Near-infrared Wavelengths Research Articles

Enhanced Visible‐NIR Dual‐Band Performance of GaAs Nanowire Photodetectors Through Phase Manipulation

AbstractHigh‐quality 1D nanowires (NWs) are widely used in photodetectors due to their exceptional optoelectronic properties. However, internal structural defects and surface states trap carriers, limiting device performance. In this study, low‐defect‐density GaAs NWs are synthesized using molecular beam epitaxy (MBE) combined with the droplet wetting method, effectively reducing non‐radiative recombination due to defect states and enabling high‐performance dual‐band photodetectors for visible (VIS) to near‐infrared (NIR) wavelengths. Compared to defect‐rich GaAs NWs, the high‐quality GaAs NW photodetector shows a 6.5‐fold increase in responsivity and a 4.7‐fold improvement in detectivity at a VIS wavelength of 532 nm, achieving values of 615.2 A W−1 and 9.1 × 1012 Jones. Similarly, the devices exhibit a 10.7‐fold increase in responsivity and a 12.1‐fold improvement in detectivity at a NIR wavelength of 808 nm. Furthermore, response time measurements highlight the influence of defects on photoelectric characteristics. Carrier transport mechanisms under varying defect densities are analyzed in detail through numerical simulations. These results emphasize the potential of high‐quality NWs with exceptional photoelectric properties to drive advancements in next‐generation nanoscale optoelectronic devices.

Development of NIR photocleavable nanoparticles with BDNF for vestibular neuron regeneration

Among nanoparticle platforms, light or photoresponsive nanoparticles have emerged as a promising drug delivery strategy with spatiotemporal control while minimizing off-target effects. The characteristic absorption spectrum of the photoresponsive moiety dictates the wavelength of light needed to activate bond cleavage. However, the low tissue penetration depth limit and short-wavelength ultraviolet (UV) cellular toxicity are considered disadvantageous. This study developed a vestibular ganglion neuron organoid as a model for vestibulopathy. UV and near-infrared (NIR) radiation targeted the inner ear and neural cells, followed by toxicity evaluation. A significantly smaller toxicity of NIR light was confirmed. The photocleavage release of brain-derived neurotrophic factor (BDNF) was used by applying NIR wavelength. The results indicate that polyethylene glycol octamethylene diamine derivative conjugated with leucomethylene blue with an ethanolamine linker nanoparticle can be effectively disassembled and release BDNF when using the 808 nm laser as a trigger. The findings of the cytotoxicity assay suggest that photocleavable nanoparticles (PCNs) and laser irradiation are safe and biocompatible for human-derived and neural progenitor types of cells. Phototriggered BDNF release by NIR laser supported the growth and differentiation of human neural progenitor cells in culture. In addition, the vestibulopathy organoid exhibited a significant regenerative effect. This study harnesses the full potential of NIR laser PCNs to treat vestibular neuropathies.Graphical abstract

The effects of spatial scales on the in situ photometric analysis of the Chang'e-4 landing region

Visible and near-infrared reflectance spectroscopy is widely used to determine the surface composition and maturity of the Moon, but it may be influenced by the observation geometry. In situ observation is crucial for understanding the angular scattering behaviour of the lunar surface and can help to link laboratory measurements with orbital remote sensing. The Chang’e-4 (CE-4) rover has been exploring on the lunar surface for five years and has collected in situ spectral data covering a wide range of measurement angles. Our aim is to investigate the impact of different spatial scales (from several centimetres to tens of centimetres) on the photometric analysis results of the CE-4 landing region and the phase reddening effects. We constructed four sets of spectrophotometric data with different spatial scales (∼2 cm, ∼5.5 cm, ∼10.5 cm, and ∼15 cm×21 cm) based on the spectral data acquired by the CE-4 imaging spectrometer and employed the Hapke model for photometric inversion analysis. For the four different spatial scales, the derived phase function parameters lie outside the `hockey stick' area and the photometric roughness parameter is smaller than $10^∘$. These parameters show clear variation trends as the spatial scale increases. The reflectance phase curves show a distinct bowl-like shape with a turning point near $90^∘$ of phase angle. The colour ratios (ratios of reflectance at two different wavelengths) manifest significant phase-angle dependence, which may affect the estimation of surface maturity. The colour ratio phase curves exhibit a distinct arch shape when involving visible bands (< 745 nm), whereas it appears as a monotonically increasing pattern when both bands are in the near-infrared wavelength range (R945/R745). Varied spatial scales have no significant effect on the phase curve shape and phase reddening effects, but do influence the photometric parameters derived using the Hapke model. This study could serve as a reference to link the discrepancies between laboratory and orbital research.

