Photoluminescence Quantum Yield Research Articles

Cation-substitution-induced high spectral tunability and thermosensitivity in double halide perovskite Cs2InCl5∙H2O

The advancement of non-contact temperature measurement has brought about significant interest due to its rapid response, broad applicability, and minimal thermal inertia. However, challenges such as spectral peak position modulation, sensitivity improvement, and reliable performance enhancement continue to persist in this field. In this study, a double halide perovskite single-crystal Cs2InCl5∙H2O was synthesized, with the introduction of Bi3+ ions modulating the photoluminescence from orange to blue. Meanwhile, the deep-blue emission peaked at 410 nm, boasting a high photoluminescence quantum yield (PLQY) of nearly 46 % under 340 nm excitation. Furthermore, by incorporating varying concentrations of Bi3+ ions, two distinct emission peaks were generated, facilitating effective signal differentiation for temperature detection. Utilizing the thermal quenching responses of these two emission peaks, a temperature-detection methodology based on the fluorescence intensity ratio (FIR) was developed, using donor-acceptor pair emission as detection signals and self-trapped emission as reference signals. The designed Cs2InCl5∙H2O:0.07Bi3+ exhibits a maximum Sa of 0.082 K-1 and Sr of 3.349 %K−1, respectively. The spectral adjustability and high sensitivity achieved through cation-substitution strategy in this study offer a promising pathway for the development of advanced optical thermometry materials with enhanced performance characteristics.

Blue thermally activated delayed fluorescence excimers with high external quantum efficiency and accelerated reverse intersystem crossing

This study reports for the first time the development of an efficient blue excimer with thermally activated delayed fluorescence (TADF) properties using a multi-resonance TADF-type fused indolo[3,2,1-jk]carbazole-derived compound with a planar structure for facile excimer formation. The blue excimer was efficiently generated by doping the indolo[3,2,1-jk]carbazole-derived emitter at a high doping concentration. The photophysical analysis demonstrated that the photoluminescence quantum yield (PLQY), rate coefficients of reverse intersystem crossing (RISC), and horizontal emitting dipole orientation values were improved by excimer formation in the solid film compared with the monomer-dominant solid film by suppressing the concentration-quenching effect. Specifically, the delayed PLQY increased because of the efficient RISC process at high doping concentrations. Consequently, an enhanced maximum external quantum efficiency of 26.3% was obtained in the excimer device (15 wt%) compared with 15.2% in the monomer prevalent device (1 wt%). Moreover, the excimer device showed a peak wavelength of 473 nm and color coordinate of (0.13, 0.19). This demonstration is the first of excimer TADF organic light-emitting diodes with a blue emission and a high external quantum efficiency of 26.3%.

Synchronously Improved Multiple Afterglow and Phosphorescence Efficiencies in 0D Hybrid Zinc Halides with Ultrahigh Anti-Water Stabilities.

Zero-dimensional (0D) hybrid metal halides have been emerged as room-temperature phosphorescence (RTP) materials, but synchronous optimization of multiple phosphorescence performance in one structural platform remains less resolved, and stable RTP activity in aqueous medium is also unrealized due to serious instability toward water and oxygen. Herein, we demonstrated a photophysical tuning strategy in a new 0D hybrid zinc halide family of (BTPP)2ZnX4 (BTPP = benzyltriphenylphosphonium, X = Cl and Br). Infrequently, the delicate combination of organic and inorganic species enables this family to display multiple ultralong green afterglow and efficient self-trapped exciton (STE) associated cyan phosphorescence. Compared with inert luminescence of [BTPP]+ cation, incorporation of anionic [ZnX4]2- effectively enhance the spin-orbit coupling effect, which significantly boosts the photoluminescence quantum yield (PLQY) up to 30.66% and 54.62% for afterglow and phosphorescence, respectively. Synchronously, the corresponding luminescence lifetime extend to 143.94 ms and 0.308 μs surpassing the indiscernible phosphorescence of [BTPP]X salt. More importantly, this halide family presents robust RTP emission with nearly unattenuated PLQY in water and harsh condition (acid and basic aqueous solution) over half a year. The highly efficient integrated afterglow and STE phosphorescence as well as ultrahigh aqueous state RTP realize multiple anti-counterfeiting applications in wide chemical environments.

