Tunable Emission Research Articles

From Ancient Blue Pigment to Unconventional NIR Phosphor: A Thermal-Stable Near-Infrared I/II Broadband Emission from Ca1-xSrxCuSi4O10 Solid Solution.

Phosphors used in NIR spectroscopy require broadband emission, high external quantum yield, good ability, as well as a tunable spectral range to meet the detection criteria. Two-dimensional copper silicates MCuSi4O10 (M = Ca, Sr, Ba) play an important part in ancient art and technology as synthetic blue pigments. In the recent years, these compounds were reported to show a broad near-infrared emission when excited in the visible region. Inspired by the tunable structure of MCuSi4O10, a series of broadband phosphors Ca1-xSrxCuSi4O10 were designed for realizing continuously tunable NIR emission by a modulated Cu2+ crystal field environment. The emission maximum exhibits a red shift from 915 to 950 nm and the integral intensity enhances as the Sr2+ content varies in the range of 0-0.50, which is led by the lattice expansion and the following weakened crystal field splitting on tetrahedral-coordinated Cu2+. Compared to CaCuSi4O10, the optimized sample Ca0.5Sr0.5CuSi4O10 shows enhanced NIR emission by about 2.0-fold. It exhibits quite a high external quantum efficiency covering the NIR-I and -II regions (λmax = 950 nm, fwhm = 135 nm, EQE = 26.3%) with a strong absorption efficiency (74.7%) and a long excited-state lifetime (134 μs). These solid-solution phosphors (x = 0.0-0.5) show excellent thermal stability and maintain over 50% of the RT intensity at 200 °C. The optimized phosphor was encapsulated with red-light chips to fabricate NIR pc-LED and put into night-vision application. These good properties make these Cu2+-activated NIR phosphors appealing for multiple applications such as nondestructive testing, night version, lasers, and luminescent solar concentrators.

Synthesis of Bi3+ and Eu3+ co-doped Na4CaSi3O9 blue-red light tunable emission phosphors for inducing plant growth

Sunlight is an important factor in plant growth. In this regard, both blue and red lights provide significant contributions. Blue–red light dual-emission phosphors, which can be achieved by regulating energy transfer between two independent luminous centers, have recently been investigated extensively. In this study, Bi3+ and Eu3+ co-doped Na4CaSi3O9 (NCSO: Bi3+, Eu3+) phosphors are successfully synthesized via a high-temperature solid-phase method at approximately 900 °C for a few hours. X-ray powder diffraction is used to verify the crystal structure, phase purity, and structural refinement of the NCSO-based phosphors. Upon light excitation at 299 nm, the phosphors show blue–red dual emission. The blue emission (300–500 nm) may have originated from the 3P1 → 1S0 transition of Bi3+, whereas the red emission (575–725 nm) is attributable to the 5D0 → 7FJ (J = 1, 2, 3 and 4) transition of Eu3+ ions. Energy transfer from Bi3+ to Eu3+ is systematically investigated and the thermal stability of the phosphors is analyzed using temperature-dependent spectroscopy. The emission spectra of NCSO: Bi3+, Eu3+ are consistent with the absorption spectra of chlorophyll a, chlorophyll b, phytochrome PR, and phytochrome PFR. These results indicate that the obtained phosphors exhibit significant potential for inducing plant growth.

Nickel(II)-Doped Lead-Free Halide Crystals Exhibiting Highly Efficient Tunable Blue-Emitting out of Antiferromagnetic Ni-Ni Coupling.

Metal halide crystals are widely used in optoelectronic fields due to their excellent optical properties. The hunt for a lead-free halide semiconductor with superior optical performance is a particularly fascinating topic in order to avoid the toxicity of lead. Here, we incorporate Ni2+ into a series of halide nanocrystals (NCs) through solution-phase synthesis. By modifying the A-site and varying the halide compositions, we successfully achieved significant tunability of the blue emission of the Ni2+-doped AX (A = K+, Rb+, NH2CH = NH2+ (FA), CH3NH3+ (MA); X = Br, I) NCs, ranging from 375 to 490 nm, due to the antiferromagnetic polaron (AMP), which is in contrast with the excitonic magnetic polarons (EMP) from those with ferromagnetic (FM) coupling between transition metal ions in similar compounds. This work shows that Ni2+-doped halide crystals could become a typical example providing AMP excitation as the optional emission centers for use in light emitting devices.

