Multimode Emission Research Articles

Multimode evaluating the fluctuation of lipid droplets polarity in acute kidney injury and tumor models

Lipid droplets (LDs) polarity changes are closely associated with the occurrence and development of various diseases. Simultaneously observing the LDs polarity fluctuations through fluorescence intensity, fluorescence wavelength, and fluorescence lifetime could greatly improve the accuracy of different pathological processes. We herein present a novel multimode two-photon aggregation-induced emission fluorescent probe (TP-LDs) for sensitively detecting the polarity changes in LDs. TP-LDs showed good photostability and high selectivity for LDs even at low concentrations. Furthermore, TP-LDs could detect the LDs polarity changes in the acute kidney injury (AKI) cell model and distinguish lung cancer cells and normal cells through fluorescence intensity, fluorescence lifetime, and fluorescence wavelength. Moreover, for the first time, we revealed LDs polarity changes in the AKI mouse model and its treatment. Most importantly, TP-LDs can differentiate tumor tissues from normal tissues in the A549 tumor-bearing mouse model and distinguish normal lung tissues from cancerous tissues in humans. Thus, the multimode polarity-sensitive fluorescent probe holds a robust tool for AKI and tumor evaluation in cells and animals as well as provides new insights into lung cancer diagnosis in clinical.

Dual‐mode optical thermometry and multicolor anti‐counterfeiting based on Bi3+/Er3+ co‐activated BaGd2O4 phosphor

AbstractHere, Bi3+, Er3+ co‐activated gadolinium phosphors with multimode emission properties are prepared, which can emits blue, green, and orange light under the excitation of ultraviolet, 980 and 1550 nm, respectively. Moreover, BaGd2O4:Bi3+, Er3+ can show multicolor luminescence under different excitation conditions, such as pump light source, ambient temperature, working current, and other factors. Based on the dynamic luminescence characteristics, the dynamic anti‐counterfeiting experiments are designed based on the phosphor. At the same time, the material also shows multimode temperature sensing characteristics. Under the excitation of 980 nm laser, three strong up‐conversion signals Er3+ ions are generated at 528 nm (2H11/2), 555 nm (4S3/2), and 668 nm (4F9/2), which have different temperature dependences. Based on the fluorescence intensity ratio between thermal‐coupled energy levels (2H11/2/4S3/2) and nonthermal‐coupled energy levels (2H11/2/4F9/2) of Er3+ ions, respectively, the dual‐mode temperature thermometer was constructed with high‐temperature sensitivity. In addition, the fluorescence lifetime of Bi3+ ions also has a strong temperature dependence, which can be used as another temperature detection signal, greatly improving the stability of thermometers under harsh conditions. Therefore, the material has a bright prospect in the field of anti‐counterfeiting and temperature sensing.

Multimode laser emission from BODIPY dye-doped polymer optical fiber

We report the fabrication and investigations of lasing properties of dipyrromethene boron difluoride (BODIPY) dye-doped polymer optical fibers (DDPOFs) using two different pumping schemes. Here, we have explored BDIPA dye, a π-extended BODIPY derivative as the gain medium. A Q-switched Nd:YAG laser operating at 532 nm was used, as the pump source for the lasing studies. Stripe illumination using a cylindrical lens produces amplified spontaneous emission (ASE) in the fiber whereas a multimode laser emission at a low lasing threshold of 50 μJ was observed by spot illumination technique using a convex lens. The cylindrical surface of the optical fiber acts as a cavity and it provides the necessary optical feedback for the gain medium resulting in the observed lasing properties. The photostability of the fiber was investigated at higher pump energy of 2 mJ using a convex lens. Excellent results such as very low lasing threshold, high cavity Q-factor and photostability were observed for the fabricated BDIPA DDPOF, clearly indicating the use of the BDIPA dye as a prominent lasing material in solid-state dye lasers.

Designing Color-tunable luminescent thermometers and information encryption based on Pr3+ or Sm3+ doped SrNb2O6: Tb3+ phosphors via energy transfer

Color-tunable luminescence intensity ratio thermometers and information encryption are firstly designed through different energy transfer mechanism. Herein, two types thermometric materials, SrNb2O6: Tb3+, Pr3+ and SrNb2O6: Tb3+, Sm3+ are prepared. The Tb3+ and Pr3+ typical emissions show luminescence mechanism between two intervalence charge transfer states. Whereas, Tb3+ and Sm3+ emissions are related to energy migration from intervalence charge transfer state to 4f level. Interestingly, (5D4→7F5)Tb3+/(1D2→3H4)Pr3+ or (5D4→7F5)Tb3+/(4G5/2→6H7/2)Sm3+ have different temperature sensing properties due to distinct energy transfer processes and provide visualization of temperature measurement. The former gains high sensitivity (Sa = 0.012 K−1) at high temperature region, and the latter reach as high as Sa = 0.028 K−1 at low temperature. Besides, using multi-mode color emission of Tb3+ or Pr3+ doped SrNb2O6 achieves information hiding. This work not only shows new strategy to develop high-efficiency luminescent thermometers but also develop flexible optical encryption technology.

