High PLQY Research Articles

High concentration quenching, improved PLQY and high color purity of novel Gd2TiO5:Eu3+ triggered by complete solubility of dopant

In the surge of new inorganic luminescent host for lanthanide ion for efficient solid-state lighting, Ln2TiO5 comes as a new class of materials with all optically suited properties. Triggered by very high solubility of Eu3+ ion in Gd2TiO5 with minimal lattice strain, negligible doping induced structural distortion and no charge compensating defects; Gd2TiO5:Eu3+ (GTOE) delivered an extraordinary credentials as novel phosphor material. GTOE demonstrated no concentration quenching up to 10 mol % doping; monotonic rise in emission intensity, higher excited state lifetime, high red color purity∼99% and PLQY∼ 14%. Luminescence lifetime spectroscopy suggested stabilization of Eu3+ in both GdO7 with distorted pentagonal bipyramid (DPB) and distorted hexagonal bipyramid (DHB) geometry having similar coordination and symmetry and is well supported by two stark components in 5D0→7F0 transitions. Positron annhilation lifetime spectroscopy (PALS) suggested that average positron lifetime remained constant in all the samples indicating no charge compensating defects formation further justifying occupancy of Eu3+ in isovalent Gd3+ site. Judd-Ofelt analysis suggested that local symmetry around Eu3+ ion and polarizability of Eu–O bonds in GTO host doesn't change throughout the concentration range. This work proposed an excellent candidate for red emitting materials towards phosphor converted white light emitting diodes (pcLEDs) having high dopant solubility, PLQY and color purity.

Ultra-stable CsPbBr3 nanocrystals encapsulated in mesoporous silica KIT-6 for LED applications

Metal halide perovskite nanocrystals (NCs) with strong absorption, high photoluminescence quantum yield (PL QY) and narrow bandwidth have shown great potential for display applications. However, their poor stability hinders their long-term device applications. Herein, we encapsulate CsPbBr3 NCs in closed-hole mesoporous silica KIT-6 through the facile high temperature solid reaction method. The obtained CsPbBr3@KIT-6 composites exhibit a high PL QY of 64% and a narrow bandwidth of 24 nm. Particularly, the collapsed mesoporous silica can protect the CsPbBr3 NCs from the impact of water or light irradiation. For instance, the PL QY of the NCs maintains 90% of the initial value after being immersed in water for 30 days. Ultimately, white-light-emitting diode (WLED) with a wide color gamut of 126.5% National Television System Committee (NTSC) standard was fabricated by packaging green-emitting CsPbBr3@KIT-6 powders, K2SiF6: Mn4+ red phosphor and blue diode chip. The WLED maintained 88% of its initial luminous efficacy after 30 days of operation, exhibiting good device stability.

Highly Efficient Solution-Processed Bluish-Green Thermally Activated Delayed Fluorescence Compounds Using Di(pyridin-3-yl)methanone as Acceptor

Solution-processed devices with thermally activated delayed fluorescence (TADF) compounds have gained great attention due to their low cost and high performance. Here, two solution-processable TADF emitters named ACCz-DPyM and POxCz-DPyM were synthesized by coupled 9,10-dihydro-9,9-dimethylacridine or phenoxazine modified carbazole as donor with di(pyridin-3-yl)methanone as acceptor. Both TADF compounds show same small ΔΕST of 0.04 eV and high PLQY of 66.2% and 58.2%. The devices fabricated by ACCz-DPyM and POxCz-DPyM as emitters show excellent performance as solution-processed with low turn-on voltage of 4.0 and 3.4 V, high luminance of 6209 and 3248 cd m−2 at 8 V, the maximum current efficiency of 9.9 and 15.9 cd A−1, the maximum external quantum efficiency of 6.6% and 6.5% and low efficiency roll-off. The solution-processed device based on ACCz-DPyM shows bluish-green emission. These results show that ACCz-DPyM and POxCz-DPyM are suitable for solution processing devices.

