Multimode Emissions Research Articles

Multicolor and multimode luminescent lanthanide-doped Cs2NaInCl6:Sb3+ from visible to near infrared for versatile applications

Double halide perovskites have shown admirable potential in promising optoelectronic applications due to simple synthesis, good stability and high structural tolerance. However, the poor optical properties caused by the parity-forbidden transitions posts a stringent limitation on their potential applications. Herein, we dope the lanthanide (Ln3+) ions with abundant energy levels into the Cs2NaInCl6:Sb3+ single crystals, which not only achieve multicolor visible emissions spectra from blue to red light, but also expand to the near infrared region from 800 to 1900 nm. In addition, the phosphors enable the multimode emissions with the up-conversion and down-conversion photoluminescence. Intriguingly, the excitation source, and the excitation light intensity also endow the multicolor emissions. Thus, combining with the multicolor and multimode luminescent properties, Cs2NaInCl6:Sb3+/Ln3+ could be applied to night vision imaging, substance detection, optical thermometry, white-light-emitting diodes (WLEDs) and anti-counterfeiting. The maximum value of relative temperature sensitivity reaches as high as 1.207 % K−1, which is relatively higher than those of most metal halide perovskites. Moreover, the single-source WLED displays Commission Internationale de L'Eclairage color coordinates (0.32, 0.31), a correlated color temperature of 6673 K, and color rendering index of 81.7. These results demonstrate the potential applications in the multifunctional photoelectric applications.

Tunable multimode emissions of Yb3+/Er3+-doped rare-earth-based Cs2NaYCl6 double perovskite crystals for versatile applications

Lead-free halide double perovskite materials are gaining recognition because of their excellent optoelectronic performance. However, achieving multimode luminescence with tunable emission colors in single-component double perovskites remains a significant challenge. Understanding the mechanism of trivalent lanthanide-ion doping could provide a valuable solution. Herein, we report the synthesis of rare-earth-based Cs2NaYCl6 double perovskites using a hydrothermal method. Efficient visible to near-infrared down-shifting (DS) photoluminescence and green up-conversion (UC) emissions were realized by incorporating Er3+ ions with abundant energy levels into the hosts. Notably, the DS and UC emission colors could both be adjusted by further introducing Yb3+ ions that acted as sensitizers, and the photoluminescence was significantly enhanced due to the strong absorption at 980 nm. Spectral analysis revealed that the high compatibility of lanthanide ions with the rare-earth-based double perovskites and cross-relaxation processes played a key role in achieving modulated emission and multiple excitation modes. This study aimed to understand the photophysical mechanism of lanthanide-ion-doped double perovskites, as well as to highlight their ability to modulate emissions. Furthermore, this study expands the versatile applications of lanthanide-ion-doped double perovskites in the fields of high-security anti-counterfeiting, tissue imaging, and night-vision systems.

Multi-color and multi-mode luminescence tuning in persistent phosphors by trap engineering

Conventional persistent luminescent phosphors face a significant challenge in developing a single material for multi-color anti-counterfeiting. In this study, a wide range of Cr3+ activated gallium germanate-based persistent phosphors are successfully synthesized using high-temperature solid phase approach. By incorporating Cr3+ and Er3+ as dual emitting centers, and utilizing Yb3+ as a sensitizer and electron traps, the resulting phosphors exhibit an exceptional combination of photoluminescence, up-conversion luminescence, persistent luminescence, photo/thermo-stimulated luminescence, followed by photo-stimulated persistent luminescence in a single material system. Beyond its multi-mode emissions, the luminescence color output can be conveniently controlled by adjusting annealing time, Yb3+ ion doping concentration, excitation wavelength, or excitation power. A systematic study of trap distribution related to PersL has been conducted by regulating annealing temperature, time, doping concentration and type. The responding multi-mode luminescent mechanisms are also proposed. Particularly, these phosphors demonstrated outstanding performance as security labels in advanced anti-counterfeiting applications. This research holds the potential to inspire the design and development of more intricate luminescence anti-counterfeiting materials and technologies.

Optical activity levels of metal centers controlling multi-mode emissions in low-dimensional hybrid metal halides for anti-counterfeiting and information encryption.