Room Temperature Lasing in GeSn Microdisks Enabled by Strain Engineering

AbstractThe success of GeSn alloys as active material for infrared lasers could pave the way toward a monolithic technology that can be manufactured within mainstream silicon photonics. Nonetheless, for operation on chip, lasing should occur at room temperature or beyond. Unfortunately, despite the intense research in recent years, many hurdles have yet to be overcome. An approach exploiting strain engineering to induce large tensile strain in micro‐disk made of GeSn alloy with Sn content of 14 at% is presented here. This method enables robust multimode laser emission at room temperature. Furthermore, tensile strain enables proper valence band engineering; as a result, over a large range of operating temperatures, lower lasing thresholds are observed compared to high Sn content GeSn lasers operating at similar wavelength.

Upconversion/Downshifting Multimode Luminescence of Lanthanide-doped Nanocrystals for Multidimensional Information Encoding Security.

Information encoding security has always been a research hotspot in the optical field. Although many studies focused on luminescent materials and techniques for information security, the optical information encoding is limited by low information capacity and security. Herein, we present new core-shell-shell (CSS) lanthanide-doped nanocrystals which display multi-stimuli-responsive and multimode emission. In the designed CSS nanostructure, the Stokes and anti-Stokes processes can be both achieved in the same nanocrystals under the excitation of 1532, 980, and 254 nm via self-excited Er3+ and Ce3+ -sensitized mechanisms. Subsequently, a group of unique multimode emission CSS nanocrystals were designed as optical modules and successfully utilized in multidimensional information encoding, which demonstrates high-level information encoding capability and security. This work brings a powerful idea for information encoding security designs based on multimode luminesce materials.

Scalable single-mode surface-emitting laser via open-Dirac singularities.

Single-aperture cavities are a key component of lasers that are instrumental for the amplification and emission of a single light mode. However, the appearance of high-order transverse modes as the size of the cavities increases has frustrated efforts to scale-up cavities while preserving single-mode operation since the invention of the laser six decades ago1-8. A suitable physical mechanism that allows single-mode lasing irrespective of the cavity size-a 'scale invariant' cavity or laser-has not been identified yet. Here we propose and demonstrate experimentally that open-Dirac electromagnetic cavities with linear dispersion-which in our devices are realized by a truncated photonic crystal arranged in a hexagonal pattern-exhibit unconventional scaling of losses in reciprocal space, leading to single-mode lasing that is maintained as the cavity is scaled up in size. The physical origin of this phenomenon lies in the convergence of the complex part of the free spectral range in open-Dirac cavities towards a constant governed by the loss rates of distinct Bloch bands, whereas for common cavities it converges to zero as the size grows, leading to inevitable multimode emission. An unconventional flat-envelope fundamental mode locks all unit cells in the cavity in phase, leading to single-mode lasing. We name such sources Berkeley surface-emitting lasers (BerkSELs) and demonstrate that their far-field corresponds to a topological singularity of charge two, in agreement with our theory. Open-Dirac cavities unlock avenues for light-matter interaction and cavity quantum electrodynamics.

A Solvent-Mediated Excited-State Intermolecular Proton Transfer Fluorescent Probe for Fe3+ Sensing and Cell Imaging.

