Low-power Laser Irradiation Research Articles

A Machine Learning-Optimized System for Pulsatile, Photo- and Chemotherapeutic Treatment Using Near-Infrared Responsive MoS2-Based Microparticles in a Breast Cancer Model.

Multimodal cancer therapies are often required for progressive cancers due to the high persistence and mortality of the disease and the negative systemic side effects of traditional therapeutic methods. Thus, the development of less invasive modalities for recurring treatment cycles is of clinical significance. Herein, a light-activatable microparticle system was developed for localized, pulsatile delivery of anticancer drugs with simultaneous thermal ablation by applying controlled ON-OFF thermal cycles using near-infrared laser irradiation. The system is composed of poly(caprolactone) microparticles of 200 μm size containing molybdenum disulfide (MoS2) nanosheets as the photothermal agent and hydrophilic doxorubicin or hydrophobic violacein, as model drugs. Upon irradiation, the nanosheets heat up to ≥50 °C leading to polymer softening and release of the drug. MoS2 nanosheets exhibit high photothermal conversion efficiency and require low-power laser irradiation. A machine learning algorithm was applied to acquire the optimal laser operation conditions. In a mouse subcutaneous model of 4T1 triple-negative breast cancer, 25 microparticles were intratumorally administered, and after 3-cycle laser treatment, the system conferred synergistic phototherapeutic and chemotherapeutic effects. Our on-demand, pulsatile synergistic treatment resulted in increased median survival up to 39 days post start of treatment compared to untreated mice, with complete eradication of the tumors at the primary site. Such a system is therapeutically relevant for patients in need of recurring cycles of treatment on small tumors, since it provides precise localization and low invasiveness and is not cross-resistant with other treatments.

Titanium Carbide-Based Spatiotemporally Selectable-Activated Entropy-Driven DNA Nanoplatform for Amplified MicroRNA Imaging and Photothermal Therapy In Vivo.

Engineering an elaborate nanotheranostic platform that can achieve spatiotemporally selective microRNA (miRNA) imaging and imaging-guided therapy in time is critical for precise cancer diagnosis and efficient treatment, yet remains a challenge. Herein, we present an on-site-activatable nanotheranostic platform (Ti3C2-NEDR) that engineers a photothermal-activated entropy-driven strand displacement reaction (NEDR) module on a photothermal conversion module (Ti3C2) for achieving spatiotemporally controlled miRNA-21 imaging in vivo and imaging-guided photothermal therapy only by varying the power of the near-infrared (NIR) laser. The upstream NIR photothermal conversion module, Ti3C2, can act not only as a DNA circuit carrier to deliver the NEDR module but also as a photothermal agent to activate the downstream NEDR module in low-power NIR laser irradiation. Once the NEDR module is activated by the NIR laser, the entropy-driven strand displacement reaction can be innated by intracellular miRNA-21 to generate an amplified fluorescence signal for the spatiotemporally selective imaging of miRNA-21 in vivo. Thereafter, the imaging-guided in vivo photothermal therapy can be achieved in time only by switching to the high-power NIR laser. It is envisioned that this strategy of NIR light-activated spatiotemporally selective miRNA imaging and imaging-guided on-demand therapy may expand the nanotheranostic platform for precise cancer diagnosis and personalized therapy in time, providing a remarkable prospect in biomedical diagnosis and therapy.

DNA Damage-Sensitized metal phenolic nanosynergists potentiate Low-Power phototherapy for osteosarcoma therapy

Non-invasive and efficient photodynamic therapy (PDT) holds great promise to circumvent resistance to traditional osteosarcoma (OS) treatments. Nevertheless, high-power PDT applied in OS often induces photothermogenesis, resulting in normal cells rupture, sustained inflammation and irreversible vascular damage. Despite its relative safety, low-power PDT fails to induce severe DNA damage for insufficient reactive oxygen species (ROS) production. Herein, a non-ROS-dependent DNA damage-sensitizing strategy is introduced in low-power PDT to amplify the therapeutic efficiency of OS, where higher apoptosis is achieved with low laser power. Inspired by the outstanding DNA damage performance of tannic acid (TA), TA-based metal phenolic networks (MPNs) are engineered to encapsulate hydrophobic photosensitizer (purpurin 18) to act as DNA damage-sensitized nanosynergists (TCP NPs). Specially, under low-power laser irradiation, the TCP NPs can boost ROS instantly to trigger mitochondrial dysfunction simultaneously with upregulation of DNA damage levels triggered by TA to reinforce PDT sensitization, evoking potent antitumor effects. In addition, TCP NPs exhibit long-term retention in tumor, greatly benefiting sustained antitumor performances. Overall, this study sheds new light on promoting the sensitivity of low-power PDT by strengthening DNA damage levels and will benefits advanced OS therapy.