Decyl disulfide surface treatment improved photoluminescence quantum yield and stability of blue-emitting CsPbBr3 nanoplatelets

Improving the photoluminescence quantum yields (PL QYs) and stability of blue-emitting CsPbBr3 nanoplatelets (NPLs) is essential for the application in high-quality displays. Herein, highly luminescent CsPbBr3 NPLs with PL peak at 462 nm were prepared by a modified supersaturated recrystallization synthesis strategy at room temperature. The resulting blue CsPbBr3 NPLs show high PL QY of 98% and a full width at half maximum of 13 nm, benefiting from the decyl disulfide (DF) surface treatment. Besides, the DF-treated CsPbBr3 NPLs show lower Urbach energy (15 meV) and more outstanding water, acetone, and UV-light resistance stabilities than the pristine ones, suggesting that the surface ligand treatment can reduce Br− vacancy defects and inhibit the non-radiative recombination process. Based on the temperature-dependent PL, the exciton binding energy of CsPbBr3 NPLs is found to increase from 109 to 201 meV after DF treatment. Finally, light-emitting diodes based on the treated CsPbBr3 NPLs were fabricated.

Highly Efficient, Low‐Dose, and Ultrafast Carbazole X‐Ray Scintillators

AbstractOrganic fluorescence scintillators, owing to the ultrafast response time, versatile chemical structures, low processing temperature, and low cost, are considered as one of the promising materials for medical diagnostics, radiation detection, and X‐ray astronomy. However, the low radioluminescence (RL) intensity and low sensitivity hinder their practical applications. In this work, a highly efficient organic fluorescent scintillator, 4,4′‐bis(9‐carbazolyl)biphenyl (CBP), is presented, exhibiting a high X‐ray RL intensity, narrow full width at half‐maximum of 49 nm, and ultrafast decay time of 1.15 ns. More importantly, it has a low detection limit of 25.5 nGy s−1, which is only 1/215 dose rate compared with the commercial X‐ray diagnostics. Such an excellent scintillation performance is mainly attributed to its high photoluminescence quantum yield (PLQY = 61.92%) and good carrier transport (average hole mobility of 0.094 cm2 V−1 s−1). By mixing the CBP into polydimethylsiloxane, the fabricated large area flexible film can be applied in X‐ray radiography, which exhibits a high spatial resolution of 14.3 lp mm−1 at MTF > 0.2. This work paves a way for the implementation of organic fluorescence dyes with high PLQY, high carrier mobility in efficient X‐ray scintillation and imaging.

High-efficiency narrow-band green-emitting Tb-doped fluorosilicate glass for X-ray detectors

High-efficiency scintillators for radiation detections are urgently desired in many fields such as nondestructive inspection, medical imaging, and space exploration. Nowadays, commercial scintillators still face challenges of costly and time-consuming fabrication techniques and restricted size. Here, we present a high-efficient narrow-band green-emitting Tb3+-doped fluorosilicate (SF) glass scintillator with manufacturing of large size and low cost. Its emission (530–565 nm, ∼58% photons of total) highly superimposes with the peak sensitivity wavelength (∼550 nm) of silicon photomultipliers or charge-coupled device detectors. Moreover, owing to the particularly designed glass matrix, the photoluminescence (PL) quantum yield (QY) reaches up to 83%, which is high compared with other reported Tb3+-doped scintillators. The high PLQY combined with negligible self-absorption (400–800 nm) enables the high scintillation relative integral area (171% relative to commercial Bi4Ge3O12 single crystal). Therefore, the Tb3+-doped SF glass will be one of the promising alternatives for scintillator-based indirect-type X-ray detectors.

Slower Auger Recombination in 12-Faceted Dodecahedron CsPbBr3 Nanocrystals.