Near infrared quantum ghost spectroscopy for threats detection

Quantum sensing is a rapidly growing branch of research within the area of quantum science and technology offering key resources, beyond classical ones, with potential for commercialization of novel (quantum) sensors. The exploitation of quantum resources offered by photons can boost the performance of quantum sensors for innovative and challenging applications. In this paper, we build on the idea that quantum ghost spectroscopy (QGS), i.e. the counterpart in the frequency domain of quantum ghost imaging (QGI), can target specific applications in the detection of possible threats. This is implemented by exploiting the opportunities offered by quantum optics, i.e. the generation of photon pairs characterized by spectral correlations. We will discuss our main results obtained with pure QGS experiments showing that it is possible to assess the presence of a target dealing with a low resources measurement. The time-frequency domain reveals a huge potential for several applications, and frequency correlations represent a versatile tool that can be exploited to enable the spectral analysis of objects where a direct measurement would not be feasible (e.g. due to security). The use of non-degenerate sources of correlated photons allowed to reveal spectral features in the near-infrared wavelengths employing the usual detectors for the visible region, showing the effectiveness of this technique.

Photobiomodulation Promotes Wound Healing in a Diabetic Cellular Model

Abstract Wound healing is a critical process that activates tissue repair after injury. In diabetes mellitus however, this process is deregulated and leads to the development of non-healing diabetic ulcers. Current treatments, which include glycaemic control and wound debridement are moderately effective as there is a challenge of recurrence. Therefore, improved therapeutic strategies are required for the treatment of diabetic ulcers. Photobiomodulation (PBM) at the red and near-infrared (NIR) wavelength range has been shown to improve the healing of cutaneous wounds by promoting cell proliferation and wound closure. The aim of this study was to determine if PBM at a wavelength of 660 nm and a fluence of 5 J/cm2 can induce wound healing in a diabetic wounded (DW) cellular model. Human dermal fibroblasts (WS1) were continuously cultured in a high-glucose environment to induce a diabetic state. Prior to irradiation/PBM, a central scratch was created to create the “wound”. Cell migration and cell viability analyses were performed 24 and 48 h post-PBM. The results showed that cell migration was increased in irradiated diabetic wounded (DW) cells compared to the non-irradiated control cells. The Trypan blue and MTT data showed no statistical difference in cell viability and proliferation between irradiated and non-irradiated cells at 24 and 48 h post-PBM. The preliminary findings of this study indicate that PBM does not cause significant cell death and promotes “wound” closure in diabetic wounded cells in vitro.

16-band single-photon imaging sensor based on Fabry-Perot resonance

We have demonstrated a 16 wavelength selective spectral bands imaging sensor-based Fabry-Perot (FP) structure for use in the near-infrared wavelength band (715 nm-915 nm). The designed structure consists of two symmetric SiC/SiO2 distributed Bragg reflector (DBR) multilayer structures that sandwich a SiO2 interval layer. We tuned the thickness of the SiO2 interval layer to achieve wavelength selectivity and tunability. Fabrication and measurement results based on the FP structure show high resolution and good uniformity. Furthermore, for the first time, we combined the ultra-narrow band FP filter with single photon avalanche diode (SPAD). Finally, a category algorithm to reconstruct the narrow-band filter and improve the cross-talk caused by the overlap of the FP curve is proposed. The combination of FP hyper-spectral filter with SPAD opens the door to several novel applications.

Study of Minor Chromophores in Biological Tissues by Diffuse Optical Spectroscopy (Review).