Constructing excited-state intermolecular proton transfer (ESIPT-e) fluorophores represents significant challenges due to the harsh requirement of bearing a proton donor-acceptor (D-A) system and their matching proton donating-accepting ability in the same molecule. Herein, we synthesized a new-type ESIPT-e fluorophor (2-APC) using the “four-component one-pot” reaction. By the installing of a cyano-group on pyridine scaffold, the proton donating ability of -NH2 was greatly enhanced, enabling 2-APC to undergo ESIPT-e process. Surprisingly, 2-APC exhibited dual-emissions in protic solvents ethanol and normal fluorescence in aprotic solvents, which is vastly different from that of conventional ESIPT-a dyes. The ESIPT emission can be obviously suppressed by Fe3+ due to the coordination reaction of Fe3+ with the A-D system in 2-APC. From this basis, a highly sensitive and selective method was established using 2-APC as a fluorescent probe, which offers the sensitive detection of Fe3+ ranging from 0 to 13 μM with the detection limit of 7.5 nM. The recovery study of spiked Fe3+ measured by the probe showed satisfactory results (97.2103.4%) with the reasonable RSD ranging from 3.1 to 3.8%. Moreover, 2-APC can also exhibit aggregation-induced effect in poor solvent or solid-state, eliciting strong red fluorescence. 2-APC was also applied to cell-imaging, exhibiting good cell-permeability, biocompatibility and color rendering. This multi-mode emission of 2-APC is significant departure from that of conventional extended p-conjugated systems and ESIPT dyes based on a flat and rigid molecular design. The “one-pot synthesis” strategy for the construction of ESIPT molecules pioneered a new route to achieve tricolor-emissive fluorophores.

Toward robust and practical interband cascade laser frequency combs: A perspective

Multimode emission from a semiconductor laser can sometimes take the form of a low-noise frequency comb with equidistant separation between the modes. Two general types of “passive” comb operation have been explored experimentally: (1) the periodic short-pulse mode achieved by intracavity mode locking, usually obtained by incorporating a saturable absorber section into the cavity, and (2) the so-called frequency-modulated (FM) mode in which the output intensity can vary within wide bounds but does not completely turn off between pulses, and the instantaneous frequency is linearly chirped over a round trip. The FM mode sometimes manifests as a “sparse” harmonic state, with individual modes spaced by multiples of the cavity free spectral range. This Perspective reviews the current understanding of these modes, along with the conditions under which they may arise in practical devices. We then consider in detail the case of type-II mid-infrared interband cascade laser (ICL) frequency combs. Our simulations clarify the roles of carrier dynamics and group velocity dispersion and identify design modifications that may substantially improve the device performance. We find no fundamental roadblocks to the development of practical mode-locked ICL frequency combs that emit short pulses with broad spectral bandwidth for dual comb spectroscopy and other applications, alongside the FM combs that have already been demonstrated experimentally.

Emergence and control of photonic band structure in stacked OLED microcavities

We demonstrate an electrically-driven metal-dielectric photonic crystal emitter by fabricating a series of organic light emitting diode microcavities in a vertical stack. The states of the individual microcavities are shown to split into bands of hybridized photonic energy states through interaction with adjacent cavities. The propagating photonic modes within the crystal depend sensitively on the unit cell geometry and the optical properties of the component materials. By systematically varying the metallic layer thicknesses, we show control over the density of states and band center. The emergence of a tunable photonic band gap due to an asymmetry-introduced Peierls distortion is demonstrated and correlated to the unit cell configuration. This work develops a class of one dimensional, planar, photonic crystal emitter architectures enabling either narrow linewidth, multi-mode, or broadband emission with a high degree of tunability.

Tunable multi-mode laser based on robust cholesteric liquid crystal microdroplet.

To date, various studies have been dedicated to the development of cholesteric liquid crystal (CLC) microdroplet omnidirectional lasers. In this work, a stable and tunable multi-mode laser emission is achieved by designing a dye-doping CLC microdroplet. In such a structure, the polymer network only exists on the surface, maintaining stability while providing tunability, and due to the uneven distribution of the pitch, it leads to multi-mode laser emission. A large number of microdroplets are produced quickly via a new method based on ultrasonic separation. During the reaction, we introduce interfacial polymerization where monomers and photoinitiator are respectively distributed inside and outside the microdroplets through mutual diffusion, which enables one to make the polymer network exist on the surface instead of the interior. The obtained microdroplet-based multi-mode laser is shown to possess stability and tunability, demonstrating a great potential for flexible devices and 3D displays.

Sustainable Silk-Derived Multimode Carbon Dots.

Carbon dots (CDs) are widely studied for years due to their unique luminescent properties and potential applications in many fields. However, aggregation-caused quenching, monotonous emission modes, and unsustainable preparation impose restrictions on their performance and practical applications. Here, this work reports the facile synthesis of sustainable silk-derived multimode emitting CDs with dispersed-state fluorescence (DSF), aggregation-induced fluorescence (AIF), and aggregation-induced room temperature phosphorescence (AIRTP) through radiating sericin proteins in a household microwave oven (800 W, 2.5min). The structure, luminescent properties, and the mechanism are investigated and discussed. The sericin-derived CDs have graphitized cores and heteroatom-cluster-rich surfaces. The DSF corresponds to the graphitized cores and the AIF origins from the aggregation-induced abundant orbital energy levels on the heteroatom-cluster-rich surfaces. The presence of abundant hydrogen bonds and small gap between the lowest singlet and triplet excited states induces AIRTP. Finally, based on the unique multimode emission of the prepared CDs, their applications in high-performance white-light-emitting diode, information encryption, anti-counterfeiting, and visual humidity sensors are demonstrated.

