Photoluminescence Decay Lifetime Research Articles

Thermally stable luminescence and dosimetric features of Ho(III) activated tungstate double perovskite

Luminescent efficient tungstate double perovskites Ca3WO6 doped with Ho3+ were synthesized via the solid-state reaction at 1200 C°. The resulting phosphors were analyzed using Rietveld refinement of X-ray diffraction (XRD) data, confirming a monoclinic crystal structure with crystallite sizes ranging between 50 and 55 nm. Optical bandgap determination was facilitated by diffusion reflectance spectra (DRS). Fourier transform infrared (FTIR) studies were conducted to identify functional group vibrations. The optical excitation of the Ca3WO6:Ho3+ phosphors under different excitation conditions resulted in intense green photoluminescence (PL) emission at 545 nm, indicative of the 5F4–5I8 transition of Ho3+ ions. Thermal stability assessment of Ca3WO6:1 % Ho3+ phosphor under blue excitation (454 nm) revealed good thermally stable luminescence about 85.32 % at LED working temperature (150 °C). PL decay studies were conducted to analyze fluorescent behaviour, wherein by means of PL decay lifetime, the PL quantum efficiency of Ca3WO6:1 % Ho3+ phosphor is computed to be 91.1 %. The CIE color coordinates of the phosphors being investigated reside within the green spectral region, with a calculated color purity of 93.25 % observed for Ca3WO6:1%Ho3+. Furthermore, the phosphors under study exhibited high-quality thermoluminescence (TL) after beta irradiation. The detailed TL characterization conducted to assess dosimetric properties. The impact of Ho3+ concentrations and beta dose on TL intensity are two major aspects that have been investigated in detail. TL fading experiments were performed to determine dose storage capacity over a month after beta irradiation. Additionally, the various heating rate (VHR) experiments are conducted to determine the TL kinetic parameters. Besides, the glow curve deconvolution (GCD) for trap parameter determination is also applied, where the results obtained are comparable with the VHR results.

High-performance pure red perovskite light-emitting diodes utilizing conformational transformation of ionic liquid additive

The performance of perovskite light-emitting diodes (PeLEDs) depends highly on the defect density and carrier transport properties of the perovskite layer. Some long-chain ligands are good at passivating the defects, but they hinder the charge injection into the perovskite because of their insulating nature. Notably, red PeLEDs suffer from spectral shift under bias caused by ion migration inside the mixed cation perovskite layer. This study proposes the use of silver bis(trifluoromethanesulfonyl)imide (AgTFSI) a conducting ionic liquid as a multifunctional additive to the perovskite to overcome the aforementioned problems. The TFSI anion comprises strong electronegative -CF3 and Lewis base -SO2 groups. These functional groups interact with undercoordinated Pb2+, efficiently suppressing defects and reducing nonradiative recombination in the perovskite film. AgTFSI displays two distinct conformations: cisoid and transoid. The opposing orientations of the two functional groups enable the cisoid structure to exclusively engage with the perovskite through the -SO2 groups. In contrast, the semi-linear arrangement of the transoid structure provides accessibility to both -SO2 and -CF3 groups for interaction. Owing to their conformational flexibility, the TFSI anions in AgTFSI undergo a transition from the zigzag cisoid to a more linear transoid structure when added to the perovskite, enabling efficient packing and tight binding with the Pb defects. As a result, the perovskite film shows a twofold increase in photoluminescence quantum yield and decay lifetime. Consequently, the red PeLEDs achieve a maximum external quantum efficiency of 13.52%, nearly double that of the control device. This study confirms AgTFSI's potential as an effective additive for high-performance pure red PeLEDs.

Synthesis and tunable photoluminescence properties of Er3+/Eu3+ co-doped Na5La(MoO4)4 phosphors

The tunable emission characteristics of Er3+ doped and Er3+/Eu3+ co-doped Na5La(MoO4)4 phosphors prepared via high-temperature solid phase method were investigated. The microstructure of the modified phosphor was studied by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy, and its luminescence properties were analyzed by photoluminescence excitation and photoluminescence spectra. The energy transfer mechanism of Er3+ ions to Eu3+ ions was investigated by changing the concentration of Eu3+ ions to induce the spectral changes, and the photoluminescence decay lifetime was measured to validate the findings. Notably, under excitation at 380 nm, the co-doped phosphors exhibited tunable emission ranging from green to orange-red. Furthermore, Na5La(MoO4)4:0.04Er3+/0.04Eu3+ phosphor, when combined with a 380 nm chip, achieved desired warm white light emission. These promising results underscore the potential application of Na5La(MoO4)4:0.04Er3+/0.04Eu3+ phosphor in solid-state lighting.

