Local Spectroscopy Research Articles

Simulation and experimental study of local high frequency resistance distribution in proton exchange membrane fuel cells under steady and dynamic conditions

Proton-exchange membrane (PEM) dry–wet variation during PEM fuel cell (PEMFC) operation markedly affects PEMFC lifespan. Therefore, deeper insights into the mechanical degradation mechanism of PEM require analysis of the membrane dry–wet change process. The stress changes caused by PEM dry–wet variations may induce mechanical failure. In practice, although high-frequency resistance (HFR) is often used to indirectly characterize PEM dry–wet degrees, numerical simulation can effectively analyze the mass transfer inside a PEMFC for parameters that are difficult to measure directly experimentally (such as membrane water content). Additionally, three-dimensional (3D) model validation requires more comprehensive experimental methods. In this study, we validate the simulated resistance distribution results through local electrochemical impedance spectroscopy. We also discuss the mass- and heat-transfer distribution characteristics under different current densities and analyze the influence of these characteristics on local HFR distribution variations. The calculated HFR distribution results show a certain degree of agreement with the experimental results. Due to the membrane self-humidification effect, the position of the minimum HFR value shifts upstream of the cathode at a high current density. The observed change in membrane stress results from variations in membrane water and temperature distributions with changes in current density. Steady-state HFR distribution analysis to uncover the membrane dry–wet variations caused by load changes—which would affect the HFR distribution changes—reveal that the HFR at the air outlet and the membrane dry–wet variations are more pronounced than at other locations due to the influence of reaction rate and gas velocity. Overall, this study demonstrates that 3D simulations can reliably predict the local HFR distribution of PEMFCs, enabling membrane stress variation analysis and providing guidance for fuel cell design and operation.

Imaging Brain Tissue with Quantum Light at Low Power.

Light-induced tissue damage is a crucial limitation for traditional microscopy of the living brain, underscoring the need for new techniques that minimize exposure of samples to light. Here, we tested the hypothesis that quantum light, i.e., entangled photons, could detect brain structures at a lower excitation energy. In a proof of principle, we show microscopic images of fixed brain tissue in the hippocampus area created by fluorescence selective excitation in the process of entangled two-photon absorption in a scanning microscope. Quantum-enhanced entangled two-photon microscopy (TPM) had brain imaging capabilities at an unprecedented low excitation intensity of ∼3.6 × 107 photons/s, orders of magnitude lower than the excitation level for the classical two-photon fluorescence image obtained in the same microscope. The extremely low light probe intensity demonstrated in entangled TPM is of critical importance in the investigation of neural activity to minimize heating and photobleaching during repetitive imaging. It may have important functional implications in optogenetic technology, removing unintended heating and accumulated photodamage effects. This technology also opens avenues in spatially resolved brain tissue investigations with quantum light, providing new capabilities in local spectroscopy.

Quantitatively Deciphering the Local Structure and Luminescence Spectroscopy of Pr3+-Doped Yttrium Lithium Fluoride.

Praseodymium (Pr3+)-doped LiYF4 nanophosphors have garnered significant interest for their potential applications in lasers, phosphors, and quantum memories. However, there remains a lack of comprehensive research on the local coordination environment and luminescence spectroscopy of Pr3+:LiYF4 nanocrystals. This study presents the first investigation of the ground-state structure of Pr3+:LiYF4 crystals by employing the crystal structure prediction method, and a [PrF8]5- ligand complex with S4 local symmetry is determined. The complete energy levels of the Pr3+ ions in LiYF4 nanocrystals are unveiled by using our newly developed well-established parametrization matrix diagonalization method. A novel set of free-ion and crystal-field parameters is derived through a good simulation with 45 experimental energy levels. Many of the emissions of Pr3+-doped LiYF4 are successfully reproduced based on Judd-Ofelt theory, and these transitions are comparable to the experimental ones. Moreover, two new prominent emission bands with their peaks at 675 and 849 nm originating from 1I6 → 3F4 and 1I6 → 1G4 transitions, respectively, are predicted by us for the first time. This study could provide a feasible method to search for practical laser transition channels of solid-state lasers based on Pr3+: LiYF4 nanophosphors.