Multifunctional Laser-Induced Graphene-Based Microfluidic Chip for High-Performance Oocyte Cryopreservation with Low Concentration of Cryoprotectants.

Oocyte cryopreservation is essential in the field of assisted reproduction, but due to the large size and poor environmental tolerance of oocytes, cell freezing technology needs further improvement. Here, a Y-shaped microfluidic chip based on 3D graphene is ingeniously devised by combining laser-induced graphene (LIG) technology and fiber etching technology. The prepared LIG/PDMS microfluidic chip can effectively suppress ice crystal size and delay ice crystal freezing time by adjusting surface hydrophobicity. In addition, LIG endows the microfluidic chip with an outstanding photothermal effect, which allows to sharply increase its surface temperature from 25 to 71.8°C with 10s of low-power 808nm laser irradiation (0.4Wcm-2). Notably, the LIG/PDMS microfluidic chip not only replaces the traditional cryopreservation carriers, but also effectively reduces the dosage of cryoprotectants (CPAs) needed in mouse oocyte cryopreservation. Even when the concentration of CPAs is cut in half (final concentration of 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO)), the survival rate of oocytes is still as high as 92.4%, significantly higher than the control group's 85.8%. Therefore, this work provides a novel design strategy to construct multifunctional microfluidic chips for high-performance oocytes cryopreservation.

The Effect of NF-κB Deactivation on Cancer Cell Response to ALA Mediated Photodynamic Therapy.

Breast cancer is one of the most widespread tumors among women worldwide, which is difficult to treat due to the presence of chemoresistance and the risk of tumor recurrence and metastasis. There is a pressing necessity to develop efficient treatments to improve response for treatment and increase prolong survival of breast cancer patients. Photodynamic therapy (PDT) has attracted interest for its features as a noninvasive and relatively selective cancer treatment. This method relies on light-activated photosensitizers that, upon absorbing light, generate reactive oxygen species (ROS) with powerful cell-killing outcomes. Nuclear factor kappa B (NF-κB), a transcription factor, plays a key role in cancer development by regulating cell proliferation, differentiation, and survival. Inhibiting NF-κB can sensitize tumor cells to chemotherapeutic agents. Dimethyl fumarate (DMF), an NF-κB inhibitor approved by the FDA for multiple sclerosis treatment, has further shown promise in suppressing breast cancer cell growth in vitro. We hypothesized that combining PDT with Dimethyl fumarate (DMF) could further enhance therapeutic efficacy for both treatment modalities. In the current study, we explored the PDT effect of 1 and 2 mM aminolaevulinic acid (ALA) and low-power He-Ne laser irradiation combined with different concentrations of DMF (2.5, 1.25, or 0.652 µg/ml) against hormone nonresponsive AMJ13 breast cancer cell line that is derived from Iraqi patient. Our results demonstrated that co-administration with all tested DMF concentrations significantly enhanced the cytotoxicity of PDT antitumor effect. The combination index analysis showed presence of synergism in combining PDT with DMF. This finding suggests that the combination of PDT with DMF could be a promising novel strategy against triple negative breast cancer that could be applied clinically due to the fact that both of these treatments are already clinically approved therapies.

Kerr coefficient and third-order nonlinear optical absorption coefficient of isotropic diacrylate mesogens at 632.8 nm wavelength

ABSTRACT Third-order optical nonlinearities of diacrylate mesogens RM82 and RM257 in the isotropic phase for a low-power continuous wave laser irradiation at 632.8 nm wavelength have been studied. In their isotropic state, the diacrylate mesogens exhibit quite large nonlinear absorption. We observe a large two-photon absorption coefficients, on an order of 10−6 m/W, for the mesogens. The Kerr coefficients of the mesogens are characterised using single beam Z-scan technique, and found to reach an order of 10−7 m/W. Both diacrylate mesogens exhibit a good material figure of merit.

Making the Brightest Ones Dim: Maximizing the Photothermal Conversion Efficiency of BODIPY-Based Photothermal Agents.