Stimuli responsive lanthanide ions doped layered piezophotonic microcrystals for optical multifunctional sensing applications

Multifunctional optical sensing devices are of decisive significance to the miniaturization and integration of optoelectronic devices. However, the development of stimuli responsive materials with multimode emission is still in the early stage, limiting the application of integrated optical sensing. Here, we report the multimode emission piezophotonic material fabricated by doping lanthanide ions into the quaternary piezoelectric semiconductor SrZnOS, achieving multimode emission under various stimulus/excitation sources (ultraviolet, near-infrared laser, X-ray, and force), due to its multifunctional optical properties. Particularly the mechanoluminescence has been realized covering both the visible and near-infrared spectral bands. Optical stress sensing was achieved by establishing a quantitative relationship between force and light conversion. Moreover, near-infrared mechanoluminescence can effectively resist the interference of ambient light. The temperature detection performance and the power-dependent color tunability of the sample were also evaluated for multifunctional applications. All the results indicate that the developed multifunctional optical materials with inherent multimode light-emitting characteristics have the potential in advanced optical sensing and anti-counterfeiting applications. The piezophotonic material with multimode emission has been developed by doping lanthanide ions into layered quaternary piezoelectric semiconductor SrZnOS. The materials can be responsive to external stimuli (X-ray, UV light, NIR laser, stress), which could be used for energy conversion and optical stress/temperature dual-sensing. • Lanthanide ions doped SrZnOS is synthesized for stress/temperature dual-sensing. • It can be responsive to multi-mode stimuli (X-ray, UV light, NIR laser, stress). • The material can generate mechanoluminescence covering visible and NIR region. • The developed flexible composite can be used for energy conversion and sensing.

Unusual Polarization Relation between Single-Mode Lasing Emission and Excitation Laser from an Evanescent-Wave Pumped Micro-Cavity Laser

Using a fiber of that is 125 μm in diameter in rhodamine 6G ethanol solution, controllable multi- and single-whispering-gallery-mode (WGM) optofluidic lasers based on evanescent-wave-coupled gain are both available. With multi-mode WGM emission, lasing emission with almost pure TM (transverse magnetic) or almost TE (transverse electric) modes can be obtained when the pump laser has an electric field parallel (perpendicular) to the fiber axis, i.e., the polarization direction of output laser is the same as that of the pump laser. On the other hand, when the laser emission is single-mode, the TE output laser always emerges firstly above lasing threshold, then keeps TE mode while the pump laser’s intensity increases with polarization direction perpendicular to the fiber axis; on the contrary, TE emission will dwindle relatively, while the TM emission emerges and dominates the spectra, when the pump laser’s intensity increases with polarization parallel to the fiber axis. Our work proves that controlling the leakage of the evanescent wave from high-Q microcavities is crucial for both modes of lasing emission and its polarization.

Rare-earth coordination polymers with multimodal luminescence on the nano-, micro-, and milli-second time scales

SummaryWe present a coordination polymer based on rare-earth metal centers and carboxylated 4,4′-diphenyl-2,2′-bipyridine ligands. We investigate Y3+, Lu3+, Eu3+, and a statistical mixture of Y3+ with Eu3+ as metal centers. When Y3+ or Lu3+ is exclusively present in the coordination polymer, biluminescence from the ligand is observed: violet emission from the singlet state (417 nm, 0.9 ns lifetime) and orange emission from the triplet state (585 nm, 76 ms (Y3+) and 31 ms (Lu3+)). When Eu3+ is present in a statistical mixture with Y3+, red emission from the Eu3+ (611 nm, ) is observed in addition to the ligand emissions. We demonstrate that this multi-mode emission is enabled by the immobility of singlet and triplet states on the ligand. Eu3+ only receives energy from adjacent ligands. Meanwhile, in the broad inhomogeneous distribution of ligand energies, higher energy states favor singlet emission, whereas faster intersystem crossing in the more stabilized ligands enhances their contribution to triplet emission.

