Search Results (106)

Organic optoelectronic devices receive appreciable attention due to their low cost, ecology, mechanical flexibility, band-gap engineering, brightness, and solution process ability over a broad area. In this study, we designed and studied organic light-emitting diodes (OLEDs) consisting of an assembly of natural dyes, extracted from noble fir leaves (evergreen) and blue hydrangea flowers mixed with poly-methyl methacrylate (PMMA) as light emitters. We experimentally demonstrate the effective conversion of blue light emitted by an inorganic laser/photodiode into longer-wavelength red and green tunable photoluminescence due to the excitation of natural dye–PMMA nanostructures. UV-visible absorption and photoluminescence spectroscopy, ellipsometry, and Fourier transform infrared methods, together with optical microscopy, were performed for confirming and characterizing the properties of light-emitting diodes based on natural dyes. We highlighted the optical and physical properties of two different natural dyes and demonstrated how such characteristics can be exploited to make efficient LED devices. A strong pure red emission with a narrow full-width at half maximum (FWHM) of 23 nm in the noble fir dye–PMMA layer and a green emission with a FWHM of 45 nm in blue hydrangea dye–PMMA layer were observed. It was revealed that adding monolayer MoS₂ to the nanostructures can significantly enhance the photoluminescence of the natural dye due to a strong correlation between the emission bands of the inorganic–organic emitters and back mirror reflection of the excitation blue light from the monolayer. Based on the investigation of two natural dyes, we demonstrated viable pathways for scalable manufacturing of efficient hybrid OLEDs consisting of assembly of natural-dye polymers through low-cost, purely ecological, and convenient processes. Full article

Failure of the endodontic treatment is often associated with persistent polymicrobial biofilms, particularly those involving Enterococcus faecalis (E. faecalis) and Candida albicans (C. albicans), which display synergistic pathogenicity and resistance to standard disinfection methods. This in vitro study compared the antimicrobial activity and oxidative damage induced by indocyanine green (ICG)–mediated laser ablation (LA) with that produced by antimicrobial photodynamic therapy (aPDT) using methylene blue (MB) or curcumin (CUR) in root canals infected with dual-species biofilms. The samples were divided into five experimental groups (n = 20): Group A—Methylene Blue + Red Laser (RL), Group B—Curcumin + Blue LED (BL), Group C—Indocyanine Green + Infrared Diode Laser (DL), Group D—saline solution (Negative Control—NC), Group E—2.5% sodium hypochlorite (Positive Control—PC). One hundred treated bovine incisors (20 per group) were analyzed for microbial viability (colony-forming unit (CFU/mL)), the metabolic functionality of biofilms was assessed through the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) based reduction method, and oxidative stress markers, including Thiobarbituric Acid Reactive Substances (TBARS), protein carbonyl content, total oxidant capacity (TOC), and total protein levels. All experimental treatments significantly reduced microbial load compared to the negative control (p < 0.05), with ICG achieving the greatest reduction. ICG also induced the highest levels of oxidative stress across all parameters (p < 0.05). These findings suggest that LA with ICG is more effective than aPDT with MB or CUR, achieving disinfection outcomes comparable to those of 2.5% sodium hypochlorite, and warrant further investigation in complex clinical models. Full article

Objective: This study investigates the efficacy of indocyanine green-mediated photodynamic therapy (PDT) in targeting MCF-7 breast cancer cells, a representative model of luminal A subtype, compared to healthy breast epithelial cells. Methods: MCF-7 cells and healthy breast cells were cultured in a three-dimensional (3D) hollow fiber bioreactor to mimic the tumor microenvironment in vivo. Cells were treated with ICG at concentrations ranging from 1 to 1000 μM and then photoactivated using a diode laser. Cell viability was assessed by trypan blue staining, and the production of reactive oxygen species (ROS), including singlet oxygen (¹O₂) was measured. Results: Cell viability, assessed via trypan blue exclusion, decreased dose-dependently with ICG concentrations (1–1000 μM), with MCF-7 viability dropping from 94.5% ± 0.8% at 0.1 μM to 15.83% ± 0.66% at 1000 μM, compared to healthy cells retaining >50% viability up to 500 μM (55.2% ± 2.0% at 1000 μM). Student’s t-tests confirmed significant differences (p < 0.05) between MCF-7 and control (0 μM) at all concentrations, and between MCF-7 and healthy cells, indicating selective cytotoxicity (IC₅₀: ~75 μM for MCF-7). Flow cytometry revealed MCF-7 cell concentrations were significantly lower than healthy cells’ across all ICG doses and seeding densities (p < 0.05). Spectroscopic analyses showed ICG absorption peaks at 800–900 nm, fluorescence at 800–820 nm, and singlet oxygen phosphorescence at 1270 nm, confirming effective ROS generation. Conclusions: Cell concentrations confirmed selective MCF-7 cytotoxicity (p < 0.05). Spectroscopic data validated ROS generation, supporting ICG-PDT’s potential as a selective therapy for early-stage breast cancer within a 50–500 μM therapeutic window. Full article

