Absolute Photoluminescence Quantum Yield Research Articles

Circularly Polarized Electroluminescence of Thermally Activated Delayed Fluorescence-Active Chiral Binaphthyl-Based Luminogens.

Two pairs of thermally activated delayed fluorescence (TADF)-active chiral luminogens (R/S-1 and R/S-2) can be achieved by introducing D-A-type groups to chiral BINOL skeletons. The resulting chiral luminogens can exhibit aggregation-induced emission properties in THF-water mixtures and TADF emission in a doped-film state. The absolute photoluminescence quantum yield (ΦPL) and delayed fluorescence lifetimes (τdelayed) were measured to be 18.5% and 1.03 μs for R-1 and 15.7% and 0.97 μs for R-2. However, only R/S-1 with the fixed conjugation structure can emit circularly polarized luminescence signals, and glum can reach 1.6 × 10-3 in toluene solution and 9.2 × 10-4 in the neat film. Most importantly, R/S-1 was chosen as the emitting layers for orange-red circularly polarized organic light-emitting diodes, which can display low turn-on voltage (Von) of 3.4 V, high maximum brightness (Lmax) up to 40 470 cd m-2, moderate external quantum efficiency of 4.1%, as well as circularly polarized electroluminescence signal with gEL = -0.9 × 10-3/+1.0 × 10-3.

Solvent‐Free Aerosol Deposition for Highly Luminescent and Thermally Stable Perovskite‐Ceramic Nanocomposite Film

AbstractLuminescent perovskite structure has been used in a polymer‐encapsulated form for display applications. However, insulating polymers as a host matrix are intrinsically vulnerable to thermal stresses which cause softening distortion or deterioration in thermoplastic polymers. Here, nanostructured CsPbBr3/Al2O3 composite film is developed by aerosol deposition method. At first, CsPbBr3/Al2O3 composite powders with bright and saturated green emission are synthesized. Then, the ceramic composite powder comprising monoclinic CsPbBr3 nanocrystals supported on submicron α‐Al2O3 particles is successfully transformed to a film‐type by aerosol deposition, which enables a nonsolvent‐induced process at room temperature. The deposited films show a pure green spectrum with a narrow full width at half maximum of 17 nm, high long‐term stability at 150 °C for over 20 d, and an absolute photoluminescence quantum yield of 8%–15%. In general, inorganic films are known to have difficulty with flexibility and patterns. However, the deposited film can be employed in useful applications such as down‐converting materials for an LCD backlight with a wide‐color gamut of 89.2% in Rec. 2020, highly flexible ceramic composite films, multilayer films, patterning of surfaces for an advanced color filter array, and deposition on curved substrates toward diverse display fields.

Brightening of Long, Polymer-Wrapped Carbon Nanotubes By Large Scale sp3 Functionalization

Networks of long, polymer-sorted semiconducting single-walled carbon nanotubes (SWNTs) show excellent transport of both electrons and holes and are thus perfectly suited for electrically-driven light emission in the near-infrared (NIR) [1,2]. So far, their application in near-infrared light-emitting devices has been hampered by their low photoluminescence quantum yield (PLQY) and strong self-absorption owing to their small Stokes shift. In recent years, the controlled introduction of a low density of sp3 defects as exciton trapping sites was shown to lead to red-shifted emission with longer exciton lifetimes and improved PLQYs. However, due to the polarity of the employed diazonium salt reagent, this approach was limited to aqueous dispersions of SWNTs with often short tube lengths and the undesired presence of stabilizers. Here, we present a novel route to sp3 functionalization with diazonium salts in organic, non-halogenated solvents, thereby making it compatible with polymer-wrapped long SWNTs produced by shear force mixing. As a result of the low density of exciton quenching sites on shear mixed SWNTs [3], the excitons are efficiently channeled to the emissive defect sites, leading to absolute PLQYs of 4 % for functionalized (6,5) SWNT dispersions in toluene. This new method paves the way toward the large scale production of high-quality sp3 functionalized SWNTs and hence also thin films for optoelectronic devices with narrowband near-infrared emission. [1] Rother et al., ACS Appl. Mater. Interfaces 2016, 8, 5571-5579. [2] Brohmann et al., J. Phys. Chem. C 2018, 122, 19886-19896. [3] Graf et al., Carbon 2016, 105, 593-599. Figure 1

Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires.

All inorganic mixed-halide perovskite, CsPb(Br xI1- x)3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br xI1- x)3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.

