Multimode Emission Research Articles

Cr3+-Activated Deep Trap Electron-Trapping Biphasic Mixture of Zn (Al,Ga)2O4 and Zn2GeO4 for Multilevel Information Storage by Trap Multiplexing and Wavelength Multiplexing.

Double wavelength emitting phosphors with hypersensitive thermal response are important for optical/thermal sensors and multiplexing optical data storage technology. However, it is a daunting challenge to develop multicolor electron-trapping materials with superheat sensitivity and anomalous quenching luminescence characteristics for information storage. Here, based on the selection of host lattice and the control of doping ion types, we have designed Mn2+- and/or Cr3+-activated persistent materials with excellent fluorescence properties. Among these phosphors, Mn,Cr co-activated biphasic mixture exhibits not only sensitive anomalous thermosensitive fluorescence properties but also multicolor and multimode fluorescence emission characteristics derived from Mn and Cr simultaneously. The corresponding multimode fluorescence mechanism is proposed based on afterglow energy transfer and deepening trap effect. Especially, based on the excellent fluorescence performances, these phosphors as information storage medium demonstrate multilevel information storage by a combination of the trap multiplexing and wavelength multiplexing technologies. The study here provides not only the ideas for designing and synthesizing new electronic materials but also a material foundation for the fourth generation of optical information storage and encryption.

Constructing Organic Phosphorescent Scintillators with Enhanced Triplet Exciton Utilization Through Multi-Mode Radioluminescence for Efficient X-Ray Imaging.

The development of organic phosphorescent scintillators with high exciton utilization efficiency has attracted significant attention but remains a difficult challenge because of the inherent spin-forbidden feature of X-ray-induced triplet excitons. Herein, a design strategy is proposed to develop organic phosphorescent scintillators through thermally activated exciton release to convert stabilized spin-forbidden triplet excitons to spin-allowed singlet excitons, which enables singlet exciton-dominated multi-mode emission simultaneously from the lowest singlet, triplet, and stabilized triplet states. The resultant scintillators demonstrate a maximum photoluminescence efficiency of 65.8% and a minimum X-ray radiation detection limit of 110nGys-1; this allows efficient radiography imaging with a spatial resolution of ≈10.0 lp mm-1. This study advances the fundamental understanding of exciton dynamics under X-ray excitation, significantly broadening the practical use of phosphorescent materials for safety-critical industries and medical diagnostics.

Hydroxyl-driven construction of dual-emitting CsPbBr3/EuWO4(OH) composite for radiometric thermometer and information encryption applications

Self-assembled inorganic metal halide perovskite composites with high emitting efficiency, tunable multimode emission and stimuli-responsive luminescence demonstrated great potential in diversified luminescence applications. Here, a novel CsPbBr3/EuWO4(OH) composite was successfully prepared through the surface adsorption of Pb2+ ions on hydroxylated EuWO4(OH) microsheets and subsequent nucleation of CsPbBr3 peroviskite quantum dots (PQDs) by the anti-solvent crystallization in CsBr containing N,N-dimethylformamide (DMF) solution. Due to the distinct fluorescent thermochromic switching properties of temperature-insensitive Eu3+ and sensitive CsPbBr3 PQDs emitting centers, the resultant CsPbBr3/EuWO4(OH) composite exhibits excellent ratiometric temperature sensing performance. The CsPbBr3/EuWO4(OH) thermometer based on the fluorescence intensity ratio (FIR) technique originating from emissions of Eu3+ to CsPbBr3 PQDs was then explored with a high temperature sensitivity (Sr) of 5.8 % ℃−1 at 54 ℃. In addition, a high-security-level information encryption scheme was proposed by utilizing the excitation-wavelength-dependent switchable fluorescence of CsPbBr3/EuWO4(OH) composite. This study provides a simple and feasible strategy for assembling dual-emission CsPbBr3/EuWO4(OH) composite, showing potential applications in optical ratiometric thermometry and information encryption fields.

The Role of Bone Edema in Plantar Fasciitis Treated with Temperature-Controlled High-Energy Adjustable Multi-Mode Emission Laser (THEAL) and Exercise: A Prospective Randomized Clinical Trial.