Photoluminescence and Nonlinear Optical Properties of Two Terpyridine-Based Hybrid Zn/Cd Halides.

Hybrid metal halides (HMHs) with low-dimensional structures have attracted increasing attention due to their striking optical properties. Herein, two new zero-dimensional HMHs have been fabricated by CdCl2/ZnCl2 and 4'-(4-pyridyl-phenyl)-2,2':6',2″-terpyridine (Tpy), including (TpyH3)[CdCl4][Cl] (Tpy-Cd) and (TpyH3)[ZnCl4][Cl] (Tpy-Zn). Their structures are consisted of a [TpyH3]3+ organic cation, an inorganic [ZnCl4] or [CdCl4] tetrahedron, and one isolated Cl- anion. Tpy-Cd crystallizes to a noncentrosymmetric structure and possesses a moderate second harmonic response of 0.72 × KH2PO4, while Tpy-Zn features a centrosymmetric space group. Though Tpy-Cd and Tpy-Zn crystallize into space groups of completely different symmetry due to distinct connection mode and molecular distortion, they display quite similar photoluminescence of bright green light emission under ultraviolet excitation, nearly identical in Stokes shift, photoluminescence quantum yield, decay lifetime, and energy. The photoluminescence quantum yields of green light emission were measured to be nearly 25%, outperforming most of the Cd/Zn low-dimensional HMHs.

Highly flexible, green luminescent down converting and hydrophobic 0-D cesium lead bromide (Cs4PbBr6)/ poly (vinylidene difluoride) polymer nanocomposites for photonics and display applications

Halide perovskite materials have emerged as a promising new research topic in recent years, with potential applications in solar cells and optoelectronic devices, among others. These materials have significant limitations, including instability to water, heat, UV radiation, and light, limiting their research to the lab scale only. Encapsulation of perovskite with polymers is a solution for addressing the shortcoming of stability. This study illustrates the synthesis of zero-dimensional cesium lead bromide (Cs4PbBr6), as well as its poly (vinylidene difluoride) (PVDF) nanocomposites, optical, morphological, cell properties and increased stability towards the environmental stress. Different concentrations of synthesized perovskite was encapsulated in PVDF, namely 0.0, 0.5, 1.0, 1.5 and 2.0 wt/wt%. The UV–Visible spectral result depicts that the strong absorbance band ranges from 280 to 320 nm confirms the formation of Cs4PbBr6. X- ray diffraction (XRD) reveals the existence Cs4PbBr6 and good interaction between the perovskite and polymer matrix. The size of prepared perovskite is in nano scale and with high phase purity with rhombohedral unit cell with are depicted by using high-resolution transmission electron microscope (HR-TEM), selected area electron diffraction (SAED). The nanocomposites exhibit emission from 490 to 520 nm, and 2 wt/wt% of perovskite in PVDF exhibits the highest emission intensity analyzed using photoluminescence (PL) spectral results which is excited at 370 nm. PL lifetime decay measurements of the fabricated PVDF perovskite nanocomposites shows 34.744 ns for 2 % Cs4PbBr6/PVDF nanocomposites due to delayed exciton radiative recombination which infers that the fabricated nanocomposites finds potential application in the arena of photonics, UV-radiations blockers, and LEDs.