LOCAL DIELECTRIC SPECTROSCOPY AND ITS APPLICATION TO POLYMERS

ABSTRACT The advent of nanodielectrics, nanocomposite materials based on a polymeric matrix, and materials with physical properties ruled by interfacial effects in general demands techniques to characterize functional properties on a local scale with high spatial resolution. Scanning probe microscopies (SPMs), in their electrical modes, have emerged as indispensable tools to access physical quantities such as dielectric constant, surface potential, and static charge, with nanometer-scale lateral resolution and with surface selectivity, being influenced mainly by the outermost layer of the specimen. In this tribute, the development of various SPM electrical modes is illustrated, focusing on the measurement of dielectric permittivity and its spectroscopic extension to access the local, frequency-dependent dielectric function (local dielectric spectroscopy [LDS]). The application to nanostructured polymers in the form of ultrathin films, nanometer-scale–separated blends, and self-assembled block copolymer structures is described. LDS appears to be a promising technique for characterizing the electric properties of polymers and their composites as well as other glass formers and nanostructured systems.

Simultaneous laser ultrasonic measurement of sound velocities and thickness of plates using combined mode local acoustic spectroscopy

Standard ultrasonic thickness measurements require the sound velocity of the sample to be known and vice versa. We present a method, which we have termed combined mode local acoustic spectroscopy (CoMLAS) for simultaneously determining a plate’s thickness and sound velocities without requiring such a priori knowledge. It is based on a combination of three guided wave modes sustained by a plate at discrete frequencies, which we generate and detect using laser ultrasound. We use a pulsed laser that is shaped into a periodic line pattern on the sample’s surface to generate elastic waves and measure the response at the pattern’s center with a vibrometer. The surface acoustic wave mode produces an interference peak in the response spectrum at the frequency corresponding to the wavelength matching the pattern line spacing. By limiting the total size of the excitation pattern, we can simultaneously generate two zero-group-velocity plate resonances, providing two additional peaks in the spectrum. The plate’s local thickness and longitudinal and transverse sound velocities are calculated from the peak frequencies. We demonstrate the feasibility of CoMLAS on steel and aluminum sheets with a thickness of around 2mm by resolving thickness steps and temperature-induced changes in the sound velocities. Using numerical simulations and control experiments, we provide insights into the method’s accuracy and limitations. The choice of excitation pattern, the method’s sensitivity, and the influence of sample inhomogeneity and anisotropy are discussed. CoMLAS does not require scanning mechanics and provides local plate properties. The results shown are achieved with low-energy lasers and signal averaging. Considerations on signal-to-noise ratio indicate that a realization with available lasers of higher energy will enable single-shot measurements. This qualifies the method for use on moving samples in an industrial environment.

SNDM Study of the MOS Interface State Densities on the 3C-SiC / 4H-SiC Stacked Structure

The layer structure of 3C-SiC stacked on 4H-SiC is implemented by simultaneous lateral epitaxy (SLE). The SLE, involving spontaneous nucleation of 3C-SiC(111) on the 4H-SiC(0001) surface followed by step-controlled epitaxy, facilitates the creation of a single-domain 3C-SiC layer with an epitaxial relationship to the underlying 4H-SiC, establishing a coherent (111)//(0001) interface aligned in the basal plane. An extremely low state density at an interface between thermally grown SiO2 and SLE-grown 3C-SiC layer is revealed by local deep level transient spectroscopy (local-DLTS) based on scanning nonlinear dielectric microscopy (SNDM).

Unveiling nanoscale THz-STM imaging techniques on graphene nanoribbons with zigzag edge topology.

The development of near-field THz microscopes has transcended the diffraction limitation traditionally constraining THz super-resolution imaging, heralding a new era of precision. Notably, Terahertz combined scanning tunneling microscopy (THz-STM) has distinguished itself by achieving unparalleled spatial resolution alongside remarkable temporal precision. Despite the significant advancements in THz-STM imaging research, a thorough exploration of its unique imaging features remains elusive, particularly in resolving local electronic spectroscopy. This study methodically explores THz-STM imaging over atomically precise 6-zigzag-edged graphene nanoribbons (6-ZGNR) on Au(111), employing a constant-current mode. The investigation reveals that intense THz-driven electric fields can induce irreversible alterations to the occupied and unoccupied state densities of the 6-ZGNR. Utilizing these THz-modified nanoribbons, analyses of both THz-driven STM imaging and THz current imaging with an external lock-in amplifier are carried out, and experimental factors affecting their imaging qualities have been investigated. It is demonstrated that the imaging with an external lock-in amplified THz current signal accurately captures the local electronic spectroscopy variations at the nanoscale. What we believe is a novel imaging technique proficiently delineates the features on the Au(111) surface and the 6-ZGNR, showcasing superior performance over direct terahertz-driven STM imaging of the samples.

