Tunable Room Temperature Research Articles

Excitation wavelength and time dependent colour tunable room temperature phosphorescence from boron doped carbon nanodots.

Developing metal free room temperature phosphorescence (RTP) materials have received tremendous attention due its potential application in various fields such as sensing, optoelectronics and anticounterfeiting. Herein, we have synthesized an excitation wavelength and time dependent phosphorescent boron doped carbon nanodots (BCNDs) by thermal treatment of ethanolamine and boric acid at 240°C, where boric acid act as both doping and host agents. The obtained BCNDs display blue to orange fluorescence in both aqueous medium and solid state. In addition, the BCNDs display tunable orange-yellow-green phosphorescence in solid state under UV and visible light, lasting upto 10s, visible to naked eye. The boron and nitrogen doping regulates the band gap of the BCNDs, resulting the phosphorescence colour tunability. The average phosphorescence lifetime and quantum yield of BCNDs are found to be 1.27s and 8.61% respectively. Based on the optical properties, the BCNDs are applied as security ink in information encryption and security marking. Hence, this work can promote the development of metal free phosphorescent carbon based materials which may find application in various emerging fields.

Unexpected tunable photoluminescence and emission mechanism during the gradual increase of cyclic glucose units

Excitation-dependent (λex-dependent) emission is one of the most common emission characteristics of nonconventional luminophores. Previously, we have reported D-xylose crystals has an obvious λex-dependent color tunable persistent room temperature phosphorescence (p-RTP) from blue to green, but its p-RTP emission at long wavelength is very weak. To further explore this attractive multicolor p-RTP behavior, and to enhance its tunability, the photoluminescence (PL) behavior of three common cyclodextrins (CDs), namely α-CD, β-CD and γ-CD, including solution and single crystals, were studied. Their single crystals demonstrate λex-dependent multicolor p-RTP properties in the order of β-CD>α-CD>γ-CD, rather than the strongest with the least glucose units (α-CD). Among them, the λex-dependent tunable p-RTP of β-CD and α-CD is superior to that of D-(+)-xylose single crystal. The above unexpected phenomena could be explained reasonably through detailed single crystal structure analysis and theoretical calculations. The emission behavior of solution and single crystals of CDs can be reasonably explained by the clustering-triggered emission (CTE) mechanism. Furthermore, CD-based covalent organic frameworks (COF) and supramolecules are readily fabricated, which own significantly enhanced p-RTP emission. Due to the intriguing PL property as well as hydrophilic rim and low biotoxicity of CDs, successful imaging of HCT116 cells and encryption applications were demonstrated. It is believed that the intrinsic PL properties of CDs, especially their regularly adjustable multicolor p-RTP that varies with the number of glucose units, have significant guidance for the development of a series of multicolor luminescent materials.

Carbon dot-based afterglow composite with tunable room temperature phosphorescence and thermally activated delayed fluorescence and their anti-counterfeiting and encryption application

Carbon dots (CDs) based afterglow materials have attracted much attention owing to their low toxicity, environmental protection, stable luminescence, abundant raw materials, and low cost. However, CD-based afterglow materials with both room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) characteristics are rarely reported, which greatly limits their in-depth application in advanced anti-counterfeiting, intelligent sensing, and other fields. In this paper, Cu, N co-doped CDs (Cu, N-CDs) with dual emission centers were synthesized via a simple solvothermal method by heteroatom doping to enhance the spin–orbit coupling of CDs and regulate the luminescence properties of CDs. Then, boric acid (BA) was used as the matrix to synthesize Cu, N-CDs@BA composites by matrix-assisted method, and the electron transfer enhancement afterglow was realized by the inorganic electronic defects of the matrix. Cu, N-CDs@BA can realize the mutual conversion of TADF and RTP by changing the excitation wavelength or increasing the temperature. At the excitation of 285 nm, the room temperature afterglow of Cu, N-CDs@BA exhibit TADF, and the average afterglow lifetime is 94.21 ms. At the excitation of 365 nm, they exhibit RTP, and the average afterglow lifetime is 347.96 ms. Based on three different emission properties (fluorescence, RTP, and TADF), Cu, N-CDs@BA was applied in anti-counterfeiting and encryption, which shows good application potential.

