High PLQY Research Articles

A highly Mn2+-doped narrowband green phosphor toward wide color-gamut display applications

The highly doped phosphor La0.827Al11.9O19.09:Mn2+ exhibits intense green emission with a narrow FWHM, high PL QY and excellent thermal stability, which confer great potential for wide-color gamut LCD backlight applications.

A universal supramolecular assembly strategy for achieving efficient tunable white emission and anti-counterfeiting in antimony doped tin(iv)-based vacancy-ordered double perovskites

Three compounds with high PLQY, (AC)2SnCl6:Sb3+ (A = K, Rb, and Cs), were developed using a supramolecular assembly strategy. The samples doped with Sb3+ were used to achieve tunable WLEDs, anti-counterfeiting, and information encryption.

Synergistic engineering of the Stokes shift for highly efficient and stable quasi-2D perovskite luminescent solar concentrators

Three new quasi-2D perovskite/PVDF composite films with a high PLQY and large Stokes shift are obtained, PEA2MAx−1PbxBr3x+1/PVDF (x = 2, 3, 4) (PMx−1PF). Among them, the LSC based on PM2PF exhibits a remarkable ηext of up to 4.9%.

Encapsulated TADF macrocycles for high-efficiency solution-processed and flexible organic light-emitting diodes.

Macrocyclic thermally activated delayed fluorescence (TADF) emitters have been demonstrated to realize high efficiency OLEDs, but the design concept was still confined to rigid π-conjugated structures. In this work, two macrocyclic TADF emitters, Cy-BNFu and CyEn-BNFu, with a flexible alkyl chain as a linker and bulky aromatic hydrocarbon wrapping units were designed and synthesized. The detailed photophysical analysis demonstrates that the flexible linker significantly enhances the solution-processibility and flexibility of the parent TADF core without sacrificing the radiative transition and high PLQY. Moreover, benefiting from sufficient encapsulation of both horizontal and vertical space, the macrocyclic CyEn-BNFu further isolated the TADF core and inhibited the aggregation caused quenching, which benefits the utilization of triplet excitons. As a result, the non-doped solution-processed OLEDs based on CyEn-BNFu exhibit high maximum external quantum efficiencies (EQE) up to 32.3%, which were 3 times higher than those of the devices based on the parent molecule. In particular, these macrocyclic TADF emitters ensure the fabrication of flexible OLEDs with higher brightness, color purity and bending resistance. This work opens a way to construct macrocyclic TADF emitters with a flexible alkyl chain linker and highlights the benefits of such encapsulated macrocycles for optimizing the performance of flexible solution-processed devices.

Enhanced narrow green emission via efficient energy transfer from Eu2+ to Mn2+ in KAl4Ga7O17 for backlit LCD displays

Nearly single-band and high PLQY narrow-green-emitting phosphor was obtained by constructing efficient Eu2+ → Mn2+ energy transfer in the KAl4Ga7O17 host.

Enabling efficient near-infrared emission in lead-free double perovskite via a codoping strategy

The codoping of Ln3+ (Ln = Yb, Nd) in the Cs2NaInCl6:Sb3+ host not only produces PL components from visible to near-infrared regions, but also achieves a high near-infrared PLQY of ∼48.95%.

Zero-dimensional organic–inorganic hybrid indium halide perovskite with broadband yellow light emission

0D indium halide [1-Me-Pipz]2[InCl6]Cl·H2O exhibits strong broadband yellow emission with a high PLQY of 52%. This crystal also demonstrated excellent structural and spectral stability, allowing its use in efficient white light-emitting diodes.

Facile synthesis of phase-adjustable CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> composite nanocrystals and <i>in-situ</i> study of phase transformation process