Stable Broadband Bright Green Emission of Self‐trapped Excitons Triggered by Sb3+ Doping in Zero‐Dimensional Cs3BiCl6

AbstractLow‐dimensional lead‐based metal halide perovskites (MHPs) have many exceptional photoelectric capabilities thanks to the 6 s2 electron structure of lead ion (Pb2+). Pb2+′s toxicity, however, has prevented its widespread development and use. Finding ions in the valence layer that have a comparable electrical structure thus makes sense as Pb2+ replacements. In this work, all inorganic zero‐dimensional (0D) Cs3BiCl6 single crystal was synthesized by the anti‐solvent crystallization method. There is no obvious photoluminescence (PL) phenomenon for Cs3BiCl6 at room temperature (RT). It is found that the extremely strong exciton‐phonon interaction leads to seriously non‐radiative recombination. After doping with Sb3+, Cs3BiCl6: Sb achieved broadband emission with a significant Stokes shift, the photoluminescence quantum yield (PLQY) up to 15.85 %, which has a microsecond PL decay lifetime and excellent environmental stability. Systematic spectroscopic characterizations unveil the PL mechanism of Cs3BiCl6: Sb is self‐trapped excitons (STEs) emission, and theoretical calculation revealed the indirect bandgap properties of Cs3BiCl6 and Cs3BiCl6: Sb.

What is TADF (thermally activated delayed fluorescence) compared to the mechanisms of FL (fluorescence), PH (phosphorescence), and TTA (triplet–triplet annihilation) based on a novel naphthalimide sulfonylphenyl derivative as a host?

One of the biggest challenges in the field of optoelectronics is to easily identify the mechanisms involved in light-emitting materials. There are several different mechanisms of emission, and the best known are fluorescence (FL), phosphorescence (PH), thermally activated delayed fluorescence (TADF), and triplet–triplet annihilation (TTA). In this study, simple ways to diagnose these mechanisms are presented with an example. N,N-di(benzenesulfonylphenyl)-N-(N-2-aminomethylpyridine-1,8-naphthalimide)amine is synthesized as a host compound due to its high HOMO-LUMO and ionization potential (IP) values and three emitters consisting of 50 wt% Bis (1phenylisoquinoline))(acetylacetonate)iridium(III) (Ir(piq)2(acac)), 10-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (DMAC-TRZ) and 1,1′-(2,5-Dimethyl-1,4-phenylene)dipyrene (DMPPP) were considered. Overall, the host compound, doped Ir(piq)2(acac) and doped DMPPP follow the mechanisms of FL, the combination of FL and PH, and the combination of FL and TTA, as the photoluminescence (PL) decay life time and the PL intensity increased with decreasing temperature. However, DMAC-TRZ doped with the host compound showed the TADF mechanism, as the PL decay lifetime and the PL intensity increase simultaneously with increasing temperature. In addition, the difference between the singlet excited state (S1) and the triplet excited state T1 (ΔEST) from the PL and PH spectra at 77 K for the spin-coated DMAC-TRZ-doped host show the lowest value in between the samples at 0.02 eV, and the reverse intersystem crossing (rISC) effect is activated. Moreover, the linear slopes of the power dependence analysis of the DMPPP-doped host were calculated to be 2.04 and 0.91, indicating that there are two components (photons) for this sample which is strong evidence for the TTA mechanism. Taking into account the synthesized host compound, (Ir(piq)2(acac):host), (DMAC-TRZ:host) and (DMPPP:host) as emitter layers, the organic light emitting diodes (OLEDs) were fabricated via solution processing, and the TADF OLED exhibited the highest efficiency among the other OLEDs.

White light-emitting calcium tungstate microspheres synthesized via co-precipitation at room temperature and application to UV-LED chip

Crystalline CaWO4 was synthesized by a co-precipitation method at room temperature. XRD peak at a position like that in the reference pattern, and the signal was detected from the (112) plane. Raman signals suggested the presence of symmetrical vibrations of the WO4 bond. The absorption was observed in the UV region, and the bandgap calculated from the Tauc plot was 4.47 eV. When the sample was excited at 230 nm, blue emission with a peak at 430 nm was observed. Crystalline CaWO4 was doped with Dy3+ ions to synthesize a white light-emitting phosphor. The addition of Dy3+ ions altered the crystal structure and shifted the Raman signals slightly. The sample was excited at 230 nm, both 430 nm and 575 nm emissions were observed, and the intensity of the 575 nm emission increased with increasing Dy3+ concentration. The CaWO4:0.1Dy3+ sample showed the highest luminescence intensity, and excessive doping decreased the luminescence intensity owing to concentration quenching. The photoluminescence decay lifetime initially increased with increasing Dy3+ concentration but decreased at concentrations greater than 0.1 mol% because of concentration quenching. The synthesized white light emitting CaWO4:Dy3+ powder was mixed with PDMS to form a flexible composite. The composite could be easily bent with a finger and emitted white light when applied on a UV-LED chip.