Diffuse optical spectroscopy (DOS) is a rapidly advancing non-invasive diagnostic technique to investigate biological tissue, based on probing the target object with optical radiation in the visible and/or near-infrared wavelength range and detecting the diffusely scattered light from the tissue. The signals obtained through DOS provide extensive information about the biochemical composition of tissues due to the presence of light-absorbing compounds known as chromophores. To date, DOS is widely employed to detect major chromophores such as deoxygenated (Hb) and oxygenated (HbO2) hemoglobin, water, lipids, and melanin. The concentrations of Hb and HbO2 in biological tissues are highly significant in clinical research, as they offer valuable insights into tissue oxygenation status and enable the detection of hypoxia. However, biological tissues also contain less-studied chromophores - minor chromophores - which also contribute to the overall absorption spectrum. These include various globins, such as methemoglobin, carboxyhemoglobin, and myoglobin, as well as cytochromes and cytochrome c oxidase. Identifying minor chromophores using DOS is challenging due to their relatively low absorption contributions compared to major chromophores, as well as the limited understanding of their specific absorption spectra. Nevertheless, the simultaneous detection of both major and minor chromophores could provide a comprehensive understanding of metabolic processes within vascular, intracellular, and mitochondrial compartments of tissues. This would substantially expand the potential applications of DOS in both research and clinical studies. In this review we examine literature sources that explore the investigation of minor chromophores in biological tissues by DOS, discuss the role of major chromophores, and evaluate the potential for simultaneous detection of both major and minor chromophores with DOS.

Accurate Estimation of Methemoglobin and Oxygen Saturation in Skin Tissue Using Diffuse Reflectance Spectroscopy and Artificial Intelligence.

In this paper, we present a noninvasive method for the accurate estimation of methemoglobin concentration. The proposed technique incorporates a novel machine learning model using the artificial neural network to detect methemoglobin and oxygen saturation from the diffuse reflectance spectra of skin tissue. Sixty-six spectra were simulated using a four-layer tissue model with varying oxygen saturation and methemoglobin concentration. A multifiber probe-based DRS setup in the visible and near-infrared wavelength range was used. The best accuracy, with a mean absolute error (MAE) of 0.0392% for the concentration of methemoglobin and 0.0273% for the percentage of oxygen saturation on the created data set, was achieved. Our method was also experimentally verified using DRS spectra collected from human subjects. Consequently, the findings demonstrate the ability of broadband DRS to noninvasively differentiate subtle changes in methemoglobin and hemoglobin levels despite their overlapping spectral features.

Asynchronous equal optical path difference sampling method for MEMS-based Fourier transform spectrometers

In a MEMS micromirror-based Fourier transform (FT) spectrometer (FTS) working in the near-infrared (NIR) range, a laser with a NIR wavelength is usually used to accurately detect the position of the MEMS mirror plate in real-time. The interference signal generated by the NIR laser for position measurement is acquired synchronously with the broadband interference signal from the sample under test, causing strong coupling of the laser signal into the sample signal. In this work, an asynchronous equal optical path difference (AEOPD) sampling method is proposed to avoid the optical coupling due to the synchronous signal acquisition. In this method, the sample interference signal is acquired when the laser is turned off, i.e., the laser is turned on periodically. A MEMS FTS system based on an electrothermal MEMS micromirror has been built to verify the feasibility of this method. Experimental results show that the period of the laser pulses can be as long as 12.5 minutes when maintaining the MEMS FTS with its spectral repeatability within 0.0005. Experiments also demonstrate that the laser coupling is eliminated and the signal-to-noise ratio (SNR) is increased. Thus the method proposed in this work can be applied in MEMS-based FTS spectrometers in the future.

Research on the Inversion Method of Dust Retention in Grassland Plant Canopies Based on UAV-Borne Hyperspectral Data

Monitoring the dust retention content in grassland plants around open-pit coal mines is of significant importance for environmental pollution monitoring and the development of dust control strategies. This paper focuses on the HulunBuir grassland in the Inner Mongolia Autonomous Region, China. UAV-borne hyperspectral data and measured dust retention content in plant canopies are used as data sources. The spectral response characteristics of canopy dust retention are analyzed, and four types of optimized spectral indices are constructed, including the difference index (DI), ratio index (RI), normalized difference index (NDI), and inverse difference index (IDI). The spectral index with the highest absolute value of the correlation coefficient with the canopy dust retention is selected as the feature variable for each spectral index. In addition, machine learning methods such as the partial least squares regression (PLSR), support vector machine (SVM), and random forest (RF) methods are used to develop models for the inversion of canopy dust retention. The results show that as the dust retention content increases, the canopy reflectance in the visible wavelength initially increases and then decreases, while the reflectance in the near-infrared wavelength gradually decreases. The spectral reflectance values at different dust retention levels exhibit significant differences in the 400–420 nm, 579–698 nm, and 714–1000 nm ranges. The four types of spectral indices constructed exhibit high correlations with the canopy dust retention content, and the spectral index with the highest absolute value of the correlation coefficient is composed of near-infrared bands. The dust retention inversion model established using the RF method is more accurate than those established using the PLSR and SVM methods and yields a higher prediction accuracy. The high canopy dust retention areas are mainly distributed within 900 m of the mining area, and the dust retention gradually decreases with distance. In addition, with increasing dust retention, the fractional vegetation cover (FVC) decreases. The results of this study provide a theoretical basis and technical support for monitoring dust retention in grassland plant canopies and for dust control measures.