The successful implementation of photothermal therapy (PTT) in cancer treatment hinges on the development of highly effective photothermal agents (PTAs). Boron dipyrromethene (BODIPY) dyes, being well known for their high brightness and quantum efficiencies, are the antithesis of PTAs. Nonetheless, a systematic exploration of the photophysics and photothermal characteristics of a series of π-extended BODIPY dyes with high absorptivity in the near-infrared (NIR) region has achieved superior photothermal conversion efficiencies (>90%), in both monomeric state and nanoparticles after encapsulation in a biocompatible polyethyleneglycol 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy-(polyethylene glycol)-2000]. Optimal PTA candidates combine strong NIR absorption provided by extended donor-acceptor conjugation and an optimization of the electronic and steric effects of meso-substituents to maximize photothermal conversion performance. The PTT-optimized meso-CF3-BODIPY, TCF3PEn exhibits exceptional efficacy in inducing cancer cell apoptosis and in vivo tumor ablation using low-power NIR laser irradiation (0.3 Wcm-2, 808 nm) as well as excellent biological safety, underscoring its potential for advancing light-induced cancer therapies.

Amplifying Photon Upconversion in Alloyed Nanoparticles for a Near-Infrared Photodetector.

Photon upconverison has attracted a substantial amount of interest in diverse fields due to its characteristic anti-Stokes emissions. However, obtaining intense emission under low-power laser irradiation has remained a challenge. Here we report a mechanistic design of activator-sensitizer alloyed nanoparticles to achieve bright upconversion under weak infrared irradiation. This design allows a nearest sensitizer-activator separation to facilitate efficient energy transfer that results in remarkably enhanced upconversion (>2 orders of magnitude) under 0.26 W cm-2 irradiation compared to that of the Er sublattice, and the upconversion quantum yield also shows a 20-fold increase. Interestingly, the alloyed nanoparticles exhibit a gradual change in emission color with an increase in Yb3+ content, and moreover, their emission colors can be dynamically controlled by simply modulating the excitation laser power and pulse widths. Such alloyed nanoparticles show great promise for application in a near-infrared photodetector.

Biomimetic Copper-Doped Polypyrrole Nanoparticles for Enhanced Cancer Low-Temperature Photothermal Therapy.

Photothermal therapy (PTT) has a significant potential for its application in precision tumour therapy. However, PTT-induced hyperthermia may damage healthy tissues and trigger the expression of heat shock proteins (HSPs), thereby compromising the long-term therapeutic efficacy of PTT. In this study, a biomimetic drug delivery system comprising CuP nanozymes as the inner core and platelet membrane (PM) as the outer shell was successfully developed for administering synergistic chemodynamic therapy and mild PTT. PM is encapsulated on CuP to form this biomimetic nanoparticle (PM-coated CuP nanoparticles, PC). PC possesses peroxidase (POD) activity, can facilitate the conversion of hydrogen peroxide into ·OH, thereby inhibiting the expression of HSPs. Upon exposure to low-power laser irradiation (0.5 W/cm2, 1064 nm), PC can convert near-infrared II laser energy into heat energy, thereby enabling the administration of enhanced mild PTT. In vitro and in vivo experiments have demonstrated that this synergistic approach can induce over 90% tumour eradication with favourable biocompatibility. PC exhibits high efficacy and biocompatibility, making it a promising candidate for future applications.

EFFECT OF LOW-POWER LASER IRRADIATION ON THE SHEAR BOND STRENGTH AND THERMAL CHANGES ACROSS DIFFERENT ZIRCONIA THICKNESSES USING DIFFERENT IRRADIATION TIMES.

To investigate the effect of irradiation time and zirconia thickness using low power Er,Cr:YSGG laser irradia)on (for debonding purposes) on the thermal changes and shear bond strength (SBS) of resin-bonded 3% mol yIrium oxide stabilized tetragonal zirconia polycrystal (3YTZP) specimens. 3Y-TZP slices of 0.5-, 2-, and 3- mm thick were used. The temperatures during laser irradiation using single spot irradiation at different times (30 seconds, 60 seconds, 90 seconds, and 120 seconds) and line scanning irradiation from one spot to another at three different distances (2, 4, and 6 mm) were recorded. Single spot and line scanning irradiation data were analyzed using three-way ANOVA (α = .05) and generalized linear mixed model, respectively. Nonirradiated (control) and irradiated resin-bonded 3Y-TZP specimens were shear tested, and the data were analyzed using two-way ANOVA (α = .05). Under single spot irradiation, the laser-induced temperature was higher through thin 3Y-TZP at any time compared to thick 3Y-TZP. For the line scanning method, short distances (2 and 4 mm) resulted in a significant increase in temperature for 0.5-mm thick specimens. Laser irradiation significantly decreased the SBS of the 0.5-mm group compared to the nonirradiated group. After irradiation, the bond strength of the 2- and 3-mm thick 3Y-TZP was similar to the nonirradiated group. The temperature and bond strength of low-power laser irradiated 3Y-TZP specimens was affected by the specimen thickness but not by the irradiation time tested. Low-power laser irradiation is an effective debonding method for thin Y-TZP restorations.