Aim: This ex vivo study aimed to evaluate the effect of low-energy 445 nm diode laser irradiation on permanent fluoride retention in human enamel. Materials and Methods: Eighty caries-free extracted permanent human teeth were used to prepare 480 enamel discs (2 × 2 mm). Baseline fluoride content in untreated enamel specimens (control group E) was measured using particle-induced gamma-ray emission (PIGE). All specimens then received a topical application of acidulated phosphate fluoride for 5 min, followed by rinsing with double-distilled water for 1 min. Fluoride quantification was subsequently repeated. Specimens were randomly allocated into two groups: fluoridated only (EF; n = 240) and fluoridated plus laser-treated (EFL; n = 240). Each group was further subdivided based on storage conditions: either in air or in double-distilled water at 36 °C for 7 days. Laser irradiation was performed using a 445 nm diode laser in continuous-wave mode at 350 mW for 30 s, with a beam diameter of 10 mm, an energy density of 13.375 J/cm², and a power density of 0.445 W/cm². Results: At baseline, mean fluoride content across all specimens was 702.23 ± 201 ppm. Immediately after fluoridation, fluoride levels increased to 11,059 ± 386 ppm in the EF group and 10,842 ± 234 ppm in the EFL group, with no significant difference between groups. After 7 days of storage in air, fluoride retention decreased to 5714 ± 1162 ppm in EF and 5973 ± 861 ppm in EFL, again without significant difference. However, after 7 days of immersion in double-distilled water, the EF group exhibited complete loss of acquired fluoride, with values falling below baseline (337 ± 150 ppm). In contrast, the EFL group retained a substantial portion of the fluoride acquired during fluoridation (total 1533 ± 163 ppm), indicating that laser irradiation significantly prevented fluoride loss (p < 0.001). Conclusions: Low-energy 445 nm diode laser irradiation of fluoridated enamel significantly enhances fluoride retention under aqueous conditions simulating osmotic processes. Laser treatment preserved a substantial portion of fluoride acquired during fluoridation, whereas fluoridated but unlased enamel lost nearly all fluoride, with levels dropping below baseline. This approach may offer clinical benefits for improving enamel fluoride enrichment, thereby increasing resistance to acid challenge and reducing caries risk. Full article

Earlier quantum calculations of the optical response of Nakamura’s blue laser diode, assuming Kronig–Penney-like band-edge profiles, omitted the effects of charge polarization, cladding-layer asymmetry, and recombination delay times, while such simplified model reproduces the overall emission structure, underestimates the spectral width and fails to capture the decrease in peak intensities at higher energies. Here, we present a detailed quantum theory of polarized-asymmetric superlattices that explicitly incorporates spontaneous and piezoelectric polarization, confining-layer asymmetry, and recombination lifetimes. Local Stark fields are modeled by linear band-edge potentials, and the corresponding Schrödinger equation is solved using Airy functions within the Theory of Finite Periodic Systems. This approach enables the exact calculation of subband eigenvalues, eigenfunctions, transition probabilities and optical spectra. We show that to faithfully reproduce Nakamura’s blue laser spectra, smaller effective masses must be considered, unless unrealistically small barrier heights and widths are assumed. Furthermore, by employing the time distribution of transition probabilities, we capture the energy dependence of recombination lifetimes and their influence on peak intensities. The resulting analysis reproduces the observed spectral broadening and peak-height evolution, while also providing estimates of the magnitude of the Stark effect and mean recombination lifetimes. Full article