Study on the stable and efficient white-emitting Bi/Tb/Eu tridoped single-phase borate Sr3YB3O9 phosphors

Several series of novel broad band white light emitting Bi/Tb/Eu tridoped in multiple lattice sites of single-phase Sr3YB3O9 (SYBO) borate phosphors, which covered almost all visible range through mixing the separate blue, green and red emissions from dopants of Bi, Tb and Eu, respectively, were successfully obtained by using the facile and conventional solid-state reaction method under air condition. Rietveld refinements based on XRD data together with the combination match of charge and ion radius for dopants of Bi, Tb, Eu and lattice cations of Sr, Y and B show that Bi is more inclined to replace the Sr site while Tb/Eu are more likely to enter the Y site, respectively. Through spectrum analysis of photoluminescence excitation (PLE), PL and decay lifetime, the efficient energy transfer (ET) from the Bi to both Tb and Eu, and from Tb to Eu are all testified via the dipole-dipole interactions, indicating that the non-rare-earth activator Bi is acting both as the blue luminescence center and ET sensitizer, while the Tb contributes both as ET bridge and green luminescence center to better connect the Bi and Eu. The optimal tridoped white emission SYBO phosphor appears good thermal stability, which could continue to have its PL intensity above 75% at 150 °C as compared with the original room temperature PL intensity. Altogether, the single-component SYBO:Bi/Tb/Eu phosphor could be well served as potential white light phosphor for n-UV pumped wLED devices.

Visible White‐Light Emission and Carrier Dynamics Observed in Full‐Series GaSe1‐xSx (0≤x≤1) Multilayers

AbstractNear‐band‐edge emissions ranging from red (≈630 to 602 nm) to green (≈550 to 534 nm) and blue (≈494 to 480 nm) colors have been detected in full‐series GaSe1‐xSx (0≤x≤1) multilayers using micro‐photoluminescence (µPL) measurements from 4 to 300 K. The multilayered chalcogenides crystallize in a hexagonal structure, with observed mixed stacking phases of ε and β polymorphs through X‐ray diffraction and Raman measurements. The µPL results, along with experimental band‐edge characterization through thermoreflectance, identify the ε‐stacked phase as the crucial phase responsible for direct recombination and the emission of free excitons within the visible range. A mixed‐color white light is created by PL, which is emitted from the layered GaSe1‐xSx series of different colors, and is positioned at the center of the CIE coordination plot (i.e., white color). To assess the emission properties of both band edges and defects in the layered compounds, time‐resolved photoluminescence (TRPL) is employed, using an area mapping function. The photoluminescence decay lifetime increases as the sulfur content is increased, owing to the greater occurrence of mixed‐phase stacking faults near the β‐GaS end within the GaSe1‐xSx (0≤x≤1) series. The multilayer GaSe1‐xSx (0≤x≤1) represents a distinct 2D chalcogenide series well‐suited for emitting full‐color visible light.

Substrate temperature dependence of structure and optical properties of ZnTiO3:Er3+/Yb3+ thin films synthesized by pulsed laser deposition

ZnTiO3:Er3+,Yb3+ thin film phosphors were successfully deposited by pulsed laser deposition (PLD) at different substrate temperatures. The distribution of the ions in the films was investigated and the chemical analysis showed that the doping ions were homogeneously distributed in the thin films. The optical response of the phosphors revealed that the reflectance percentages of the ZnTiO3:Er3+,Yb3+ vary with the silicon substrate temperature due to the differences in the thickness and morphological roughness of the thin films. Under 980 nm diode laser excitation, the ZnTiO3:Er3+,Yb3+ film phosphors displayed up-conversion emission from the Er3+ electronic transitions, with violet, blue, green, and red emission lines at 410, 480, 525, 545 and 660 nm from 2H9/2 → 4I15/2, 4F7/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. The up-conversion emission was enhanced by increasing the silico (Si) substrate temperature during the deposition. Based on the photoluminescence properties and decay lifetime analysis, the energy level diagram was established and the up-conversion energy-transfer mechanism was discussed in detail.