Over the past two decades, intensive research efforts have been devoted to suppressions of Auger recombination in metal-chalcogenide and perovskite nanocrystals (PNCs) for the application of photovoltaics and light emitting devices (LEDs). Here, we have explored dodecahedron cesium lead bromide perovskite nanocrystals (DNCs), which show slower Auger recombination time compared to hexahedron nanocrystals (HNCs). We investigate many-body interactions that are manifested under high excitation flux density in both NCs using ultrafast spectroscopic pump-probe measurements. We demonstrate that the Auger recombination rate due to multiexciton recombinations are lower in DNCs than in HNCs. At low and intermediate excitation density, the majority of carriers recombine through biexcitonic recombination. However, at high excitation density (>1018 cm-3) a higher number of many-body Auger process dominates over biexcitonic recombination. Compared to HNCs, high PLQY and slower Auger recombinations in DNCs are likely to be significant for the fabrication of highly efficient perovskite-based photonics and LEDs.

Donor Extension on Spiro‐Acridine Enables Highly Efficient TADF‐OLEDs with Relieved Efficiency Roll‐Off

AbstractOrganic light emitting diodes based on thermally activated delayed fluorescent (TADF) emitters with both high external quantum efficiency (EQE) and low efficiency roll‐off are under urgent pursuing. Three TADF emitters based on fluorene‐spiro‐acridine derivatives as donors are developed. Composing of rigid donor and acceptor, all emitters exhibit high PLQYs of 96–99%. Direct conjugation attached on acridine offers an enhanced reverse intersystem crossing (kRISC) in IA‐TRZ, while the extension via spiro‐junction accelerates the radiative decay rate (kr) in 2S‐TRZ and IT‐TRZ. Remarkably, all emitters enable high electroluminescent performance with EQE of 35.6% for 2S‐TRZ, 36.1% for IT‐TRZ and 32.0% for IA‐TRZ, respectively, and very high luminance of up to 100 000 cd m−2. Surprisingly, 2S‐TRZ and IT‐TRZ that hold larger kr and smaller kRISC than that of IA‐TRZ exhibit more relieved efficiency roll‐off, indicating the significance of kr. More importantly, IT‐TRZ with a moderate kr and kRISC among these emitters shows the lowest roll‐off which demonstrates that the comprehensive consideration of all photophysical processes is important to attain excellent devices. It also emphasizes the molecular modulation method through side group that can induce elaborate control on decay channels for finely optimizing emitters. This study can provide a useful perspective in designing practical emitters.

Red‐Emitting Organic–Inorganic Hybrid Manganese(II) Halides for X‐Ray Imaging

AbstractLow‐dimensional organic–inorganic hybrid manganese(II) halides are emerging as a highly promising class of candidate materials for X‐ray imaging due to their excellent radioluminescence performance. Here, a red‐emitting (Gua)2MnCl4 (Gua = guanidine, CH6N3+) single crystal scintillator grown by a simple solution‐processing method is reported. (Gua)2MnCl4 crystallizes into a zero‐dimensional (0D) crystal structure consisting of trimeric [Mn3Cl12]6− units. It has a high PLQY of 76% and a large Stokes shift of 125 nm. (Gua)2MnCl4 flexible scintillation screen demonstrates a decent X‐ray detection limit of 145.3 nGyair s−1 and a superior imaging resolution of 8 lp mm−1. These results highlight the potential of low‐dimensional red‐emitting Mn‐based hybrids for X‐ray imaging applications.

Supermolecule-assisted synthesis of perovskite nanorods with high PLQY for standard blue emission.

We fabricated CsPbBr3 nanorods with standard blue emission (462 nm) and a high PLQY of ∼90% with the assistance of supermolecules. The β-CD works as a co-ligand and confine the isotropic growth of the nanocrystals to produce anisotropic nanorods. The strong coordination between β-CD and Pb favors the improvement of the PLQY and stability.

Continuous synthesis of all-inorganic low-dimensional bismuth-based metal halides Cs4MnBi2Cl12 from reversible precursors Cs3BiCl6 and Cs3Bi2Cl9 under phase engineering

Continuous synthesis of all-inorganic, low-dimensional, bismuth-based metal halides Cs4MnBi2Cl12 with high PLQY from reversible precursors Cs3BiCl6 and Cs3Bi2Cl9 under phase engineering and application of an orange light source.