Background: Candida albicans is increasingly recognized in peri-implantitis due to its capacity to form resilient biofilms on implant surfaces, limiting treatment success. Antimicrobial photodynamic therapy (aPDT) may offer a non-invasive adjunct by leveraging photosensitizer activation to produce reactive oxygen species that disrupt microbial cells. This in vitro study assessed the antifungal efficacy of QroxB2, a dual-photosensitizer containing riboflavin and curcumin, activated by 450 nm blue light against C. albicans biofilms on titanium implants. Methods: C. albicans biofilms were formed on 63 titanium implants and randomly assigned to nine groups (n = 7): untreated control (GC), chlorhexidine (CHX), riboflavin (RIB), curcumin (CUR), QroxB2 (QBX), laser only (L), and three photodynamic therapy groups combining laser irradiation with each photosensitizer (L + RIB, L + CUR, L + QBX). Treatments were followed by colony-forming unit (CFU) enumeration. Results: The L + QBX group showed the strongest antifungal effect, achieving a 94% reduction in fungal load, with median CFU counts decreasing from 49,000 in the untreated control to 2800 CFU/mL. CHX eradicated all viable cells (0 CFU/mL). Among photosensitizer-only groups, QBX produced a moderate reduction (median 21,800 CFU/mL), whereas laser irradiation alone (L) exhibited no meaningful antifungal activity, with median counts comparable to the untreated control (49,000 CFU/mL). Conclusions: QroxB2-mediated aPDT achieved a significant reduction in Candida albicans colony-forming units on implant surfaces. While not as potent as chlorhexidine, this light-activated, biocompatible approach may serve as a complementary tool in managing peri-implant fungal infections. Clinical validation is warranted. Full article

External-cavity GaN semiconductor lasers at blue wavelengths enable narrow-linewidth and high-power output but is difficult at >500 nm green wavelengths due to the so-called ‘green gap’. In this Letter, we demonstrate a watt-level, narrow-linewidth, tunable green semiconductor laser based on external-cavity synchronous-locking technique. The laser consists of two green edge-emitting laser diodes (LDs), beam-shaping devices and a visible-wavelength diffraction grating. Because the two green (∼518 nm) LDs have similar spectral and lasing characteristics and are adjacently parallel in spatial mode, synchronous locking of both beam can readily generated with the help of diffraction grating. Namely, the two green LDs are locked at the same wavelength and the 3dB–linewidth is sharply narrowed from 4 nm to 0.06 nm. The locked wavelength can be tuned from 512.2 to 520.2 nm. The maximum output power reaches 1.53 W at 518 nm with a 3dB–linewidth of 0.15 nm. This is, for the first time, to the best of our knowledge, an external-cavity synchronous-locking green semiconductor laser with watt-level output power. Full article

This research proposes a non-penetration lap welding process for joining T2 copper power module terminals in high-frequency and high-power electronic applications, using a hybrid laser system combining a 445 nm blue diode laser and a 1080 nm fiber laser. The composite laser beam, formed by coupling a circular blue laser beam with a spot-shaped fiber laser beam, was oscillated along circular, sinusoidal, and 8-shaped trajectories to control weld geometry and joint quality. Results indicate that all trajectories produced U-shaped weld cross-sections with smooth toe transitions and good surface quality. Specifically, the circular trajectory provided uniform energy distribution and stable weld formation; the 8-shaped trajectory achieved a balanced width-to-depth ratio; and the sinusoidal trajectory exhibited sensitivity to welding speed, often resulting in uneven fusion width. Increased welding speed promoted grain refinement, but excessive speed led to porosity and poor surface quality in both 8-shaped and sinusoidal trajectories. Oscillating laser welding facilitated equiaxed grain formation, with the circular and 8-shaped trajectories yielding more uniform microstructures. The circular trajectory maintained consistent weld dimensions and hardness distribution, while the 8-shaped trajectory exhibited superior tensile strength. This work highlights the potential of circular and 8-shaped trajectories in hybrid laser welding for regulating weld microstructure, enhancing mechanical performance and ensuring weld stability. Full article

Yeasts of the genus Candida (C.) and the bacterium Staphylococcus aureus (S. aureus) are among the most common pathogens responsible for infections that are difficult to treat, including those resistant to standard therapy. In recent decades, this has become an increasing clinical problem. In response to the limitations of traditional procedures, antimicrobial photodynamic therapy (aPDT), which combines light, a photosensitizer, and oxygen, is gaining growing interest. The aim of this study was to evaluate the in vitro effectiveness of aPDT using a 635 nm diode laser in combination with toluidine blue O (TBO) against Candida spp. and S. aureus. Reference strains of C. albicans, C. glabrata, C. krusei, and S. aureus were subjected to aPDT. In phase I of this study, the optimal TBO incubation time was assessed with constant laser parameters. In phase II, the impact of the physical parameters of the laser, irradiation time, and output power, was analyzed, with the TBO incubation time set based on the phase I results, to evaluate the degree of microbial reduction (CFU/mL). Statistical analyses were then conducted to assess significance. TBO-mediated aPDT significantly reduced microbial viability, depending on incubation time and laser settings. The minimal effective incubation times were 10 min for Candida spp. and 5 min for S. aureus. The highest pathogen inactivation efficacy was observed at an output power of 400 mW and an irradiation time of 120 s. The use of the photosensitizer or laser alone did not result in significant antimicrobial effects. TBO-mediated aPDT may serve as an effective complement to conventional antimicrobial therapy and, in selected cases (e.g., drug resistance), has the potential to partially or fully replace it. The observed minimal effective incubation times provide a practical baseline, but further statistical comparisons are required to determine whether these durations are truly optimal. Full article

