Quantifying the interfacial triboelectricity in inorganic-organic composite mechanoluminescent materials.

Mechanoluminescence (ML) sensing technologies open up new opportunities for intelligent sensors, self-powered displays and wearable devices. However, the emission efficiency of ML materials reported so far still fails to meet the growing application requirements due to the insufficiently understood mechano-to-photon conversion mechanism. Herein, we propose to quantify the ability of different phases to gain or lose electrons under friction (defined as triboelectric series), and reveal that the inorganic-organic interfacial triboelectricity is a key factor in determining the ML in inorganic-organic composites. A positive correlation between the difference in triboelectric series and the ML intensity is established in a series of composites, and a 20-fold increase in ML intensity is finally obtained by selecting an appropriate inorganic-organic combination. The interfacial triboelectricity-regulated ML is further demonstrated in multi-interface systems that include an inorganic phosphor-organic matrix and organic matrix-force applicator interfaces, and again confirmed by self-oxidization and reduction of emission centers under continuous mechanical stimulus. This work not only gives direct experimental evidences for the underlying mechanism of ML, but also provides guidelines for rationally designing high-efficiency ML materials.

Controlling the Fluorescence Behavior of Hydrophobic Pigments by Supramolecular Self-Assembling on Organic Layered Silicate Minerals.

This research focused on the supramolecular self-assembly of organic fluorescent molecules on organically modified layered silicate minerals to design and prepare layered nanocomposites with excellent fluorescence properties. Aromatic hydrocarbons are hydrophobic and poorly loaded on the hydrophilic surface of layered silicate minerals, but they are easily captured by an organically modified mineral surface. Montmorillonite (MMT) and saponite (SAP), typical 2:1 type layered silicate minerals with different octahedral cations, were modified with the cationic surfactant octadecyl trimethylammonium chloride (OTAC) and loaded with pyrene (an aromatic hydrocarbon dye) with different molar ratios to the cationic surfactant by supramolecular self-assembling to construct fluorescent nanocomposites. The effect of pyrene concentration and the octahedral cation of the 2:1 type layered silicate minerals on photoluminescence properties was investigated. The fluorescence spectra of the nanocomposites prepared under low pyrene concentrations showed two bands at around 400 and 470 nm, corresponding to the monomer and excimer emissions; the band intensity of the excimer shoots up with the increase of pyrene concentration, reflecting different contributions from monomer and dimer species and the formation of radical aggregates. The excellent heat resistance of the layered silicate structure can effectively protect pyrene molecules from external environmental influences.

Vacancy-Enhanced Self-Reduction of Eu in Pyrophosphate Phosphor.

The self-reduction mechanism in pyrophosphate phosphors is currently explained through nonequivalent substitution for charge compensation. Nevertheless, the impact of oxygen vacancies on the self-reduction enhancement requires further investigation. Herein, heterovalent Ba1-xZn1-yP2O7:xEu2+/3+, yMg phosphors with rigid structures were prepared through conventional solid-phase technology in air. The cation substitution strategy leads to different chemistry electronegativity and adjustable crystal field environments and creates vacancy defects. Crystal structure and component analysis indicate the gradual phase segregation change from BaZnP2O7 to BaMgP2O7 with increasing Mg2+ content. The CIE coordinates that are tuned from (0.514, 0.334) to (0.326, 0.152) and realize color-tunable emission from red-orange to blue-violet can be used as multicolor functional materials. Besides, the phosphor demonstrates its maximum Sa of 0.4725% K-1 (498 K) and Sr of 1.376% K-1 (423 K). These results demonstrate that the phosphors have the potential for contactless optical temperature measurement and anticounterfeiting. This work not only investigates the self-reduction of the Eu3+ → Eu2+ phenomenon but also provides a supplementary explanation and data support to complete the effect of the oxygen vacancy on self-reduction.

Facile synthesis strategy for cesium tin halide perovskite crystals toward light emitting devices and anti-counterfeiting flexible fiber.