Ferromagnetic Dirac half-metallicity in edge-modified zigzag boron nitride nanoribbons

Fully spin polarized Dirac fermions, with tunable gaps and room temperature ferromagnetism are discovered, by passivating single and both edges of ZBNNRs.

A photoinduced electron-transfer strategy for switchable fluorescence and phosphorescence in lanthanide-based coordination polymers.

Smart optical materials with tunable fluorescence and room temperature phosphorescence (RTP) exhibit promising application prospects in the field of intelligent switches, information security, etc. Herein, a tetraimidazole derivative was grafted to one-dimensional lanthanum-diphosphonate through H-bonds, generating a coordination polymer (CP), (H4-TIBP)·[La2Li(H2-HEDP)4(H-HEDP)]·3H2O (termed La; TIBP = 3,3,5,5-tetra(imidazole-1-yl)-1,1-biphenyl; H4-HEDP = 1-hydroxyethylidene-1,1-diphosphonic acid) with a three-dimensional supramolecular structure. La shows dynamic fluorescence from blue to red and switchable monotonous yellowish-green RTP, which can be manipulated by reversible photochromism. It is worth noting that Eu3+/Tb3+-doped CPs exhibit time-resolved (red to yellow) and monotonous green afterglow, respectively, which can be attributed to multiple emissions with different decay rates. The dynamic and multicolor luminescence endows these CPs with potential for application in the domains of optical communications, multi-step encryption, and anti-counterfeiting. This work not only integrates color-adjustable fluorescence, switchable RTP, and photochromism in one material, but also realizes the manipulation of the resultant optical performances via photochromism, paving the pathway for the design and synthesis of smart optical materials.

Single-crystalline oligomer-based conductors modeling the doped poly(3,4-ethylenedioxythiophene) family.

Conductive polymers with highly conjugated systems, such as the doped poly(3,4-ethylenedioxythiophene) (PEDOT) family, are commonly used in organic electronics. However, their structural inhomogeneity with various chain lengths makes it difficult to control their conductivities and structural details. On the other hand, low-molecular-weight materials have well-defined structures but relatively narrow conjugate areas with a limited range of Coulomb repulsion between carriers (Ueff), which hamper the flexible control of conductivities. To bridge this gap, we developed oligomer-based conductors, which are intermediate materials between polymers and low-molecular-weight materials. Using a library of single-crystal charge-transfer salts of oligo(3,4-ethylenedioxythiophene) (oligoEDOT) analogs that model the doped PEDOT family, we have investigated the structure-determining factors affecting their conductivities, such as counter anion variations, lengths of oligomer donor, and band fillings. Through the screening study, we developed oligoEDOT analogs with tunable room temperature conductivities by several orders of magnitude, including a metallic state above room temperature. In this study, we consistently evaluated the electronic structural insights by first-principles calculations and revealed that Ueff is the dominant factor that determines the relationship between the structures and conductivities. The unique features of oligoEDOT conductor systems with widely variable Ueff can differentiate these systems from strongly electron-correlated systems.

Mechanochromism, tunable pure organic room temperature phosphorescence, single-molecule near-white emission, digital encryption, and anti-counterfeiting