Background: This case series study aims to evaluate the spontaneous eruption of impacted canines following diode laser disinclusion surgery without orthodontic traction, and to analyze the correlation with five prognostic factors: age, sex of the patient, angle α, sector, and height of inclusion of the canine. Methods: The sample included 15 patients aged 13–30 years and 20 palatally impacted canines. The patients’ records were collected, and prognostic factors were assessed. All patients underwent disinclusion surgery using a diode laser (K-Laser, Eltech, Blue Derma) and post-surgery, canines were monitored with intraoral scans and photos at 1 week, 8 weeks (T1), and 16 weeks (T2). The STL files were superimposed with the open-source software MeshLab (MeshLab 2023.12, Visual Computing Lab, Pisa, Italy), and the eruption values were measured. Through multiple linear regression analysis, the relationships between the five prognostic factors and the total spontaneous eruption value were analyzed. Results: The canines treated in this study responded with an average eruption of 4.70 mm. For the prognostic factors sex (p = 0.94) and angle α (p = 0.12), no statistically significant relationship with eruption was found. The variables age (p < 0.001), sector II (p = 0.02), sector III (p = 0.03), sector IV (p = 0.06), and inclusion height (p < 0.001) had negative linear coefficients. Consequently, as the values of these three prognostic factors increased, a lower eruption of the included element measured in millimeters was obtained. Conclusions: All canines successfully erupted following the disinclusion procedure, avoiding the use of orthodontic traction. Patient sex and the α angle of impaction were not reliable predictors of eruption outcomes. In contrast, age, sector, and inclusion height measured via CBCT showed high statistical significance and could be used as prognostic factors to predict the eruptive response following disinclusion surgery. Full article

Background/Objectives: The laser beam absorption and thermal relaxation time (TRT) in oral tissues are key to optimizing treatment parameters. The aim of this study is to (1) evaluate, in an ex vivo study, the percentage of attenuation and transmittance of each wavelength as a function of tissue thickness; (2) determine the global absorption coefficient, α, of pig gingival tissue for the most commonly used wavelengths in dentistry; (3) calculate the thermal relaxation time (TRT) of oral tissue for these wavelengths; and (4) determine their corresponding penetration depths. Methods: We measured the transmission of different laser wavelengths through pig oral gingival tissues (Mandibular labial gingiva). We placed each tissue sample between two glass slides with minimal light attenuation. The input and output powers were measured after irradiating the tissue at different specific wavelengths: 450 nm, 480 nm, 532 nm, 632 nm, 810 nm, 940 and 980 nm, 1064 nm, 1341, 2780 nm and 2940 nm. After calculating the transmittance values, we plotted transmittance curves for each wavelength. Using the Beer–Lambert law, we then calculated the absorption coefficient (α) of each wavelength in the oral gingival tissue. Absorption coefficients were then used to calculate the TRT and penetration depth for each wavelength. Results: Among the tested wavelengths, 810 nm exhibited the lowest absorption in ex vivo porcine gingival tissue (α = 9.60 cm⁻¹). The 450 nm blue laser showed moderate absorption (α = 26.8 cm⁻¹), while the Er:YAG laser at 2940 nm demonstrated the highest absorption (α = 144.8 cm⁻¹). We ranked the wavelengths from most absorbed to least absorbed by porcine oral gingival mucosa as follows: 2940 nm > 2780 nm > 450 nm > 480 nm > 532 nm > 1341 nm > 632 nm > 940 nm > 980 nm > 1064 nm > 810 nm. Conclusions: Absorption and the TRT vary significantly across wavelengths. Erbium lasers are characterized by the highest absorption and minimal light penetration. Infrared diodes, particularly the 810 nm wavelength, showed the lowest absorption and deepest tissue penetration and exhibited the highest thermal relaxation time. The 480 nm laser demonstrated greater absorption by porcine gingival tissue compared to the 532 nm laser. These findings provide evidence-based guidance for wavelength selection in dental treatments and photobiomodulation, enabling improved precision, safety, and therapeutic efficacy in clinical practice. Full article