In-depth insight into the electronic competition principles between inorganic units and organic ligands proves to be extremely challenging for controlling multi-mode emissions in low-dimensional hybrid metal halides (LHMHs). Herein, an efficient blue emission from organic ligand was engineered in (DppyH)2MCl4 (Dppy = diphenyl-2-pyridylphosphine, M = Zn2+, Cd2+) due to the reverse type I band alignment constructed by optically inert units with nd10 shell electrons. By contrast, the optically active [MnCl4]2- with semi-fully filled 3d5 shell electrons prompts the band alignment of type II, resulting in the narrowband green emission of Mn2+, along with an energy transfer from DppyH+ to [MnCl4]2-. Beyond that, the band alignment of (DppyH)SbCl4 is further reversed to type I due to the strong stereochemical activity of 5s2 lone-pair electrons, resulting in the triplet-state (3P1 → 1S0) self-trapped exciton (STE) emission of [SbCl4]-. The conclusion is that the electronic configurations of metal centers govern the optical activity levels of inorganic units, which in turn controls the multi-mode emissions by maneuvering the band alignments. This research provides an enlightening perspective on the multi-mode emissions with tunable photoluminescence and resulting electronic transitions of LHMHs, whose derived emitters can be employed in anti-counterfeiting and information encryption.

Multifunctional core-shell nanoparticles for temperature sensing and anti-counterfeiting

In this paper, the multi-functional multi-layer core-shell structure NaYF4: Ce3+/Eu3+@NaYF4 @NaYF4: Ho3+/Yb3+ nanoparticles (NPs) were prepared. These multi-layer NPs can be applied in temperature sensing with high relative sensitivity. Moreover, these NPs can be used in multimode optical anti-counterfeiting. Based on structure design and doped earth ions optimized, the maximum relative sensitivity is further promoted from 0.9 %·K−1 at 234 K (Eu/Ho) to 5.1 %·K−1 at 113 K (Ce/Eu@Y@Ho/Yb) by the blocking effect of the inter layer and by cross-relaxation of introducing Ce3+ and Yb3+ ions. Meanwhile, by introducing Ce3+ and Yb3+ ions, the NPs provide multimode emissions under multiple excitations, which are beneficial for the application of optical anti-counterfeiting. The NPs present increased sensitivity of temperature sensing and improved security of optical anti-counterfeiting, which has promising applications in biological cell calibration, micro-integrated circuits, etc.

Single-Component Color-Tunable Smart Organic Emitters with Simultaneous Multistage Stimuli-Responsiveness and Multimode Emissions.

Achieving color-tunable emission in single-component organic emitters with multistage stimuli-responsiveness is of vital significance for intelligent optoelectronic applications, but remains enormously challenging. Herein, we present an unprecedented example of a color-tunable single-component smart organic emitter (DDOP) that simultaneously exhibits multistage stimuli-responsiveness and multimode emissions. DDOP based on a highly twisted amide-bridged donor-acceptor-donor structure has been found to facilitate intersystem crossing, form multimode emissions, and generate multiple emissive species with multistage stimuli-responsiveness. DDOP pristine crystalline powders exhibit abnormal excitation-dependent emissions from a monomer-dominated blue emission centered at 470 nm to a dimer-dominated yellow emission centered at 550 nm through decreasing the ultraviolet (UV) excitation wavelengths, whereas DDOP single crystals show a wide emission band with a main emission peak at 585 nm when excited at different wavelengths. The emission behaviors of pristine crystalline powders and single crystals are different, demonstrating emission features that are closely related to the aggregation states. The work has developed color-tunable single-component organic emitters with simultaneous multistage stimuli-responsiveness and multimode emissions, which is vital for expanding intelligent optoelectronic applications, including multilevel information encryption, multicolor emissive patterns, and visual monitoring of UV wavelengths.

Pr3+–Gd3+ co-doped Ba2SiO4 for multilevel anti-counterfeiting encryption

Developing anti-counterfeiting technology with a higher level of security is vital to boycott the fake commodities. Here, we report the detailed optical property of Ba2SiO4:Pr3+, Gd3+, and their potential applications in fluorescent anti-counterfeit. It has been confirmed that Pr3+ ions could emit the ultraviolet-C (UVC) photons upon excitation of a 450 nm laser, which originates from a two-photon upconverted mechanism. Moreover, the ultraviolet-B (UVB) light also appears simultaneously when co-doping Gd3+ into the host, due to the energy transfer from Pr3+ to Gd3+. Depending on the multimode emissions of Pr3+-Gd3+-codoped phosphors, including the routine magenta emission of Pr3+, as well as the UVC photons of Pr3+ and the UVB light of Gd3+, we successfully achieve multi-level anti-counterfeiting applications.