Multifunctional epoxy coatings reinforced with LDHs-modified silica microspheres: Synergistic effects on corrosion resistance, thermal insulation, and flame retardancy

This research encapsulated hollow silica microspheres with Mg-Al layered double hydroxides (LDHs) via in-situ solution deposition, integrating them into an epoxy matrix to enhance its properties. Electrochemical impedance spectroscopy revealed that SiO2@Mg-Al-NO2-LDHs-EP maintained a high impedance of 1.42×109 Ω·cm2 after a 50-day immersion period, significantly outperforming the base epoxy. The impedance change in the scratch area in the local electrochemical impedance spectroscopy demonstrates the self-healing property of the coating. According to the thermal conductivity meter test results, adding SiO2-LDHs to the coating can reduce the thermal conductivity of the coating by about 20 %. Furthermore, microcalorimeter and cone calorimeter tests show that SiO2@Mg-Al-NO2-LDHs can significantly improve the flame retardancy properties of the coating. This study demonstrates the potential advantages of LDHs-coated silica microspheres in functional coatings.

A distributed constant equivalent circuit model and a method for estimating parameters for paper-based lactate biofuel cells

In this study, a distributed constant-type equivalent circuit model for paper-based lactate biofuel cells (PBFCs) where the anode and cathode are formed on the same plane was constructed, and a method of determining parameter values in the equivalent circuit model was proposed. When PBFC were prepared and the electrochemical impedance of the entire cell was measured, the Nyquist diagram produced a spectrum due to the current line distribution. Parameters, such as charge transfer and solution resistances, were calculated from the obtained spectrum using theoretical impedance equations derived from the proposed equivalent circuit model proposed. In addition, the behavior of the current distribution in the battery was evaluated in detail by moving the reference electrode on and performing local electrochemical impedance spectroscopy at multiple points on the electrode. The models and methods proposed in this study are good for evaluating systems affected by distributed current lines, such as flat batteries, and for determining cell design, electrode areas, and arrangements.

Ultrasonic assessment of aging in lithium metal pouch cells

Lithium metal anodes are prone to non-uniform lithium plating that can lead to dendrite formation, internal short circuits, and catastrophic ignition. This type of structural defect is not captured by battery management systems, prompting the need to advance nondestructive evaluation (NDE) techniques that are suitable for periodic monitoring of the internal structure. An ultrasonic inspection technique is evaluated here as a means of identifying flaws and irregular lithium plating that can be a precursor to dendrite formation and, ultimately, battery failure.Lithium metal pouch cell batteries were aged through electrochemical cycling at a range of moderate constant-current charging and discharging rates. They were inspected intermittently using a tailored local ultrasonic resonance spectroscopy (LURS) approach that measures the local through-thickness resonances of the battery as an indicator of the underlying structure. LURS results showed clear structural resonances in cells in the range of 3–7 MHz, which shifted significantly to lower frequencies as batteries aged. In addition to point measurements, scanning LURS measurements were implemented to map resonance frequencies over the electrode surface. These resonance maps revealed spatial variations in structure that developed during aging and showed better contrast to structural variation than achieved using conventional amplitude-based c-scans of the specimens.NDE results from pouch cell measurements were compared to a destructive physical analysis of the electrode structures using scanning electron microscopy (SEM). The SEM results showed differences in the end-of-life lithium anode structure at different charge rates. The results of this study show the capability of LURS as a means for identifying changes in battery structures during aging and establish resonance trends that may be applied in future work for prognostic modeling of batteries in service.