Plantar fasciitis is one of the most common causes of foot pain; in 35% of cases, it is also associated with bone edema of the heel. The aim of this study was to investigate the relationship between bone edema and the outcomes of temperature-controlled high-energy adjustable multi-mode emission laser (THEAL) and/or exercises in patients with plantar fasciitis. A prospective randomized clinical trial was designed, in which 48 patients suffering from plantar fasciitis, with or without bone edema, were treated with temperature-controlled high-energy adjustable multi-mode emission laser and exercises (the laser group) or with exercises only (the control group). The patients were evaluated at recruitment (T0) and at 2 (T1) and 6 months (T2), monitoring pain (with the Visual Analogue Scale), functionality (with the Foot Function Index), perception of improvement (with the Roles and Maudsley Score), and fascia thickness (with ultrasound examination). In both groups, there was a significant improvement in pain, functional recovery, perception of remission, and a reduction in plantar fascia thickness at T1 and T2. The laser group presented statistically better values at T2 for the Roles and Maudsley Score (z: 2.21; 0.027). The regression analysis showed that a greater reduction in fascia thickness occurred in the laser group (p-value: 0.047). In conclusion, the two conservative treatments were effective in patients suffering from plantar fasciitis, even in the presence of bone edema, but with lesser results.

Multi-mode up-conversion emission of Tm@Yb@Er phosphors for color modulation and thermometry

Rare earth doped up-conversion materials play an important role in information security, colorful display and temperature sensing. In this work, the up-conversion luminescence of NaYF4:0.2Tm/20Yb@NaYF4:20Yb@NaYF4:2Er/20Yb phosphors, synthesized by typical co-precipitation method, are investigated under different excitation condition. The emission color of sample can be tuned from yellow to blue-green through changing pump laser from 1550 to 980 nm because the Tm3+ ions in the core cannot be excited by 1550 nm laser. More interesting, the value of red-to-green (R/G) and blue-to-green (B/G) can be finely manipulated by tuning the excitation pulse width and frequency. This phenomenon can be interpreted by different rising processes of the green, red and blue up-conversion emission. In addition, the core-shell structured sample displays a temperature-dependent color change, ranging from blue-green to purple. The green emissions, radiated from thermal coupled levels (2H11/24S3/2), are used in thermometry and the max relatively sensing sensitivity reaches 0.01 K−1 at 303 K. The findings indicate that the core-shell Tm@Yb@Er phosphors, with excitation-dependent and temperature-dependent up-conversion luminescence, have potential applications in information security and temperature sensing.

Eu2+-Eu3+ Co-doping provoking polyhedron-cluster-based emission structural unit evolution triggering phases transition and blue-green-red multimode luminescence emission

A series of Ca2-xSiO4:xEu2+/Eu3+ and Ca2-2xSiO4:xEu2+/Eu3+, xM (M = Na+, K+) phosphors were prepared by co-doping Eu2+-Eu3+ in Ca2SiO4 solid solution for selectively locating Eu2+-Eu3+ ions deriving polyhedron-distorted emitting structure units’ evolution. During β, γ1,2-C2S matrix phase transitions, the structure and luminescence properties were analyzed by XRD, diffuse reflection, PL and luminescence thermal stability. The results show that Eu2+/Eu3+ occupying 6 Ca2+ sites forms 10 emission structural units in the matrix and the phase transition of γ1-Ca2-xSiO4(x = 0.0001–0.0004)→β-Ca2-xSiO4 (x = 0.0005–0.04)→β, γ2-Ca2-xSiO4 mixed phase (x = 0.08–0.32) is generated by the extrusion of structural units. Ultraviolet–visible diffuse reflectance spectra confirm the band gap difference caused by structural unit rotation. According to the bond energy method, the priority occupation order for the Eu2+/3+ ions was determined. The energy transfer of Eu2+→Eu3+ occurs when the structural units 3–10 of β, γ2-Ca2-xSiO4 mixtures coexist. After co-doped M+ as charge compensator, the luminescence intensity/thermal stability of Ca2-2xSiO4:xEu3+, xM(M = Na+, K+) were improved by 33.88 %/57.12 %, and 5.1 %/6.6 % than that of Ca2-xSiO4:xEu3+, respectively. These characteristics indicate that phosphors have broad application prospects in the field of solid-state lighting.

Multimode Emission in GaN Microdisk Lasers

AbstractQuantum well nanolasers usually show single‐mode lasing, as gain saturation suppresses emissions in other modes. In contrast, for whispering gallery mode microdisk lasers with GaN quantum wells as active material, above threshold multimode laser emission is observed. This intriguing emission feature is manifested in the fact that several modes simultaneously show the characteristic kink in the input–output curve at the onset of lasing. A quantum theory for nanolasers is used to support the experimental finding and to analyze this behavior in the presence of gain saturation. Coupling effects between neighboring modes are identified as the origin of multimode lasing, which initiate photon exchange between modes via population pulsations similar to classical wave‐mixing effects. A reduction of this type of mode coupling with increasing mode spacing is demonstrated. The results can pave the way for multimode application of nanolasers in integrated photonic circuits.