Optimizing the horizontal dipole orientation and dipole–dipole interaction of thermally activated delayed fluorescence emitters for high efficiency and low roll-off red OLEDs

Three TADF molecules are developed with high PLQYs and red-shifted EL. By changing the dipole moment of the host, high efficiency and low roll-off red OLEDs are achieved.

Diverse CsPbI3 assembly structures: the role of surface acids.

Surface ligand engineering, seed introduction and external driving forces play major roles in controlling the anisotropic growth of halide perovskites, which have been widely established in CsPbBr3 nanomaterials. However, colloidal CsPbI3 nanocrystals (NCs) have been less studied due to their low formation energy and low electronegativity. Here, by introducing different molar ratios of surface acids and amines to limit the monomer concentration of lead-iodine octahedra during nucleation, we report dumbbell-shaped CsPbI3 NCs obtained by the in situ self-assembly of nanospheres and nanorods with average sizes of 89 nm and 325 nm, respectively, which showed a high photoluminescence quantum yield of 89%. Structural and surface state analyses revealed that the strong binding of benzenesulfonic acid promoted the formation of a Pb(SO3-)x-rich surface of CsPbI3 assembly structures. Furthermore, the addition of benzenesulfonic acid increases the supersaturation threshold and the solubility of PbI2 in a high-temperature reaction system, and controls effectively the lead-iodine octahedron monomer concentration in the second nucleation stage. As a result, the as-synthesized CsPbI3-Sn NCs exhibited different assembly morphologies and high PLQYs, among which the role of sulfonate groups can be further verified by UV absorption and surface characteristics. The strategy provides a new frontier to rationally control the surface ligand-induced self-assembly structures of perovskites.

Deciphering the roles of ammonium doping for lead-free (NH4)xCs3-xCu2I5 perovskites to regulate the photoelectronic properties.

Inorganic ammonium (NH4+) is the simplest amine cation with perfect symmetry, the smallest radius and many H atoms, allowing itself to be used as a potential dopant in achieving high-quality perovskite materials. As a composition-modulation strategy, NH4+-doped (NH4)xCs3-xCu2I5 (0 < x < 1.5) lead-free perovskites were successfully synthesized via the eco-friendly ball milling method in this work. As the ammonium content increases, the lattice constants of (NH4)xCs3-xCu2I5 shrink and the grain sizes increase. The doping of NH4+ effectively passivates the lattice defects, suppresses the non-radiative recombination and tunes the energy band structure, resulting in better fluorescence properties. UV-pumped deep-blue LEDs based on (NH4)xCs3-xCu2I5 phosphors were fabricated, which showed improved performance and tunable emission. These results demonstrate the potential of the NH4+-doping strategy for improving the performance of lead-free perovskite optoelectronics.

Molecular engineering with triptycene groups endows homoleptic Ir(iii) complexes with enhanced electroluminescence properties

Complex Ir2 exhibited a high PLQY of 0.87, a Td of 445 °C and a peak EQE of 27.5%.

Efficient narrow green organic light-emitting diodes with low efficiency roll-offs based on iridium(iii) complexes containing indolo[3,2,1-jk]carbazole and pyrimidine units

Two green Ir(iii) complexes based on the ligands containing indolo[3,2,1-jk]carbazole and pyrimidine units show high PLQYs and small FWHMs. The OLEDs show good performances with an EQEmax of 31.3% and extremely low efficiency roll-offs.