Constructing PANI@CF hybrids enhanced epoxy coatings with integrated functionalities of interfacial enhancement, erosion wear resistance and anti-corrosion

Factors such as sediment erosion and diffusion of corrosive ions in the splash zone result in a serious decrease in the protective performance of organic coatings. Carbon fiber (CF) reinforced polymer coatings have attracted much attention due to the impressive high mechanical strength and reliable chemical stability, but their protection period for steel structures is usually limited by the surface inertness and poor interfacial compatibility of the original CF. Herein, we created a composite coating with excellent erosion and wear resistance and corrosion resistance through simple self-polymerization of polyaniline on carbon fibers. The PANI layer not only helped to improve the interfacial compatibility between fibers/resin, but also exerted its corrosion inhibition effect. The interfacial shear strength (IFSS) value of the modified PANI4@CF monofilament and resin (60.63 MPa) was 46.73 % larger than that of the unmodified CF monofilament. In the simulated splash zone, PANI4@CF5/EP composite coating showed the best erosion resistance and corrosion resistance, and the mass loss and volume loss after erosion test were reduced by 53.39 % and 50.10 %, respectively, compared with pure epoxy coating. The local electrochemical impedance spectroscopy (LEIS) value of PANI4@CF5/EP coating with artificial defect was one order of magnitude higher than the epoxy coating after 48 h immersion. Finally, the environmental conditions of the splash zone were simulated to evaluate the anti-corrosion performance and erosion resistance of the CF reinforced composite coatings, and the protective mechanism was discussed in depth, which has great significance to the development of protective coatings for the splash zone under extreme marine environments.

Cleaner flotation separation of chalcopyrite from pyrite at low alkalinity: Based on calcium hypochlorite oxidative modification in acid mine drainage system

Efficient and clean flotation separation of copper-sulfur has attracted soaring interest in the beneficiation of sulfide ore. The objective of this work was to examine the influence of calcium hypochlorite (Ca(ClO)2) oxidative modification on the flotation separation of chalcopyrite from pyrite in acid mine drainage (AMD) system. A maximum recovery difference of 69.70 % between both minerals was observed under the recommended conditions (initial pH = 8.5 ± 0.2, [Ca(ClO)2] = 100 mg/L, [EX] = 32 mg/L, and the volume ratio of AMD to pure water = 1:1). A high-grade concentrate with 77.35 % Cu recovery and 29.01 % Cu grade was obtained, demonstrated by mixed-mineral micro-flotation experiments. Analysis of Cu and Fe ions influence indicated that low concentrations of Fe3+ and Cu2+ favored the selective separation of pyrite and chalcopyrite. Moreover, analysis of the pulp ion concentrations showed that Ca(ClO)2 promoted the dissolution of iron ions on the pyrite surface compared to chalcopyrite, thereby enhancing pyrite oxidation. The Ca(ClO)2 interacted more intensively with the pyrite surface, forming a passivated layer that impeded the adsorption of collector, as demonstrated by Zeta potential and contact angle results. The generation of hydrophilic products caused by oxidation on the pyrite surface, such as CaSO4, CaOH+, Fe(Ⅲ)–OOH, and/or Fe2(SO4)3 was confirmed by XPS analysis, further reducing the floatability of pyrite. Furthermore, local electrochemical impedance spectroscopy and scanning electron microscopy analyses further afforded favorable evidence for selective inhibition of pyrite by Ca(ClO)2 in the AMD system. This study provides a new approach to achieve cleaner separation of pyrite and chalcopyrite and offers new perspectives for AMD treatment solutions.

Atypical components in the composition of nepheline from rocks of the Khibiny massif according to IR spectroscopy data

Nepheline is one of the main rock-forming minerals of the rocks of the Khibiny alkaline massif. Nepheline composition changes depending on the crystallization temperature, which makes it an indicator of rock formation conditions. In addition, nepheline is one of the main concentrators of hydrocarbon gases. The study of nepheline from different rocks of the Khibiny massif by local IR spectroscopy with Fourier transformation (micro-FTIR) has revealed the presence of water and acetylene in its structure. The water content estimated according to the method of statistical quantitative determination of water in nominally anhydrous minerals varies in the range from 0 to 0.78 wt.%. The highest water content has been observed in high-temperature nepheline of early formations (foyaite of the central and outer parts of the massif), and the lowest – in relatively low-temperature nepheline of later rocks of the Main Ring Fault (urtite, apatite-nepheline rock and poikilitic (kalsilite)-nepheline syenite – rischorrite). The study reveals that water enters the structure of nepheline in the form of H2O molecules that occupy vacancies in the potassium sites. The water content in nepheline is controlled by the number of vacancies in its structure. The presence of acetylene has been determined on a qualitative level. Additional studies are required to assess its quantitative content.