Regulating ligand length to improve the PL QY and stability of CsPbCl0.9Br2.1 nanocrystals for LEDs and photoelectric applications

Perovskite luminescent materials have been extensively investigated due to their comprehensive applications for full-color display, lighting, and communication. However, the development of blue-emissive perovskites has seriously lagged behind that of green and red counterparts, primarily because of their low photoluminescence quantum yield (PL QY) and poor stability. Here, we prepared blue-emissive CsPbCl0.9Br2.1 perovskite nanocrystals (PeNCs) and enhanced their QY from 61.3 % to 90.4 % by regulating the chain lengths of ligands. Post-treated PeNCs also exhibit good stability, their PL intensity is maintained at about 90 % after storage at ambient conditions for 10 days. The exciton dynamics results obtained from time-resolved fluorescence spectra and transient absorption spectra show that dodecyldimethylammonium bromide (DDAB), featuring double 12-hydrocarbon chains, is more capable of passivating surface defects and inhibiting non-radiative composites than the other double 8- or double 16-carbon chain ligands, which greatly improved the probability and rate of radiative recombination. Subsequently, the mechanism of ligand chain length regulation on the PL properties and stability of PeNCs was analyzed in terms of ligand-NC surface interaction, ligand polarity, hydrophobicity, and spatial effects. Furthermore, the device based on DDAB-CsPbCl0.9Br2.1 demonstrated stable EL and long operation lifetime, indicating its significant potential as an efficient blue emitter for backlighting in display technologies.

Mechanochromism and aggregation-induced emission in a fluorene-fumaronitrile-based molecular system: The influence of supramolecular control on donor-acceptor interactions

Effective control and reversible switching of solid-state luminescence in organic molecules are crucial for optoelectronic applications. This study presents a novel molecular system based on fluorene-diphenylfumaronitrile-fluorene (FDF), which exhibits mechanochromism and aggregation-induced emission (AIE). The design utilizes fluorene as the donor, leveraging its high photoluminescent quantum yield, thermal stability, and optimal solubility. The diphenylfumaronitrile moiety, used as the acceptor, is characterized by antiparallel dipoles, which align orthogonally with the chromophore's long axis, promoting effective self-assembly and supramolecular control of interchromophore interactions, in association with the cooperative hydrogen bonding of the amide end-functional groups. FDF demonstrates significant mechanochromic properties, in which mechanical stress induces a reversible shift from greenish-yellow to red emission due to alterations in molecular packing and hydrogen bonding. Additionally, FDF exhibits pronounced AIE behavior in DMF/water mixtures, transitioning from non-emissive in DMF to highly fluorescent upon nanoparticle formation. The investigation reveals that the control over donor-acceptor interactions is critical in modulating these luminescent properties, offering potential applications in stress sensing, bioimaging, and optoelectronic devices. These findings provide deeper insights into the molecular mechanisms underlying mechanochromism and AIE, highlighting the dual-functional nature of FDF and its applicability in advanced materials sciences.

Multimode Luminesce Tailoring PMA4Na(In,Sb)Cl8 Organic-inorganic Hybrid Metal Halidevia Rigid Benzene Ring Induced Local Lattice Distortion.

