Multicolor Luminescence Research Articles

Multi-color luminescence and energy transfer behavior of Ba3Lu4O9:Tb3+,Eu3+ phosphor for solid-state lighting

A multi-color-emitting phosphor Ba3Lu4O9:Tb3+,Eu3+ was synthesized by the high-temperature solid-state reaction. Under UV excitation, the characteristic emissions of Tb3+ and Eu3+ in Ba3Lu4O9 were observed simultaneously. The energy transfer behavior from Tb3+ to Eu3+ was verified and investigated through the photoluminescent spectra and the decay curves. The energy transfer efficiency was estimated to be 94.6% when the concentration of Eu3+ was 10 mol%, and the energy transfer process was determined by the dipole–dipole mechanism. The critical distance for the energy transfer between Tb3+ and Eu3+ was around 16.52 Å. Furthermore, the activation energy of Tb3+ (5D4-7F5) and Eu3+ (5D0-7F2) in Ba3Lu4O9 were calculated to be 0.323 eV and 0.499 eV, respectively. With the increase of Eu3+ concentration, the emitting color of the phosphors can be regulated from green (0.2923, 0.5228) to reddish orange (0.6196, 0.3346) with their respective CCT of 6463 K to 8909 K. All these findings indicate that the phosphor can be utilized as the multi-color component for solid-state lighting.

First-Principles Calculation of Photoelectric Property in Upconversion Materials through In3+ Doping.

Multicolor turning holds great promise in optical intelligent recognition and optical imaging. Here, Er3+, Yb3+, and In codoped ZnO (Er/Yb/IZO) with a uniform block strucuture is obtained. The doping of In3+ ions enhances the multicolor upconversion luminescence (UCL) intensity of Er/Yb/IZO. Particularlly, the UCL of Er/Yb/I2ZO turns from red through yellow to dominant green emission via increasing density power from 2.54 to 10.19 W/cm2, thus realizing the power sensitiviy. First-principles theory is used to design a In3+, Yb3+, and Er3+ codoped ZnO. The band structure, total density of state and optical coefficient of Er/Yb/IZO have been studied via a generalized gradient approximation within density functional theory (DFT). The potential electron density and total electron density of the O atom increase with In3+ and Er3+/Yb3+ doping, which indicate that substitution of Zn2+ by In3+ and Er3+/Yb3+ generate positive vacancies on the surface. The band gap of Er/Yb/IZO decreases compare with that of pure ZnO. Furthermore, the optical coefficient of In3+ doping is enhanced compare with that of pure ZnO via using DFT calculations.

Multicolor luminescence of hexagonal NaYF4:Yb3+/Ho3+/Ce3+ microcrystals with tunable morphology under 940 nm excitation for temperature-responsive anti-counterfeiting

In this study, the hexagonal NaYF4:Yb3+/Ho3+/Ce3+ microcrystals were synthesized controllably, and upconversion luminescence excited at 940 nm and its application in temperature-responsive anti-counterfeiting are reported. It is clarified that the Ln3+ (Ln = Y + Yb + Ho + Ce) density ratio of bottom plane to side plane in the unit cell can be regulated by Ce3+ doping. It is also proved that the energy transfer of Yb3+ to Ho3+ is responsible for the activation of Ho3+ under 940 nm excitation, while the cross relaxation between Ho3+ and Ce3+ participates in the redistribution of electron population of 5S2/5F4 and 5F5 levels. Both theory and experiment confirm that the intensity ratio of red to green emission (IR/IG) as a function of temperature as an independent variable has good linear characteristics in the temperature range of 300–500 K. Due to the good responsiveness of multicolor luminescence to temperature, the hexagonal NaYF4:Yb3+/Ho3+/Ce3+ with tunable morphology is a promising candidate for advanced temperature-responsive upconversion anti-counterfeiting. Our results provide a new pathway for the controllable synthesis of hexagonal NaYF4 microcrystals as well as the regulation of upconversion luminescence that is excited by wavelengths other than 980 nm and its application in anti-counterfeiting.