The development of tunable pure organic room temperature phosphorescence and single-molecule white light emitters still faces a great challenge due to ineffective intersystem crossing and sensitive triplet excitons. Here, two phenothiazine based luminogens named PtzIP and PtzIPCN were designed and synthesized. PtzIP exhibits mechanochromic activity with hypsochromic shift of 25 nm, tunable room temperature phosphorescence from 613 nm to 530 nm and 560 nm, then to 540 nm and 585 nm by crushing and grinding, and single-molecule near-white light emission with the (CIE: Commission International de I'Eclairage) CIE coordinates of (0.33, 0.25), but PtzIPCN shows mechanochromism and room temperature phosphorescence inertness in crystalline state. By choosing polymethyl methacrylate (PMMA) and 4-fluorobenzophenone(F-BP) as host materials, as well PtzIP and PtzIPCN as guest materials, a series of host-guest doping systems were constructed and optimized by tuning doping ratio. PtzIP/PMMA and PtzIPCN/PMMA doping systems present concentration dependent fluorescence and phosphorescence emission, and RTP lifetime and afterglow of PtzIPCN/PMMA are up to 185.31 ms of 2.0 s. Furthermore, the lifetime of F-BP/PtzIPCN increases to 216.63 ms at doping ratio of 1:1000 for F-BP and PtzIPCN. Based on different luminescent properties of PtzIP and PtzIPCN in the doping systems, a series of high-level digital encryption and anti-counterfeiting patterns were successfully constructed. More importantly, the underlying mechanism behind luminescent properties were explored in detail by photophysical testing, crystal analysis, and theoretical calculations.

Tunable Room Temperature Phosphorescence in Heavy-Atom-Free Metal–Organic Frameworks by Ligand Functionalization

Tunable Room Temperature Phosphorescence in Heavy-Atom-Free Metal–Organic Frameworks by Ligand Functionalization

Room-temperature creation and manipulation of skyrmions in MgO/FeNiB/Mo multilayers

Magnetic skyrmions in multilayer structures are considered as a new direction for the next generation of storage due to their small size, strong anti-interference ability, high current-driven mobility, and compatibility with existing spintronic technology. In this work, we present a tunable room temperature skyrmion platform based on multilayer stacks of MgO/FeNiB/Mo. We systematically studied the creation of magnetic skyrmions in MgO/FeNiB/Mo multilayer structures with perpendicular magnetic anisotropy (PMA). In these structures, the magnetic anisotropy changes from PMA to in-plane magnetic anisotropy (IMA) as the thickness of FeNiB layer increases. By adjusting the applied magnetic field and electric current, stable and high-density skyrmions can be obtained in the material system. The discovery of this material broadens the exploration of new materials for skyrmion and promotes the development of spintronic devices based on skyrmions.

Host‐Guest Chemistry of Chiral MOFs for Multicolor Circularly Polarized Luminescence Including Room Temperature Phosphorescence

AbstractExploiting the chirality transfer and amplification in the hierarchical chiral systems by the visible and accurate structures is still a challenge. Herein, a pair of homochiral metal‐organic frameworks (MOFs) DCF‐12 and LCF‐12 with high rigidity and high porosity are synthesized via reticular chemistry. Interestingly, these two enantiomers can act as nano‐containers, in which four chromophores, covering acridine, pyrene, 9,10‐Bis(phenylvinyl) anthracene (BPEA), and coronene can be introduced by in situ encapsulation. Importantly, the precise single crystal structures of all guest‐loaded MOFs by X‐ray diffraction technique can be obtained smoothly. It not only clearly reveals the chirality transfer from chiral host framework to achiral guest emitters through space chirality transfer, but also circularly polarized luminescence can be achieved and modulated through the synergistic effect. Extraordinarily, both pyrene@DCF‐12 and pyrene@LCF‐12 exhibit fascinating multi‐color tunable room temperature phosphorescence (RTP) and dynamic circularly polarized luminescence. Besides, the RTP quantum yields of pyrene@DCF‐12 and pyrene@LCD‐12 are high up to 75.39% and 73.43%, which exceeds most of that of RTP materials. These results demonstrate that chiral MOFs can serve as an accurate platform to investigate the mechanism of chirality transfer and amplification and to prompt the development of CPL‐active materials.

