifts as the substrate temperature increases. Illumination current density–voltage test of ITO/CdS/PbS/Au heterojunction with different thicknesses of PbS layer has been evaluated. The optimal results are obtained in ITO/CdS/PbS/Au solar cell where thickness of PbS layer is of 0.9 μm with maximum short circuit current, open circuit voltage, and fill factor as well as highest efficiency.

Ab Initio Study of Vibronic and Magnetic 5f-to-5f and Dipole-Allowed 5f-to-6d and Charge-Transfer Transitions in [UX6]n- (X = Cl, Br; n = 1, 2).

The absorption spectra of the octahedral [UX6]n- (X = Cl, Br; n = 1, 2) complexes in the near-infrared (NIR) and UV-vis spectral regions were studied theoretically, using a relativistic restricted active space second-order perturbation theory (RASPT2) wavefunction framework, with the spin-orbit (SO) coupling treated by state interaction, in conjunction with Kohn-Sham density functional theory calculations for determining the vibrational normal modes. The electric-dipole-allowed ligand-to-metal charge-transfer (LMCT) and 5f-to-6d transitions, and the electric-dipole-forbidden 5f-to-5f ligand field (LF) transitions, are thereby obtained within the same theoretical framework. For the 5f-to-5f LF transitions, the observed absorption intensity is mostly due to vibronic coupling with low-energy electric-dipole-allowed transitions, but in some cases, the magnetic dipole intensity of the purely electronic transition has comparable intensity to the vibronic transitions. Experimental LF spectra of 5f2 open-shell systems have been reported decades back, but ab initio calculations of their vibronic intensity have not yet been reported in the literature. Although the LF spectra for the 5f2 systems can be assigned in detail, based on the calculations, the spectra are very complex and the underlying electronic states are strongly multiconfigurational. Therefore, the usefulness of the LF spectra beyond serving as a "fingerprint" of the LF and the metal oxidation state appears to be limited.

Quinoline‑ and Benzoselenazole-Derived Unsymmetrical Squaraine Cyanine Dyes: Design, Synthesis, Photophysicochemical Features and Light-Triggerable Antiproliferative Effects against Breast Cancer Cell Lines.

Photodynamic therapy is an innovative treatment approach broadly directed towards oncological diseases. Its applicability and efficiency are closely related to the interaction of three main components, namely a photosensitizer, light and molecular triplet oxygen, which should drive cell death. Recently, several studies have demonstrated that squaraine cyanine dyes have a set of photophysical and photochemical properties that have made of these compounds’ potential photosensitizers for this therapeutic modality. In the present research work, we describe the synthesis and characterization of four quinoline- and benzoselenazole-derived unsymmetrical squaraine cyanine dyes. Except for the precursor of aminosquaraine dyes, i.e., O-methylated derivative, all dyes were evaluated for their behavior and absorption capacity in different organic and aqueous solvents, their ability to form singlet oxygen, their light-stability, and in vitro phototherapeutic effects against two human breast cancer cell cultures (BT-474 and MCF-7). Regardless of the nature of the used solvents, the synthesized dyes showed intense absorption in the red and near-infrared spectral regions, despite the formation of aggregates in aqueous media. Dyes showed high light-stability against light exposure. Despite the low ability to produce singlet oxygen, aminosquaraine dyes demonstrated worthy in vitro phototherapeutic activity.