All-inorganic metal halide perovskites are widely studied because of their excellent photoelectric properties. However, due to the toxicity of CsPbX3 (X = Cl, Br, I) perovskites, it is difficult to apply them on a large scale. The lead-free nature and air stability make Cs2SnX6 (X = Cl, Br, I) perovskites possible candidates to replace CsPbX3 perovskites. Herein, we report the perovskite crystals (PCs) based on Te(IV)-doped Cs2SnCl6: Cs2Sn1-xTexCl6. Cs2Sn1-xTexCl6 PCs showed yellow emission under a 365 nm ultraviolet lamp. The photoluminescence quantum yield (PLQY) of Cs2Sn0.94Te0.06Cl6 PCs was 57.09%, which was proposed to be from the triplet Te(IV) ion 3P1 → 1S0 self-trapping excitons (STE) recombination. The perovskite crystals can be used to fabricate light-emitting diodes (LEDs). The fiber paper prepared from aramid chopped fibers (ACFs) and polyphenylene sulfide (PPS) fibers showed a bright yellow light under 365 nm ultraviolet light after being post-processed with Cs2Sn1-xTexCl6 PCs solution. The ACFs/PPS compound fiber paper modified with Cs2Sn1-xTexCl6 PCs maintained exceptional optical properties and could be stored in air for more than 4500 h. The fluorescence performance of the modified ACFs/PPS compound fiber paper could be applied to fluorescence anti-counterfeiting. The modification strategy and the applications in this work will provide a good choice for studying the optical performance of perovskites and broaden the application of ACFs/PPS compound fiber paper.

Tb3+ and Sm3+ co-doped Ca2La3(SiO4)3F phosphor: synthesis, color regulation, and luminescence properties.

The polychromatic phosphor with an apatite structure Ca2La3(SiO4)3F:0.15Tb3+,xSm3+ (CLSOF:0.15Tb3+,xSm3+) was synthesized via a solid-state route. The phase and morphology of the phosphor has been investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The structures of the as-prepared phosphor were verified by means of the Rietveld method. The optical performance was investigated thoroughly and the phosphors could emit multicolor light from short wavelengths to long wavelengths by gradually increasing the doping contents of samarium. All the results support that the energy transfer in CLSOF:0.15Tb3+,xSm3+ contributes to the color tunable property of the phosphor.

Structure and Photoluminescence Properties of Dy3+ Doped Phosphor with Whitlockite Structure.

Whitlockite has the advantages of a low sintering temperature, high stability, and a low fabrication cost, and it is widely used as the host for luminescent material. In this study, Ca1.8Li0.6La0.6-x(PO4)2:xDy3+ phosphor was prepared by the high-temperature solid-state method, and its structure, composition, and luminescence properties were systematically studied. The results showed that a new whitlockite type matrix was prepared by replacing Ca2+ in whitlockite with monovalent and trivalent cations. The prepared phosphors belonged to a hexagonal crystal system with a particle size in the range of 5-20 µm. Under the excitation of 350 nm UV light, the samples emitted white light, and there were mainly two stronger emission peaks at 481 nm in the blue band and 573 nm in the yellow band, which correspond to the electron transitions at 4F9/2→6H15/2 and 4F9/2→6H13/2 of Dy3+, respectively. The optimal doping concentration of Dy3+ in Ca1.8Li0.6La0.6(PO4)2 matrix was 0.03 (mol%). The main mechanism of concentration quenching in the sample was dipole-dipole energy transfer. When the temperature was 130 °C, the luminescence intensity of the samples was 78.7% of that at 30 °C, and their thermal quenching activation energy was 0.25 eV. The CIE coordinates of the sample at 30 °C were (0.2750, 0.3006), and their luminescent colors do not change with temperature. All the results indicate that Ca1.8Li0.6La0.6-x(PO4)2:xDy3+ phosphor is a luminescent material with good luminescence performance and thermal stability, which shows a promising application in the field of LED display.

Simultaneous Spectral Tuning and Thermal Stability Adjustment in Ca8ZnGa(1-x)Lax(PO4)7:Eu2+ Phosphors.