Green hydrothermal synthesis of multifunctional carbon dots from cassava pulps for metal sensing, antioxidant, and mercury detoxification in plants

Carbon dots (CDs) have been attracted to nanocarbon materials for metal ion sensing, biological activity, and plant phytotoxicity due to their excellent photophysical properties, such as low cytotoxicity, high quantum yield, tunable fluorescence emission, and biocompatibility. Cassava pulp, which consists mainly of starch, has been identified as a low-cost biomass waste from the cassava starch industry. Therefore, this research developed CDs and nitrogen-doped CDs (NCDs) from cassava pulp using a one-step hydrothermal process in deionized water at 200 °C. The effects of the synthesis conditions, including reaction time (6–24 h) and the nitrogen doping derivatives, were also investigated. CDs and ethylenediamine doped-NCDs exhibited tunable fluorescence emission, strong quantum yield, high photostability, and tolerance to photobleaching. Furthermore, the potential applications of CDs-12 h were demonstrated such as fluorescent sensors for metal ion sensing, antioxidant activity, and mercury detoxification in plants. Fluorescence quenching of the CDs-12 h via both static and dynamic quenching mechanisms was observed in the presence of several metal ions such as Hg2+, Cu2+, and Fe3+ with the detection limit in micromolar levels and further applied to real water samples with good recovery and acceptable relative standard derivation. The paper test strip coated with CDs-12 h could also detect these metal ions under UV light. CDs and NCDs-EDA also showed potential DPPH radical scavenging activity and alleviated mercury toxicity in the Chinese cabbage seedlings with the incubation of CDs-12 h and NCDs-EDA-12 h (30 mg/L).

Wide-Range Color-Tunable Organic Scintillators for X-Ray Imaging Through Host-Guest Doping.

With the increasing demands of X-ray detection and medical diagnosis, organic scintillators with intense and tunable X-ray excited emission have been becoming important. To guarantee the X-ray absorption, heavy atoms were widely added in reported organic scintillators, which led to emission quenching. In this work, we propose a new strategy to realize organic scintillators through the host-guest doping strategy. Then the X-ray absorption centers (host) and emission centers (guest) are separated. Under X-ray excitation, these materials displayed intense and readily tunable emissions ranging from green (520 nm) to near infrared (NIR) regions (682 nm). Besides, the relationship between the X-ray absorption and spatial arrangement of the heavy atoms in the host matrix was also revealed. The potential application of these wide-range color tunable organic host-guest scintillators in X-ray imaging were demonstrated. This work provides a new feasible strategy for constructing high-performance organic scintillators with tunable luminescence properties.

Wide‐Range Color‐Tunable Organic Scintillators for X‐Ray Imaging Through Host‐Guest Doping

AbstractWith the increasing demands of X‐ray detection and medical diagnosis, organic scintillators with intense and tunable X‐ray excited emission have been becoming important. To guarantee the X‐ray absorption, heavy atoms were widely added in reported organic scintillators, which led to emission quenching. In this work, we propose a new strategy to realize organic scintillators through the host‐guest doping strategy. Then the X‐ray absorption centers (host) and emission centers (guest) are separated. Under X‐ray excitation, these materials displayed intense and readily tunable emissions ranging from green (520 nm) to near infrared (NIR) regions (682 nm). Besides, the relationship between the X‐ray absorption and spatial arrangement of the heavy atoms in the host matrix was also revealed. The potential application of these wide‐range color tunable organic host‐guest scintillators in X‐ray imaging were demonstrated. This work provides a new feasible strategy for constructing high‐performance organic scintillators with tunable luminescence properties.

Highly efficient and tunable dual-state emission from diarylmaleimide derivatives in both solution and solid states for sensing and lighting

Dual-state emission (DSE) materials have attracted widespread attention for their strong luminescence in both solution and solid states. However, it is still a challenge to obtain tunable DSE materials. Through tailoring the terminal groups, a series of diphenylmaleimide derivatives DPM1-DPM7 with twisted structure are designed and synthesized. These compounds not only achieve a wide range adjustment of emission color from blue to red, but also exhibit effective DSE performance. Their quantum yields in solution range from 58.2 % to 88.2 %, while the ones in solid exceed 80 %, with a maximum of nearly 100 % for three derivatives. In addition, DPM6 with tert-butoxycarbonylamino terminal group obtains three different crystals with yellow, orange and red emission. DPM6 crystals realize the reversible switching of three colors under the stimulation of solvent vapor, which can be used to identify chloroform and dichloromethane. DSE-active DPMs can be utilized to detect selectively Fe3+ ions in solution, and also has an important application in the field of solid-state lighting, realizing white light with ultra-high luminous efficiency up to 320 lm/W.