Designing tunable emissions and mechanoluminescence in piezoelectric luminescent ions doped oxysulfide compounds by cations substitution for optical sensing

Piezoelectric mechanoluminescent materials capable of directly converting external mechanical stimulation into light are decisive for the development of optoelectronic sensing devices. However, emission spectral modulation is highly demanded for mechanoluminescent materials, which is important for applications. Here, we have doped luminescent ions into the piezoelectric semiconductor oxysulfide compounds (Sr,Ba)ZnOS using the salt-fusion method to form multi-mode emission materials. The prepared luminescent compounds can simultaneously generate photoluminescence and mechanoluminescence for temperature and stress sensing. The tunable photoluminescence can be obtained for multi-color emissions by controlling concentrations of luminescent ions Mn2+ and Er3+. Subsequently, the materials are combined with polydimethylsiloxane matrix to prepare smart mechanoluminescence films for optical sensing. The mechanoluminescence and tunable emissions from prepared film make this luminescent materials promising in the fields of dynamic imaging of force and anti-counterfeiting.

Optical Information Transmission and Multimode Fluorescence Anticounterfeiting of Ca2-xMgxGe7O16:Mn2.

Multimode emission of Mn2+ for multimode fluorescence anticounterfeiting is achieved by cation site and interstitial occupancy in Ca2-xMgxGe7O16. The rings in Ca2-xMgxGe7O16 have a significant distortion for Mn2+ ions to enter the ring interstitials with a luminescence center at 665 nm, which is supported by XRD refinement results and first-principles calculations. The interstitial Mn2+ ion has good thermal stability with an activation energy of 0.36 eV. Surprisingly, these two luminescence centers, the cation site Mn and the interstitial Mn, have an obvious afterglow, and the disappearing afterglow will reappear by heating or irradiating with the 980 nm laser. The afterglow is significantly enhanced, as MnO2 is used as the manganese source, which is explained in detail by the thermal luminescence spectrum. Finally, Ca2-xMgxGe7O16:Mn2+ fully demonstrates its excellent prospects in fluorescent anticounterfeiting, information encryption, and optical information storage.

Quantum cascade lasers as broadband sources via strong RF modulation

In this work, we demonstrate that in a regime of strong modulation, by generating pulses of the length of the order of a few cavity lifetimes (hundreds of ps), a broadband quantum cascade laser can be driven to lase on a bandwidth (250 cm−1) limited by the gain. In addition, the amplitude noise of the radiation was shown to be limited by the detector. A laser linewidth study has been performed under different operating conditions, finding values spanning from 20 to 800 MHz, indicating a trade-off between emission bandwidth, amplitude stability, and coherence. The pulsed intensity of the output arises from the gain switching dynamics of the laser, while the self-seeded nature of the emission is responsible for the low amplitude noise and the relatively narrow linewidth of the individual spectral lines of the multimode emission.

Thermal enhancement of the upconversion luminescence of Zn2+ ion-doped KYb(MoO4)2:Er3+ phosphors for multimode temperature sensing

KYb(MoO4)2:Er3+,Zn2+ exhibit multi-mode emission and thermal enhancement (TE). The proposed the TE mechanism and optical thermometry (OT) method open up a new way for UCL intensity TE theory and OT.

Tunable multimode emission induced by charge transfer and multiple resonance effect

Single-component luminescent materials with dual emission properties show great promise in material and life science. Here, we report a novel thermally activated delayed fluorescence (TADF) emitter BO-PST based on a rigid B-embedded dioxygen-bridged acceptor (A) and flexible phenothiazine donor (D). The flexibility of D unit contributes to different charge transfer characteristic and interesting multimode emission in various environment, including D-A-type TADF emission, multi-resonant (MR) fluorescence emission and MR induced afterglow with long lifetime of 1.55 s. Single-crystal structures and theoretical calculations prove that dual emission originates from the quasi-equatorial and quasi-axial conformers of the phenothiazine unit, respectively. The dynamic multicolor properties demonstrate the potential of the novel BO-PST molecule in the volatile organic compounds (VOCs) detection and the stimulus-responsive application.