Optical Spectroscopy of Cerebral Blood Flow for Tissue Interrogation in Ischemic Stroke Diagnosis.

Ischemic stroke remains a leading cause of morbidity and mortality worldwide, and early diagnosis is critical for improving clinical outcomes. This paper presents an optical design framework combining speckle contrast optical spectroscopy (SCOS) with multiwavelength reflectance spectroscopy to monitor subtle changes in cerebral blood flow during ischemic events. The research aims to enable precise tissue interrogation using high-resolution, low-scatter imaging. Key to the system's accuracy is a 1.55 μm small beam waist, a grating density of 1300 grooves/mm, and a 15.53 μm depth of focus. The calculated effective focal length of 8333.33 μm enhances the resolution to 4.07 μm, improving the detection of minor changes in tissue optical properties. We investigate the sensitivity of various near-infrared wavelengths (660, 785, 800, and 976 nm) to ischemic-induced changes, with particular emphasis on the 976 nm wavelength, which demonstrates superior tissue penetration and increased sensitivity to variations in blood perfusion and tissue density during ischemia. Optical markers such as spot-size widening, spatial intensity shifts, and central intensity decrease are identified as reliable indicators of ischemia. Our findings suggest that multiwavelength reflectance analysis, particularly in the near-infrared range, provides a practical, noninvasive approach for continuously monitoring ischemic strokes. This technique indicates potential for improving early diagnosis and real-time monitoring of cerebral perfusion, which allows for continuous, noninvasive monitoring of cerebral perfusion and management of ischemic strokes, improving patient outcomes and clinical decision-making.

Organic Synaptic Transistors Based on C8-BTBT/PMMA/PbS QDs for UV to NIR Face Recognition Systems.

Developing optoelectronic synaptic devices with low power consumption, broadband response, and biological compatibility is crucial to simulate the functions of optic nerve. Here, an organic synapse transistor based on C8-BTBT/PMMA/PbS quantum dots (PbS QDs) is fabricated, which has good stability, low power consumption (as low as 0.49 fJ per event under 800 nm near-infrared optical pulse), and broadband response from ultraviolet to near-infrared wavelengths. Based on the trap and release of photogenerated carriers by PbS QDs, a series of synaptic behaviors are simulated by the device. Furthermore, we use artificial neural network as the model to realize the recognition of facial feature image in the broad spectral range; the recognition rate reached 96.25% (350 nm ultraviolet), 92.14% (580 nm visible), and 90.03% (800 nm near-infrared). This work is beneficial for advancing the development of future artificial intelligence vision sensing.

High-speed short-wavelength communications utilizing thin-film lithium niobate.

We demonstrate a low half-wave voltage (0.7 V), high-bandwidth modulator in thin-film lithium niobate operating at near-infrared wavelengths (850 nm) and show the ability to transmit 60 GBd signals with direct electrical driving (400 mVpp). This paves the way for high-bandwidth, low-power, and compact optical engines for short-range optical communication.

Strain-Induced Bandgap Narrowing in Crumpled TMDs for NIR Light Detection.

Transition metal dichalcogenides (TMDs)such as MoS2 and WS2 emerge as promising materials in optoelectronics, especially for flexible photo- /image-sensors due to their direct bandgap nature. However, the intrinsic bandgaps of these semiconductor monolayers (e.g., MoS2 ≈1.86eV and WS2 ≈2.0eV) restrict the operational wavelength range of developed photosensors in the visible spectrum. In addition, their ultrathin nature provides a limited optical absorption cross-section that restricts the device's performance. Exploiting the strong impact of strain on the electronic band structure, strain engineering has emerged as a promising approach for adjusting the electrical and optical characteristics of layered semiconductors. In particular, the application of tensile strain in MoS2 and WS2 can decrease their bandgaps, which potentially can extend the optical absorption toward the near-infrared (NIR) wavelength. Herein, a non-conventional crumpling approach is employed to incorporate uniaxial tensile strain into a graphene/TMD/graphene metal-semiconductor-metal photodetector (PD) array. The utilized crumpled geometry provides exclusive photon management with enhanced light scattering and trapping at the sinusoidal surface that results in increased light absorption in NIR wavelength range.

