Patterning of red, green, and blue luminescent films based on CaWO4:Eu3+, CaWO4:Tb3+, and CaWO4 phosphors via microcontact printing route

Role of thermal decomposition process in the photocatalytic or photoluminescence properties of BiPO4 polymorphs

Thermal decomposition process was used to obtain modified photocatalytic and/or photoluminescence properties of bismuth phosphate polymorphs. The precursor BiPO₄ , 0.7H₂ O was synthesized by a coprecipitation route. The observed polymorphs were the hexagonal P3₁ 21 hydrate phase BiPO₄ , 0.7H₂ O at 25°C, a mix system of hexagonal and monoclinic P2₁ /n phases at 200°C and 400°C, a mix system of monoclinic phases P2₁ /n and P2₁ /m at 600°C, and a unique monoclinic phase P2₁ /m at 900°C. The X-ray diffraction analyses allowed evidencing lattice deformations due to structural defects. The photocatalytic activities in the presence of rhodamine B in aqueous solution were determined using UV light irradiation. The best photocatalytic efficiencies were observed with the mix systems resulting from thermal decomposition at 400 and 600°C. Photoluminescence experiments performed under UV-laser light irradiation revealed unexpected emissions in the green-orange range, with optimal intensities for the mix systems observed at 400°C. The role of structural defects resulting from decomposition process is discussed. PRACTITIONER POINTS: Thermal decomposition is used to introduce structural defects in BiPO₄ polymorphs The BiPO₄ intermediate systems are used to photodegrade rhodamine B Active species trapping experiments are performed Photoluminescence experiments highlight green-orange emissions Structural defects are at the origin of this photoluminescence.

Effects of slight structural distortion on the luminescence performance in (Ca1-x Eux )WO4 luminescent materials

(Ca_1-x Eu_x )WO₄ (x = 0-21 mol%) phosphors were prepared using the classical solid-state reaction method. The influence of Eu³⁺ ion doping on lattice structure was observed using powder X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO₄ lattice with a scheelite structure in the form of a Eu³⁺ ion, which introduced a slight lattice distortion into the CaWO₄ matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f-f excitation transitions of Eu³⁺ activators. When the Eu³⁺ concentration was increased to 21 mol%, a local luminescence centre of [WO₄ ]^2- groups was detected in the matrix and manifested as the decay curves of [WO₄ ]^2- groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu³⁺ between different energy levels (such as ⁷ F₀ →⁵ L₆ , ⁷ F₀ →⁵ D₂ ) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO₄ ]^2- →Eu³⁺ was efficient and incomplete.

Luminescence properties and energy transfer of Tb3+, Eu3+ co-doped YTaO4 phosphors obtained via sol-gel combustion process

Tantalate is considered as a valuable and efficient luminescence host because of its intense absorption in the ultraviolet area and excellent chemical properties. In this work, a series of pure YTaO4:Eu3+ and/or Tb3+ crystals were prepared via a sol-gel combustion method. The morphology, structure, and optical properties of the samples were discussed in detail. The Eu3+, Tb3+ co-doped YTaO4 samples are consisted of small spherical particles of around 18 nm. The prepared YTaO4:Tb3+ and/or Eu3+ samples exhibit the characteristic wide excitation band around 210-300 nm, the characteristic narrow red emission of Eu3+ (5D0 → 7F2) transitions and green emission of the Tb3+ (5D4 → 7F5) transitions when excited by UV light. It is focused on the energy transfer processes from the YTaO4 to Tb3+ as well as Eu3+ ions and from Tb3+ to Eu3+ ions of YTaO4:Eu3+/Tb3+ phosphors. Color-tunable emissions are realized through adjusting the types of rare earth ion (Eu3+ and Tb3+) and relative doping concentrations excited by a single wavelength. That is to say, the obtained Tb3+ and Eu3+ co-doped YTaO4 phosphors have a promising prospect in lasers, white light diodes (WLED), fluorescent lamp, and field emission display devices, etc.