Low dimensional organic-inorganic hybrid metal halide materials have attracted extensive attention due to their superior optoelectronic properties. However, low photoluminescence quantum yields (PLQYs) caused by parity-forbidden transition hinder their further application in optoelectronic devices. Herein, a novel yellow-emitting PMA4Na(In,Sb)Cl8 (C7H10N+, PMA+) low-dimensional OIMHs single crystal with a PLQY as high as 88% was successfully designed and synthesized, originating from the fact that the doping of Sb3+ effectively relaxes the parity-forbidden transition by strong spin-orbit (SO) coupling and Jahn-Teller (JT) interaction. The as-prepared crystal shows an efficient dual emission peaking 495 and 560 nm at low temperature, which are ascribed to different levels of 3P1 → 1S0 transitions of Sb3+ in [SbCl6]3- octahedral caused by JT deformation. Moreover, wide-range luminescence tailoring from cyan to orange can be achieved through adjusting excitation energy and temperature because of flexible [SbCl6]3- octahedral in the PNIC lattice. Based on a relative stiff lattice environment, the 560 nm yellow emission under 350 nm light excitation exhibits abnormal anti-thermal quenching from 8 to 400 K owing to the suppression of non-radiative transition. The multimode luminescence regulation enriches PMA4Na(In,Sb)Cl8 great potential in the field of optoelectronics such as temperature sensing, low temperature anti-counterfeiting and WLED applications.

Full-color biomass carbon dots for high-level information encryption and multi-color light emitting diode applications.

Six biomass carbon dots (BCDs) with adjustable emission from 450 to 680nm under a single wavelength excitation were successfully synthesized from spinach via solvent control strategy. The obtained BCDs show blue, green, yellow, violet, pink, and red emission with high photoluminescence quantum yield (PLQY = 12.68 ~ 30.77%). Detailed characterizations disclose that the tunable-emission mechanism is caused by the synergistic effect of carbon conjugate and surface oxidation degree. Meanwhile, full-color photoluminescence BCDs/PVP powder and BCDs/PVP/PVA films were fabricated by utilizing the prepared BCDs combined with polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA), respectively, which presented excellent high-level information encryption application. Importantly, multi-color and white light-emitting diode (LED) with Commission Internationale de L' Eclairage (CIE) of blue (0.25, 0.29); green (0.25, 0.31); yellow (0.42, 0.45); red (0.52, 0.31); and white (0.32, 0.31) were achieved by only using our prepared BCDs. This work provides a valuable strategy of preparing multi-color BCDs using readily available biomass materials and paves a way for high-level information encryption and LED applications.

Room-Temperature Persistent Phosphorescence of Aggregated Gold Nanoclusters under Molecular Crystal Confinements.

We report color-tunable and solvent-processable persistent fluorescence to phosphorescence switching at room temperature by doping gold nanoclusters (AuNCs) inside molecular crystals. This provides a significant insight into the tunability of the photoluminescence property of the dopant depending on the crystal environment and compactness of confinement, with the possibility of energy transfer from crystal to aggregated AuNCs. For test cases, we have doped histidine-stabilized AuNCs (HIS-AuNCs) inside histidine (HIS-AuNCs-HIS) and isophthalic acid (HIS-AuNCs-IPA) crystals, respectively, and glutathione-stabilized AuNCs (GSH-AuNCs) inside histidine crystals (GSH-AuNCs-HIS). The maximal phosphorescence decay time recorded for crystal doped aggregated AuNCs was 9.38 ms, and the photoluminescence quantum yield value was measured as 25%. The possible energy states and potential interactions between aggregated NCs and host crystals were accounted for through density functional theory calculations and docking techniques, respectively. This finding opens new possibilities for designing and producing color-tunable persistent AuNC-based luminous crystals for multilayer information encryption, display, and biological applications.

Exciton-harvesting enabled efficient charged particle detection in zero-dimensional halides