D-A Structured High-Performance Photothermal/Photodynamic Thionin-Synthetic Melanin Nanoparticles for Rapid Bactericidal and Wound Healing Effects.

Synthesized melanin nanoparticles (SMNPs) are used as advanced photothermal materials. However, their internal structures are complex and disordered, and tuning the photothermal performance of nanoparticles is still a hot spot of concern. This article presents thionin (Th)-doped SMNPs, namely Th-SMNPs, which are the first SMNPs formed using the one-pot polymerization of Th with Levodopa. Th can undergo Michael addition and Schiff base reaction between indole dihydroxy/indolequinone and their oligomers to form donor-acceptor pairs in the structure to modulate the photothermal performance of SMNPs. Structural and spectroscopic analyses and density functional theory simulations further confirm the existence of the donor-acceptor structure. Th-SMNPs exhibit excellent total photothermal efficiency (34.49%) in the near-infrared region (808nm), which is a 60% improvement compared to SMNPs. This allows Th-SMNPs to exhibit excellent photothermal performance at low power 808nm laser irradiation. Meanwhile, Th not only enhances the photothermal properties of SMNPs, but also imparts photodynamic effects to SMNPs. Th-SMNPs can produce 1 O2 under 660nm laser irradiation. A dual-function photothermal and photodynamic textile named Th-SMNPs@cotton is constructed based on Th-SMNPs, which can act as a rapid photothermal/photodynamic sterilization and is promising for wound healing treatment of bacterial infections under low-power dual laser irradiation.

Engineering J-aggregates for NIR-induced meso-CF3-BODIPY nanoparticles by activated apoptosis mechanism in photothermal therapy

Forming J-aggregates by organic monomer is a fascinating strategy to urge spectroscopic redshift with respect to that of the monomer. Herein, we designed 1,7-diphenyl-substituted meso‑CF3-BDP monomer confirmed by X-ray crystallographic analysis. The low-barrier rotation of the –CF3 group in meso‑CF3-BDP 1 significantly enhances the non-radiative efficiency, and the photothermal conversion efficiency (PCE) of the self-assembled nanoparticles (1-NPs: λabs = 746 nm) by J-aggregates was 82%. 1-NPs could effectively block cell cycle progression, inhibit cancer cell proliferation and trigger cell apoptosis under low power laser irradiation (0.2 W/cm2). This study proposes an alternate molecular design platform by J-aggregates to promote PCE through the insertion of rotating segment and trigger the cancer cells apoptosis in photothermal therapy at low power laser density.

The Utility of Photobiomodulation as a Supplement to Orthobiologic Interventions

Several mechanisms may influence recovery and act as a complementary intervention to regenerative medicine. One area of consideration that may improve clinical outcomes in patients receiving regenerative medicine treatments is the utilization of supplementary interventions referred to as regenerative rehabilitation. One such intervention may be the use of light therapy also known as photobiomodulation (PBM). Terms synonymous with PBM include low-level light therapy (LLLT), low-power laser irradiation or cold laser. As a musculoskeletal intervention, PBM is administered via a mechanism that creates light through optical amplification. These interventions describe a form of PBM or light therapy that uses specific param-eters to target tissues through direct or indirect contact with or without heat or structural tissue alterations. PBM may improve treatment outcomes based on synergistic effects that are thought to modulate inflammation and facilitate cellular repair. This manuscript provides an overview of the current evidence supporting the use of PBM as a complementary intervention to regenerative medicine with a focus on managing conditions related to the musculoskeletal system.