Design and Development of Flow Fields with Multiple Inlets or Outlets in Vanadium Redox Flow Batteries

In vanadium redox flow batteries, the flow field geometry plays a dramatic role on the distribution of the electrolyte and its design results from the trade-off between high battery performance and low pressure drops. In the literature, it was demonstrated that electrolyte permeation through the porous electrode is mainly regulated by pressure difference between adjacent channels, leading to the presence of under-the-rib fluxes. With the support of a 3D computational fluid dynamic model, this work presents two novel flow field geometries that are designed to tune the direction of the pressure gradients between channels in order to promote the under-the-rib fluxes mechanism. The first geometry is named Two Outlets and exploits the splitting of the electrolyte flow into two adjacent interdigitated layouts with the aim to give to the pressure gradient a more transverse direction with respect to the channels, raising the intensity of under-the-rib fluxes and making their distribution more uniform throughout the electrode area. The second geometry is named Four Inlets and presents four inlets located at the corners of the distributor, with an interdigitated-like layout radially oriented from each inlet to one single central outlet, with the concept of reducing the heterogeneity of the flow velocity within the electrode. Subsequently, flow fields performance is verified experimentally adopting a segmented hardware in symmetric cell configuration with positive electrolyte, which permits the measurement of local current distribution and local electrochemical impedance spectroscopy. Compared to a conventional interdigitated geometry, both the developed configurations permit a significant decrease in the pressure drops without any reduction in battery performance. In the Four Inlets flow field the pressure drop reduction is more evident (up to 50%) due to the lower electrolyte velocities in the feeding channels, while the Two Outlets configuration guarantees a more homogeneous current density distribution.

Magnetic anisotropy and ferromagnetic resonance in inhomogeneous demagnetizing fields near edges of thin magnetic films

Using local ferromagnetic resonance spectroscopy, we have studied the magnetic properties near edges of thin tangentially magnetized permalloy films, in which a well-defined uniaxial magnetic anisotropy was induced perpendicular to one of the edges. In the experiment, two samples with thicknesses of 90 and 300 nm and with slightly different compositions were examined. To explain the magnetization dynamics near edges, we propose a simple yet effective model of a film in the form of a rectangular prism, which yields the modified Kittel formula for the resonance frequency. In this formula, the locally averaged distance-dependent demagnetizing field that emerges near the edges is included as an additional uniaxial anisotropy term. The measurements reveal that at a certain distance from the edge, the resulting (apparent) anisotropy, determined from the angular dependencies of the resonance field, almost vanishes. Moreover, its easy axis reorients to become parallel to the edge. The model predictions agree well with these results, proving that the main resonance mode behavior near the film edges can be accurately described by introducing additional effective uniaxial anisotropy, provided the measuring area is relatively large. However, for the thick (300 nm) sample, additional precession modes are also observed. These modes distort the angular dependence of the main mode, thus demonstrating the limitations of the model.

Effect of Coating Damage on the Micro Area Corrosion Performance of HDR Duplex Stainless Steel

In order to determine the effect of damaged insulating enamel on the corrosion of high-chromium (H), duplex (D), and corrosion-resistant (R) duplex stainless steel, the corrosion characteristics of HDR duplex stainless steel in 3.5% NaCl solution were studied by means of local electrochemical impedance spectroscopy (LEIS) and micro-morphology analysis. It was shown that the LEIS impedance was stable at about 7.0 × 103 Ω within 10 days when the HDR duplex stainless steel was not coated. The minimum LEIS impedance of exposed HDR at the damaged area fluctuated around 6.5 × 103 Ω within 15 days when the coating of the self-control insulating enamel damaged area was 1 mm × 10 mm. The coating-damaged area from 1 mm × 10 mm reduced to a circular hole with a diameter of φ1 mm, and the LEIS impedance of the exposed HDR increased at the damaged coating. When extending along the damaged coating to the intact coating area, the impedance rapidly increased, and the further the distance from the damage, the greater the increase in impedance. The impedance of coated HDR increased with the prolongation of immersion time and ultimately stabilized. The thicker the coating, the longer the impedance took to reach a stable state. The stabilized coating had a better effect on improving the corrosion resistance of HDR duplex stainless steel. Within 15 days, the HDR ferrite structure at different areas of coating damage prioritized corrosion. Cl− mainly comes from the solution, and Si and S elements mainly come from elements of the collective itself, with Cl− adsorption, S, and Si element inclusion being the main factors influencing the corrosion of the ferrite structure.

Unconventional Charge-Density-Wave Gap in Monolayer NbS2.