SiO2:Tb3+@Lu2O3:Eu3+ Core-Shell Phosphors: Interfacial Energy Transfer for Enhanced Multicolor Luminescence.

Uniform and well-dispersed SiO2:x%Tb3+@Lu2O3:y%Eu3+ core-shell spherical phosphors were synthesized via a solvothermal method followed by a subsequent calcination process. The structure, phase composition, and morphology of the samples were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the Lu2O3:Eu3+ layer was evenly coated on the surface of SiO2:Tb3+ spheres and the shell thickness was about 45-65 nm. The PL spectra and fluorescence lifetimes of the samples were further studied. It was proved that the multicolor luminescence of the samples could be realized by changing the doping concentration ratio of Eu3+ or by changing the excitation wavelengths. Compared with SiO2@Lu2O3:3%Tb3+,6%Eu3+, SiO2:3%Tb3+@Lu2O3:6%Eu3+ showed stronger luminescence intensity, longer fluorescence lifetime, and higher energy transfer efficiency, which was attributed to the effective interfacial energy transfer, and the interfacial energy transfer mechanism from Tb3+ to Eu3+ was a dipole-dipole interaction mechanism. The XPS results indicated that the sample contained a high content of Si-O-Lu bonds, which proved that there was a strong interaction between the SiO2 core and the Lu2O3 shell, making the interfacial energy transfer possible. These results provided a new idea for luminescence enhancement and multicolor luminescence.

Small-molecule based thermally activated delayed fluorescence materials with dual-emission characteristics

Organic thermally activated delayed fluorescence (TADF) emitters have attracted increasing concerns, owing to their atypical photophysical features that can pave the way to the innovative engineering applications. As cutting-edge type of luminescent molecules, however, most of them only exert a single-wavelength emission from the lowest excited state, according to Kasha’s rule. To develop their potential applications in multicolor luminescence and multi-functional luminescent probes for biological imaging, researchers have begun to turn their attention to design organic TADF molecules with dual-emission characteristics, by employing an additional fluorescence, phosphorescence, or TADF signal within a single-component system. We herein summarized the design principles as well as the luminescence mechanism of organic donor-acceptor TADF compounds with dual-emission characteristics, the superiority of which can cover unique material applications in modern luminescence-related fields.

Excitation dependent multicolour luminescence and colour blue-shifted afterglow at room-temperature of europium incorporated hydrogen-bonded multicomponent frameworks

Multicoloured luminescence and long-lived blue-shifted afterglow have been obtained in a europium-doped hydrogen-bonded organic framework (HOF). The material displays multi-stimuli responsive emission with anticounterfeiting application potential.

Water-sensitive multicolor luminescence in lanthanide-organic framework for anti-counterfeiting

The development of high-level anti-counterfeiting techniques is of great significance in economics and security issues. However, intricate reading methods are required to obtain multi-level information stored in different colors, which greatly limits the application of anti-counterfeiting technology on solving real world problems. Herein, we realize multicolor information anti-counterfeiting under simply external stimulation by utilizing the functional groups and multiple emission centers of lanthanide metal organic framework (Ln-MOFs) to tune luminescence color. Water responsive multicolor luminescence represented by both the tunable color from red to blue within the visible region and high sensitive responsivity has been achieved, owing to the increased nonradiative decay pathways and enhanced Eu³⁺-to-ligand energy back transfer. Remarkably, information hidden in different colors needs to be read with a specific water content, which can be used as an encryption key to ensure the security of the information for high-level anti-counterfeiting.

An advanced color tunable persistent luminescent NaCa2GeO4F:Tb3+ phosphor for multicolor anti-counterfeiting.

