Advanced Optical Materials最新文献

Infrared Up-Conversion in Double-Step Asymmetric Subwavelength Grating Structure

In article number 2401070, Varun Raghunathan and co-workers study the nonlinear optical up-conversion of the mid-infrared to visible wavelength range through third-order sum-frequency generation (TSFG) process using novel double-step amorphous germanium one-dimensional sub-wavelength grating structures supporting quasi-bound states in the continuum (quasi-BIC) resonances in the mid-infrared (3–3.5 mm). One-dimensional dual step gratings on the quartz substrate are shown in the bottom part of the image. The primary (with central hole) and secondary mirrors inside the reflective objective are shown as discs (glassy brown) in the middle part. Cylindrical beams represent two mixing beams: pump (orange) and mid-infrared (pink) along with the generated TSFG signal (green). Pulses with arrows represent the incoming (illumination) and outgoing (collection) beams. The central obscuration caused by the secondary mirror is also clearly illustrated, which is the main theme of the work.

Fiber-Integrated van der Waals Quantum Sensor

The cover image illustrates a fiber-integrated van der Waals quantum sensor. The circular Bragg grating cavity fabricated from hexagonal boron nitride (hBN) with optically active spin defects, is integrated with an optical fiber using a deterministic transfer technique. The fiber-integrated hBN cavity enables efficient excitation and collection of signal without the need of a confocal microscope. The fiber-based quantum sensing platform may pave the way to a new generation of robust, remote, multi-functional quantum sensors. For further details, see article number 2401987 by Je-Hyung Kim, Igor Aharonovich, and co-workers.

Room-Temperature Phosphorescence Cellulose Filaments

This cover image, referring to article number 2401419 by Xingxing Li, Shi-Jian Su, Haisong Qi, and co-workers, depicts cellulose-based filaments with remarkable room-temperature phosphorescence (RTP) properties when exposed to ultraviolet light, and the afterglow color of the filaments can be effectively modulated. The large-scale production of multicolored filaments with ultralong RTP will broaden the functional cellulose materials and expand applications in many fields.

Single Crystals for Ultraviolet Nonlinear Optics

Nonlinear optical crystals can convert one color of light to another, as artistically depicted in this cover image. They are central to generating a wide spectrum of laser light for both fundamental science and a range of optical technologies. In the work by Saugata Sarker, Venkatraman Gopalan, and co-workers (see article number 2401437), a new family of crystals are reported that can convert visible light to ultraviolet light where there is a dearth of efficient crystals.

Lead halide perovskite nanocrystals are attractive for light emitting devices both as electroluminescent and color-converting materials since they combine intense and narrow emissions with good charge injection and transport properties. However, while most perovskite nanocrystals shine at green and red wavelengths, the observation of intense and stable blue emission still remains a challenging target. In this work, a method is reported to attain intense and enduring blue emission (470–480 nm), with a photoluminescence quantum yield (PLQY) of 40%, originating from very small CsPbBr₃ nanocrystals (diameter < 3 nm) formed by controllably exposing Cs₄PbBr₆ to humidity. This process is mediated by the void network of a mesoporous transparent scaffold in which the zero-dimensional Cs₄PbBr₆ lattice is embedded, which allows the fine control over water adsorption and condensation that determines the optimization of the synthetic procedure and, eventually, the nanocrystal size. The approach provides a means to attain highly efficient transparent and stable blue light-emitting films that complete the palette offered by perovskite nanocrystals for lighting and display applications.