Orthogonally and linearly polarized green emission from a semipolar InGaN based microcavity

Abstract Polarized light has promising applications in biological inspections, displays, and precise measurements. Direct emission of polarized light from a semiconductor device is highly desired in order to reduce the size and energy-consumption of the whole system. In this study, we demonstrate a semipolar GaN-based microcavity light-emitting diode (MCLED) that could simultaneously produce green light with perpendicular and parallel polarizations to the c*-axis. Orthogonally polarized emission with a narrow linewidth (∼0.2 nm) arises from the valence band splitting and birefringent nature of the semipolar GaN material, as well as the mode selection of the resonant cavity. By modulating the cavity length, the device is capable of switching between single- and multi-mode emission spectra. We believe that the approach of employing a cavity structure and semipolar GaN can be extended to produce orthogonally and linearly polarized blue, red, and violet light by adjusting the material compositions.

Optical cryptographic communications with non-identical chaotic laser systems

"We report secure data transmission performed using chaotic lasers with different external cavity geometries and applying the chaotic masking method based on subcarrier and phase modulations of the chaotic optical carrier. Two semiconductor lasers with similar multimode emission spectra and self-optical feedback provided, respectively, by ring and linear external cavities, were optically coupled and chaotically synchronized into a master – slave scheme. The transmitted message frequency modulates the radio frequency signal which modulates in phase the master chaotic carrier. Based on the robustness of the used encryption method and the synchronization characteristics of the two lasers, the decryption is conducted by the simple radio frequency spectrum monitoring of the slave emission."

Aggregation-regulated room-temperature phosphorescence materials with multi-mode emission, adjustable excitation-dependence and visible-light excitation

Constructing room-temperature phosphorescent materials with multiple emission and special excitation modes is fascinating and challenging for practical applications. Herein, we demonstrate a facile and general strategy to obtain ecofriendly ultralong phosphorescent materials with multi-mode emission, adjustable excitation-dependence, and visible-light excitation using a single organic component, cellulose trimellitate. Based on the regulation of the aggregation state of anionic cellulose trimellitates, such as CBtCOONa, three types of phosphorescent materials with different emission modes are fabricated, including blue, green and color-tunable phosphorescent materials with a strong excitation-dependence. The separated molecularly-dispersed CBtCOONa exhibits blue phosphorescence while the aggregated CBtCOONa emits green phosphorescence; and the CBtCOONa with a coexistence state of single molecular chains and aggregates exhibits color-tunable phosphorescence depending on the excitation wavelength. Moreover, aggregated cellulose trimellitates demonstrate unique visible-light excitation phosphorescence, which emits green or yellow phosphorescence after turning off the visible light. The aggregation-regulated phenomenon provides a simple principle for designing the proof-of-concept and on-demand phosphorescent materials by using a single organic component. Owing to their excellent processability and environmental friendliness, the aforementioned cellulose-based phosphorescent materials are demonstrated as advanced phosphorescence inks to prepare various disposable complex anticounterfeiting patterns and information codes.

Improving performance prediction of diode end-pumped solid-state Nd:YAG rod amplifiers by incorporating pump mode evolution.

Master Oscillator Power Amplifier (MOPA) systems find extensive use in laser development to increase the optical power of laser emissions from a Master Oscillator (MO). Commonly used are the cylindrical rod MOPAs that are optically excited using a multimode fiber-coupled (FC) diode laser emission in an end-pumped configuration. Current analytical 3D models that incorporate thermal effects, gain saturation, and iterative Fourier beam propagation methods, collectively, rely on static approximations of the evolution of the FC pump beam profile over the longitudinal volume of the amplifier crystal. Furthermore, in general, the spectral behavior of the FC diode emission is assumed to be static, and the thermal wavelength shift is not accounted for in the simulation. In this work, we demonstrate a novel approach for accurate modeling of the multimode FC pump beam emission as a complex field using a phase-only Gaussian to flat-top (FT) diffractive optical element, thus allowing for the inclusion of the pump beam into the iterative propagation method. Additionally, we present a method for precise calibration of the model using simple experimental measurements of the diode emission spectrum. The theoretical model is experimentally validated using an end-pumped Nd:YAG crystal rod to perform single-pass amplification of a Gaussian beam, showing excellent agreement with predicted output powers over the calibrated range of pump powers. Furthermore, we provide experimental data that exhibits a strong correlation between the Gaussian to FT phase-only transformation and the multimode FC diode evolution in free-space propagation.