Luminescent materials play an important role in anticounterfeiting applications due to their superior properties of visual convenience and high concealment. However, traditional luminescent materials usually exhibit monochromatic emission and are easily counterfeited. Therefore, in this work, we report a multicolor long persistent luminescence (PersL) material, NaCa2GeO4F:Tb3+ (abbreviated as NCGOF:Tb3+), where the color of PersL can be tuned from blue to cyan and bright green by changing the concentration of Tb3+, and the afterglow (concentration) can last for 5.62 h (0.1%), 8.52 h (0.4%) and 7.14 h (0.8%) at the corresponding concentrations of Tb3+, respectively. Investigation revealed that the multicolor PersL is essentially associated with the opportune traps and cross-relaxation effect of Tb3+ in NCGOF. Based on the unique features of PersL, anticounterfeiting devices have been fabricated, and the results indicate that their multicolor features can be easily detected using a portable ultraviolet lamp, and that they are impossible to counterfeit using any substitute so far, meaning that they provide a high level of security for use in practical applications.

Multi-color mechanochromic luminescence of three polymorphic crystals of a donor–acceptor-type benzothiadiazole derivative

The three polymorphic crystals of a donor–acceptor dye exhibited different luminescence colors, which changed in response to mechanical grinding.

Supramolecular oligourethane gels as light-harvesting antennae: achieving multicolour luminescence and white-light emission through FRET

Multicolour and white-emitting oligourethane gels have been prepared; their supramolecular assembly and proof-of-concept photonic applications are reported.

Intense multi-colored luminescence in a series of rare-earth metal-organic frameworks with aliphatic linkers.

Two series of highly luminescent yttrium(iii), europium(iii) and terbium(iii) metal-organic frameworks containing diimine aromatic ligands and the dicarboxylate linker trans-1,4-cyclohexanedicarboxylate (chdc2-) which can be described by the general formulas [M2(bpy)2(chdc)3], where M = Y3+ (1), Eu3+ (2), and Tb3+ (3) and bpy = 2,2'-bipyridyl, and [M2(phen)2(chdc)3], where M = Y3+ (4), Eu3+ (5), and Tb3+ (6) and phen = 1,10-phenanthroline, were synthesized and characterized. All compounds are based on the same dinuclear {M2(L)2(OOCR)6} building blocks and possess a similar topology of the 3D framework with narrow pores. The chelate aromatic ligands act as efficient light-harvesting antennas for subsequent energy transfer to the emitting metal center (M = Eu3+, Tb3+) or intraligand photoemission (M = Y3+). As a result, the reported compounds display intense emission in the red (Eu3+), green (Tb3+) or blue (Y3+) regions representing three basic colors (RGB) of visible light. The measured quantum yields (QYs) of the solid-state luminescence for individual compounds were found to be 63% (1), 46% (2), 59% (3), 2.3% (4), 55% (5) and 49% (6). The drastic reduction of the luminescence efficiency for 4 is explained by the strong disorder of phen ligands. The high thermal stability (up to 300 °C) and exceptional moisture resistance of the bpy-based frameworks 1-3 were confirmed by TG and PXRD measurements. Various bimetal or trimetal compositions were also prepared for the bpy-series. The luminescence properties of these mixed-metal compounds depend on both the chemical composition and excitation wavelength (λex). Remarkably, pure white emission with color temperature = 6126 K was achieved for [Y1.68Eu0.08Tb0.24(bpy)2(chdc)3] at λex = 360 nm with QY = 20%. The reported results suggest that the obtained coordination framework series is a convenient platform for the design of highly efficient light emitting materials with tunable properties.

NaY(MoO4)2-based nanoparticles: synthesis, luminescence and photocatalytic properties.

We report on a novel synthesis method, which produces NaY(MoO4)2 nanoparticles having an almost spherical shape and hydrophilic character. The procedure is also suitable for the preparation of NaY(MoO4)2-based nanophosphors by doping this host with lanthanide cations (Eu3+, Tb3+ and Dy3+), which, under UV illumination, exhibit intense luminescence whose color is determined by the selected doping cation (red for Eu3+, green for Tb3+ and yellow for Dy3+). The effects of the cations doping level on the luminescent properties are analyzed in terms of emission intensities and luminescent lifetime, to find the optimum phosphors. Finally, the performance of these nanophosphors and that of the undoped system for the photocatalytic degradation of rhodamine B, used as a model compound, is also analyzed.