Supramolecular Copolymerization Strategy for Realizing the Broadband White Light Luminescence Based on N-Deficient Porous Graphitic Carbon Nitride (g-C3N4)

The N-deficient porous g-C₃N₄ with broadband white light emission was constructed by supramolecular copolymerization design, which combined organic copolymers cyanuric acid and 2,4,6-triaminopyrimidine with melamine upon the mixture gas environment of (95%)N₂/(5%)H₂. Herein, we achieved great breakthrough in narrowing the band gap of g-C₃N₄ from 2.64 to 1.39 eV. Furthermore, in contrast to pristine g-C₃N₄, we demonstrated that the emission wavelengths of N-deficient porous g-C₃N₄ can be tuned from narrow blue to broadband white range, where the optimal white light coordinate position is (0.297, 0.345). The prepared N-deficient porous g-C₃N₄ overcomes the limitation of the narrow adjusting range of optical properties while using conventional g-C₃N₄ and makes it more promising for applications in solid-state displays.

Probing emission and defects in BaWxMo1–xO4 solid solutions: achieving color tunable luminescence by W/Mo ratio and size manipulation

This work highlights the size, structure, and composition manipulation for designing color-tunable phosphors based on doped scheelite micro- and nanocrystals.

Controllable synthesis of multi-morphological SrWO4:Ln3+ (Ln = Eu, Tb) hierarchical structures and their luminescence properties

Multi-morphological SrWO₄:Ln³⁺ hierarchical structures including dumbbell-like, nanosheets, rice-like, peanut-like, etc. could be controllably synthesized through readily altering reaction conditions.

Multicolor Tuning and Temperature-Triggered Anomalous Eu3+-Related Photoemission Enhancement via Interplay of Accelerated Energy Transfer and Release of Defect-Trapped Electrons in the Tb3+,Eu3+-Doped Strontium-Aluminum Chlorites

So far, a large number of rare earth (RE) and non-RE-doped emission-tunable crystals based on controllable energy transfer have become available, but numerous mechanistic issues, particularly for those that involve temperature-dependent energy transfer between the well-shielded 4f RE ions, lack comprehensive theoretical and experimental investigation, limiting greatly their development and applications in the future. Here, we design and report a type of Tb³⁺,Eu³⁺-doped Sr₃Al₂O₅Cl₂ phosphors capable of multiemissions upon excitation at 376 nm, through using the orthorhombic Sr₃Al₂O₅Cl₂ as the host lattice while the well-shielded 4f Tb³⁺ and Eu³⁺ ions as dual luminescent centers. Our results reveal that the energy transfer from Tb³⁺ to Eu³⁺ ions, happening via an electric dipole-quadrupole (d-q) interaction, can be controlled by the doping ratio of Tb³⁺ and Eu³⁺, leading to the tunable emissions from green (0.3159, 0.5572) to red (0.6579, 0.3046). It is found from time-resolved photoluminescence (PL) spectra that this energy transfer begins at t = 5 μs and gradually ends at t ≥ 200 μs. Moreover, from temperature-dependent PL results, we reveal that the Eu³⁺ emission features an anomalous intensity enhancement at the earlier heating state. With the density functional theory (DFT) calculations, we have screened the possibilities of site preferential substitution problem. By jointly taking into account the X-ray diffraction Rietveld refinement, DFT findings, and PL and thermoluminescence spectra, a mechanistic profile is proposed for illustrating the PL observations. In particular, our discussions reveal that the temperature-triggered Eu³⁺ emission enhancement is due to the interplay of the temperature-induced accelerated energy transfer and defect-trapped electrons that are released upon the thermal stimulation. Unlike most of reported phosphor materials that are always suggested for phosphor-converted white light-emitting diodes, we propose new application possibilities for Tb³⁺,Eu³⁺-doped Sr₃Al₂O₅Cl₂ phosphors, such as anticounterfeiting, temperature-controlled fluorescence sensor, data storage, and security devices.