레이저 유도 전사를 이용한 유연기판의 액체금속 미세 패터닝

We have developed a direct conductive patterning method with micro-scale line widths using the laser-induced-forward transfer (LIFT) and liquid metal. As this method does not need post-thermal processing, there is no thermal damage even on heat-sensitive polymer substrates by low-power laser irradiation on the dynamic release layer (DRL). Unlike other liquid metal patterning processes, this procedure can easily achieve fine line widths of a few tens of micrometers corresponding to laser spot size. The solid-state UV pulse laser with 266 nm wavelength and 20 ns pulse duration was used to transfer Eutectic Gallium Indium (EGaIn) liquid metal and the results for the single and multi-pulse laser irradiation were investigated to determine the effective process conditions. The applicability of flexible circuit fabrication and selective circuit repair was successfully tested on Polyimide (PI) substrate. After the LIFT process, the electrical properties of liquid metal on the pattern were measured to be approximately 5~8 x 10SUP-3/SUP Ω/m of resistance.

Attachment of -tBu groups to aza-BODIPY core at 3,5-sites with ultra-large Stokes shift to enhance photothermal therapy through apoptosis mechanism.

By the introduction of the −tBu groups into aza-BODIPY core, di-tert-butyl-substituted aza-BODIPYs at 3,5-sites (tBuazaBDPs) were prepared for the first time. Based on the X-ray analysis of CN-tBuazaBDP, this molecular structure is twisted. Near-infrared dye SMe-tBuazaBDP has the ultra-large Stokes shift (152 ​nm) in aza-BODIPY system, combining with the twisted intramolecular charge transfer and the free rotation of the −tBu groups at 3,5-sites. Although the barrier-free rotors of the distal −tBu groups in SMe-tBuazaBDP result in low fluorescence quantum yield, the photothermal conversion efficiency is markedly enhanced. SMe-tBuazaBDP nanoparticles with low power laser irradiation were proven to block cancer cell cycle, inhibit cancer cell proliferation, and induce cancer cell apoptosis in photothermal therapy (PTT). The strategy of “direct attachment of −tBu groups to aza-BODIPY core” gives a new design platform for a photothermal therapy agent.

Effect of Low-Level Laser Therapy on Trismus, Facial Swelling, and Pain Following Surgical Extraction of Impacted Lower Third Molars

Background: Light amplification by the stimulated emission of radiation (laser) is currently used as a therapy method for decreasing inflammation followed by oral surgeries. Therefore, the present study aimed at evaluating the effect of using diode low-power laser irradiation (photobiomodulation) on the amount of pain, swelling, and trismus due to latent mandibular third molar surgery (surgical removal of latent mandibular third molars). Methods: In this double-blind randomized clinical trial study, 16 individuals with latent mandibular third molars with an identical condition were selected. The teeth were randomly assigned to two groups of laser irradiated intervention group and a non-irradiated control group. A 940 nm diode laser with an output power of 200 mW and an energy density of 12 J/cm2 was applied for 60 seconds at a distance of 1 cm three intraoral points and an extraoral point. The distance between incisal edges of upper and lower central teeth, the horizontal distance between corners of lips and auricle (LE), the vertical distance between the outer canthus of the eye and the mandibular angle (EA), and pain visual analogue scale were measured before surgery and two and seven days after surgery. Results: There was no statistically significant difference between the two groups regarding EA and LE before intervention and on days 2 and 7 after intervention (P>0.05). However, the pain score was significantly higher before intervention (3.31±0.7 vs. 2.38±0.8, P=0.001) and on day 2 after intervention (6.5±1.32 vs. 4.5±0.97, P<0.001) in the control group. On day 7, a higher maximum jaw opening (MJO) was observed in the intervention group (40.68±5.76 vs. 36.81±4.35, P=0.04). Conclusions: Adjunctive diode laser photobiomodulation after third molar surgery was associated with a significant reduction in pain and trismus.

Laser-based pretreatment of composite T-joints for improved pull-off strength and toughness

This study demonstrates the efficiency of two CO2 surface laser treatment strategies for improving the strength and toughness of the adhesive bonding of T-joints. The first strategy involves uniform laser treatment to the surface, and the second strategy involves laser patterning by alternatively applying high- and low-power laser irradiation to the T-joint stiffener and skin surfaces. All the laser-treated T-joints showed progressive failure modes during pull-off test, unlike the PP surface-treated joints that exhibited brittle failure. The uniform laser-treated joints exhibited improved strength and toughness because contaminants were removed and the fibers were exposed to be directly bonded with adhesive. The joints subjected to the laser-patterning strategy demonstrated a substantial improvement in terms of the strength and toughness, reaching values of 2.2 and 12 times those of the PP surface-treated T-joints, respectively. This is because of the crack arresting at the transition between the two treatments at the stiffener interface, inducing crack migration from the stiffener–adhesive interface to the skin–adhesive interface while forming adhesive ligaments. The formation, deformation, and breakage of these ligaments dissipated more energy, hence increasing the effective joint toughness and strength.