Deep Learning Fluorescence Imaging of Visible to NIR‐II Based on Modulated Multimode Emissions Lanthanide Nanocrystals

AbstractFluorescence bioimaging has always been a research hotspot in the field of life sciences and medicine. Although many studies focus on the promising second near infrared window (NIR‐II) imaging, the NIR‐II imaging with deep tissue penetration is limited by the broad emission band widths. Herein, a well‐designed lanthanide doped nanocrystal is presented that can modulate the energy migration processes by controlling energy migration pathway and cerium‐assisted energy transfer processes, resulting in switchable emission modes of visible and NIR‐II that dependent by the excitation wavelengths. Subsequently, the multimode emissions of dumbbell‐like nanocrystals are cooperated with deep learning, where the advantages of narrow emission peak of visible fluorescence and deep tissue penetration of NIR‐II fluorescence are combined to offer a unique deep learning fluorescence bioimaging. By this new imaging method, fluorescence signals can be obtained with narrow emission peak and high signal‐to‐noise ratio after penetrating phantom tissue. This study brings a powerful idea for cutting‐edge applications of intelligent optical materials, such as in vivo information security.

On-chip microdisk laser on Yb3+-doped thin-film lithium niobate.

We demonstrate an on-chip Yb3+-doped lithium niobate (LN) microdisk laser. The intrinsic quality factors of the fabricated Yb3+-doped LN microdisk resonator are measured up to 3.79×105 at a 976 nm wavelength and 1.1×106 at a 1514 nm wavelength. The multi-mode laser emissions are obtained in a band from 1020 to 1070 nm pumped by a 984 nm laser and with the low threshold of 103µW, resulting in a slope efficiency of 0.53% at room temperature. Furthermore, both the second-harmonic frequency of pump light and the sum frequency of the pump light and laser emissions are generated in the on-chip Yb3+-doped LN microdisk, benefiting from the strong χ(2) nonlinearity of LN. These microdisk lasers are expected to contribute to the high-density integration of a lithium niobate on insulator-based photonic chip.

Demonstration of Yb3+-doped and Er3+/Yb3+-codoped on-chip microsphere lasers.

Rare-earth-doped on-chip microlasers are of great significance in both fundamental research and engineering. To the best of our knowledge, this is the first report of Yb3+-doped and Er3+/Yb3+-codoped on-chip microsphere lasers fabricated via sol-gel synthesis. Laser emissions were observed in a band around 1040 nm in both Yb3+-doped and Er3+/Yb3+-codoped resonators pumped at 980 nm and had measured ultralow thresholds of 5.2 µW and 0.6 µW, respectively. Both single-mode and multi-mode emissions were recorded around 1040 nm in these lasers. Single-mode and two-mode emissions were obtained at 1550 nm in the Er3+/Yb3+-codoped lasers when pumped at 980 nm and 1460 nm, respectively. Furthermore, quality factors induced by different loss mechanisms in the microsphere lasers are theoretically estimated. These resonators are expected to contribute to the high-density integration of on-chip silica-based microlasers.

Room-temperature white and color-tunable afterglow by manipulating multi-mode triplet emissions

Two isomers pDCzPyCN and oDCzPyCN are designed and synthesized. Amazingly, oDCzPyCN manifest white afterglow at room temperature. This is the first time that single-component white afterglow has finally been realized.

Influence of annealing time on random lasing from ZnO nanorods

Highly stabile single mode and multi-mode random lasing emissions were observed from ZnO nanorods array prepared on glass substrates using chemical deposition technique. By varying the post-growth-annealing time, nanorod diameters between 54 and 78 nm with population densities between 75 and 95 nanorods/µm2 were obtained. Depending on the population density and diameter of the nanorods, single, double and triple random lasing emissions were observed with lowest threshold of 209 mJ/cm2. Furthermore, the lasing threshold showed an obvious dependency on the nanorods density. The lasing emission maintained its wavelength with increasing pump power, indicating high stability of the lasing mode(s).