Molecular Sensitization Enabled High Performance Organic Metal Halide Hybrid Scintillator.

Scintillators, one of the essential components in medical imaging and security checking devices, rely heavily on rare-earth-containing inorganic materials. Here, a new type of organic-inorganic hybrid scintillators containing earth abundant elements that can be prepared via low-temperature processes is reported. With room temperature co-crystallization of an aggregation-induced emission (AIE) organic halide, 4-(4-(diphenylamino) phenyl)-1-(propyl)-pyrindin-1ium bromide (TPA-PBr), and a metal halide, zinc bromide (ZnBr2 ), a zero-dimensional (0D)organic metal halide hybrid (TPA-P)2 ZnBr4 with a yellowish-green emission peaked at 550nm has been developed. In this hybrid material, dramatically enhanced X-ray scintillation of TPA-P+ is achieved via the sensitization by ZnBr4 2- . The absolute light yield (14,700±800 Photons/MeV) of (TPA-P)2 ZnBr4 is found to be higher than that of anthracene (≈13,500 Photons/MeV), a well-known organic scintillator, while its X-ray absorption is comparable to those of inorganic scintillators. With TPA-P+ as an emitting center, short photoluminescence and radioluminescence decay lifetimes of 3.56 and 9.96ns have been achieved. Taking the advantages of high X-ray absorption of metal halides and efficient radioluminescence with short decay lifetimes of organic cations, the material design paves a new pathway to address the issues of low X-ray absorption of organic scintillators and long decay lifetimes of inorganic scintillators simultaneously.

Multi‐Responsive 0D Organic–Inorganic Hybrid Cuprous Bromides Constructed via Ultra‐Facile Approaches for Multimodal Luminescent Anti‐Counterfeiting

AbstractLuminescent anti‐counterfeiting has the advantages of high secrecy, low cost, flexible design, simple operation, and convenient light‐regulation of luminescent materials, which makes it easy to achieve high‐level multimodal anti‐counterfeiting. Here, zero‐dimensional (0D) organic–inorganic hybrid luminescent crystals (TPA)CuBr2 (TPA+ = [N(CH2CH2CH3)4]+) with multiple responses to ultraviolet (UV) light, water, and thermal stimulus are synthesized through an ultra‐facile approach for multimodal luminescent anti‐counterfeiting. Water‐sensitive (TPA)CuBr2 could transform into 0D (TPA)2Cu4Br6 upon external water stimulus, accompanied by the change of luminescence color from cyan to orange under UV light irradiation. Both (TPA)CuBr2 and (TPA)2Cu4Br6 exhibit high photoluminescence quantum yields, and long photoluminescence decay lifetimes. In addition, (TPA)CuBr2 and (TPA)2Cu4Br6 show reversible “on‐off” luminescence phenomena and excellent cycling stability under thermal stimulus. Exhilaratingly, multimodal anti‐counterfeiting luminescent labels with high‐security level could be fabricated based on the multiple responsive organic–inorganic hybrid cuprous bromides. Moreover, the test paper based on (TPA)CuBr2 could be fabricated for the detection of trace water in isopropanol. This work demonstrates the capabilities of (TPA)CuBr2 and (TPA)2Cu4Br6 as high‐security anti‐counterfeiting materials and luminescent sensors, which provides an important reference for exploring 0D metal halides for high‐level luminescent anti‐counterfeiting.

The Mn-Doped CsPbCl3 Perovskite Nanocrystals as a Photoluminescent Probe for Copper Ions Detection

Trace detection of toxic heavy metal ions is a hot topic in the sensing research area, especially in the organic phase using inorganic fluorescent colloidal nanocrystals. We report Mn-doped CsPbCl3 perovskite nanocrystals (PNCs), which were synthesized via the hot-injection method, as a fluorescent probe for the detection of copper ions in hexane. The introduction of Mn altered the emission peak, and lower the toxicity of the probe material. The photoluminescence (PL) intensity of Mn-doped CsPbCl3 PNCs is significantly quenched after contact with the [Formula: see text] solution. The mechanism of Cu quenching is electron transfer, which is experimentally proved by analyzing the PL spectrum, absorption spectrum and PL decay lifetime. The sensor in solution shape and solid shape is both prepared and their detection range from 10 nM to 500 [Formula: see text]M. The limit of detection in a low concentration area reaches 10 nM, showing great potential in sensing applications. This work expands the wavelength area of the [Formula: see text] detection probe by perovskite nanocrystals, and also improves the properties of probe material in optical performance, low toxicity, and stability.