All-inorganic cesium lead halide perovskites have shown great potential applications in optoelectronic field due to their fascinating optical properties. Although perovskite materials have achieved great success in various fields, their inherent ionic properties and high dynamic surface properties have led to their poor stability, hindering their applications. The preparation of CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals has proven to be an effective strategy to enhance their photoluminescence properties and stability. Herein, we report an easy synthesis of CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals with a diphase structure at room temperature by using Cs-OA, Pb-OA and TOABr as precursors in toluene. It is found that the phase transformation and the relative composition between CsPbBr<sub>3</sub> and Cs<sub>4</sub>PbBr<sub>6</sub> are dependent on the concentration of TOABr and the ratio of Cs/Pb. The <i>in-situ</i> PL experiments reveal that the formation of ~12 nm CsPbBr<sub>3</sub> nanocubes experiences the fast nucleation, the focusing growth of size-distribution in early growth stage and Ostwald ripening growth in the later stage at a TOABr concentration of 0.16 mmol. With the increase of concentration of TOABr or molar ratio of Cs/Pb > 1 (Cs/Pb < 1), [PbBr<sub>4</sub>]<sup>2–</sup> complex and [PbBr<sub>3</sub>]<sup>–</sup> complex can coexist and compete with each other in toluene, and the CsPbBr<sub>3</sub> nucleations dominate in the early stage, then CsPbBr<sub>3-</sub>Cs<sub>4</sub>PbBr<sub>6</sub> nanocomposites are gradually formed on CsPbBr<sub>3</sub> nucleations as photoluminescence centers due to the continuous generation of [PbBr<sub>4</sub>]<sup>2–</sup> complex between TOABr and Pb<sup>2+</sup>. The relative composition of Cs<sub>4</sub>PbBr<sub>6</sub> in CsPbBr<sub>3-</sub>Cs<sub>4</sub>PbBr<sub>6</sub> nanocomposites can be improved from 4% to 85% with the concentration of TOABr increasing or Cs/Pb < 1. The optimized CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> composite nanocrystals possess high PLQY and stability. Our work provides an understanding of the mechanism of phase transformation in cesium lead halide perovskite materials.

The isomeric effect of thienopyridazine-based iridium complexes

Complex IrM exhibited a high PLQY of 0.99, a Td of 425 °C and a peak EQE of 26.7%.

One-dimensional hybrid copper halides with high-efficiency photoluminescence as scintillator.

A new one-dimensional hybrid [APCHA]Cu2I4 was designed and applied as an X-ray scintillator. It exhibits broad-band green emission with a high PLQY of 74.80% and excellent stability. It demonstrates radioluminescence property with a light yield of 28 336 photons MeV-1, detection limit of 41 nGyair s-1, and high spatial limit of 13.95 lp mm-1 in X-ray imaging.

Elucidating The Horizontal Orientation Mechanism of Emissive Transition Dipole Moment in A Series of Stick‐Like Delayed Fluorescent Emitters for Ultra‐High‐Efficiency OLEDs

AbstractThe horizontal orientation of the emissive transition dipole moment (TDM) of emissive molecules is a crucial factor in improving the efficiency of organic light‐emitting diodes (OLEDs). However, the mechanism of this horizontal orientation remains unclear. Herein, to elucidate the horizontal orientation mechanism of the TDM of the molecules in thermally activated delayed fluorescent (TADF) emitters, the relationship between the horizontal orientation ratio (Θ) of the TDM and the key parameters of stick‐like TADF emitters dispersed in carbazole‐based host materials is systematically and quantitatively investigated. The introduction of functional groups containing weak CH/n (n = O, N) hydrogen bonds into the host material is found to significantly increase the Θ values up to 30%. The physical parameters of the dispersed emitter exhibit a strong relationship with the Θ values, with the following influence order: glass transition temperature (Tg) ≥ total surface area of the largest π‐plane and the corresponding parallel π‐plane > molecular weight > aspect ratio > permanent dipole moment. The Tg value of the host material is another key parameter determining the Θ values. By using a P=O‐based host material, namely mCP2PO, a high PLQY of 97%, a high Θ value of 88%, and a sky‐blue OLED with an EQE of 37.6% are simultaneously realized.

Organic hybrid tetranuclear clusteroluminogens: Blue-light-excitable LED with ultrahigh luminous efficacy