Facile preparation, optical mechanism elaboration, and bio-imaging application of fluorescent cellulose nanocrystals with tunable emission wavelength

Interfacing cellulose nanocrystals (CNCs) with fluorescent materials provides more possibilities for constructing of sensory/imaging platforms in biomedical applications. In this work, by harnessing the efficient extraction accompanied modification of CNCs and adjustable optical properties of carbon dots (CDs), we report the constructions and emission wavelength tuning of fluorescent CNCs (F-CNCs) composed of CNC nano-scaffolds and CDs. The as-prepared CNCs are densely decorated with citric acid (CA), which plays the role of carbon source for the in-situ synthesis of CDs on CNCs. For the F-CNCs carrying blue, green, and red emissive CDs, ethylenediamine (EDA), urea, and thiourea are the N or N/S sources. Fingerprints of chemical groups, morphological characters, and redox activities are resolved to elaborate the optical mechanisms of CDs with varying emission colors. The emission wavelength is adjusted by either changing the particle size or introducing new emission centers. Both are primarily achieved via precursor engineering. The F-CNCs reveal quantum yields (QYs) >22 % and negligible fluorescence quenching (< 6 %) upon continuous excitation as long as 24 h. Benefited from their cell membrane penetration capability, the F-CNCs with different emission wavelengths were challenged for multiplexed cytoplasm imaging.

Wearable and Wavelength-Tunable Near-Infrared Organic Light-Emitting Diodes for Biomedical Applications.

Near-infrared organic light-emitting diodes (NIR OLEDs) have significant potential for wearable phototherapeutic applications because of the unique properties of the OLEDs, including their free-form electronics and the excellent biomedical effects of NIR emission. In spite of their tremendous promise, given that the majority of NIR OLEDs in previous research have relied on the utilization of an intrinsically brittle indium tin oxide (ITO) electrode, their practicality in the field of wearable electronics is inherently constrained. Here, we report wearable and wavelength-tunable NIR OLEDs that employ a high-performance NIR emitter and an innovative architecture by replacing the ITO with a silver (Ag) electrode. The NIR OLEDs permit wavelength tuning of emissions from 700 to 800 nm and afford stable operation even under repeated bending conditions. The NIR OLEDs provide a lowered device temperature of 37.5 °C even during continuous operation under several emission intensities. In vitro experiments were performed with freshly fabricated NIR OLEDs. The outcomes were evaluated against experimental results performed using the same procedure utilizing blue, green, and red OLEDs. When exposed to NIR light irradiation, the promoting effect of cell proliferation surpassed the proliferative responses observed under the influence of visible light irradiation. The proliferation effect of human hair follicle dermal papilla cells is clearly related to the irradiation wavelength and time, thus underscoring the potential of wavelength-tunable NIR OLEDs for efficacious phototherapy. This work will open novel avenues for wearable NIR OLEDs in the field of biomedical application.

Chiral‐Guest Induced Multicolor‐Tunable Circularly Polarized Room Temperature Phosphorescence

AbstractThe development of organic circularly polarized room temperature phosphorescence (CP‐RTP) materials with tunable emission colors has important value in the field of optoelectronic applications but remains a challenging issue. Herein, a CP‐RTP doped system with green, yellow, and red afterglow is constructed by introducing chiral groups into three phosphors naphthalene, phenanthrene, and pyrene as guests respectively, using polyvinyl pyrrolidone (PVP) as the host. The phosphorescence quantum yield of the doped system is 7.3%–13.6%, the phosphorescence lifetime is 341 ms–1017 ms, and the asymmetry factor is 0.001–0.0021. Further doping three guests simultaneously into the PVP resulted in the four‐component doped materials. Benefiting from the different excitation wavelengths of three guests, when the excitation wavelength changes from 300 to 365 nm, the afterglow of the four‐component doped materials changes from green to yellow and finally to red. Moreover, due to the different phosphorescence lifetimes of different guests, the afterglow can in turn change from red to green after excitation at 365 nm, demonstrating a time‐dependence phosphorescence emission property. This doped strategy provides an effective platform for constructing organic multicolor CP‐RTP materials.

Manipulating Interlayer Excitons for Near-Infrared Quantum Light Generation.

Interlayer excitons (IXs) formed at the interface of van der Waals materials possess various novel properties. In parallel development, strain engineering has emerged as an effective means for creating 2D quantum emitters. Exploring the intersection of these two exciting areas, we use MoS2/WSe2 heterostructure as a model system and demonstrate how strain, defects, and layering can be utilized to create defect-bound IXs capable of bright, robust, and tunable quantum light emission in the technologically important near-infrared spectral range. Our work presents defect-bound IXs as a promising platform for pushing the performance of 2D quantum emitters beyond their current limitations.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED’s and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303–483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED’s and photodynamic therapy for the cancer treatment.