Tunable room temperature ferromagnetism in fullerene thin film induced by 1 MeV proton microbeam irradiation

We report tunable ferromagnetic properties of thin films of fullerene upon 1 MeV proton microbeam ion irradiation, by varying the ion fluence. Focused microbeam scanning of 1 MeV proton ions have been performed on the fullerene thin films. Consequently, a stable and significant ferromagnetic ordering at room temperature has been observed in the fullerene thin films. The proton microbeam irradiation induces a maximum magnetic ordering in fullerene with optimum dosage and subsequently higher fluence irradiations yield, diminishing effect upon the observed ferromagnetic ordering due to the higher degree of damages. The X-ray diffraction and Raman analysis confirm the damage due to proton microbeam irradiation. The reduction in the saturation magnetic moment induced, is very sharp as a result of exposure to the larger ion fluence. The approximate distance between defects has been simulated computationally, and its relation with observed ferromagnetism has been established. The irradiation has been performed at moderate ion flux (low microbeam current) to avoid the possible annealing effects of the ion irradiation.

Room temperature phosphorescence of heavy-atom-free indole carboxylic acid/polyacrylamide: Low cost, long lifetime and good luminescent efficiency

Functional organics doped polymers have displayed tunable room temperature phosphorescence (RTP), emerging as promising applications in optical information encryption and organic electronic devices. However, the present doped polymer systems confront a difficulty of constructing a low-cost heavy-atom-free doped systems with ultra-long RTP lifetime and high luminescent efficiency by a facile and environmental-friendly approach, which retards large-scale and commercialized applications. In this work, based on indole derivatives of high quantum efficiency and water-soluble polyacrylamide (PAM) of high H-bond capacity, several kinds of commercialized indole carboxylic acid (ICA), with different extended benzoic acid arms, were respectively combined with PAM based on intermolecular hydrogen bonding by water-promoted dispersion, thereby effectively retarding non-radiative transition. The average RTP lifetimes of 5-ICA/PAM-0.3% and IDCA/PAM-0.3% films could reach 1.997 and 0.992 s respectively at room temperature. Moreover, to adjust the positions of substituted carboxy groups, the luminescent colors can be tuned from blue to yellowish green. Anti-counterfeiting patterns can be facilely fabricated with ICA-doped PAM by environmental-friendly and low-cost screen printing and brush writing, which gives an insight into commercialized production for information security.

Correction to: Tunable room temperature ferromagnetism and optical bandgap of CdS:Er nanoparticles

Correction to: Tunable room temperature ferromagnetism and optical bandgap of CdS:Er nanoparticles

Ambient, tunable room temperature phosphorescence from a simple phthalimide phosphor in amorphous polymeric matrix and in crystalline state

Harvesting triplet excitons via room temperature phosphorescence (RTP) from purely organic chromophores has been a formidable challenge, which has a potential applications in displays, lighting, and bio-imaging. Herein, a simple phthalimide phosphor derivative is reported, which exhibits visible cyan emissive phosphorescence in solution-processable thin films and orange-red emitting phosphorescence in the crystalline state. Presence of carbonyl group and the bromine atom in the molecular design effectively increases the inter-system crossing (ISC) and spin-orbit coupling efficiency (SOC) between singlet and triplet states, which play a crucial role in achieving efficient phosphorescence under ambient conditions.

Electrically Tunable Room Temperature Hysteresis Crossover in Underlap MoS2 Field-Effect Transistors.

Clockwise to anticlockwise hysteresis crossover in current-voltage transfer characteristics of field-effect transistors (FETs) with graphene and MoS2 channels holds significant promise for nonvolatile memory applications. However, such crossovers have been shown to manifest only at high temperature. In this work, for the first time, we demonstrate room temperature hysteresis crossover in few-layer MoS2 FETs using a gate-drain underlap design to induce a differential response from traps near the MoS2-HfO2 channel-gate dielectric interface, also referred to as border traps, to applied gate bias. The appearance of trap-driven anticlockwise hysteresis at high gate voltages in underlap FETs can be unambiguously attributed to the presence of an underlap since transistors with and without the underlap region were fabricated on the same MoS2 channel flake. The underlap design also enables room temperature tuning of the anticlockwise hysteresis window (by 140×) as well as the crossover gate voltage (by 2.6×) with applied drain bias and underlap length. Comprehensive measurements of the transfer curves in ambient and vacuum conditions at varying sweep rates and temperatures (RT, 45 °C, and 65 °C) help segregate the quantitative contributions of adsorbates, interface traps, and bulk HfO2 traps to the clockwise and anticlockwise hysteresis.