The development of highly emissive luminescent materials is vital for future light-emitting diodes, display, and scintillation applications. A series of novel organic hybrid metal halide clusters are presented here, that is, non-emission (C4H12N2)3(NH4)4Cd4Cl18 (namely, 1), pink-emission (C4H12N2)3(NH4)4Mn4Cl18 (namely, 2) and 1–2 alloy (namely, Mn-1). The crystal structure of alloy compound provides a clear insight into the Mn(II) effect. Mn(II) alloying in the host lattice successfully induces large octahedral distortion, hybrid of d/p orbitals and lower local symmetry resulting in a breaking d-d forbidden transition. The intense blue light absorption and high PLQY (92.6 %) inspire us to assemble Mn-1 as a blue-light-excited white light-emitting diode (WLED). The WLED has a minimized trade-off among luminous efficacy (182 lm/W), color-rendering index (82) and CCT (4536 K), which is achieved by the trichromatic combination (blue light chip, green (Ba, Sr)2SiO4:Eu2+, red Mn-1) and the red emission edge below 700 nm. The luminous efficacy of 182 lm/W is the highest among the previous WLEDs based on the lead-free metal halides, comparable to the market standard (185 lm/W) in 2020 set by The United States Department of Energy. In addition, the water-soluble Mn-1 further gives potential applications in X-ray scintillators, luminescent ceramics, flexible films and luminescent imaging agents. The discovery of tetranuclear metal halide clusters establishes a new strategy for constructing promising emissive materials.

Stable two-dimensional tin-based perovskites for warm-white light emitters

Two-dimensional (2D) Sn-based organic-inorganic hybrid perovskites are useful materials for white light emitters due to their super high fluorescence efficiency and higher stability when compared to their three-dimensional (3D) counterparts. Herein, 2D Ruddlesden-Popper (RP) perovskites (BA)2Sn(Br1-x Ix)4 (BA = n-butylammonium, x: 0–1) were prepared and regulated using halogen doping. As iodine content increased, the band gap of (BA)2Sn(Br1-xIx)4 was finely regulated from 2.35 eV to 2.0 eV, thereby tuning the photoluminescence from yellow to red with relatively high PLQY exceeding 40 %. The use of small amounts of Pb2+ to stabilize Sn2+ through the addition of PbO in the precursor solution resulted in high air- and photo stable (BA)2Pb0.1Sn0.9(Br–I)4 phosphors with bright yellow to red light. The mixture with (BA)2PbBr4 (blue light phosphor) followed by excitement by UV LED chips (285 nm) resulted in cold and warm white Sn–Br–I perovskite LEDs. The CIE coordinates and correlated color temperature (CCT) indicated Br0.4I0.6 LED as an ideal warm-white emitter with suitable CIE (0.352, 0.330) and CCT (4376.3 K). The prepared white LEDs showed high photo and air stability without significant luminescence decay (<5 % relative) under continuous UV light excitation over 200 min and exposure to air for 3 months.

Stable and Highly Luminescent Silver Nanoclusters in the 13X Zeolite Enabled by Mg2+ Doping and Their Luminescence Tuning by Heating Temperature.

Zeolite-confined silver nanoclusters (Ag-zeolite) have aroused vast interest due to their remarkable luminescence. The countercations within a zeolite play critical roles in determining the luminescent properties of the resulting Ag-zeolite. We observed, in this work, that introducing Mg2+ enabled the Ag-13X zeolite a stable and bright yellow emission with a high PLQY of 94.6%, the first report on the luminescence enhancement of the Ag-13X zeolite by Mg2+, to the best of our knowledge. The formation of specific internal electric fields inside 13X and the structural contraction of the zeolite framework due to the high charge density and the small ionic radius of Mg2+ are believed to be responsible for the enhanced stable and bright yellow emission. The stabilization effect of Mg2+ is removed by increasing the heating temperature above 700 °C, which leads to the variation of silver nanoclusters as a result of the framework collapse of the zeolite. The Ag-zeolite synthesized by us, featured with a broad emission band, a high PLQY of 94.6%, and good thermal stability, can be considered a suitable candidate to replace the traditional commercial yellow-emitting phosphor YAG:Ce3+ for light-based applications. This work contributes to a valuable reference for the rational design of silver nanoclusters confined in zeolites with promising new functionalities and stimulates potential applications as novel phosphors for near-ultraviolet light-emitting diodes (NUV-LEDs).