Chromatically polarized Afterglow: Photo-controlled and anisotropic persistent luminescence from doped polymeric systems

Organic persistent luminescent (OPL) materials showing persistent luminescence at room temperature have caught significant research attention for decades. Integrating chromatic polarization into an OPL system with tunable emissions is attractive and challenging but rarely reported. Herein we propose a strategy to realize linear-polarization-dependent afterglow color with reversible photo-patterning capability. This is accomplished through the use of an acridone-based Förster-resonance energy transfer (FRET) system, which is coupled with aligned Au-nanorods. The composite shows reversible UV-lithographic capability attributed to the generation of radicals by the acridone luminophore. Importantly, this system allows for the variation of chromatic afterglow based on the linear polarized angles relative to the aligned direction of AuNRs. The multiple delayed emission peaks are absorbed in a polarized-dependent manner due to the anisotropic plasmonic resonance of the aligned Au-nanorods. With the photo-patterning capability, polarization- and humidity-dependent afterglow, this approach holds the potential to contribute to various applications of OPL materials, such as sensors, information encryption, and anti-counterfeiting.

Investigating the Potential of Perovskite Nanocrystal-Doped Liquid Scintillator: A Feasibility Study

Liquid scintillators are extensively employed as targets in neutrino experiments and in medical radiography. Perovskite nanocrystals are recognized for their tunable emission spectra and high photoluminescence quantum yields. In this study, we investigated the feasibility of using perovskites as an alternative to fluor, a substance that shifts the wavelengths. The liquid scintillator candidates were synthesized by doping perovskite nanocrystals with emission wavelengths of 450, 480, and 510 nm into fluor PPO with varying nanocrystal concentrations in a toluene solvent. The several properties of the perovskite nanocrystal-doped liquid scintillator were measured and compared with those of a secondary wavelength shifter, bis-MSB. The emission spectra of the perovskite nanocrystal-doped liquid scintillator exhibited a distinct monochromatic wavelength, indicating energy transfer from PPO to the perovskite nanocrystals. Using a 60Co radioactive source setup with two photomultiplier tubes (PMTs), the light yields, pulse shape, and wavelength shifts of the scintillation events were measured. The light yields were evaluated based on the observed Compton edges from γ-rays, and compared across the synthesized samples. A decrease (or increase) in area-normalized PMT pulse height was observed at higher perovskite nanocrystal (or PPO) concentrations. The results demonstrated the sufficient potential of perovskite nanocrystals as an alternative to traditional wavelength shifters in a liquid scintillator.

Multi-color tunable emission of Bi3+,Eu3+ co-doped Ca3LiZnV3O12 phosphors for warm white light-emitting diodes

Bi3+,Eu3+ co-doped Ca3LiZnV3O12 (CLZV) phosphors were manufactured by conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. Their crystal structure, luminescent properties, energy transfer processes and quantum efficiency were investigated in detailed. CLZV host can be efficiently excited by 345 nm near-ultraviolet light and exhibit self-activating blue emission. When Bi3+ ions are introduced into CLZV, VO43− and Bi3+ can be co-excited by 345 nm light. Benefiting from energy transfer from VO43− to Eu3+ and Bi3+ to Eu3+, multi-color tuning emission from green to yellow can be observed in CLZV:Bi3+,Eu3+ phosphors. Warm white emission was achieved in CLZV:0.015Bi3+,0.01Eu3+ and CLZV:0.015Bi3+,0.02Eu3+ phosphors. Importantly, their internal quantum efficiencies are 35.2 % and 39.6 %, respectively. Our results indicate that CLZV: Bi3+,Eu3+ phosphors might be promising candidates for white light emitting diodes under ultraviolet excitation.