The modifications of local structure in solid solution are a crucial step to regulate the photoluminescence properties of rare-earth ion-based phosphors. However, the structural diversity of host matrices and the uncertain occupation of activators make it challenging to obtain phosphors with both high stability and tailored emission. Herein, We synthesized a series of ß-Ca3(PO4)2-type Ca8ZnGa(1-x)Lax(PO4)7:Eu2+ solid solution phosphors by design. By modifying the Ga/La ratio, controllable regulation of the emission spectrum and thermal stability of the phosphors can be achieved at the same time. The introduction of La3+ can regulate the crystal field splitting strength of the Eu2+ activators, causing redshifts in the emission spectrum while increasing Ga3+ content will lead to enhanced energy transfer between the oxygen vacancy and Eu2+, as well as improved thermal stability. Through local structure modification, the spectrum and thermal stability of phosphors can be facilely tuned. The results indicate that this series of phosphors have versatile potentials in various applications.

Structure, luminescence properties and energy transfer of terbium and samarium co-doped barium based apatite phosphor with tunable emission colour.

Ba2La2.85-x Tb0.15Sm x (SiO4)3F (BLSOF:0.15Tb3+,xSm3+) is a polychromatic phosphor with an apatite structure that was manufactured through a solid-state process. X-ray diffraction (XRD) and a scanning electron microscope (SEM) were utilized to examine the phosphor's phase and morphology. Using the Rietveld technique, the as-prepared phosphor structure was validated. By progressively raising the doping contents of the samarium, the phosphors emitted multicoloured luminescence from short to long wavelengths as indicated by analysis of the optical performance. Overall, the data provide strong evidence that the transfer of energy in BLSOF:0.15Tb3+,xSm3+ is responsible for the phosphor's colour-tunable property.

A novel and facile synthesis strategy for highly stable cesium lead halide nanowires.

As promising low-dimensional semiconductor materials, cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite-like nanowires (NWs) can be widely applied to the field of semiconductor devices and integrated optoelectronics. Therefore, developing a facile and efficient synthesis method of cesium lead halide perovskite-like NWs can bring both fundamental and practical impacts to the field of optoelectronics. Here, we developed a synthesis strategy of all-inorganic cesium lead halide CsPbI3 perovskite-like NWs under catalyst-free, solution-phase, and low-temperature conditions. The synthesis strategy was designed such that no inert gas is required and thus enables the synthesis to be carried out in air, which significantly reduces temperature, steps, time, and cost required for the reaction. The as-synthesized NWs were 7 µm in length and 80-100 nm in diameter with ideal morphology. Most of the CsPbI3 NWs were crystallized in orthorhombic phases that were arranged orderly with a uniform growth direction. In addition, the CsPbI3 NWs showed a photoluminescence peak near 610 nm and the fluorescence lifetime was 7.34 ns. The photoluminescence mechanism of CsPbI3 NWs involves the self-trapping behaviour in the radiative recombination process. The composition of CsPbI3 NWs is highly related to the synthesis temperature. The facile synthesis strategy has opened up a novel path for the synthesis of perovskite-like NWs, laying the foundation for the application of nano-optoelectronic devices, fluorescent anti-counterfeiting, and fluorescent composite materials.

Controllable crystal form transformation and luminescence properties of up-conversion luminescent material K3Sc0.5Lu0.5F6: Er3+, Yb3+ with cryolite structure.

In this paper, a novel cryolite-type up-conversion luminescent material K3Sc0.5Lu0.5F6: Er3+, Yb3+ with controllable crystal form was synthesized by a high temperature solid state method. K3Sc0.5Lu0.5F6: Er3+, Yb3+ can crystallize in monoclinic or cubic form at different temperatures. The composition, structure and up-conversion luminescence (UCL) properties of K3Sc0.5Lu0.5F6: Er3+, Yb3+ samples with different crystal form were investigated in detail. It is impressive that both monoclinic and cubic forms of K3Sc0.5Lu0.5F6: Er3+, Yb3+ show green emission (2H11/2/4S3/2→4I15/2). The luminescence intensity of cubic K3Sc0.5Lu0.5F6 is much higher than that of the monoclinic form, and the reasons are also discussed in detail. The results show that the luminescence intensity of up-conversion materials can be effectively tuned by controlling the crystal form. According to the power dependent UCL intensity, the UCL mechanism and electronic transition process were discussed. In addition, the fluorescence decay curves were characterized and the thermal coupling levels (TCLs) of Er3+ (2H11/2/4S3/2 → 4I15/2) in the range of 304-574 k were used to study the optical temperature sensing characteristics. All the results show that K3Sc0.5Lu0.5F6: Er3+, Yb3+ can be used in electronic components and have potential application value in temperature sensing fields.