Mn4+ doped Mg2ScSbO6 deep-red-emitting double-perovskite phosphors for plant-cultivation

Non-rare earth Mn4+-doped oxide matrix phosphors are of increasing interest in the field of light-emitting diodes due to their good spectral properties. Herein, Mn4+-doped Mg2ScSbO6 phosphor was successfully synthesized via the conventional solid-state reaction method. The crystal structure of the sample was determined using a variety of characterization methods such as X-ray powder diffraction and Rietveld refinement analysis. The phosphor has a broadband absorption from near ultraviolet to blue light and emits deep red (∼682 nm) light of 2Eg → 4A2g transition. The photoluminescence intensity and decay lifetime of the Mn4+-doped Mg2ScSbO6 are observed to be strongly dependent on temperature, and the results of quenching analysis were reported. The optimal Mg2ScSbO6:Mn4+ phosphor has a high color purity of 99.4% with an internal quantum efficiency value of 61.93% modulated by charge compensation of Li+ ions. The photoluminescence peak position of the phosphor can be well matched with the absorption peak of red and far-red phytochrome. Therefore, the deep-red-emitting phosphors have tremendous application merits and potential markets in plant growth.

Structural, luminescence and photoconversion properties of Lu3Al5O12:Ce single crystalline film phosphors for WLED application

This work focuses on the detailed investigation of structural, luminescence and photoconversion properties of Ce doped Lu3Al5O12:Ce (LuAG:Ce) single crystalline films (SCFs) grown using the Liquid Phase Epitaxy (LPE) method onto Y3Al5O12 (YAG) single crystal substrates as promoting converting film material for high-power WLED. The structure and chemical composition were analyzed using X-ray diffraction (XRD) and High-Resolution Scanning Transmission Electron Microscopy (HR-STEM). HR-STEM analysis and composition analysis revealed an interface with high structural quality including the formation of a transition layer with a 6 nm thickness between LuAG:Ce SCF and YAG substrate. The composition of this layer changes smoothly from YAG substrate towards LuAG:Ce SCF, and after equalizing the SCF/substrate misfit, stable LuAG:Ce film growth is observed. The optical characterization of LuAG:Ce films were performed using absorbance, cathodoluminescence and photoluminescence emission/excitation spectra and photoluminescence decay lifetime, as well as photoconversion measurements under blue, LED excitation. The corresponding color coordinates, color temperatures, color rendering index and luminous efficacy of white light sources based on blue LEDs and LuAG:Ce film converters with thicknesses in the 19–160 nm range were estimated and best characteristics are achieved for the 92 µm thick sample.

Multicolor Luminescent Carbon Dots: Tunable Photoluminescence, Excellent Stability, and Their Application in Light-Emitting Diodes

Carbon dots (CDs) are attracting much interest due to their excellent photoelectric properties and wide range of potential applications. However, it is still a challenge to regulate their bandgap emissions to achieve full-color CDs with high emissions. Herein, we propose an approach for producing full-color emissive CDs by employing a solvent engineering strategy. By only tuning the volume ratio of water and dimethylformamide (H2O/DMF), the photoluminescence (PL) emission wavelengths of the CDs can be changed from 451 to 654 nm. Different fluorescence features of multicolor CDs were systematically investigated. XRD, SEM, TEM, Abs/PL/PLE, XPS, and PL decay lifetime characterizations provided conclusive evidence supporting the extent to which the solvent controlled the dehydration and carbonization processes of the precursors, leading to a variation in their emission color from red to blue. The as-prepared CDs exhibited excellent and stable fluorescence performance even after being heated at 80 °C for 48 h and with UV light continuously irradiated for 15 h. Based on their excellent fluorescent properties and photothermal stability, bright multicolor light-emitting diodes with a high CRI of up to 91 were obtained. We anticipate that these full-color emissive CDs are beneficial for applications in lighting, display, and other fields.