Sr2MgWO6:Ni2+-A highly efficient and tunable photoluminescence near-infrared phosphor for NIR-II light source applications

The rapid development of near-infrared (NIR) phosphorescent conversion light-emitting diodes (pc-LED) in imaging and detection indicates a strong demand for NIR-II region luminescent materials. Unfortunately, the lack of effective IR-II phosphors that can be excited by commercial blue LED chips has hindered the application of NIR spectroscopy. In this paper, we introduce a novel ultra-broadband NIR phosphor Sr2MgWO6:Ni2+ characterized by an emission peak at 1400 nm with a full width at half maximum (FWHM) of 237 nm. A tunable NIR emission from 1400 to 1485 nm is achieved by cation co-substitution of Ca2+ for Sr2+, and the corresponding FWHM can be modified from 237 to 292 nm. NIR-II pc-LEDs was fabricated by combining prepared near-infrared phosphors with blue LED chips to visually demonstrate their potential applications in authentication artistic works such as oil paintings. These results not only have theoretical significance for further understanding of the structure-property relationship of NIR-II luminescent materials, but also have reference value for developing more practical materials.

Phase transitions and optical properties of Tb3+ activated NaY(WO4)2 phosphors

Well-defined NaY(WO4)2:Tb3+ nanoflowers were prepared through the controllable structural transition of hydroxyl sodium yttrium tungstate precursor, which exhibit a fascinating luminescent property as activated by Tb3+ dopant. NaY(WO4)2:Tb3+ nanoflowers were systematically characterized with a series of tests including XRD, SEM, FT-IR, TG-DTA, UV–Vis, and PL. XRD analyses indicate that NaY(WO4)2:Tb3+ crystalizes in the scheelite structure with broadened diffraction peaks and expanded cell volume with increasing Tb3+ content as revealed by Rietveld refinement. FT-IR and TG-DTA results show that NaY(WO4)2:Tb3+ is formed via the structural transition of hydroxyl sodium yttrium tungstate at calcination temperature above 600 °C. UV–Vis test discloses the bandgap red-shift of NaY(WO4)2 via doping Tb3+ ions. Noticeably, PL measurement discloses the green luminescence of NaY(WO4)2:Tb3+ attributable to 5D4→7F5 transition with the optimal Tb3+ doping content of 13 mol%, which manifests the effective energy transfer from WO42− groups to Tb3+ ions and reveals relatively good thermal stability. Furthermore, the tunable color emission from blue to green to yellowish green can be achieved in flower-like NaY(WO4)2:Tb3+ phosphors by controlling the doping content of Tb3+ ions, which may provide promising application in the field of multicolor lighting and displays.

Tunable Emission and Energy Transfer of the Novel KY1−x(MoO4)2−y(WO4)y:xLn3+ (Ln3+ = Dy3+, Eu3+, and Tm3+) Single-phase White Luminescence Phosphor for White LEDs

Tunable Emission and Energy Transfer of the Novel KY1−x(MoO4)2−y(WO4)y:xLn3+ (Ln3+ = Dy3+, Eu3+, and Tm3+) Single-phase White Luminescence Phosphor for White LEDs

Distinct Excitonic Emissions in 2D (C7 H7 N2 )2 PbX4 (X=Cl, Br) under Compression.

Two dimensional (2D) hybrid metal halides (HMHs) usually exhibit free excitonic (FE) emission, and self-trapped excitonic (STE) emission can also be achieved by adopting appropriate halogens and organic cations. Recently, significant efforts have been made to modulate and then clarify the transformation and connection between these two types of excitonic emissions in 2D HMHs. In this study, intriguing pressure-tuned transitions between FE emission and STE emission are observed in 2D (C7 H7 N2 )2 PbCl4 . In contrast, only FE emissions with tunable emission energies are observed in 2D (C7 H7 N2 )2 PbBr4 which possesses a similar structure with (C7 H7 N2 )2 PbCl4 under compression. Such distinct halide-dependent optical responses under pressure are experimentally revealed to arise from the intricate interplay among several factors in these HMHs, including the stiffness of the structure, the Coulomb force between the organic cations and the inorganic octahedra, and the magnitude of inorganic octahedral distortion. These high-pressure optical explorations can unravel the underlying interrelationship between the crystal structure and excitonic emission in 2D HMHs.

Adaptive thermally tunable radiative cooling with angle insensitivity using phase-change-material-based metasurface

Radiative cooling is the passive cooling of a material with the help of a specific spectral response to emit thermal energy into space through atmospheric transparency windows. However, most of the proposed designs have no dynamically tunable emission response. In this paper, we present a feasible inverse pyramid structure made of a phase change material (PCM) on top of a metallic mirror to realize an adaptive radiative cooler with almost angle-independent emission response. The design uses the thermally controlled PCM called Samarium nickelate (SmNiO3) to actively tune the spectral response of the design, which, in turn, allows the design to radiatively cool itself. The emission response of the design is compatible with atmospheric transmissive windows. As the design heated up to higher temperatures, the peak of the emission spectrum red-shifts and moves toward the atmospheric transparency window.