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The progressive stacking of chalcogenide single layers gives rise to two- dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide （InSe） is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness （as large as 0.2 eV for three single layers）. First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.

This work presents a new method to effectively improve the optical temperature behavior of Er 3+ doped Y 2 O 3 microtubes by co-doping of Tm 3+ or Ho 3+ ion and controlling excitation power. The influence of Tm 3+ or Ho 3+ ion on optical temperature behavior of Y 2 O 3 :Er 3+ microtubes is investigated by analyzing the temperature and excitation power dependent emission spectra, thermal quenching ratios, fluorescence intensity ratios, and sensitivity. It is found that the thermal quenching of Y 2 O 3 :Er 3+ microtubes is inhibited by co-doping with Tm 3+ or Ho 3+ ion, moreover the maximum sensitivity value based on the thermal coupled 4 S 3/2 / 2 H 11/2 levels is enhanced greatly and shifts to the high temperature range, while the maximum sensitivity based on 4 F 9/2(1) / 4 F 9/2(2) levels shifts to the low temperature range and greatly increases. The sensitivity values are dependent on the excitation power, and reach two maximum values of 0.0529/K at 24 K and 0.0057/K at 457 K for the Y 2 O 3 :1%Er 3+ , 0.5%Ho 3+ at 121 mW/mm 2 excitation power, which makes optical temperature measurement in wide temperature range possible. The mechanism of changing the sensitivity upon different excitation densities is discussed.

Photopolymer resins used in stereolithographic 3D printing are limited to penetration depths of less than 1 mm. Our approach explores the use of near-infrared (NIR) to visible upconversion (UC) emissions from lanthanide-based phosphors to initiate photopolymer crosslinking at a much higher depth. This concept relies on the use of invisibility windows and non-linear optical effects to achieve selective crosslinking in photopolymers. SLA resin formulation capable of absorbing light in the visible region (420–550 nm) was developed, in order to take advantage of efficient green-UC of Er3+/Yb3+ doped phosphor. NIR-green light UC shows versatility in enhancing curing depths in laser patterning. For instance, a structure with a curing depth of 11 ± 0.2 mm, cured width of 496 ± 5 µm and aspect ratios of over 22.2:1 in a single pass via NIR-green light UC. The penetration depth of the reported formulation approached 39 mm. Therefore, this technique would allow curing depths of up to 4 cm. Moreover, it was also demonstrated that this technique can initiate cross-linking directly at the focal point. This shows the potential of NIR-assisted UC as a low-cost method for direct laser writing in volume and 3D printing.

This study presents the fabrication of new, non-toxic perovskite solar cells using 2D cobalt-based perovskite materials. Three cobalt-based Organic–inorganic 2D hybrid perovskite (HOIP) materials were synthesized, and their photovoltaic properties were evaluated: [NH 3 (CH 2 )nNH 3 ]CoCl 4 (n = 4, 9) and [NH 3 (CH 2 ) 7 NH 3 ]CoBr 2 Cl 2 . These materials encompassed varying organic chain lengths (short, medium, and long) as well as chloride and mixed chloride/bromide anions. The molecular structure was examined to establish correlations with the structural and optical properties. The synthesized compounds exhibited visible light absorption, with varying bandgap energy from 1.7 eV to 2.7 eV. To test the application of Co-based perovskites, two distinct solar cell architectures were employed. The first architecture, denoted as Architecture 1, consisted of the following layers: Glass/FTO/c-TiO 2 /m-TiO 2 /ZrO 2 /2D Co-based HOIP/C-electrode. The second architecture, referred to as Architecture 2, utilized a planar heterojunction structure deposited with different transport layers for electrons and holes. Specifically, it comprised the layers: Glass/ITO/SnO 2 /2D Co-based HOIP/Spiro-OMeTAD/Au. Among these architectures, Architecture 2 exhibited notable performance. It achieved a maximal open circuit voltage (Voc) of 0.93 V, and current density (Jsc) of 0.24 mA/cm 2 , with efficiency of 0.47%, and a fill factor (FF) of 78%. These findings demonstrate the effectiveness of adjusting the perovskite material composition and controlling the deposition conditions in raising solar cell efficiency.