Spectroscopic Imaging with an Ultra-Broadband (1–4 THz) Compact Terahertz Difference-Frequency Generation Source

We demonstrate spectroscopic imaging using a compact ultra-broadband terahertz semiconductor source with a high-power, mid-infrared quantum cascade laser. The electrically pumped monolithic source is based on intra-cavity difference-frequency generation and can be designed to achieve an ultra-broadband multi-mode terahertz emission spectrum extending from 1–4 THz without any external optical setup. Spectroscopic imaging was performed with three frequency bands, 2.0 THz, 2.5 THz and 3.0 THz, and as a result, this imaging technique clearly identified three different tablet components (polyethylene, D-histidine and DL-histidine). This method may be highly suitable for quality monitoring of pharmaceutical materials.

Laser-driven x-ray and proton micro-source and application to simultaneous single-shot bi-modal radiographic imaging

Radiographic imaging with x-rays and protons is an omnipresent tool in basic research and applications in industry, material science and medical diagnostics. The information contained in both modalities can often be valuable in principle, but difficult to access simultaneously. Laser-driven solid-density plasma-sources deliver both kinds of radiation, but mostly single modalities have been explored for applications. Their potential for bi-modal radiographic imaging has never been fully realized, due to problems in generating appropriate sources and separating image modalities. Here, we report on the generation of proton and x-ray micro-sources in laser-plasma interactions of the focused Texas Petawatt laser with solid-density, micrometer-sized tungsten needles. We apply them for bi-modal radiographic imaging of biological and technological objects in a single laser shot. Thereby, advantages of laser-driven sources could be enriched beyond their small footprint by embracing their additional unique properties, including the spectral bandwidth, small source size and multi-mode emission.

Theoretical approach to quantum cascade micro-laser broadband multimode emission in strong magnetic fields

We have theoretically explored the influence of the magnetic field on supporting the multimode Risken-Nummendal-Graham-Haken (RNGH) self-pulsations seen in the optical spectrum as two broad modulations sidebands at the Rabi flopping frequency [25–27]. On the example of microcavity quantum cascade lasers (μ-QCLs), we demonstrate that Landau quantization in an external magnetic field slows down the effective decoherence and diffusion rates. The pump current required to reach the broadband multimode RNGH self-pulsations is lowered with the magnetic field strength, while the Rabi flopping frequency and the overall optical spectrum width remain practically unchanged. Our theoretical results indicate that an external magnetic field can be a valuable tool for achieving high-power broadband QCL self-pulsations in practice.

Resonant random laser emission from graphene quantum dots doped dye solution

In this letter, we report on the fabrication of dye doped graphene quantum dots (GQDs) random lasers with resonant feedback that are optically pumped with nanosecond pulses. GQDs, synthesized by the pyrolysis of citric acid, are used as the scattering elements in an ethylene glycol solution of rhodamine B dye. It is experimentally demonstrated that using GQDs instead of titania nanoparticles not only results in the multimode random lasing emission, but also increases the operating lifetime, significantly. We observe discrete lasing modes with subnanometer linewidths at the pump fluences above the threshold. Furthermore, the dependences of the random lasing emission characteristics on the pumping position and concentration of GQDs are investigated, experimentally.

Experimental and theoretical studies of the solid-state performance of electrodeposited Yb2O3/As2Se3 nanocomposite films

The influence of the rare-earth oxide (Yb2O3) on arsenic selenide (As–Se) host is currently investigated and documented in this study. Nanocomposite films were grown using the electrodeposition (ED) technique with the addition of 1 – 4 mol% Yb2O3. The film’s optical structural, optical, morphological, and electronic features were studied. The host matrix presents the monoclinic structure whereas the composite films present two phases –cubic and orthorhombic crystal structure. Crystallites within nano sizes (36.2 nm) were recorded for the pristine film while the composite films showed sizes ranging from 37.2 to 48.1 nm. Moreover, the Raman spectra revealed low energy Raman phonons characteristic of Se8 rings, As4Se4 cages, As–Se hetero-polar bonds whose cleavage was due to the diffusion of the Yb ions into the host matrix as shown by the Raman shift. More so, the refractive index peaked at n = 2.66 in the λ interval of 350–600 nm, while the SEM images showed nano-balls and nanoclusters which are fairly homogeneous. PL studies exhibited multimode emission bands spanning the UV–Vis–NIR regions. First-principles calculations were employed to investigate the structural properties and electronic structure of the pristine (As–Se) film, as well as Yb contribution. It was found that Yb addition leads to reduce the bandgap energy and consequently the lone pair p-states of Se contribute nearby to Fermi energy level. Hence, the experimental and theoretical results of films afford potential applications in phase-change memory (PCM) and downconverting solar cell window layer.