Free carrier absorption (FCA) is established to be the cause of nonlinear losses in plasma-enhanced chemical vapor deposition (PECVD) silicon-rich nitride (SRN) waveguides. To validate this hypothesis, a photo-induced current is measured in SRN thin films with refractive indices varying between 2.5 and 3.15 when a C-band laser light is illuminating the SRN films at various powers, indicating the generation of free carriers. Furthermore, nonlinear loss dynamics is, for the first time, measured and characterized in detail in SRN waveguides by utilizing high peak power C-band complex shape optical pulses for estimation of free carrier generation (FCG) and free carrier recombination (FCR) lifetimes and their dynamics. Both FCG and FCR are found to decrease with an increase in the refractive index of SRN, and, specifically, the FCR lifetimes are found (92 ± 7) ns, (39 ± 3) ns, and (31 ± 2) ns for the SRN indices of 2.7, 3, and 3.15, respectively. Lastly, nonlinear losses in high refractive index SRN waveguides are demonstrated to be minimized and altogether avoided when the pulse duration reduced below the free carrier generation lifetime, thus providing a way of taking a full advantage of the large inherent SRN nonlinear properties.

Environment-benign ZnSeTe quantum dots (QDs) are regarded promising blue electroluminescent (EL) emitters alternative to Cd-based ones for the next-generation QD-display platform. Herein, the core/shell heterostructural variation of blue-emitting ternary ZnSeTe QDs by manipulating ZnSeTe core size (small versus large) and ZnSe inner shell thickness (thin versus thick), while ZnS outer shell thickness remains unaltered, is explored. EL outcomes of the resulting core/shell QDs having photoluminescence quantum yields of 59−80% within the blue color regime (454−463 nm) are found to be dependent on their heterostructural dimension, exhibiting the highest performances of 31709 cd m⁻² in luminance and 11.4% in external quantum efficiency (EQE) from large-ZnSeTe/thick-ZnSe/ZnS QDs. Furthermore, to address the chronic issues of excessive electron injection and exciton quenching at emitting layer/electron transport layer (ETL) interface, the surface of ZnMgO (ZMO) nanoparticle (NP) is modified by bicarbonate functional species. Bicarbonate passivation not only leads to the effective reduction of defective sites on the ZMO NP surface toward the suppression of exciton quenching but induces the upshift of ETL band alignment in favor of charge balance. As a result, the optimized blue device incorporated with bicarbonate-functionalized ZMO NPs delivers a peak luminance of 39739 cd m⁻² and a maximum EQE of 17.1%.

Recently, it is shown (Popov et al, Sci. Rep, 2017, 7, 1603) that chiral nematic liquid crystal films adopt biconvex lens shapes underwater, which may explain the formation of insect eyes, but restrict their practical application. Here it is demonstrated that chiral ferroelectric nematic liquid crystals, where the ferroelectric polarization aligns parallel to the air interface, can spontaneously form biconvex lens arrays in air when suspended in submillimeter-size grids. Using Digital Holographic Microscopy, it is shown that the lens has a paraboloid shape and the curvature radius at the center decreases with increasing chiral dopant concentration, i.e., with decreasing helical pitch. Simultaneous measurements of the imaging properties of the lenses show the focal length depends on the pitch, thus offering tunability. The physical mechanism of formation of the self-assembled ferroelectric nematic microlenses is also discussed.

Photomodulable fluorophores constitute advanced materials as they possess the ability to modify their photophysical properties upon photoirradiation. A new mechanism of photoconversion is recently established, called Directed Photooxidation Induced Conversion based on the coupling of fluorophores with Aromatic Singlet oxygen Reactive Moieties (ASORMs). In this work, The Directed Photooxidation Induced Conversion (DPIC) mechanism is intended to be applied to Perylene BisImide (PBI) due to its appealing photophysical properties. The experimental results showed that coupling two ASORMs to the PBI core, here furan and pyrrole, led to impressive photomodulable fluorophores. While PBI-F exhibited a photoconversion of 100 nm shift, PBI-P displayed an 80-fold fluorescence intensity enhancement upon photoactivation. Analysis of the photoproducts showed that the conversion do not involve an addition of singlet oxygen on the ASORM. Instead, photoconversion occurred through efficient successive photocyclizations. Finally, intracellular vesicles are successfully photoconverted by means of endocytosed PLGA-polymer nanoparticles loaded with PBI-F. This study highlights the unique capability of furan- and pyrrole-conjugated fluorophores to enable advanced optical materials with phototransformation properties.