Tunable morphologies, multicolor properties and applications of RE3+ doped NaY(MoO4)2 nanocrystals via a facile ligand-assisted reprecipitation process

Rare earth (RE3+)-doped NaY(MoO4)2 nanocrystals are efficient materials for realizing multicolor emission, which plays an important role in displays, W-LEDs, solar cells and biolabeling. Up to now, research on the multicolor tuning properties of RE3+-doped NaY(MoO4)2 nanoparticles has mostly focused on traditional preparation routes such as the hydrothermal method and sol-gel process. However, the products obtained using these methods are usually large in size (on the micron/submicron scale) and agglomeration problems are inevitable. With the development of nano optoelectronic devices and bioluminescence labeling, there is an urgent need to find an efficient method to prepare nanoscale, monodispersed and NaY(MoO4)2:RE3+ nanocrystals (NCs) with good crystallinity and stronger emission properties. In this work, we demonstrate a simple, fast, reproducible and one-step synthesis of NaY(MoO4)2:Eu3+ NCs with sizes varying from 1-20 nm via a ligand-assisted reprecipitation strategy. The reaction mechanism and emission intensities of NaY(MoO4)2:Eu3+ NCs with various morphologies have been discussed in detail. Furthermore, Tb3+ and Eu3+ ion co-doped NaY(MoO4)2 NCs were also prepared, and various emission colors were obtained and tuned from red, orange-red, yellow and yellow-green to green. Energy transfer between the Tb3+ and Eu3+ ions in the NaY(MoO4)2 host matrix has also been demonstrated. Finally, a highly efficient and stable NaY(MoO4)2:0.05Tb,0.04Eu NC-based W-LED device was built, which indicates the promising future application for this material in the field of lighting. The tunable multicolour emission, ease of preparation and nanosize reveal that NaY(MoO4)2:RE3+ NCs have a potential application in full color displays and W-LEDs.

Controllable synthesis of lanthanide Yb3+ and Er3+ co-doped AWO4 (A = Ca, Sr, Ba) micro-structured materials: phase, morphology and up-conversion luminescence enhancement

The combination of CDs can mainly maintain the morphologies of AWO₄:Yb³⁺,Er³⁺ but prominently increase their up-conversion luminescence performance.

Controlled synthesis of 3D flower-like MgWO4:Eu3+ hierarchical structures and fluorescence enhancement through introduction of carbon dots

3D flower-like MgWO₄:Eu³⁺ structures composed of many nanosheets were synthesized and their luminescence can be enhanced through introduction of CDs.

Multicolor Tunable Luminescence Based on Tb3+/Eu3+ Doping through a Facile Hydrothermal Route

Ln³⁺-doped fluoride is a far efficient material for realizing multicolor emission, which plays an important part in full-color displays, biolabeling, and MRI. However, studies on the multicolor tuning properties of Ln³⁺-doped fluoride are mainly concentrated on a complicated process using three or more dopants, and the principle of energy transfer mechanism is still unclear. Herein, multicolor tunable emission is successfully obtained only by codoping with Tb³⁺ and Eu³⁺ ions in β-NaGdF₄ submicrocrystals via a facile hydrothermal route. Our work reveals that various emission colors can be obtained and tuned from red, orange-red, pink, and blue-green to green under single excitation energy via codoping Tb³⁺ and Eu³⁺ with rationally changed Eu³⁺/Tb³⁺ molar ratio due to the energy transfer between Tb³⁺ and Eu³⁺ ions in the β-NaGdF₄ host matrix. Meanwhile, the energy transfer mechanism in β-NaGdF₄: x Eu³⁺/y Tb³⁺ (x + y = 5 mol %) submicrocrystals is investigated. Our results evidence the potential of the dopants' distribution density as an effective way for analyzing energy transfer and multicolor-controlled mechanism in other rare earth fluoride luminescence materials. Discussions on the multicolor luminescence under a certain dopant concentration based on single host and wavelength excitation are essential toward the goal of the practical applications in the field of light display systems and optoelectronic devices.