One-step synthesis of boron-doped graphene quantum dots for fluorescent sensors and biosensor

Heteroatom doping can endow graphene quantum dots (GQDs) with various new or improved structural, optical and physicochemical properties. In contrast to the widely reported oxygen, nitrogen or sulfur doping in GQDs, simple and scalable synthesis of boron-doped GQDs (B-GQDs) with high yield and quantum yields remains challenge. In this work, B-GQDs are one-step synthesized and serve as the fluorescence probes for the fabrication of sensors towards Fe3+ ion or phosphate (Pi) as well as biosensor towards cytochrome C (Cyt C). The B-GQDs are facile synthesized using one-step bottom-up molecular fusion between 1,3,6-trinitropyrene and borax in sodium hydroxide under hydrothermal process. The synthesis can be performed using large volume autoclave (500 ml) with a high yield of 71%, indicating possibility for gram-scale production of B-GQDs. The as-prepared B-GQDs exhibit single or bilayer graphene structure, high crystallinity, uniform size, bright (absolute photoluminescence quantum yield of 16.8%) and excitation-independent green fluorescence (maximum excitation wavelength and emission wavelength of 480 nm and 520 nm, respectively). Successful doping of B atoms in the lattice of GQDs enables high selectivity towards Fe3+. Based on quenching of fluorescence of B-GQDs by Fe3+ (turn-off model), detection of Fe3+ (with limit of detection-LOD of 31.2 nM) and Fe3+-rich Cyt C (with LOD of 5.9 μg/ml) are demonstrated. As Pi can recover Fe3+-quenched fluorescence of B-GQDs (turn-off-on model), indirect fluorescent detection of Pi is also achieved with LOD of 340 nM. In addition, detection of Fe3+, Cyt C and Pi in real samples is achieved.

Effective Mn-Doping in AgInS₂/ZnS Core/Shell Nanocrystals for Dual Photoluminescent Peaks.

We developed the effective Mn-doping procedure for AgInS2(AIS)/ZnS core/shell nanocrystals (NCs) to exhibit dual photoluminescence (PL) peaks. Although the AIS/ZnS core/shell NCs showed solely a single PL peak at ~530 nm, incorporation of a small amount of Mn as a dopant within the AIS/ZnS NCs resulted in the simultaneous emergence of dual PL peaks at ~500 nm (green PL) arising from AIS/ZnS NCs and ~600 nm (orange PL) from the Mn dopants. Furthermore, we succeeded in significantly increasing the absolute PL quantum yield value of dual emissive AIS/ZnS NCs incorporated with Mn dopants from 10% to 34% after surface passivation with another ZnS shell for the formation of core/shell/shell structures.

Solution processed and low-temperature annealed Eu3+-doped YVO4 thin films

Semiconducting and luminescent thin films could be served as the emitting layer in electroluminescent devices. In this work, Eu3+-doped yttrium vanadium oxide (YVO4) luminescent thin films were directly deposited by a solution processing method, and they were annealed at a low temperature of 400 °C. Such low annealed temperature is compatible with commonly used transparent conductive electrodes, such as tin-doped indium oxide and fluorine-doped tin oxide. In addition, the luminescent thin films have a band gap of 3.94 eV and an absolute photoluminescence quantum yield of 23%. These results revealed that Eu3+-doped YVO4 luminescent thin films have a high potential in electroluminescent devices.

Aqueous Synthesis of Lead Halide Perovskite Nanocrystals with High Water Stability and Bright Photoluminescence.

Lead halide perovskite nanocrystals (NCs) have attracted intense attention because of their excellent optoelectronic properties. The ionic nature of halide perovskites makes them highly vulnerable to water. Encapsulation of perovskite NCs with inorganic or organic materials has been reported to enhance their stability; however, they often suffer from large aggregation size, low water solubility, and difficulty for further surface functionalization. Here, we report a facile aqueous process to synthesize water-soluble CsPbBr3/Cs4PbBr6 NCs with the assistance of a fluorocarbon agent (FCA), which features a novel mechanism of the perovskite crystallization at the oil/water interface and direct perovskite NCs/FCA self-assembly in an aqueous environment. The products exhibit a high absolute photoluminescence quantum yield (PLQY) of ∼80% in water with the PL lasting for weeks. Through successive ionic layer adsorption and reaction, BaSO4 was further applied to encapsulate the NCs, which greatly enhanced their stability in phosphate-buffered saline solutions. The high stability in water and saline solution, high PLQY, and tunable emission wavelength, together with the successful demonstration of brain tissue labeling and PL under X-ray excitation, make our perovskite NCs a promising choice for X-ray fluorescent biolabels.

High photoluminescence quantum yields generated from N-Si-O bonding states in amorphous silicon oxynitride films.