Materials for radiation detection are critically important and urgently demanded in diverse fields, starting from fundamental scientific research to medical diagnostics, homeland security, and environmental monitoring. Low-dimensional halides (LDHs) exhibiting efficient self-trapped exciton (STE) emission with high photoluminescence quantum yield (PLQY) have recently shown a great potential as scintillators. However, an overlooked issue of exciton-exciton interaction in LDHs under ionizing radiation hinders the broadening of its radiation detection applications. Here, we demonstrate an exceptional enhancement of exciton-harvesting efficiency in zero-dimensional (0D) Cs3Cu2I5:Tl halide single crystals by forming strongly localized Tl-bound excitons. Because of the suppression of non-radiative exciton-exciton interaction, an excellent α/β pulse-shape-discrimination (PSD) figure-of-merit (FoM) factor of 2.64, a superior rejection ratio of 10−9, and a high scintillation yield of 26 000 photons MeV−1 under 5.49 MeV α-ray are achieved in Cs3Cu2I5:Tl single crystals, outperforming the commercial ZnS:Ag/PVT composites for charged particle detection applications. Furthermore, a radiation detector prototype based on Cs3Cu2I5:Tl single crystal demonstrates the capability of identifying radioactive 220Rn gas for environmental radiation monitoring applications. We believe that the exciton-harvesting strategy proposed here can greatly boost the applications of LDHs materials.

Regulation of Brightness Attributes of High-Stability Carbon Quantum Dots Applicable in LED Digital Color Display.

Fluorescent carbon dots (CDs) attract much attention due to high stability and low toxicity. For high brightness, multi-color emission and fluorescence stability, polystyrene (PS)/CDs composite films were prepared. First, three types of CDs and three PS/CDs films were prepared. Then, three light-emitting-diode (LED) devices were achieved. Compared to CDs solutions, CDs filled films show almost unchanged photoluminescence (PL) spectra. PL peaks of blue, green and red films appear at 462nm, 544nm and 603nm, separately. Blue CDs lead to highest photoluminescence quantum yields (PLQYs) of 76% (solution) and 49% (film). A certain level of thermal stability and fluorescent reversibility of blue film were verified. After 60 days of air exposure, PL intensities of blue and green films reach 97% and 93% of original values, separately. Improving work time cannot vary PL wavelengths of devices. For blue-emitted device, PL intensity reaches 55% of original value after working for 600min. For green-emitted device, PL intensity reaches 80% after working for 300min. The novelty is effective PS encapsulation and uniform dispersion of CDs to yield favorable fluorescence properties of devices. This work inspires ideas for large-scale preparation of fluorescent films for LED digital color display.

Revelation of room temperature liquid crystallinity and yellow-orange electroluminescence (EQE>7%) in a columnar self-assembled N-annulated perylene bisimide

The synthesis of highly fluorescent compounds is a critical necessity to facilitate cost-effective and metal-independent production of organic light-emitting diodes (OLEDs). This investigation introduces a readily soluble, electron-deficient N-annulated perylene bisimide (PBI-NST) equipped with a swallow tail, exhibiting room temperature columnar oblique mesophase with a low clearing point and high photoluminescence quantum yield, positioning it as a promising candidate for efficient OLEDs. Leveraging the luminescent properties of PBI-NST, a series of OLED devices were fabricated with PBI-NST as the sole emitter and at various concentrations in CBP host material. Impressively, doped devices employing the compound at 0.5 wt% emitter within the host material CBP displayed an exceptional external quantum efficiency (EQE) of 7.2 %, accompanied by a luminance of 2689 cd/m2. Further, a voltage dependent emission tuning was also noticed. The notable increase in EQE is mainly attributed to the contributions of hybrid local and charge transfer (HLCT) and triplet–triplet annihilation (TTA) process. The substantial enhancement in EQE marks a significant advancement in the application of multifunctional columnar self-assembled materials for OLED development.

Biexciton Emission in CsPbBr3 Nanocrystals: Polar Facet Matters.

The metal halide perovskite nanocrystals exhibit a remarkable tolerance to midgap defect states, resulting in high photoluminescence quantum yields. However, the potential of these nanocrystals for applications in display devices is hindered by the suppression of biexcitonic emission due to various Auger recombination processes. By adopting single-particle photoluminescence spectroscopy, herein, we establish that the biexcitonic quantum efficiency increases with the increase in the number of facets on cesium lead bromide perovskite nanocrystals, progressing from cube to rhombic dodecahedron to rhombicuboctahedron nanostructures. The observed enhancement is attributed mainly to an increase in their surface polarity as the number of facets increases, which reduces the Coulomb interaction of charge carriers, thereby suppressing Auger recombination. Moreover, Auger recombination rate constants obtained from the time-gated photon correlation studies exhibited a discernible decrease as the number of facets increased. These findings underscore the significance of facet engineering in fine-tuning biexciton emission in metal halide perovskite nanocrystals.