In this work, the unique optical properties of surface plasmon polaritons (SPPs), i.e. subwavelength confinement or strong electric field concentration, are exploited to demonstrate the propagation of light signal at 600 nm along distances in the range from 17 to 150 μm for Au nanostripes 500 nm down to 100 nm wide (30 nm of height), respectively, both theoretically and experimentally. A low power laser is coupled into an optical fiber tip that is used to locally excite the photoluminescence of colloidal quantum dots (QDs) dispersed in their surroundings. Emitted light from these QDs is generating the SPPs that propagate along the metal waveguides. Then, the above-referred propagation lengths were directly extracted from this novel experimental technique by studying the intensity of light decoupled at the output edge of the waveguide. Furthermore, an enhancement of the propagation length up to 0.4 mm is measured for the 500-nm-wide metal nanostripe, for which this effect is maximum. For this purpose, a simultaneous excitation of the same QDs dispersed in poly(methyl methacrylate) waveguides integrated with the metal nanostructures is performed by end-fire coupling an excitation laser energy as low as 1 KW/cm . The proposed mechanism to explain such enhancement is a non-linear interference effect between dielectric and plasmonic (super)modes propagating in the metal-dielectric structure, which can be apparently seen as an effective amplification or compensation effect of the gain material (QDs) over the SPPs, as previously reported in literature. The proposed system and the method to create propagating SPPs in metal waveguides can be of interest for the application field of sensors and optical communications at visible wavelengths, among other applications, using plasmonic interconnects to reduce the dimensions of photonic chips.

Optimizing upconversion (UC) composites is challenging as numerous effects influence their unique emission mechanism. Low scattering mediums increase the number of dopants excited, however, high scattering mediums increase the UC efficiency due to its non-linear power dependency. Scattering also leads to greater thermal effects and emission saturation at lower excitation power density (PD). In this work, a photoluminescence quantum yield (PLQY) increase of 270% was observed when hexagonal NaYF 4 :(18%)Yb 3+ ,(2%)Er 3+ phosphor is in air compared to a refractive index-matched medium. Furthermore, the primary inner-filter effect causes a 94% PLQY decrease when the excitation focal point is moved from the front of the phosphor to 8.4 mm deep. Increasing this effect limits the maximum excitation PD, reduces thermal effects, and leads to emission saturation at higher excitation PDs. Additionally, self-absorption decreases the PLQY as the phosphor’s thickness increases from 1 to 9 mm. Finally, in comparison to a cuboid cuvette, a 27% PLQY increase occurs when characterizing the phosphor in a cylindrical cuvette due to a lensing effect of the curved glass, as supported by simulations. Overall, addressing the effects presented in this work is necessary to both maximize UC composite performance as well as report their PLQY more reliably.

Much scientific equipment requires the use of humidity control technologies. This includes instruments with hygroscopic optics, such as infrared spectrometers, OPOs and some lasers. The most common strategies include nitrogen purging or desiccant bag replacement, which involve maintenance and running costs. In this work we present a dual strategy, combining both ionic membranes and silica desiccant, which results in a reusable and maintenance-free scheme for humidity control. The desiccant action of the silica gels, the membrane, and combinations thereafter, are studied. It is shown that the combination of the silica gel desiccants and the membrane is the most efficient configuration, reducing the humidity from 73% to only 15% in 20 h in a 70 L volume and from 80% to 20% in 40 h in a 230 L volume. An experiment over 5 days showed that the status of the silica gel desiccants that had adsorbed high water vapor levels returned to normal after they were enclosed together with the ionic membrane in the 70 L volume. Finally, measurements taken by a commercial infrared spectrometer of the reduction in the H2O lines absorption in the mid-infrared region under the operation of the combined configuration are examined. It was demonstrated that H2O lines with low to moderate absorption almost disappeared when the humidity levels inside the spectrometer dropped from 42.5% to 15.1% in the span of 90 min, while lines with stronger absorption remained present even though they showed the highest percentage of change.