We investigated the high absolute photoluminescence quantum yields (PL QYs) from tunable luminescent amorphous silicon oxynitride (a-SiNxOy) films. The PL QY of 8.38 percent has been achieved at PL peak energy of 2.55 eV in a-SiNxOy systems, which is higher than those of reported nanocrystal-Si embedded silicon nitride films. The existence of N-Si-O bonding states was confirmed by performing FTIR, XPS and EPR measurements. The PL QY is proportional to the concentration of Nx defects, indicating the dominant contribution of luminescent N-Si-O bonding states in radiative recombination processes. Particularly, we precisely monitored the ns-PL lifetimes evolution profile versus detected emission wavelengths, and further verified that the N-Si-O bonding states are responsible for highly efficient PL.

Layer-Stacking-Driven Fluorescence in a Two-Dimensional Imine-Linked Covalent Organic Framework

Schiff-condensation reactions carried out between 1,6-diaminopyrene (DAP) and the tritopical 1,3,5 benzenetricarbaldehyde (BTCA) or 2,4,6-triformylphloroglucinol (TP) ligands give rise to the formation of two-dimensional imine-based covalent-organic frameworks (COFs), named IMDEA-COF-1 and -2, respectively. These materials show dramatic layer-packing-driven fluorescence in solid state arising from the three-dimensional arrangement of the pyrene units among layers. Layer stacking within these 2D-COF materials to give either eclipsed or staggered conformations can be controlled, at an atomic level through chemical design of the building blocks used in their synthesis. Theoretical calculations have been used to rationalize the different preferential packing between both COFs. IMDEA-COF-1 shows green emission with absolute photoluminescence quantum yield of 3.5% in solid state. This material represents the first example of imine-linked 2D-COF showing emission in solid state.

Interplay between the Conformational Flexibility and Photoluminescent Properties of Mononuclear Pyridinophanecopper(I) Complexes.

The macrocyclic ligand conformational behavior in solution, solid-state structures and the photophysical properties of copper(I) cationic and neutral mononuclear complexes supported by tetradentate N, N'-dialkyl-2,11-diaza[3.3](2,6)-pyridinophane ligands RN4 (R = H, Me, iBu, secBu, neoPent, iPr, Ts) were investigated in detail. Steric properties of the alkyl group at the axial amine in the RN4 ligand were found to strongly affect the conformational preferences and dynamic behavior in solution. Several types of conformational exchange processes were revealed by variable-temperature NMR and 2D exchange spectroscopy, including degenerative exchange in a pseudotetrahedral species as well as exchange between two isomers with different conformers of tri- and tetracoordinate RN4 ligands. These exchange processes are slower for the complexes containing bulky alkyl groups at the amine compared to less sterically demanding analogues. A clear correlation is also observed between the steric bulk of the alkyl substituents and the photoluminescent properties of the derived complexes, with less dynamic complexes bearing bulkier alkyl substituents exhibiting higher absolute photoluminescence quantum yield (PLQY) in solution and the solid state: PLQY in solution increases in the order Me < neoPent < iBu < secBu ≈ iPr < tBu. The electrochemical properties of the cationic complexes [(RN4)CuI(MeCN)]X (X = BF4, PF6) were also dependent on the steric properties of the amine substituent.

Simultaneous biosensing of CA125 and CA15-3 tumor markers and imaging of OVCAR-3 and MCF-7 cells lines via bi-color FRET phenomenon using dual blue-green luminescent carbon dots with single excitation wavelength

Here, we developed a facile route to synthesize two CDs with the maximum emission locates at 326 nm and 443 nm under 230 nm excitation. The absolute photoluminescence quantum yield (QY) is as high as 29% and 52% for CD-1 and CD-2 with strong blue-green fluorescence, respectively. The functionalized CDs (CDs-NH2, CDs-COOH) conjugated with antibodies used for simultaneous detection of two tumor-markers using fluorescence resonance energy transfer (FRET) strategy, when MoS2 nanosheets functionalized with ssDNA related aptamers applied as quencher. The response of sensor enhanced gradually with increasing of targets at range 0.05–8 pg/mL with detection limit (DL) 5.0 fg/mL for CA125, while for CA15-3 concentration range was 1.0–35 pg/mL and DL was 0.5 pg/mL. This strategy revealed a stable analytical performance for the detection of OVCAR-3 and MCF-7 cells lines ranging from 1000 to 10,000 cells/mL with DL 2–3 cells in 10 μL of injected sample. When the CDs-Ab was used in selective imaging of MCF-7 and OVCAR-3 cancer cells, a strong PL emission was observed. After incubation times, both the cells size and shape clearly remained without any change. The results demonstrate that the CDs are a potentially excellent bioimaging component in pathological diagnosis, biomedicine research and management of cancer diseases.