Photoluminescence properties of InP/GaP/ZnS core/shell/shell colloidal quantum dots treated with halogen acids

InP quantum dots (QDs) with low toxicity are considered to be the most promising materials. However, the oxidation problem of In and P has become to the major factor affecting the optical properties of InP QDs. In this work, the effect of luminescence properties of InP/GaP/ZnS QDs with halogen acid treatment have been studied. The results show that HF and HCl are beneficial to improve the optical properties of QDs, HBr especially HI are not conductive to promote the photoluminescence quantum yield (PL QY) of QDs. HF and HCl can etch the oxidative layer effectively, the F− and Cl− can also passivate the surface indium dangling bonds in the form of atomic ligands. The proposed model of charge carrier recombination show that the PL QY improved significantly after HA treatment attributed to the recombination of electron-hole pairs through radiative pathways mainly from the conduction band and valence band. The InP QDs with HF treatment has the best luminescence properties with high PL QY of 96%, offering great potential for advanced optoelectronic devices.

Layered array Al2O3-LuAG: Ce composite ceramic phosphors for high-brightness display

Thermally robust and efficient composite ceramic phosphors (CCPs) combined both the merits of matrix and phosphor have received growing interests. However, high matrix content (e.g., Al2O3 >40 wt%) brings diluted activated ion concentration and dropped photoluminescence (PL) quantum yield (QY). Here, a novel layered array Al2O3-LuAG: Ce CCP, where Al2O3 and LuAG: Ce thin layers (10–250 µm) are alternately arranged, was presented. Owing to the special structure, thermal phonons and photons are respectively routed into Al2O3 layers and LuAG: Ce layers, which weakens the influence of Al2O3 and heat accumulation on PL properties. Consequently, it exhibits high PLQY (84.1%) and good thermal conductivity (17.1 W·m−1·K−1). When it is irradiated under high-power density (27.2 W·mm−2) blue laser, the luminous efficiency and lumen-density are promoted to 220 lm·W−1 and 5994 lm·mm−2, respectively. This work provides a promising new microstructure in developing novel phosphor converters for high-brightness laser phosphor display.

Charge transfer of cocrystal complex featuring efficient aggregation-induced emission and self-powered photo-electrochemical photodetector

A novel cocrystal complex CZIPA-AD assembled by twisting D-A molecule 5-(9H-carbazol-9-yl)isophthalic (CZIPA) and acridine (AD) through a facial solution volatilization process is reported. The combination of photophysical investigation and DFT analysis verify a reasonable cooperation of hybridized local and charge transfer (HLCT) and aggregation-induced emission (AIE) character. The orbital overlap on CZIPA (for local excited (LE) state) and orbital spatial separation between CZIPA and AD (for charge transfer (CT) state) satisfy the formation of HLCT character. The presence of AD molecules preclude the formation of π-stacking between the carbazole halves, preventing the quenching of PL emission in the aggregate state. It shows intense orange emission in aggregated solid state with high PLQY of 80% and prolonged PL lifetime of 38.57 ns. A self-powered photo-electrochemical photodetector fabricated from the cocrystal thin film exhibits a remarkable detectivity (4.78 × 1010 Jones) in neutral aqueous solution, which is at lest one order of magnitude higher than other reported inorganic materials measured in alkaline solution with additional bias potential.

Tuning the optical properties of high quantum-yield g-C[formula omitted]N[formula omitted] with the inclusion of ZnS via FRET for high electron–hole recombination

Luminescent polymeric graphitic composites have the potential to be efficient energy converters for sophisticated displays and light sources. Thermal condensation is used to synthesize g-C3N4-ZnS composites. The XRD, and FTIR analyses confirmed the synthesis of the pure host, filler, and composites. FESEM, and TEM images revealed that the ZnS nanosheets were evenly distributed over the g-C3N4 sheets. As a result of ZnS incorporation, the melting point of g-C3N4 has been raised to 748.5 °C, and the thermal stability of gZ has been increased by 27 %. The optimized gZ15 band gap is determined to be 2.98 eV with a crystallite size of 4.2 nm and a micro stain of 35.42 × 10−3. With a purity of 63.4 %, gZ15 demonstrated a significant rate of recombination in the blue region. gZ15 has a high PLQY of 98 % and a FRET efficiency of 92%. All of the improved properties demonstrated that polymeric g-C3N4-ZnS was the optimum materials for usage in the active or emissive layer of optoelectronic devices.