Investigation of concurrent emissions in visible, UV and NIR region in Gd2O2S: Er, Yb nanophosphor by diverse excitation wavelengths as a function of firing temperature

Herein, we report the concurrent emissions in Visible, Ultraviolet (UV) and Near-Infrared (NIR) range by a single Gadolinium Oxysulphide (Gd2O2S) nanophosphor doped with Erbium (Er3+) – Ytterbium (Yb3+) and the optimization of its multiplexed photoluminescence (PL) profile as a function of firing temperature. The multimode emissions sensitized by an assortment of excitation wavelengths – 285 nm, 450 nm, 808 nm, and 1064 nm, revealed the roles of complex energy transition processes between several Er3+ excited states and single Yb3+ excited state. Stoke's shift of excitation by 285 nm in the visible region giving dominant violet emission along with green and red emissions portrayed the downconversion (DC) characteristics of the synthesized nanophosphor. The excitation by 450 nm produced emissions with anti-Stoke's shift to UV region; and, Stoke's shift to visible and NIR bands; disclosing the presence of simultaneous upconversion (UC), DC and NIR Quantum cutting (NIR-QC). Apart from usual UC of 808 nm excitation in the visible region, a vast anti-Stoke's shift to UV region displaying high-energy UC along with DC to NIR band displayed the multifarious excitation conversion by Gd2O2S nanophosphor. Incidence of 1064 nm also leads to large anti-Stoke's shift to UV, visible and NIR region strengthening the upconverting profile of the fabricated nanophosphor. The emission intensity of multiplexed PL investigated as a function of firing temperature (1000°C–1250 °C) divulged the optimization cycle of the synthesized nanophosphor for each excitation wavelength. The nanophosphors fabricated at lower firing temperature were found to be more efficient in absorbing and converting higher frequency photons whereas for upper firing temperatures the lower frequency photons were more favored. The obtained broad spectral conversion by a single Gd2O2S nanophosphor can be exploited to give a tailormade phosphor for the desired application such as sunlight harvesting, NIR detectors, biomedical imaging, and others.

Tunable afterglow luminescence and triple-mode emissions of thermally activated carbon dots confined within nanoclays

Tunable afterglow luminescence and interesting multi-mode emissions (fluorescence (FL), delayed fluorescence (DF), and room-temperature phosphorescence (RTP)) via excitation wavelength and temperature variations were achieved.

Sideband generation of coupled-cavity terahertz semiconductor lasers under active radio frequency modulation.

The radio frequency (RF) modulation is a powerful tool, which is used for generating sidebands in semiconductor lasers for active mode-locking. The two-section coupled-cavity laser geometry shows advantages over traditional Fabry-Pérot cavities in the RF modulation efficiency, because of its reduced device capacitance of short section cavity. Further, it has been widely used for active/passive mode-locking of semiconductor diode lasers. For semiconductor-based quantum cascade lasers (QCLs) emitting in the far-infrared or terahertz frequency bands, the two-section coupled-cavity configuration can strongly prevent the laser from multimode emissions. This is because of its strong mode selection (loss modulation), which the cavity geometry introduces. Here, we experimentally demonstrate that the coupled-cavity terahertz QCL can be actively modulated to generate sidebands. The RF modulation is efficient at the frequency that equals the difference frequency between the fundamental and higher order transverse modes of the laser, and its harmonics. We show for the first time that, when the laser is modulated at the second harmonic of the difference frequency, the sideband generation in coupled-cavity terahertz QCLs and the generated sidebands are equally spaced by the injected microwave frequency. Our results, which are presented here, provide a novel approach for modulating terahertz coupled-cavity lasers for active mode-locking. The coupled-cavity geometry shows advantages in generating dense modes with short cavities for potential high-resolution spectroscopy. Furthermore, the short coupled-cavity laser consumes less electrical power than Fabry-Pérot lasers that generate a similar mode spacing.