Low-temperature sintering of silver patterns on polyimide substrate printed with particle-free ink.

In this study, a transparent particle-free reactive silver ink was used to fabricate conductive patterns on a flexible substrate. Thermal annealing and plasma irradiation at low temperature were utilized to improve the conductivity of the as-printed patterns. The effects of sintering process parameters on the microstructure and resistivity of the patterns were investigated. Under the optimized processing conditions, the resistivity of the pattern reached 1.2 × 10 -7 Ω · m by thermal sintering, while it was 8 × 10 -8 Ω · m after plasma sintering. Combined with these two sintering techniques, the resistivity was reduced to 6 × 10-8 Ω · m, close to that of bulk silver. This work provides an alternative solution for the fabrication of highly conductive feature patterns on common flexible substrates.

Preparation, structure and up-conversion luminescence properties of novel cryolite K3YF6:Er3+, Yb3.

Cryolite is a suitable host for up-conversion luminescent materials due to its low phonon energy and good optical transparency. In this work, a novel up-conversion material K3YF6:Yb3+, Er3+ with a cryolite structure was prepared successfully by a solid state method. The crystal structure, morphology, composition and up-conversion luminescence properties of the as-prepared sample were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (SEM) and fluorescence spectrometer in detail. K3YF6:Er3+, Yb3+ has a cryolite structure. Under 980 nm excitation, the as-prepared sample can generate slight green emission at 524 and 546 nm (attributed to 2H11/2 → 4I15/2 transition, 4S3/2→4I15/2 transition of Er3+) and strong red emission at 661 and 672 nm (corresponding to 4F9/2 → 4I15/2 transition, 4I9/2 → 4I15/2 transition of Er3+). All the green and red up-conversion emission of K3YF6:Er3+, Yb3+ transfer and electronic transition process of the red and green light the sample emitted, the possible luminescence mechanism is discussed in this paper.

Structure and luminescence properties of a novel broadband green-emitting oxyapatite-type phosphor.

In recent years, synthetic apatite-doped rare-earth luminescent materials and their optical properties have attracted extensive worldwide attention. In this study, a series of novel green phosphors Sr2Y3(SiO4)2(PO4)O:Eu2+ with apatite structure was fabricated via a high temperature solid-state reaction. X-ray diffraction, structure refinement, photoluminescence excitation, emission spectra, and temperature-dependent emission intensity were employed to describe the phase and property of the samples. Under the excitation of 365 nm, the phosphors emit strong green emission in the broad band range from 400 nm to 700 nm, which almost covers the visible light spectrum. The quenching concentration of Eu2+ in Sr2Y3(SiO4)2(PO4)O was about 0.05, which was attributed to the dipole-dipole interactions. The evidence that the as-prepared phosphor can be successfully excited by near ultraviolet light indicates that it can be potentially used as a near UV-convertible phosphor for white light-emitting diodes.

Synthesis of Ce-doped Mn3Gd7-xCex(SiO4)6O1.5 for the enhanced catalytic ozonation of tetracycline.