Multimode Emission from Lanthanide‐Based Metal–Organic Frameworks for Advanced Information Encryption

AbstractAlthough remarkable progress on luminescent materials is made in advanced optical information storage and anti‐counterfeiting applications, many challenges still remain in these fields. Currently, most luminescent materials are based on a single photoluminescent model that can be easily imitated by substitutes. In this work, a series of multimodal emission lanthanide‐based metal–organic frameworks (MOFs) are developed, where they emit red and green light originating from Eu3+ and Tb3+ under ultraviolet light irradiation. Meanwhile, under 980 nm near‐infrared laser irradiation, these MOFs show cyan upconversion cooperative luminescence derived from Yb3+ and characteristic upconversion luminescence from lanthanide activators (Eu3+, Tb3+, or Ho3+), respectively. Based on the integrated optical functionality, the functional information storage applications are successfully designed, which indicates that multimodal emission features can be easily detected under ultraviolet lamps (254 or 393 nm) or 980 nm near‐infrared laser. And, the unique optical features show a high level of security in the advanced information storage application, which would be sufficiently complex to be forged.

Silicon-thulium hybrid microdisk lasers with low threshold and wide emission wavelength range.

We demonstrate low-threshold and wide emission wavelength range hybrid-integrated silicon-thulium microdisk lasers based on a pulley-coupled design. The resonators are fabricated on a silicon-on-insulator platform using a standard foundry process and the gain medium is deposited using a straightforward, low-temperature post-processing step. We show lasing in 40- and 60-µm diameter microdisks with up to 2.6 mW double-sided output power and bidirectional slope efficiencies of up to 13.4% with respect to 1620 nm pump power launched to the bus waveguides. We observe thresholds less than 1 mW versus on-chip pump power and both single-mode and multimode laser emission spanning across wavelengths from 1825 to 1939nm. These low threshold lasers with emissions over a > 100 nm range open the door to monolithic silicon photonic integrated circuits with broadband optical gain and highly compact and efficient light sources in the emerging ∼1.8-2.0 µm wavelength band.

Rare earth ions doped Bi2MoO6 luminescent materials: Pechini sol-gel synthesis, down-conversion and up-conversion multicolor emissions, and potential applications

A series of rare earth ions (Eu3+, Sm3+, Yb3+/Er3+, Yb3+/Ho3+, Yb3+/Tm3+) doped bismuth molybdate (Bi2MoO6) phosphors with excellent multicolor luminescence have been synthesized by a facile Pechini sol-gel method. XRD, EDX, and XPS results confirm the highly crystalline orthorhombic phase of Bi2MoO6 and verify that the rare earth ions (RE3+) are effectively integrated into the Bi2MoO6 matrix. During the synthesis process, the calcination conditions play an important role in obtaining the luminescent host matrix, and the optimal calcination condition for the Bi2MoO6 products is determined of 800 °C for 2 h. The Eu3+ and Sm3+ doped Bi2MoO6 samples display intense red and orange-red light under UV/visible excitation whereas the Yb3+/Ln3+ (Ln = Er, Ho, and Tm) doped Bi2MoO6 materials emit green, green, and blue colors when excited by NIR light. Both down-conversion (DC) and up-conversion (UC) multicolor luminescence are obtained by doping the proper Ln3+ activators into the Bi2MoO6 host. The doping concentrations of various RE3+ ions are optimized to generate advantageous phosphors and the luminescence mechanisms of RE3+ ions are systematically studied. The LED devices fabricated by Bi2MoO6:Yb3+/Ln3+ UC phosphors exhibit dazzling multicolor emissions under an injection current, which directly discloses that the as-prepared materials may be of great potential in LEDs and optoelectronic devices. Interestingly, the Bi2MoO6:Yb3+/Er3+/Eu3+ phosphors can simultaneously exhibit red and yellow-green DC emissions and green UC light under excitation of 464, 488, and 980 nm. The multi-mode emission features illustrate that the as-synthesized phosphors may have application prospects in anti-counterfeiting applications.

Intensity Modulation of Two Weakly Coupled Stimulated Oscillating Mechanical Modes in an Optomechanical Microbubble Resonator

We report that when two stimulating mechanical modes in an optomechanical microbubble resonator are weakly coupled to each other, strong oscillation intensity modulation occurs. The modulation was theoretically expected and experimentally observed. We theoretically derived the expressions of the coupling coefficient between the mechanical modes and calculated the region where weak coupling happens. We found that weak coupling exists when the optical quality factor of the microcavity is high and the detuning of the pump laser is close to the beat frequency of the two mechanical modes. Experimentally, we observed that when two mechanical modes are both in stimulated oscillation, they undergo strong intensity modulation as the optical pump power changes, and the coupling coefficient of the two modes is estimated to be 0.962 at the pump power when one mode is in the stimulated region and the other mode is at a stimulating threshold; this proves that the two mechanical modes are weakly coupled. Our results extended the weak coupling conclusion in multimode laser emission to stimulated oscillation in multiple mechanical modes.