Photoacoustic imaging of rat kidney tissue oxygenation using second near-infrared wavelengths.

Conventionally, spectral photoacoustic imaging (sPAI) to assess tissue oxygenation ( ) uses optical wavelengths in the first near-infrared (NIR-I) window. This limits the maximum photoacoustic imaging depth due to the high spectral coloring of biological tissues and has been a major barrier to the clinical translation of the technique. We demonstrate the second near-infrared (NIR-II) tissue optical window (950 to 1400nm) for the assessment of blood and tissue . The NIR-II PA spectra of oxygenated and deoxygenated hemoglobin were first characterized using a phantom. Optimal wavelengths to minimize spectral coloring were identified. The resulting NIR-II PA imaging methods were then validated in vivo by measuring kidney in adult female rats. sPAI of whole blood, in a phantom, and of blood in kidneys in vivo produced PA spectra proportional to wavelength-dependent optical absorption. Using the NIR-II wavelengths for spectral unmixing resulted in a decrease in the error of the estimated blood , compared with conventional NIR-I wavelengths. In vivo measurements of kidney validated these findings, with a similar 50% reduction in error when using NIR-II wavelengths versus NIR-I wavelengths at larger illumination depths. sPAI using NIR-II wavelengths improved the accuracy of tissue measurements. This is likely due to reduced scattering, which reduces the attenuation and, therefore, the impact of spectral coloring in this wavelength range. Combined with the increased safe skin exposure fluence limits in this wavelength range, these results demonstrate the potential to use NIR-II wavelengths for quantitative sPAI of from deep heterogeneous tissues.

Detectability of Solar Rotation Period across Various Wavelengths

Abstract The light curves of old G dwarfs obtained in the visible and near-infrared wavelength ranges are highly irregular. This significantly complicates the detectability of the rotation periods of stars similar to the Sun in large photometric surveys, such as Kepler and TESS. In this study, we show that light curves collected in the ultraviolet (UV) wavelength range are much more suitable for measuring rotation periods. Motivated by the observation that the Sun’s rotational period is clearly discernible in the UV part of the spectrum, we study the wavelength dependence of the rotational period detectability. We employ the Spectral and Total Irradiance Reconstructions model to characterize the detectability of the solar rotation period across various wavelengths using the autocorrelation technique. We find that at wavelengths above 400 nm, the probability of detecting the rotation period of the Sun observed at a random phase of its activity cycle is approximately 20%. The probability increases to 80% at wavelengths shorter than 400 nm. These findings underscore the importance of UV stellar photometry.

Interfacial π-Electron Cloud Extension and Charge Transfer Between Preferable Single-Crystalline Conjugated MOFs and Graphene for Ultrafast Pulse Generation.

2D conjugated metal-organic frameworks (MOFs) have attracted significant attention in various fields due to their outstanding characteristics. However, due to the strong interlayer π-π stacking interactions, the preparation of high-quality and atomic-scale single-crystalline conjugated MOF structures continues to pose a significant challenge. The investigation of its nonlinear optical (NLO) property and application for ultrafast photonics is still rare. Herein, the ultrathin Cu3(HHTP)2 and Ni3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) nanosheets (CuHHTPNs and NiHHTPNs) with single-crystalline characteristic are prepared by surfactant-assisted solution synthesis strategy. Moreover, the π-π stacked CuHHTPNs(NiHHTPNs)/graphene van der Waals heterostructures (CuNsG-VHS and NiNsG-VHS) are achieved by ultrasound-assisted method. According to characterization analyses and theoretical simulations, this preferable stacking ultrathin van der Waals heterostructures exhibits superior π-conjugated electron cloud extension, charge transfer, and NLO properties. Noticeably, the third-order NLO polarizability of CuNsG-VHS keeps in a relatively high level compared with the reported 2D saturable absorber materials in the near-infrared wavelength range. Based on these outstanding properties, CuNsG-VHS can serve as an excellent saturable absorber to achieve fundamental mode-locking with femtosecond pulse duration, and high-order harmonic mode-locking with GHz repetition frequency. These demonstrations provide a valuable strategy for the development of promising conjugated MOFs for ultrafast photonics and advanced optoelectronic devices.