In Situ Monitoring Charge Transfer on Topotactic Epitaxial Heterointerface for Tetracycline Degradation at the Single-Particle Level

Selectively constructing heterojunctions on specific crystal facets enable directional electron–hole migration and favorable charge separation. Meanwhile, in-depth monitoring and investigating charge-transfer process on specific crystal facets of individual single crystal are particularly important. Herein, we report a strategy for synthesizing SrTiO3/TiO2 epitaxial heterojunctions (ST/T), in which highly ordered SrTiO3 mesocrystals are selectively topologically grown on the TiO2 {001} facet. It exhibits good photocatalytic activity for tetracycline (TC) degradation. Notably, single-particle spectroscopy was employed to accurately monitor the transfer and recombination of carriers at the specific nanoregions of individual particle. The weaker photoluminescence (PL) intensity and longer lifetime at the epitaxial central site of ST/T particle indicate that the epitaxial heterointerface promotes the separation of charge carriers. Moreover, in situ monitoring of TC degradation on single ST/T particle confirms that the epitaxial heterojunction suppressed the PL lifetime decay, further demonstrating the pivotal role of site-selective topotactic epitaxy. This study presents a strategy for rational designing heterojunction photocatalysts and is beneficial for in-depth monitoring and understanding the structure–activity relationship at the single-particle level.

TiO2–rGO nanocomposites with high rGO content and luminescence quenching through green redox synthesis

We developed TiO2–rGO nanocomposites with high exfoliated rGO content upto 47.1% (TG4) by weight hitherto not reported, through green redox synthesis. Progressive reduction of TiO2 nanocrystal size and their in situ intercalation occurred on increasing rGO via one pot synthesis, not reported previously and forming highly stable Ti–O–C bonds. With increase in rGO content, the exfoliation in the nanocomposite was also limited to single-few layered graphene oxide sheets through use of ascorbic acid avoiding restacking, and thereby the recombination of photogenerated carriers. TG4 showed 50% photoluminescence (PL) quenching indicating long-lived electron transfer state with rGO and apparent rate of nonradiative excited state decay of 1.15 × 108 s−1. Details of lattice orientation, Raman spectra, electronic states and PL lifetime decay are discussed to elucidate effective charge carrier separation in the nanocomposite. Near complete photodegradation of Alizarin Yellow GG azo dye, an industrial pollutant, could be obtained under direct sunlight using TG4 as catalyst.

Downshifting analysis of Sm3+/Eu3+ co-doped LiBiAlBSi glasses for red emission element of white LEDs

The Sm3+, Eu3+ single doped, and Sm3+/Eu3+ co-doped lithium bismuth alumino borosilicate (LiBiAlBSi) glasses were prepared by using the melt quenching method and studied photoluminescence (PL) excitation, PL emission, and PL decay to have a better insight into their utility as red emission element for white LEDs. Sm3+ doped LiBiAlBSiSm05 glasses exhibit admirable emission features in the reddish-orange region under n-UV excitation (402 nm). Sm3+/Eu3+ co-doped LiBiAlBSi glasses can be adeptly excited by the blue and n-UV region which is confirmed from the excitation spectrum. In the Sm3+/Eu3+ co-doped LiBiAlBSi glasses, the PL decay lifetime for the Sm3+ emitting level (4G5/2) declines and the energy transfer efficiency increases with an upsurge in Eu3+ ion content, which suggests the energy transfer (ET) process occurs from Sm3+ to Eu3+ ions. The ET process from Sm3+ to Eu3+ ions is also suggested by Dexter's ET method and Reisfeld's approximation by using emission spectra due to non-radiative dipole-dipole (d-d) interaction. The calculated values of CIE chromaticity coordinate for the as-prepared glasses under n-UV excitation shifted from reddish-orange to the red spectral part with the upsurge in Eu3+ concentration. The temperature-dependent PL studies of the optimized LiBiAlBSiSE10 glass revealed its superior thermal stability. All the results obtained finally suggest that, the Sm3+/Eu3+ co-doped LiBiAlBSi glass with 0.5 mol% of Sm3+ ions and 1.0 mol% of Eu3+ ions is a thermally stable candidate to produce intense red color needed to fabricate white LEDs under n-UV and blue excitation through the downshifting process.