Amphiphilic Metallacycles with Aggregation-Induced Emission and Aggregation-Caused Quenching Luminogens for White-Light Emission and Bioimaging

Discrete metallacycles exhibiting multicolor luminescence, especially white-light emissions, are rarely used in supramolecular assemblies; however, they are crucial for fabricating fluorescent materials. Herein, three amphiphilic rhomboidal metallacycles are synthesized through the metal-ligand interactions and self-assembly of diplatinum(II) acceptors bearing hydrophilic chains, and endohedral aniline and tetraphenylethene-functionalized dipyridyl donors. To investigate the effect of bond linking variation (single, double, or triple bonds) on the supramolecular coordination complexes, the connectivity between the aniline core and dipyridyl group is varied. As the structural framework consisted of both aggregation-induced emission luminogens and aggregation-caused quenching luminophores, photophysical studies are conducted with the fabricated materials. The synthesized metallacycles exhibite solvatochromic properties and bimodal emission in some solvents. The effects of molecular aggregation in the metallacycles are studied using a CHCl3/hexane mixture. The results show the emission properties of the metallacycles could be tuned by varying the degree of molecular aggregation. Particularly, in the CHCl3/hexane mixture (1/9, v/v), fluorescence emission peaks are observed in the entire visible region, and white-light emission of a single molecule (CIE chromaticity coordinate: 0.29, 0.35) is recorded. Moreover, rhomboidal metallacycles with peripheral hydrophilic chains can form spherical micelles via hydrophilic/hydrophobic and π-π stacking interactions. The sizes of the obtained micelles are measured by transmission electron microscopy and dynamic light scattering. These micelles exhibit good biocompatibility and can be employed as cell imaging agents with satisfactory visualization outcomes. Hence, these amphiphilic rhomboidal organoplatinum(II) metallacycles help achieve the tunable emission of single molecule upon molecular aggregation and can be used in fluorescent imaging.

Multicolor luminescence evolving from single-phase Eu3+/Tb3+ co-doped SrLaAlO4 nanomaterials for advanced photonic appliances

Single-phase nanomaterials are the most promising materials, owing to their high luminous-efficiency, environmental-friendly and multicolor-luminance features. The crystal structure of Eu3+/Tb3 + co-doped SrLaAlO4 (SLAO) nanopowders were developed by combustion synthesis (CS). The formation of SLAO materials with tetragonal space group 14/mmm (139) was confirmed by Rietveld refinement of X-ray diffraction (XRD) arrangement. Multicolor luminescence has been achieved via tailoring Tb3+/Eu3+ ratio into SLAO matrix, under UV and near-UV irradiation. Moreover, energy-transfer (ET) efficiencies and analogous mechanisms have been discussed deeply. This work opens avenues for scholars to explore such nanomaterials for advanced photonic applications like white-LEDs, solar-cells, lasers, photo-detectors, etc.

Synthesis of Sub-30 nm Lanthanide-Doped KLu₂F7 Nanorods with Multicolor Upconversion Luminescence.

Sub-30 nm lanthanide-doped KLu₂F7 upconversion (UC) nanorods were synthesized using a hightemperature coprecipitation method. Highly uniform morphologies, a small size distribution and the desirable orthorhombic crystalline phase was achieved by controlling the reaction temperature; while control over the UC luminescence color was achieved by changing the dopant activator. Orthorhombic KLu₂F7 nanorods showed excellent potential as a host phase for future UC luminescence materials in applications such as bioimaging.

Aggregology: Exploration and innovation at aggregate level

Aggregology: Exploration and innovation at aggregate level

In Situ Control of Multicolor Luminescence over the Entire Visible Spectral Region in a Single Chromophore by Sol–Gel Transformation and Dynamic Metal–Ligand Coordination

Controlling multicolor luminescence in a single chromophore is of fundamental significance but remains a great challenge. In this study, a carbazole group was incorporated into terpyridine through ...