Vacancy Effect on the Luminescent and Water Responsive Properties of Vacancy-ordered Double Perovskite Derivatives.

Vacancy-ordered perovskites and derivatives represent an important subclass of hybrid metal halides with promise in applications including light emitting devices and photovoltaics. Understanding the vacancy-property relationship is crucial for designing related task-specific materials, yet research in this field remains sporadic. For the first time, we use the Connolly surface to quantitatively calculate the volume of vacancy (V□, □ = vacancy) in vacancy-ordered double perovskite derivatives (VDPDs). A relationship between void fraction and the structure, photoluminescent properties and humidity stability was established based on zero-dimensional (0-D) [N(alkyl)4]2Sb□Cl5□'-type VDPDs. Compared with the more commonly studied A2M(IV)X6□-type double perovskite (A = cation, M = metal ion, X = halide), [N(alkyl)4]2Sb□Cl5□' features double vacancy sites. Our results demonstrate an inverse relationship between the photoluminescent quantum yield and V□ in 0-D VDPDs. Additionally, structural transformation from A2SbCl5 to A3Sb2Cl9 was first reported, during which the novel 'gate-opening' gas adsorption phenomenon was observed in VDPDs for the first time, as evidenced by 'S'-shaped sorption isotherms for water vapor, indicating a cation-controlled water-vapor response behavior. A mixed-cation strategy was developed to modulate the humidity stability of VDPDs. Characterized by controllable water-responsive behavior and unique 'on-off-on' luminescent switching, A2M(III)□X5□'-type materials show great promise for multi-level information anti-counterfeiting applications.

Isomeric Effects of Au28(S-c-C6H11)20 Nanoclusters on Photoluminescence: Roles of Electron-Vibration Coupling and Higher Triplet State.

The exploration of near-infrared photoluminescence (PL) from atomically precise nanoclusters is currently a prominent area of interest owing to its importance in both fundamental research and diverse applications. In this work, we investigate the near-infrared (NIR) photoluminescence mechanisms of two structural isomers of atomically precise gold nanoclusters of 28 atoms protected by cyclohexanethiolate (CHT) ligands, i.e., Au28i(CHT)20 and Au28ii(CHT)20. Based on their structures, analysis of 3O2 (triplet oxygen) quenching of the nanocluster triplet states, temperature-dependent photophysical studies, and theoretical calculations, we have elucidated the intricate processes governing the photoluminescence of these isomeric nanoclusters. For Au28i(CHT)20, its emission characteristics are identified as phosphorescence plus thermally activated delayed fluorescence (TADF) with a PL quantum yield (PLQY) of 0.3% in dichloromethane under ambient conditions. In contrast, the Au28ii(CHT)20 isomer exhibits exclusive phosphorescence with a PLQY of 3.7% in dichloromethane under ambient conditions. Theoretical simulations reveal a larger singlet (S1)-triplet (T1) gap in Au28ii than that in Au28i, and the higher T2 state plays a critical role in both isomers' photophysical processes. The insights derived from this investigation not only contribute to a more profound comprehension of the fundamental principles underlying the photoluminescence of atomically precise gold nanoclusters but also provide avenues for tailoring their optical properties for diverse applications.