Reprecipitation synthesis and spectroscopic characterization of Cs1−xFAxPbBr3 nanocrystals for backlight display devices

In this study, a new technique called the dual-solvent-assisted reprecipitation (DSAR) was developed for synthesizing high-quality Cs1−xFAxPbBr3 PQDs. This technique eliminated the need for high temperatures, an inert atmosphere, and the hazardous solvent (dimethylformamide). Moreover, XPS analysis of PQDs synthesized using LARP revealed the presence of residual DMF, leading to formation of defects in the PQDs. The Cs0.2FA0.8PbBr3 PQDs synthesized via the DSAR method exhibited a high PLQY of 99% and a bandwidth of 20 nm. The low-temperature photoluminescence results revealed that the PQDs prepared via the LARP method exhibited high nonradiative recombination, whereas PQDs prepared via the DSAR method exhibited weak electron–phonon interaction and high efficiency. The synthesized PQDs were encapsulated to fabricate PQD films. The obtained Cs0.2FA0.8PbBr3 PQD films exhibited high environmental stability, maintaining an initial intensity of 98% for 90 days under ambient conditions. In addition, the PQD films maintained an intensity of 75% for 300 h under conditions of 60 °C and 90% relative humidity. Moreover, the white-light-emitting device combining the synthesized PQD films with commercial K2SiF6:Mn4+ phosphors and blue LED chips achieved rec. 2020 coverage of 96.7%. Overall, the results indicate that the Cs0.2FA0.8PbBr3 PQDs exhibit excellent optical properties and environmental stability for display applications.

Positional Isomeric Cyano-Substituted Bis(2-phenylpyridine)(acetylacetonate)iridium Complexes for Efficient Organic Light-Emitting Diodes with Extended Color Range.

Bis(2-phenylpyridine)(acetylacetonate)iridium, Ir(ppy)2(acac), is a benchmark green emitter for phosphorescent organic light-emitting diodes (PhOLEDs). In this work, we reported three positional isomeric cyano-substituted Ir(ppy)2(acac) complexes, i.e., Ir(3-CN), Ir(4-CN), and Ir(10-CN), with the emission in the yellow to red region (544-625 nm). Through theoretical investigation and single-crystal analysis, it was found that the introduction of cyano substitution at various positions of the ppy ligand allows for tuning the electron distribution and coordination bond length of Ir complexes. Therefore, the charge transfer property of Ir complexes is enhanced such that the energy gap of the cyano-substituted Ir(ppy)2(acac) complexes was reduced. In addition, Ir(3-CN), Ir(4-CN), and Ir(10-CN) exhibited high PLQYs of 83, 54, and 75%, respectively, with the phosphorescence lifetime in the range of 0.79-2.08 μs. Notably, the device utilizing Ir(3-CN) as the emitter exhibited a maximum external quantum efficiency (EQE) of 25.4%, current efficiency of 56.9 cd A-1, power efficiency of 68.7 lm W-1, and brightness of 61,340 cd m-2 at 8 V. The EQE of this device remained 24.3 and 19.9% at luminances of 1,000 and 10,000 cd m-2, corresponding to the efficiency roll-off of 4.3 and 21.7%, respectively. Comparing to the Ir complexes using the ligand with an extended conjugated structure, our results demonstrated a simple molecular design strategy for phosphorescence emitters with reduced molecular weight for efficient PhOLEDs in the yellow to red color region.

One-step synthesis of all-inorganic high-entropy dual-phase Cs‘B’Br3/Cs‘B’2Br5 perovskite nanocrystals by high-energy ball milling

All-inorganic lead halide perovskite nanocrystals (NCs) have attracted considerable attention in field of optoelectronics due to their excellent properties such as high PLQY, tunable emission spectra in visible light region, and narrow emission peaks. However, problems existing in the research of all-inorganic lead halide perovskite materials are high lead content, low stability, and complex synthesis processes. Those problems need to be solved urgently. Therefore, dual-phase Cs‘B’Br3/Cs‘B’2Br5 perovskite material (Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5) was synthesized by doping the B-site of CsPbBr3 and CsPb2Br5 using high-energy ball milling in this thesis. This dual-phase perovskite material has maximum absorption edge of 540 nm, a band gap width of 2.22 eV, the maximum emission peak at 600 nm with FWHM of 72 nm, PLQY of 24.50%, and an average fluorescence lifetime of 227.87 μs. After 21 days at room temperature, luminescent intensity of NCs increased to 156%, and still retained 109% at 120 days. After treatment at 150 °C, luminescent intensity decreased to 47%. Results show that this high-entropy dual-phase perovskite has great stability in different temperature. This proves that synthesis of high-entropy dual-phase halide perovskite by high-energy ball milling is feasible, and has great significance in solving poor stability and high lead content of all-inorganic lead halide perovskite in the future.