Background: This systematic review evaluated the efficacy of laser therapies and antimicrobial photodynamic therapy (aPDT) for the treatment of intraoral halitosis by synthesizing randomized controlled trials. Methods: A comprehensive search of the PubMed, Embase, Scopus, and Cochrane Library databases identified 14 eligible RCTs. Results: Laser-based interventions, including diode lasers and Er,Cr:YSGG lasers, and aPDT using photosensitizers such as methylene blue, toluidine blue, and Bixa orellana (annatto), effectively reduced volatile sulfur compound levels and associated bacterial populations compared to traditional methods like tongue scraping and antiseptic rinses. Combination treatments consistently demonstrated superior short-term efficacy, although treatment outcomes often declined after 7–14 days, indicating the necessity for repeated sessions or adjunctive oral hygiene measures. Conclusions: Methodological heterogeneity across studies regarding laser parameters, photosensitizer types, and outcome measurements highlighted the need for standardized protocols. Future research should focus on multicenter trials with extended follow-up and standardized microbiological evaluations to further validate these promising treatments and integrate them effectively into clinical practice. Full article

Objective: This study aimed to evaluate the photobiomodulatory (PBM) effects of low-power light-emitting diode (LED) irradiation on cultured human umbilical vein endothelial cells (HUVECs), focusing on changes in cellular metabolic activity and morphology. Materials and Methods: HUVECs were cultured and divided into three groups: control (no irradiation), red LED (655 nm), and blue LED (455 nm). Cells were irradiated once with a total energy dose of 4 J over 60 s. Cellular metabolic activity was assessed at 0, 1, 3, and 6 h post-irradiation using the WST-8 assay. Morphological changes were examined 3 h post-irradiation using rhodamine–phalloidin staining and confocal laser scanning microscopy. Results: Red LED irradiation significantly enhanced metabolic activity immediately and at 3 h post-irradiation compared to the control group. Blue LED irradiation showed a non-significant trend toward increased metabolic activity at 1 and 3 h. Morphometric analysis revealed increases in cell area, perimeter, and Feret diameter in both LED-irradiated groups, with more pronounced changes observed in the red LED group. Conclusions: Low-power red LED light (655 nm) effectively promotes metabolic activation and induces morphological changes in vascular endothelial cells, suggesting its potential application in angiogenesis and wound healing. Due to its safety and accessibility, LED-based PBM may serve as a promising therapeutic modality for soft tissue regeneration in both clinical and home-care settings. Full article

Europium(III) β-diketone and organic carboxylic acid complexes are designable, easy to prepare, and easy to modify and have excellent fluorescence properties (narrow emission spectral band, high colour purity, long fluorescence lifetime, high quantum yield, and a spectral emission range covering both the visible and near-infrared regions). These complexes play important roles in popular fields such as laser and fibre-optic communications, medical diagnostics, immunoassays, fluorescent lasers, sensors, anticounterfeiting, and organic light-emitting diodes (OLEDs). In the field of light-emitting materials, europium complexes are especially widely used in OLED lamps, especially because of their high-efficiency emission of red (among the three primary colours); accordingly, these complexes can be mixed with blue and green phosphors to obtain high-efficiency white phosphors that can be excited by near-ultraviolet light. This paper reviews the red-light-emitting europium complexes with β-diketone and organic carboxylic acid as ligands that have been studied over the last five years, describes the current problems, and discusses their future application prospects. Full article

In GaN-based laser diode (LD) structures, it is essential to optimize the doping concentration and profiles in p-type-doped layers because of the trade-off between laser power and operation voltage as the doping concentration varies. In this study, we proposed GaN-based blue LD structures with nonuniform doping distributions in the p-AlGaN cladding layer to reduce the modal loss and demonstrated improved efficiency characteristics using numerical simulations. We compared the laser power, operation voltage, and wall-plug efficiency (WPE) of LDs with uniform, linear, and quadratic doping profiles in the p-AlGaN cladding layer. As the doping concentration becomes increasingly inhomogeneous, the laser output power increases significantly because of the reduced overlap of the laser mode with the p-AlGaN cladding layer. However, this nonuniform doping profile also leads to an increase in the operation voltage due to the expansion of the low-doping region. By optimizing the nonuniform doping distribution in the p-type cladding layer, the WPE was found to be improved by over 5% compared to a conventional uniformly doped p-cladding layer. The proposed design of LD structures is expected to enhance the efficiency of high-power GaN-based LDs. Full article