Route to tunable room temperature electric polarization in SrTiO3-CoFe2O4 heterostructures.

Utilizing the magnetostrictive properties of CoFe2O4, we demonstrate reversible room temperature control of the Ti electronic structure in SrTiO3–CoFe2O4 heterostructures, by inducing local and reversible strain in the SrTiO3. By means of X-ray absorption spectroscopy, we have ascertained the changes that take place in the energy levels of the Ti 3d orbitals under the influence of an external magnetic field. The observed Ti electronic state when the sample is subjected to moderately large external magnetic fields and the disappearance of the induced phase upon their removal indicates lattice distortions that are suggestive of the development of a net electric polarization.

High oscillator strength interlayer excitons in two-dimensional heterostructures for mid-infrared photodetection.

The development of infrared photodetectors is mainly limited by the choice of available materials and the intricate crystal growth process. Moreover, thermally activated carriers in traditional III-V and II-VI semiconductors enforce low operating temperatures in the infrared photodetectors. Here we demonstrate infrared photodetection enabled by interlayer excitons (ILEs) generated between tungsten and hafnium disulfide, WS2/HfS2. The photodetector operates at room temperature and shows an even higher performance at higher temperatures owing to the large exciton binding energy and phonon-assisted optical transition. The unique band alignment in the WS2/HfS2 heterostructure allows interlayer bandgap tuning from the mid- to long-wave infrared spectrum. We postulate that the sizeable charge delocalization and ILE accumulation at the interface result in a greatly enhanced oscillator strength of the ILEs and a high responsivity of the photodetector. The sensitivity of ILEs to the thickness of two-dimensional materials and the external field provides an excellent platform to realize robust tunable room temperature infrared photodetectors.

Tunable room temperature phosphorescence and energy transfer in ratiometric co-crystals.

Two co-crystals (BTA-ME-1 and BTA-ME-2) assembled with the same building blocks but in different ratios exhibit alternative stacking modes, relative orientations and aggregation states, leading to color-tunable green and yellow room temperature phosphorescence (RTP) and different intermolecular energy transfer efficiencies, respectively. Based on the time-resolved afterglow properties of the RTP emission, BTA-ME-2 is further applied for signal-visualized information encryption.

Controlling Organic Room Temperature Phosphorescence through External Heavy‐Atom Effect for White Light Emission and Luminescence Printing

AbstractPure organic materials with tunable room temperature phosphorescence (RTP) have attracted considerable interest because they are promising candidates for a wide range of optoelectronic applications. Herein, a series of organic compounds of (4‐(9H‐carbazol‐9‐yl)butyl) triphenylphosphonium (CBTP) with different halide anions (CBTP‐Cl, CBTP‐Br, and CBTP‐I) are synthesized. They show emission color changes from blue to orange‐red in the solid state. Single‐crystal X‐ray diffraction analysis and theoretical calculations demonstrate that the RTP is primarily caused by the external heavy‐atom effect (EHE), which enhances the spin–orbit coupling between the singlet and triplet excited states to facilitate the intersystem crossing rate. Distinct white light emission can be achieved using the controllable RTP by doping a certain ratio of potassium iodide (KI) into a polymer matrix containing CBTP‐Cl. Moreover, luminescent information can be recorded on a paper substrate made from a polymer film containing CBTP‐Cl with KI aqueous solution as the ink. The results suggest that rational control of the EHE of these pure organic materials is promising for different optoelectronic applications, including solid‐state lighting, data recording, and security protection.

Emission mechanism understanding and tunable persistent room temperature phosphorescence of amorphous nonaromatic polymers

Intrinsic emission and persistent room temperature phosphorescence from amorphous nonaromatic polymers are observed, which can be well rationalized by the CTE mechanism.