Dual Monomeric Inorganic Units Constructed Bright Emissive Zero-Dimensional Antimony Chlorides with Solvent-Induced Reversible Structural Transition.

A5M2X11 and A3M2X9 families (A = monovalent organic cation; M = trivalent metal; X = halogen) are receiving increasing attention because of their combination of easy solution processability and superior ferroelectricity properties. However, synthesizing highly efficient A5M2X11 and A3M2X9-type fluorophores with multiple monomeric inorganic units and achieving their structural interconversion remains challenging. Here, we report two novel zero-dimensional (0D) antimony halides, (C10H16N)5Sb2Cl11·C2H3N (1) and (C10H16N)3Sb2Cl9 (2), which not only contain two distinct [SbXn]3-n units but also have excellent orange (590 nm) and yellow-green emission (540 nm) with high PLQY of 17.7% and 31.5%, respectively. Interestingly, a reversible structural conversion could be triggered by acetonitrile steam stimulation, accompanied by luminescence switching properties. This work not only enriches the structure of hybrid Sb-based halides but also provides the possibility of well-known A5M2X11 and A3M2X9 families as structural transformation materials.

Synthesis and Assembly of Core–Shell Nanorods with High Quantum Yield and Linear Polarization

AbstractThe seeded growth method offers an efficient way to design core–shell semiconductor nanocrystals in the liquid phase. The combination of seed and shell materials offers wide tunability of morphologies and photophysical properties. Also, semiconductor nanorods (NRs) exhibit unique polarized luminescence which can potentially break the theoretical limit of external quantum efficiency in light emitting diodes based on spherical quantum dots. Although rod‐in‐rod core–shell NRs present higher degree of polarization, most studies have focused on dot‐in‐rod core–shell NRs due to the difficulties in achieving uniform NR seeds. Here, this study prepares high‐quality uniform CdSe NRs by improving the reactivity of the Se source, using a secondary phosphine, namely diphenylphosphine, to dissolve the Se power, along with the conventional tertiary phosphine, namely trioctylphosphine. Starting from these high‐quality NR seeds, this study synthesizes CdSe/CdxZn1−xS/ZnS core–shell NRs with narrow emission bandwidth (29 nm at 620 nm), high PLQY (89%) and high linear polarization (p = 0.90). This study then assembles these core–shell NRs using the confined assembly method and fabricates long‐range‐ordered microarrays with programmable patterns and displaying highly polarized emission (p = 0.80). This study highlights the great potential of NRs for application in liquid crystal displays and full‐color light emitting diodes displays.

Understanding optical and structural properties of the CH3NH3PbI3 nanocrystal thin films under humidity conditions

Low-dimensional organic-inorganic hybrid perovskite materials have drawn a lot of interest in optoelectronic applications because of their unique optoelectronic performance in comparison to their bulk counterparts. There is an influence of humidity conditions on the stability of perovskite in both positive and negative ways. The passivation of surface and bulk defects in the thin film of perovskite by the H2O molecules is a positive way. The negative way is that the material's stability will hinder the commercialization of perovskite-based devices. Herein, CH3NH3PbI3 nanocrystals are synthesized by the hot-injection method. The optical and structural properties of the thin film of the synthesized nanocrystals under different humidity conditions are studied through photoluminescence (PL), TRPL, Raman, X-ray diffraction (XRD), UV–Vis, spectroscopic ellipsometry, and FTIR techniques for 4 weeks. The redshift in the PL spectra of the thin film with an increase in PL intensity and carrier lifetime is caused by the shallow trap-assisted radiative recombination and localization of the charge carriers at the interface of the CH3NH3PbI3/water. The XRD, Raman, and FTIR peaks of the thin film are also shifted due to defect formation and structure distortion of the CH3NH3PbI3 crystal lattice. The thin films of these nanocrystals exhibit very high PLQY of 56% and 60% after 5 h and 1 week respectively. The results pave the way to analyse the stability of CH3NH3PbI3 nanocrystals through their optical and structural behaviour under different humidity conditions. The results also reflect that the photoemission of the synthesized material can be tuned by regulating the defect density and the structural deformation of the nanocrystals under controlled humidity conditions.