Intracoronary stents have revolutionized the treatment of coronary obstructions, allowing for minimally invasive procedures and significantly enhancing both therapeutic efficacy and patient quality of life. Despite their clinical success, once implanted, stents act as passive elements, incapable of providing real-time data on the treated artery, thereby limiting early diagnosis of post-implantation complications such as inflammation, restenosis, or recurrence of atheromatous plaques. In this study, we introduce stents with deep tissue sensing capabilities through the incorporation of near-infrared emitting lanthanide-doped nanoparticles. Using 3D printed stent prototypes, we demonstrate that the luminescence emitted by neodymium and ytterbium ions in core/shell/shell NaYF₄ nanoparticles facilitates both deep tissue visualization and tracking of the stent position. Additionally, the temperature-dependent fluorescence lifetime of Nd,Yb:NaYF₄ nanoparticles provides thermal sensitivity, allowing precise deep tissue thermal monitoring of catheter-induced heating with sub-degree accuracy. This work highlights the potential of infrared-emitting nanoparticles to drive the next generation of coronary stents, paving the way for advanced light-based diagnostics and therapeutic procedures.

Optical probes operating in the second near-infrared window (NIR-II, 1,000-1,700 nm), where tissues are highly transparent, have expanded the applicability of fluorescence in the biomedical field. NIR-II fluorescence enables deep-tissue imaging with micrometric resolution in animal models, but is limited by the low brightness of NIR-II probes, which prevents imaging at low excitation intensities and fluorophore concentrations. Here, we present a new generation of probes (Ag 2 S superdots) derived from chemically synthesized Ag 2 S dots, on which a protective shell is grown by femtosecond laser irradiation. This shell reduces the structural defects, causing an 80-fold enhancement of the quantum yield. PEGylated Ag 2 S superdots enable deep-tissue in vivo imaging at low excitation intensities (<10 mW cm −2 ) and doses (<0.5 mg kg −1 ), emerging as unrivaled contrast agents for NIR-II preclinical bioimaging. These results establish an approach for developing superbright NIR-II contrast agents based on the synergy between chemical synthesis and ultrafast laser processing. Deep tissue imaging has been limited by the low brightness of probes emitting in the second near-infrared window. Here, the authors use femtosecond laser irradiation to grow a protective shell on Ag 2 S nanoparticles, achieving 80-fold quantum yield enhancement and imaging with low excitation intensities.

Optical upconversion from lanthanide-doped nanoparticles is promising for a variety of applications ranging from bioimaging, optogenetics, nanothermometry, super-resolution nanoscopy and volumetric displays to solar cells. Despite remarkable progress made in enhancing upconversion to fuel these applications, achieving luminescence of upconversion nanoparticles (UCNPs) that is comparable to or higher than the bulk counterparts has been challenging due to nanoscale-induced quenching effects. Here we demonstrate a size-dependent lanthanide energy transfer effect in a conceptual design of hexagonal sodium yttrium fluoride (NaYF 4 ) core–shell–shell NaYF 4 @NaYF 4 :Yb/Tm@NaYF 4 UCNPs with depleted surface quenching. We show that precise control over the domain size (or the thickness of the middle shell doped with ytterbium (Yb) and thulium (Tm) from 1.2 to 13 nm) increases the lanthanide energy transfer efficiency (from 30.2 to 50.4%) and amplifies the upconversion quantum yield to a high value of 13.0 ± 1.3% in sub-50 nm UCNPs (excitation: 980 nm, 100 W cm −2 ), which is around fourfold higher than the micrometre-scale hexagonal NaYF 4 :Yb/Tm bulk counterparts. Spectroscopic studies and theoretical microscopic modelling reveal that long-range lanthanide energy transfer (>9.5 nm) takes place and underlies the observed size-dependent phenomena. Demonstration of size-dependent lanthanide energy transfer and upconversion quantum yields at the nanoscale transforms our long-existing conceptual understanding of lanthanide energy transfer (size independence), thereby having important implications for applications of lanthanide nanophotonics and biophotonics. Researchers demonstrate a size-dependent lanthanide energy transfer effect in upconversion nanoparticles with depleted surface quenching, resulting in upconversion quantum yields of 13.0 ± 1.3%.