Extending certified spectral fluorescence standards for the calibration and performance validation of fluorescence instruments to the NIR-closing the gap from 750 to 940 nm with two novel NIR dyes.

Fluorescence techniques such as fluorescence spectroscopy, microfluorometry, and fluorescence microscopy, providing spectral, intensity, polarization, and lifetime information, are amongst the most broadly utilized analytical methods in the life and materials sciences. However, the measured fluorescence data contain sample- and instrument-specific contributions, which hamper their comparability across instruments and laboratories. Comparable, instrument-independent fluorescence data require the determination of the fluorescence instrument's wavelength-dependent spectral responsivity, also termed emission correction curve, for the same instrument settings as those used for the fluorescence measurements as a prerequisite for the subsequent correction of the measured instrument-specific data. Such a spectral correction is essential for the performance comparison of different fluorescent labels and reporters, quantitative fluorescence measurements, the determination of the fluorescence quantum yield, and the spectroscopic measure for the fluorescence efficiency of a fluorophore. Simple-to-use tools for obtaining emission correction curves are chromophore-based reference materials (RMs), referred to as fluorescence standards, with precisely known, preferably certified instrument-independent fluorescence spectra. However, for the increasingly used near-infrared (NIR) wavelength region >700 nm, at present, no spectral fluorescence standards are available. To close this gap, we developed two novel spectral fluorescence standards, BAM F007 and BAM-F009, with broad emission bands from about 580 to 940 nm in ethanolic solution. These liquid fluorescence standards currently under certification, which will be released in 2025, will expand the wavelength range of the already available certified Calibration Kit BAM F001b-F005b from about 300-730 to 940 nm. In this research article, we will detail the criteria utilized for dye and matrix selection and the homogeneity and stability tests accompanying dye certification as well as the calculation of the wavelength-dependent uncertainty budgets of the emission spectra BAM F007 and BAM-F009, determined with the traceably calibrated BAM reference spectrofluorometer. These fluorescence standards can provide the basis for comparable fluorescence measurements in the ultraviolet, visible, and NIR for the fluorescence community.

Nitrogen-Doped Ultrananocrystalline Diamond - Optoelectronic Biointerface for Wireless Neuronal Stimulation.

This study presents a semiconducting optoelectronic system for light-controlled non-genetic neuronal stimulation using visible light. The system architecture is entirely wireless, comprising a thin film of nitrogen-doped ultrananocrystalline diamond directly grown on a semiconducting silicon substrate. When immersed in a physiological medium and subjected to pulsed illumination in the visible (595nm) or near-infrared wavelength (808nm) range, charge accumulation at the device-medium interface induces a transient ionic displacement current capable of electrically stimulating neurons with high temporal resolution. With a measured photoresponsivity of 7.5mA W-1, the efficacy of this biointerface is demonstrated through optoelectronic stimulation of degenerate rat retinas using 595nm irradiation, pulse durations of 50-500ms, and irradiance levels of 1.1-4.3mW mm-2, all below the safe ocular threshold. This work presents the pioneering utilization of a diamond-based optoelectronic platform, capable of generating sufficiently large photocurrents for neuronal stimulation in the retina.

Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium

Abstract The observation of the kilonova AT2017gfo and investigations of its light curves and spectra confirmed that neutron star mergers are sites of r-process nucleosynthesis. However, the identification of elements responsible for the spectral features is still challenging, particularly at the near-infrared wavelengths. In this study, we systematically searched for all possible near-infrared transitions of heavy elements using experimentally calibrated energy levels. Our analysis reveals that most candidate elements with strong absorption lines are lanthanides (Z = 57–71) and actinides (Z = 89–103). This is due to their complex structures leading to many low-lying energy levels, which results in strong transitions in the near-infrared range. N. Domoto et al. (2022) have shown that La iii and Ce iii can explain the absorption features at λ ∼ 12000–15000 Å. While our results confirm that these two elements show strong infrared features, we additionally identify Gd iii as the next most promising species. Due to its unique atomic structure involving the half-filled 4f and the outer 5d orbitals, Gd iii has one of the lowest-lying energy levels, between which relatively strong transitions occur. We also find absorption lines caused by Gd iii in the near-infrared spectrum of a chemically peculiar star HR 465, which supports their emergence in kilonova spectra. By performing radiative transfer simulations, we confirm that Gd iii lines affect the feature at ∼12000 Å previously attributed to La iii. Future space-based time-series observations of kilonova spectra will allow the identification of Gd iii lines.