A solvent-free gaseous detonation approach for converting benzoic acid into graphene quantum dots within milliseconds

Graphene quantum dots (GQDs) in high reproducibility are synthesized by a gaseous detonation method which converts untreated benzoic acid (BA) precursor into powdered GODs without complicated post-treatment in 3–5 ms. The as-prepared GQDs resulting in an absolute photoluminescence quantum yield (PLQY) of 21.5% exhibit dual-wavelength-independent emission with the maximum PL emission at 431 nm and 460 nm under excitation maximum at 300 nm dispersed in ethyl alcohol. Based on surface structure, photoluminescence (PL) behaviors of GQDs and the characteristics of gaseous detonation, the formation mechanism of GQDs is speculated. Moreover, further study regarding the optical properties of reducing GQDs (R-GQDs) and thermal annealing GQDs (A-GQDs), it is possible to reveal PL mechanism of GQDs. This research not only provides a one-pot solvent-free route to rapid and large-scale preparation of GQDs, but also accounts for the hypothetic formation and PL mechanism of the obtained GQDs.

Highly efficient pyrene blue emitters for OLEDs based on substitution position effect

To investigate the effect of substitution position of the side group on a pyrene core, three derivatives having a triphenylbenzene group as a bulky side group at the 1,6-position, 4,9-position, and 1,8-position were successfully synthesized: 1,6-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (1,6-DTBP), 4,9-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (4,9-DTBP), and 1,8-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (1,8-DTBP). The three synthesized materials showed excellent thermal stability with a high Tg of >140 °C and a high Td of >500 °C. Due to the highly twisted structure of 1,8-DTBP in the film state, the absolute photoluminescence quantum yield value was improved. Of the three synthesized materials used as an emitter in a non-doped organic light-emitting diode device, 1,8-DTBP showed highly efficient electroluminescence performance, with a luminance efficiency of 6.89 cd/A, power efficiency of 3.03 lm/W, and external quantum efficiency of 7.10% at 10 mA/cm2. In addition, 4,9-DTBP showed a deep-blue emission of CIE x, y (0.158, 0.063) suitable for HD-TV.

One-pot Synthesis of Silver Indium Sulfide Ternary Semiconductor Nanocrystals with Highly Luminescent Performance from Low-toxic Precursors

We describe one-pot synthesis of highly luminescent nanocrystals (NCs) of silver indium sulfide (AIS) by simply heating low-toxic Ag and In precursors in the solution. Our AIS NCs with the average size of ~2.3 nm showed an optimal value of absolute photoluminescence quantum yield (PL-QY) of ~60%. Moreover, such high PL-QY values of AIS NCs were adequately stable even after gently storing at room temperature for over 21 months.

Comparison of Luminescent Properties in Solid-State and Polymer Films of Eu(III) Complexes Containing 2-Acylindandione Ligands

The Europium(III) ternary complexes Eu(BID)3(PHEN) and Eu(MBID)3(PHEN) (BID – 2-benzoyl-1,3-indandione, MBID - 2-(4-methylbenzoyl)-1,3-indandione and PHEN – 1,10-Phenantroline) were synthesized, characterized and incorporated into poly methyl methacrylate (PMMA) and poly-N-vinylcarbazole (PVK) matrixes. Emission properties in solid-state and polymer films were investigated through excitation spectra, emission spectra and absolute photoluminescence quantum yields (PLQY). Both complexes in their solid-state and films exhibited red-light luminescence with narrow bands corresponding to Eu(III) ion emission. In solid-state complexes were characterized with PLQY of 6% and 10%, in PVK matrixes quantum yield dropped down to 4%, however, in PMMA films exhibited similar luminescence PLQY than in solid-state.

Quantum Dots: Perovskite Quantum Dots with Near Unity Solution and Neat‐Film Photoluminescent Quantum Yield by Novel Spray Synthesis (Adv. Mater. 7/2018)

In article number 1705532, Hao-Wu Lin and co-workers spray-synthesize unprecedented cubic-shaped perovskite nanocrystals with a stable absolute photoluminescence quantum yield of ≈100% in both solution and the solid-state neat film. When utilized in color-conversion-type light-emission hybrid devices, the devices exhibit excellent external quantum efficiency of 28.1%, power efficiency of 121 lm W−1, and extraordinary forward-direction luminescence of 8 500 000 cd m−2 and successfully demonstrate high-definition motion pictures.