A novel cerium doped compounds Mn3Gd7-xCex(SiO4)6O1.5 with an apatite structure was found and used to achieve high-efficiency degradation of tetracycline in aqueous solution. The catalysts were characterized by XRD, XPS, EDS and other techniques. The characteristic results indicated that the catalytic activity of the compound was improved due to the introduction of Ce in the structure, because Ce3+ which was stably present in the apatite structure can serve as an active site for the reaction, and in addition, there was a high presence between Ce4+ and Ce3+ on the surface of the catalyst. The redox potential and high oxygen storage capacity were also beneficial for the catalytic reaction. The results of free radical capture indicated that both superoxide radicals and hydroxyl radicals participated in the catalytic oxidation process and played an important role in the reaction. The decomposition of tetracycline followed the pseudo second-order reaction kinetics. In addition, the catalyst exhibited long-term stability and low metal leaching during the reaction, which indicated that the novel cerium-doped apatite structure material could be a promising wastewater treatment material.

High Thermal Stability Apatite Phosphors Ca2La8(SiO4)6O2:Dy3+/Sm3+ for White Light Emission: Synthesis, Structure, Luminescence Properties and Energy Transfer.

What ideal w-LED phosphors always aim to do is to achieve a single phase near-sunlight emission phosphor simultaneously with both high luminescence efficiency and high thermal stability at operation temperature. And It is well known that apatite compound phosphors are one of the most promising optical materials to realize those above because of their unique structure enhanced luminescence properties and thermal stability. Here, we synthesized a co-doped single phase apatite phosphors Ca2La8(SiO4)6O2:Dy3+/Sm3+ (CLSO:Dy3+/Sm3+) for white light emission, which was provided with excellent thermal stability and of which luminescence intensity at 150 °C still was 92 percentage of that at room temperature. Moreover, X-ray diffraction technique, Fourier transform infrared spectroscopy, scanning electron microscope were employed to characterization of phase structure and morphology, and consequently pure apatite structure and gravel-like morphology of phosphors were proved. Analysis of photoluminescence spectra indicated that concentration quenching effect exist in single-doped CLSO:Dy3+ phosphors owing to dipole-dipole interaction between Dy3+ ions. It is revealed that maybe exist Dy3+ ↔ Sm3+ bilateral non-radiative energy transfer processes in Dy3+/Sm3+ co-doped CLSO system by PL spectra and decay curves. And variation of Sm3+ ion concentration can control color emission, namely CIE chromaticity coordinates and correlated color temperature, finally to achieve white light emission (0.309,0.309) with CCT 6848 K, able to be a potential candidate for commercial lighting applications.

Facile Controlled Synthesis of Spinel LiMn2O4 Porous Microspheres as Cathode Material for Lithium Ion Batteries.

Although the electrochemical properties of porous LiMn2O4 microspheres are usually improved compared to those of irregular LiMn2O4 particles, the effects of the different synthesis conditions on the preparation of the porous LiMn2O4 microspheres are rarely discussed in detail. In the present work, porous LiMn2O4 microspheres were successfully synthesized by using molten LiOH and porous Mn2O3 spheres as a template. Multiple factors were considered in the preparation process, including reagent concentration, pH, adding mode, heating time, etc. The morphology of the MnCO3 template was crucial for the preparation of porous LiMn2O4 microspheres and it was mainly affected by the concentration of reactants and the pH value of the solution during the precipitation process. During the lithiation of Mn2O3 microspheres, the heating temperature and the ratio between Mn2O3 and lithium salt were the most significant variables in terms of control over the morphology and purity of the LiMn2O4 microspheres. Furthermore, we demonstrated that the porous LiMn2O4 microspheres presented better rate capability and cyclability compared to commercial LiMn2O4 powder as cathode materials for lithium-ion batteries (LIBs). This study not only highlights the shape-controllable synthesis of LiMn2O4 microspheres as promising cathode materials, but also provides some useful guidance for the synthesis of porous LiMn2O4 microspheres and other LIB' electrode materials.

Preparation, crystal structure and luminescence properties of a novel single-phase red emitting phosphor CaSr2(PO4)2:Sm3+,Li.