Entanglement indicators for quantum optical fields: three-mode multiport beamsplitters EPR interference experiments

We generalize a new approach to entanglement conditions for light of undefined photons numbers given in Żukowski et al (2017 Phys. Rev. A 95 042113) for polarization correlations to a broader family of interferometric phenomena. Integrated optics allows one to perform experiments based upon multiport beamsplitters. To observe entanglement effects one can use multi-mode parametric down-conversion emissions. When the structure of the Hamiltonian governing the emissions has (infinitely) many equivalent Schmidt decompositions into modes (beams), one can have perfect EPR-like correlations of numbers of photons emitted into ‘conjugate modes’ which can be monitored at spatially separated detection stations. We provide entanglement conditions for experiments involving three modes on each side, and three-input-three-output multiport beamsplitters, and show their violations by bright squeezed vacuum states. We show that a condition expressed in terms of averages of observed rates is a much better entanglement indicator than a related one for the usual intensity variables. Thus, the rates seem to emerge as a powerful concept in quantum optics, especially for fields of undefined intensities.

The shock response of crystalline Ni with H-free and H-segregated 〈1 1 0〉 symmetric tilt GBs

The shock responses of crystalline Ni with two types of symmetric tilt grain boundaries (STGBs) are studied by large-scale molecular dynamics simulations, with special concerns on the effect of hydrogen segregated STGBs on them. The crystalline Ni with different kinds of H-free STGBs have significantly different plastic responses during the shock processes due to different mechanisms of dislocation emission from the STGBs. The segregation of hydrogen atoms at the STGBs significantly affects the dislocation emission from the H-segregated STGBs, and then heavily affects the shock plastic responses of crystalline Ni with H-segregated STGBs. On the one hand, dislocation emission from the H-segregated STGBs is delayed compared with that from the H-free ones at the low shock velocity, showing the so-called lagging effect. On the other hand, multi-mode dislocation emissions (or dislocation emission on the multi slip systems) are frequently activated from the H-segregated STGBs at the high shock velocity. In addition, the spallation behavior of the crystalline Ni under shock loading is also significantly affected by hydrogen segregation at the STGBs. In the targets with the H-free STGBs, spallation originates mainly from the interior of the grains due to strong interaction and reaction between dislocations there, however, it originates definitely from the H-segregated STGBs due to the reduced GB cohesive strength by hydrogen segregation.

Mid-Infrared Lead-Salt Surface Emitting Photonic Crystal Laser on Silicon

ABSTRACTThe lead-salt epitaxial membrane embedded with two dimensional hexagonal air holes lattice array was used to develop the mid-infrared (mid-IR) photonic crystal surface emitting laser. For the initial proof-of-concept research work, we demonstrated intensive photonic crystal coupled mid-IR vertical light emissions from the designed structure under cryogenic temperature range. In order to realize room temperature operation, we modified the photonic bands structure, aligned the photonic crystal coupled mode with the gain spectrum of active material at 300 K. As a result, under pulsed mode optical excitation, multi-mode room temperature mid-IR photonic crystal lasing emissions were achieved at wavelength ∼3.5 μm recently. With further optimization, a practical lead-salt continuous-wave operating room temperature surface emitting photonic crystal laser is anticipated soon, and this will explore promising applications in a wide variety of fields.

Room temperature mid-infrared surface-emitting photonic crystal laser on silicon

We demonstrate a mid-infrared surface-emitting photonic crystal laser on silicon substrate operating at room temperature. The active region consisting of PbSe/PbSrSe multiple quantum wells was grown by molecular beam epitaxy on Si(111) substrate patterned with a photonic crystal (PC) array. The PC array forms a transverse magnetic polarized photonic bandgap at around 2840 cm−1. Under pulsed optical pumping, room temperature multimode lasing emissions were observed at wavelength ∼3.5 μm with estimated threshold peak pumping intensity of 24 kW/cm2. Angular-dependent measurement indicates the lasing is of a Gaussian-like profile with full width at half maximum of 4.66°.

Laser emission from dye doped microspheres produced on a chip

We fabricated, in a microfluidic channel, dye molecule doped microspheres with a remarkable size monodispersivity and interesting optical properties. The microspheres were obtained by spontaneous formation of droplets and photo-polymerization of a low viscosity and UV sensitive resin. By varying the channel width and the flow rate, microspheres of radius in the range of 20–80 μm could be obtained with a size dispersivity of about 2%. When pumped with a pulsed laser at 532 nm, multi-mode laser emissions around 610 nm were detected from R6G doped microspheres at a threshold of 16 μJ/mm 2 .