Luminescence Studies of Pyrochlore Metal Oxide Nanomaterials

Designing lanthanide doped luminescent materials especially nanomaterials with multifunctional applications is highly challenging and demanding. The chemistry and structure of the host materials for lanthanide ions are critical in the selection of known phosphors and in the discovery of new phosphor materials for being used for the applications. Materials with A2M2O7 pyrochlore composition recently have displayed a variety of advanced applications in solid oxide fuel cells, photocatalysis, thermographic phosphor, thermal barrier coating, X-ray scintillator, photoluminescence, and nuclear waste host, etc. In the past few years, we have focused on the studies of pyrochlore AIII 2MIV 2O7 nanoparticles (NPs, where A = trivalent heavy element ions of both lanthanides and actinides, and M = Zr4+, Hf4+, etc.) useful for solid-state lighting, X-ray scintillators, thermometry, and bioimaging. We have achieved substantial tunability of their particle size, crystal phase, and more importantly, luminescence properties. We have gained a clear understanding of the influences of synthesis conditions, particle morphology and composition on their photoluminescence and radioluminescence. The tunable luminescence properties of these lanthanide doped pyrochlore NPs indicate their great application potentials in solid-state lighting and multicolor luminescence devices.

A stimuli-responsive pillar[5]arene-based hybrid material with enhanced tunable multicolor luminescence and ion-sensing ability.

Tunable luminescent materials are becoming more and more important owing to their broad application potential in various fields. Here we construct a pillar[5]arene-based hybrid material with stimuli-responsive luminescent properties and ion-sensing abilities from a pyridine-modified conjugated pillar[5]arene and a planar chromophore oligo(phenylenevinylene) upon coordination of Cd (II) metal cores. This new material not only shows an optimized luminescence due to the minimized π–π stacking and efficient charge transfer properties benefitting from the existence of pillar[5]arene rings, but also exhibits tunable multicolor emission induced by different external stimuli including solvent, ions and acid, indicating great application potential as a fluorescent sensory material, especially for Fe3+. With this pillar[5]arene-based dual-ligand hybrid material, valid optimization and regulation on the fluorescence of the original chromophore have been achieved, which demonstrates a plausible strategy for the design of tunable solid-state luminescent materials and also a prototypical model for the effective regulation of fluorescent properties of planar π systems using synthetic macrocycle-based building blocks.

Ultrabroadband Tuning and Fine Structure of Emission Spectra in Lanthanide Er-Doped ZnSe Nanosheets for Display and Temperature Sensing.

Realizing multicolored luminescence in two-dimensional (2D) nanomaterials would afford potential for a range of next-generation nanoscale optoelectronic devices. Moreover, combining fine structured spectral line emission and detection may further enrich the studies and applications of functional nanomaterials. Herein, a lanthanide doping strategy has been utilized for the synthesis of 2D ZnSe:Er3+ nanosheets to achieve fine-structured, multicolor luminescence spectra. Simultaneous upconversion and downconversion emission is realized, which can cover an ultrabroadband optical range, from ultraviolet through visible to the near-infrared region. By investigating the low-temperature fine structure of emission spectra at 4 K, we have observed an abundance of sublevel electronic energy transitions, elucidating the electronic structure of Er3+ ions in the 2D ZnSe nanosheet. As the temperature is varied, these nanosheets exhibit tunable multicolored luminescence under 980 and 365 nm excitation. Utilizing the distinct sublevel transitions of Er3+ ions, the developed 2D ZnSe:Er3+ optical temperature sensor shows high absolute (15.23% K-1) and relative sensitivity (8.61% K-1), which is superior to conventional Er3+-activated upconversion luminescent nanothermometers. These findings imply that Er3+-doped ZnSe nanomaterials with direct and wide band gap have the potential for applications in future low-dimensional photonic and sensing devices at the 2D limit.