Microwave synthesis of composite of AgInS2 quantum dots and zeolitic imidazolate framework-8 for application in white light emitting diodes

Preparation of AgInS2 quantum dots (AIS QDs) with high photoluminescence quantum yield (PLQY) and thermal stability remains an important challenge. In this paper, AIS QDs were successfully introduced into zeolitic imidazolate framework-8 (ZIF-8) by microwave-assisted hydrothermal method. Due to the effective isolation of the ZIF-8, the AIS QDs avoid the concentration quenching when they were assembled into white light emitting diodes (WLEDs) devices as color conversion materials. More importantly, the generation of ZnS layer between the interfaces of AIS QDs and ZIF-8 can efficiently improve the optical performance of AIS QDs, resulting in the fluorescence lifetime extended to 470.05 ns. Meanwhile, the PLQY of AIS/ZIF-8 composite reached up 34.30 % when microwave hydrothermal heating at 120 °C for 60 min with AgIn/Zn=1/3, which was higher than that of the pristine AIS QDs as 25.30 %. Finally, the WLED devices were fabricated by combining AIS/ZIF-8 composite fluorescent powder with (Ba, Sr)Si2O2N2:Eu2+ phosphors and blue LED. At 20 mA, the AIS/ZIF-8 based WLED shows the luminous efficiency (LE) of 44.54 lm/W, correlated color temperature (CCT) of 4242 K and color rendering index (CRI) of 89.1. Moreover, the Commission International de L'Eclairage (CIE) was (0.36, 0.35), indicating the WLED emited warm white light. The present strategy aims at enhancing the optical performance of AIS QDs, which also may trigger the development of QDs-based WLED.

Metal/Covalent Organic Framework Encapsulated Lead-Free Halide Perovskite Hybrid Nanocatalysts: Multifunctional Applications, Design, Recent Trends, Challenges, and Prospects.

Perovskites are bringing revolutionization in a various fields due to their exceptional properties and crystalline structure. Most specifically, halide perovskites (HPs), lead-free halide perovskites (LFHPs), and halide perovskite quantum dots (HPs QDs) are becoming hotspots due to their unique optoelectronic properties, low cost, and simple processing. HPs QDs, in particular, have excellent photovoltaic and optoelectronic applications because of their tunable emission, high photoluminescence quantum yield (PLQY), effective charge separation, and low cost. However, practical applications of the HPs QDs family have some limitations such as degradation, instability, and deep trap states within the bandgap, structural inflexibility, scalability, inconsistent reproducibility, and environmental concerns, which can be covered by encapsulating HPs QDs into porous materials like metal-organic frameworks (MOFs) or covalent-organic frameworks (COFs) that offer protection, prevention of aggregation, tunable optical properties, flexibility in structure, enhanced biocompatibility, improved stability under harsh conditions, consistency in production quality, and efficient charge separation. These advantages of MOFs-COFs help HPs QDs harness their full potential for various applications. This review mainly consists of three parts. The first portion discusses the perovskites, halide perovskites, lead-free perovskites, and halide perovskite quantum dots. In the second portion, we explore MOFs and COFs. In the third portion, particular emphasis is given to a thorough evaluation of the development of HPs QDs@MOFs-COFs based materials for comprehensive investigations for next-generation materials intended for diverse technological applications, such as CO2 conversion, pollutant degradation, hydrogen generation, batteries, gas sensing, and solar cells. Finally, this review will open a new gateway for the synthesis of perovskite-based quantum dots.

Chlorine passivation of PbS quantum dots in all solid glass matrix for high efficiency luminescence

Lead sulfide quantum dots (PbS QDs) show great potential application in near infrared range, and incorporation of PbS QDs into all solid glass matrix improves both their chemical and thermal stabilities as well as the shaping ability. However, the incorporation of PbS QDs into all solid glass matrix makes it difficult to modify their surface, resulting in the relatively low absolute photoluminescence quantum yield (PL QY) caused by the surface defects. Here, PbS QDs with tunable photoluminescence band in near-infrared range in silicate glasses were prepared by melting-quenching method. By addition of chloride and forming PbClx shell around PbS QDs in glass, defects induced by surficial lead ions of above PbS QDs can be effectively passivated, reducing subsequent trapping of photo-generated electrons accordingly. PL QY of PbS QDs inbuilt glasses is enhanced eventually and achieved as high as 49.3 %. Furthermore, thermo- and photo-stabilities of PbS QDs in glass are greatly improved compared with those without surface chlorine passivation. These high performance PbS QDs embedded glasses with excellent stability show significant potential in light-emitting diodes, lasers and fiber amplifiers in near-infrared range.