Estimation of the DNA damage in Girardia tigrina (Girard, 1850) after exposure to radiation under extreme conditions / Estimativa dos danos do DNA em Girardia tigrina (Girard, 1850) após exposição à radiação em condições extremas

The use of planarians as experimental models has been increased worldwide especially due to their high capacity of tissue regeneration and ease of laboratory maintenance. The current study aims to assess the genetic damage of Girardia tigrina after exposure of stressors in conditions such as: critical temperature, critical pH, hypergravity (4.4G) and low power laser (685nm). 18 specimens of G. tigrina were used, the extreme conditions mentioned were experimental group with 3 specimens each, and 3 for the control group, all specimens were submitted to the Comet Assay after exposure of stressors, and control group with no extreme condition exposure. The extreme stimuli of critical temperature and pH, hypergravity and low power laser irradiation, caused genetic damages to the G. tigrina, for hypergravity and low-power laser stressors the damage was higher in the pharyngeal and post-pharyngeal regions of the animal with a greatest area of comet tail dragging for the post-pharyngeal region. The extreme stimuli of critical temperature and pH, hypergravity and low power laser irradiation caused genetic damages in planarians Brazilian Journal of Development ISSN: 2525-8761 12160 Brazilian Journal of Development, Curitiba, v.8, n.2, p.12159-12177 feb. 2022. G. tigrina, especially in samples from the pharyngeal and post-pharyngeal regions of the flatworms body assessed by the Comet Assay.

Clinical and radiographic effectiveness of mineral trioxide aggregate (MTA) partial pulpotomy with low power or high power diode laser irradiation in deciduous molars: a randomized clinical trial.

This study investigated the clinical and radiographic effectiveness of MTA partial pulpotomy with low power or high power diode laser irradiation in primary molars. In this randomized single-blind clinical trial, 63 mandibular second molars were assigned into three groups (n = 21). After pulp amputation and achieving hemostasis, MTA was placed over pulp stumps in group 1 (MTA). The patients in groups 2 (LLLT-MTA) and 3 (DL-MTA) underwent low level (660nm, 200 mW) and high power (810nm, 1W) diode laser radiation prior to MTA placement, respectively. The occurrence of clinical failure (spontaneous pain, tenderness upon percussion, swelling, fistula, mobility) and radiographic failure (periodontal ligament widening, external or internal root resorption, periapical or furcal radiolucency) was recorded up to 18months after therapy.MTA and LLLT-MTA groups showed clinical success rate of 100% throughout the experiment. The clinical success rate of DL-MTA group was 95.2%, 95.2%, and 87.5% after 6, 9, and 18months. The radiographic success rates were 90.5%, 90.5%, and 87.5% in the MTA group; 100%, 95.2%, and 88.2% in the LLLT-MTA group, and 85.7%, 76.2%, and 68.7% in the DL-MTA group, at 6-, 9-, and 18-month follow-ups, respectively. No significant differences were found in the frequency of clinical or radiographic failure among the groups at any interval (p > 0.05). MTA partial pulpotomy was a suitable technique for vital pulp therapy in deciduous teeth. The addition of low power or high power diode laser radiation to the procedure did not cause a significant difference in success rate values.

Substitutional oxygen activated photoluminescence enhancement in monolayer transition metal dichalcogenides

Atomically thin transition metal dichalcogenides (TMDCs) are intriguing semiconductors for photonics and optoelectronics, and therefore enhancing their photoluminescence (PL) efficiency is crucial for these applications. Many efforts have been contributed to enhancing the PL performance of monolayer TMDCs, yet the complexity between the microstructure and the PL efficiency has hindered the manipulation of their PL properties. Here we demonstrate that the PL intensity of the monolayer TMDC can be enhanced by nearly one order of magnitude with a ∼20% narrower spectral linewidth after a pre-activation plateau using laser irradiation in ambient environment. Combined experimental and theoretical studies reveal that low-power laser irradiation generates many sulfur vacancy clusters, which are subsequently filled up by oxygen, and the lattice substitutional oxygen clusters induce the dramatic PL enhancement of monolayer WS2. Such PL enhancement phenomenon is found to be universal for other monolayer TMDCs, and thus would benefit their versatile optical applications.