1D hetero-bimetallic regularly alternated 4f-3d coordination polymers based on N-oxide-4,4'-bipyridine (bipyMO) as a linker: photoluminescence and magnetic properties.

Heterotopic divergent ligand N-oxide-4,4'-bipyridine (bipyMO) has been herein exploited for the preparation of hetero-bimetallic coordination polymers where Ln(hfac)3 and M(hfac)2 nodes regularly alternate (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), bipyMO being able to selectively use its two potential coordination sites to discriminate the metal ions. The synthesis of three coordination polymers, [Ln(hfac)3M(hfac)2(bipyMO)2]n (Ln = Eu, M = Zn, 1; Ln = Eu, M = Cu, 2, Ln = Dy, M = Co, 3), was carried out by reacting the appropriate [M(hfac)2(bipyMO)]n and [Ln(hfac)3] precursors in toluene in the presence of a given stoichiometric amount of bipyMO. The products were characterized by elemental analysis, X-ray powder diffraction, and FTIR spectroscopy. Single crystal X-ray diffraction studies carried out on 2 showed that it was formed by chains containing the hexa-coordinated 3d metal (Cu(hfac)2[N]2) and the octa-coordinated lanthanide (Eu(hfac)3[O]2) nodes, where [N] and [O] stand for the donor atom of the bridging divergent ligand. The X-ray powder diffraction patterns of the three compounds and the comparison of their cell constant values allowed establishing that the derivatives were isotypic. Photoluminescence (PL) studies on microcrystalline sample powders evidenced a bright red emission for 1 with an absolute PL quantum yield of 0.24. The sensitized emission of Eu3+ can be excited in a wide wavelength range, from UV to visible, up to ≈450 nm. Conversely, europium emissions are not detectable in 2 due to the presence of Cu(hfac)2(bipyMO) moieties whose strong absorption overlaps Eu3+ transitions. Magnetic measurements conducted on 3 revealed the presence of a weak ferromagnetic interaction below 2.1 K. An ac susceptibility study highlighted a slow relaxation of the magnetization of 3 with an applied static magnetic field of 0.1 T, which could be equally fitted with a Orbach-direct or a Raman-direct mechanism. No relaxation dynamics was detected without the application of a static magnetic field.

Perovskite Quantum Dots with Near Unity Solution and Neat-Film Photoluminescent Quantum Yield by Novel Spray Synthesis.

In this study, a novel perovskite quantum dot (QD) spray-synthesis method is developed by combining traditional perovskite QD synthesis with the technique of spray pyrolysis. By utilizing this new technique, the synthesis of cubic-shaped perovskite QDs with a homogeneous size of 14 nm is demonstrated, which shows an unprecedented stable absolute photoluminescence quantum yield ≈100% in the solution and even in the solid-state neat film. The highly emissive thin films are integrated with light emission devices (LEDs) and organic light emission displays (OLEDs). The color conversion type QD-LED (ccQD-LED) hybrid devices exhibit an extremely saturated green emission, excellent external quantum efficiency of 28.1%, power efficiency of 121 lm W-1 , and extraordinary forward-direction luminescence of 8 500 000 cd m-2 . The conceptual ccQD-OLED hybrid display also successfully demonstrates high-definition still images and moving pictures with a 119% National Television System Committee 1931 color gamut and 123% Digital Cinema Initiatives-P3 color gamut. These very-stable, ultra-bright perovskite QDs have the properties necessary for a variety of useful applications in optoelectronics.

Benzoselenadiazole-based donor-acceptor small molecule: Synthesis, aggregation-induced emission and electroluminescence

Several tetraphenylethene and triphenylamine decorated donor-acceptor (D-A) benzoselenadiazole derivatives with aggregation-induced emission (AIE) features were synthesized and characterized. The photophysical, thermal, electrochemical and electroluminescent (EL) properties, as well as the AIE property of the resulting luminogens are discussed. All the luminogens are soluble in common organic solvents and show high thermal stability with a Td of 399–460 °C. The absolute photoluminescence quantum yield in the solid state ranged from 14.2% to 36.5%. The D–A structures of TPE-Se-TPE, TPA-Se-TPE and TPA-Se-TPA enable them to have aggregation-caused quenching (ACQ) plus aggregation-induced emission enhancement (AIEE) effects dominated by the twisted intramolecular charge-transfer (TICT) and restriction of intramolecular rotations (RIR), respectively. The best device performances were obtained from TPA-Se-TPE with a maximal luminous efficiency of 2.91 cd/A and the maximal brightness is 5855 cd/m2. This is the first report of benzoselenadiazole-based fluorophore with an AIE feature for organic electronics application.