Using scanning tunneling microscopy and spectroscopy, for a monolayer of transition metal dichalcogenide H-NbS2 grown by molecular beam epitaxy on graphene, we provide unambiguous evidence for a charge density wave (CDW) with a 3 × 3 superstructure, which is not present in bulk NbS2. Local spectroscopy displays a pronounced gap on the order of 20 meV at the Fermi level. Within the gap, low-energy features are present. The gap structure with its low-energy features is at variance with the expectation for a gap opening in the electronic band structure due to a CDW. Instead, comparison with ab initio calculations indicates that the observed gap structure must be attributed to combined electron-phonon quasiparticles. The phonons in question are the elusive amplitude and phase collective modes of the CDW transition. Our findings advance the understanding of CDW mechanisms in 2D materials and their spectroscopic signatures.

Smart self-healing coating based on the covalent organic frameworks (COF LZU-1) for corrosion protection of steel

COF LZU-1 has the characteristics of a porous structure, a large specific surface area, and good chemical stability. In recent decades, extensive research has been conducted on its use as a nanomaterial for drug loading and separation. Here, we report a new corrosion inhibitor encapsulated nanostructure (LZU-1 @BTA). We synthesized LZU-1 via a hydrothermal method and loaded benzotriazole (BTA) corrosion inhibitor into LZU-1. The results show that loaded BTA can achieve effective pH-responsive release under acidic and alkaline conditions. The amino group present in the LZU-1 molecule can cross-link with epoxy resin, and its compatibility allows for good dispersion in epoxy resin without any further modification. The LZU-1 @BTA modified epoxy coating has shown remarkable anti-corrosion properties and excellent self-healing capabilities, which have been evaluated through various techniques such as potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), local electrochemical impedance spectroscopy (LEIS), scanning Kelvin probe (SKP) and salt spray testing. The high-quality dispersion of LZU-1 @BTA in the resin, the high cross-linking density, and the pH-responsive release of BTA in the epoxy resin are some of the key factors that contribute to the excellent anti-corrosion performance of the epoxy resin composite coating. This research has opened up new possibilities for designing anti-corrosion coatings with significantly better corrosion resistance.

Integrated scanning electrochemical cell microscopy platform with local electrochemical impedance spectroscopy using a preamplifier.

Local electrochemical impedance spectroscopy (LEIS) has emerged as a technique to characterize local electrochemical processes on heterogeneous surfaces. However, current LEIS heavily relies on lock-in amplifiers that have a poor gain effect for weak currents, limiting the achievements of high-spatial imaging. Herein, an integrated scanning electrochemical cell microscopy is developed by directly collecting the alternating current (AC) signal through a preamplifier. The recorded local current (sub nA-level) is compared with the initial excitation signal to get the parameters for Nyquist plotting. By integrating this method into scanning electrochemical cell microscopy (SECCM), an image of LEIS at the Indium Tin Oxide/gold (ITO/Au) electrode is obtained with a spatial resolution of 180 nm. The established SECCM platform is integrated such that it could be positioned into the limited space (e.g. glove box) for real characterization of electrodes.

Study of the kinetics of accumulation and distribution of the photosensitizer photoditazin in the oral mucosa in patients with lichen planus

Was to explore the accumulation and distribution of the photosensitizer Photoditazine in the oral mucosa when applied to pathological lesions in patients with severe forms of lichen planus. A clinical and laboratory examination was carried out in 50 patients with severe forms of lichen planus (bullous and erosive-ulcerative) aged 18 to 70 years, including 6 men and 44 women. For autofluorescent imaging a LED device with a wavelength in the violet region of the spectrum (400±10 nm) was used. Quantitative registration of the kinetics of accumulation and distribution of the photosensitizer was carried out using the method of local fluorescence spectroscopy by measuring the fluorescence spectra. The measurements were made before applying the photosensitizer, 10, 20 and 30 minutes after application. The study showed that in most patients with erosive-ulcerative and bullous forms of lichen planus, the accumulation of the photosensitizer in the lesions on the oral mucosa increased as the exposure time increased from 20 to 30 minutes. The fastest accumulation of the photosensitizer occurred in the areas of mucosal lesions with the most pronounced vascularization, namely, in the area of the tongue and the bottom of the oral cavity. Using the method of local fluorescence spectroscopy, the kinetics of accumulation and destruction of photosensitizer in pathological areas of the oral mucosa was determined, and therefore the optimal time of laser exposure to the lesion was determined.