Single-phase CaSr2(PO4)2:Sm3+,Li+ phosphors were prepared via a high-temperature solid-state method under air. The powder X-ray diffraction patterns, scanning electron microscopy images, photoluminescence spectra, and concentration-dependent emission spectra were measured to characterize the as-prepared phosphors and luminescence decay curves. The results showed that the CaSr2(PO4)2:Sm3+,Li+ phosphors exhibited red luminescence, and the emission spectra of the phosphors consisted of four sharp peaks at around 565, 601 (the strongest one), 647 and 707 nm. The optimum doping concentration of Sm3+ ions was 0.09 (mol concentration), and the mechanism of energy transfer among Sm3+ ions was defined to be quadrupole-quadrupole (q-q) interactions using Dexter's theory. The Blasse concentration quenching method was used to determine the critical distance R c for energy transfer among Sm3+ as 10.99 Å. The results indicate that the as-prepared phosphors have good thermal stability with an activation energy of 0.773 eV via temperature-dependent emission spectra. Therefore, CaSr2-2x (PO4)2:xSm3+,xLi+ materials can be used as red-emitting phosphors for UV-pumped white-light emitting diodes.

Luminescence properties and energy transfer of K3LuF6:Tb3+,Eu3+ multicolor phosphors with a cryolite structure.

In recent years, compounds with a cryolite structure have become excellent hosts for luminescent materials. In this paper, Tb3+ doped and Tb3+/Eu3+ co-doped K3LuF6 phosphors were prepared via a high temperature solid phase sintering method. The XRD, SEM, as well as photoluminescence excitation (PLE) and emission (PL) spectra were measured to investigate the structure and luminescence properties of the as-prepared samples. In the Tb3+/Eu3+ co-doped K3LuF6 samples, both characteristic emission spectra of Tb3+ and Eu3+ could be observed and the emission color of the K3LuF6:0.12Tb3+,xEu3+ phosphors could be adjusted from green to yellowish pink and the corresponding CIE values could be regulated from (0.2781, 0.5407) in the green area to (0.4331, 0.3556) in the yellowish pink area by controlling the concentration ratio of Eu3+/Tb3+. In addition, the energy transfer mechanism in Tb3+/Eu3+ co-doped K3LuF6 was calculated to be a quadrupole-quadrupole interaction from Tb3+ to Eu3+ based on the Dexter's equation.

Structure and luminescence properties of multicolor phosphor Ba2La3(GeO4)3F:Tb3+,Eu3.

A new kind of multicolor phosphor Ba2La3(GeO4)3F:0.15Tb3+,xEu3+ (BLGOF:0.15Tb3+,xEu3+) has been acquired through the traditional high temperature solid phase synthesis method. The structural information of the phosphor was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rietveld refinement. The optical properties of the phosphor have also been studied in detail, including its photoluminescence spectra (PL), photoluminescence excitation spectra (PLE), fluorescence decay curves, energy transfer mechanism and thermal quenching spectra. It has been found that the optimum concentration of Eu3+ in BLGOF:0.15Tb3+,xEu3+ is 0.24 mol and the energy transfer mechanism from Tb3+ to Eu3+ in BLGOF is quadrupole-quadrupole. The color of BLGOF:0.15Tb3+,xEu3+ phosphors can be changed from green to yellow/orange to red. Some details of the energy transfer are reviewed and the effect of complex anion regulation on thermal stability has also been studied. All the properties are good and can contribute to the promotion from the laboratory to practical application for the phosphor.

Fabrication of an AMC/MMT Fluorescence Composite for its Detection of Cr(VI) in Water.

Hexavalent chromium species, Cr(VI), which can activate teratogenic processes, disturb DNA synthesis and induce mutagenic changes resulting in malignant tumors. The detection and quantification of Cr(VI) is very necessary. One of the rapid and simple methods for contaminant analysis is fluorescence detection using organic dye molecules. Its application is limited owing to concentration quenching due to aggregation of fluorescent molecules. In this study, we successfully intercalated 7-amino-4-methylcoumarin (AMC) into the interlayer space of montmorillonite (MMT), significantly inhibited fluorescence quenching. Due to enhanced fluorescence property, the composite was fabricated into a film with chitosan to detect Cr(VI) in water. Cr(VI) can be detected in aqueous solution by instruments excellent, ranging from 0.005 to 100 mM with a detection limit of 5 µM.