Mechanism of quantum yield enhancement in Si quantum dots by high-pressure water vapor annealing from single-dot studies

High-pressure water vapor annealing (HWA) was recently demonstrated as a method that can substantially improve the photoluminescence quantum yield (PLQY) of silicon quantum dots (Si QDs) with the oxide shell. In this Letter, the mechanism of this enhancement is studied optically on a single-dot level. HWA treatment is performed on Si QDs formed on a silicon-on-insulator wafer, and their photoluminescence (PL) properties were examined before and after the treatment. Our experiments show a 2.5 time enhancement in the average blinking duty cycle of Si QDs after 2.6 MPa HWA treatment without changing the average ON-state PL intensity. This observation proves the carrier trapping process is suppressed on the HWA-built Si/SiO2 interface. We also discussed the mechanism behind the PLQY enhancement of HWA-treated Si QDs by comparing single-dot-level data to reported ensemble PL Si QDs results. HWA treatment is found to mainly brighten “grey” (not 100% efficient) QDs, a mechanism different from changing dark (non-emitting) to bright (100% efficient) Si QDs by ligand passivation.

Tweaking the structure and symmetry of Y2B2O7:Eu3+ by B-site engineering for efficient and thermally stable phosphor: Y2Zr2O7 versus Y2Ge2O7

There is an urgent need for synthesizing red emitting phosphor with high photoluminescence quantum yield (PLQY) and good thermal stability for high performing phosphor converted light emitting diodes (pc-LEDs) which are in demand to mitigate carbon emission. Here we have achieved the same through symmetry alteration and structural modification strategy which leads to high PLQY and improved thermal stability. In this work we have synthesized highly symmetric cubic fluorite Y2Zr2O7:Eu3+pyrochlore and replacing the B-site Zr4+by Ge4+ to lower the symmetry and induce structural change to tetragonal Y2Ge2O7:Eu3+ by organic solvent free solid state reactions. Among the three composition Y2Ge2O7: Eu is exhibiting higher emission intensity, higher asymmetry ratio and enhanced PLQY (32.3 %) by virtue of lower symmetry of tetragonal phase. On the other hand, higher thermal stability was achieved for Y2Zr2O7: Eu (97 % at 450 K) endowed by higher structural integrity and stability of pyrochlore phase.

Mechanochromic luminescent material with high quantum yield for multi-mode anti-counterfeiting applications

The multi-mode anti-counterfeiting materials, constructed by mechanochromic luminescent materials with high quantum yield, can effectively prevent illegal counterfeiting, but their design and construction still present significant challenges. Herein, a twisting D-A-D conjugated molecule, FBtF, is obtained with a special hybridized local and charge transfer excited state, and shows approximately 100 % photoluminescence quantum yield in the coating film. The self-assembled FBtF microplates exhibit bathochromic-shifted emission from green to orange, accompanied by the photoluminescence quantum yield increase from 47.8 % to 89.0 % upon grinding, which is the highest in reported MCL materials, to the best of our knowledge. In contrast, a D-π-D type molecule (FBenF) and a D-D’-D molecule (FAnF) maintain the blue-emission after grinding. Through mechanistic investigation, the force-induced molecular conformational planarization and the breakage of the intermolecular charge transfer collaboratively lead to the emission-color change and photoluminescence quantum yield increase. The FBtF microplates are designed as ink for anti-counterfeiting applications based on multi-mode output signals, including the UV light-excited image and the grinding-induced emission color change together with the photoluminescence quantum yield increase. The written tags exhibit high stability in various harsh environments, and demonstrate superior anti-counterfeiting performance in practical applications, such as medicine anti-counterfeiting.