Terbium-Aspartic Acid Nanocrystals with Chirality-Dependent Tunable Fluorescent Properties

Terbium-aspartic acid (Tb-Asp) nanocrystals with chirality-dependent tunable fluorescent properties can be synthesized through a facile synthesis method through the coordination between Tb and Asp. Asp with different chirality (dextrorotation/d and levogyration/l) changes the stability of the coordination center following fluorescent absorption/emission ability differences. Compared with l-Asp, d-Asp can coordinate Tb to form a more stable center, following the higher quantum yield and longer fluorescence life. Fluorescence intensity of Tb-Asp linearly increases with increase ratio of d-Asp in the mixed chirality Tb-Asp system, and the fluorescent properties of Tb-Asp nanocrystals can be tuned by adjusting the chirality ratio. Tb-Asp nanocrystals possess many advantage, such as high biocompatibility, without any color in visible light irradiation, monodispersion with very small size, and long fluorescent life. Those characteristics will give them great potential in many application fields, such as low-cost antifake markers and advertisements using inkjet printers or for molds when dispersed in polydimethylsiloxane. In addition, europium can also be used to synthesize Eu-Asp nanoparticles. Importantly, the facile, low-cost, high-yield, mass-productive "green" process provides enormous advantages for synthesis and application of fluorescent nanocrystals, which will have great impact in nanomaterial technology.

Lanthanide-activated scheelite nanocrystal phosphors prepared by the low-temperature vapor diffusion sol–gel method

The high degree of synthetic flexibility inherent to the vapor diffusion sol–gel method has enabled the synthesis of a CaWO₄:(Eu,Tb) dual-sensitized white light emitting nanocrystal phosphor.

Technetium incorporation in scheelite: insights from first-principles

The energetics of ⁹⁹Tc incorporation into the lattice of scheelite, CaWO₄, was investigated within the framework of density functional theory.

Recent progress in low-voltage cathodoluminescent materials: synthesis, improvement and emission properties

Nowadays there are several technologies used for flat panel displays (FPDs) and the development of FPDs with enhanced energy efficiency and improved display quality is strongly required. Field emission displays (FEDs) have been considered as one of the most promising next generation flat panel display technologies due to their excellent display performance and low energy consumption. For the development of FEDs, phosphors are irreplaceable components. In the past decade, the study of highly efficient low-voltage cathodoluminescent materials, namely FED phosphors, has become the focus of enhancing energy efficiency and realizing high-quality displays. This review summaries the recent progress in the chemical synthesis and improvement of novel, rare-earth and transition metal ions activated inorganic cathodoluminescent materials in powder and thin film forms. The discussion is focused on the modification of morphology, size, surface, composition and conductivity of phosphors and the corresponding effects on their cathodoluminescent properties. Special emphases are given to the selection of host and luminescent centers, the adjustment of emission colors through doping concentration optimization, energy transfer and mono- or co-doping activator ions, the improvement of chromaticity, color stability and color gamut as well as the saturation behavior and the degradation behavior of phosphors under the excitation of a low-voltage electron beam. Finally, the research prospects and future directions of FED phosphors are discussed with recommendations to facilitate the further study of new and highly efficient low-voltage cathodoluminescent materials.

Controlling the energy transfer via multi luminescent centers to achieve white light/tunable emissions in a single-phased X2-type Y2SiO5:Eu(3+),Bi(3+) phosphor for ultraviolet converted LEDs

So far, more than 1000 UV converted phosphors have been reported for potential application in white light-emitting diodes (WLEDs), but most of them (e.g., Y2O2S:Eu, YAG:Ce or CaAlSiN3:Eu) suffer from intrinsic problems such as thermal instability, color aging or re-absorption by commixed phosphors in the coating of the devices. In this case, it becomes significant to search a single-phased phosphor, which can efficiently convert UV light to white lights. Herein, we report a promising candidate of a white light emitting X2-type Y2SiO5:Eu(3+),Bi(3+) phosphor, which can be excitable by UV light and address the problems mentioned above. Single Bi(3+)-doped X2-type Y2SiO5 exhibits three discernible emission peaks at ∼355, ∼408, and ∼504 nm, respectively, upon UV excitation due to three types of bismuth emission centers, and their relative intensity depends tightly on the incident excitation wavelength. In this regard, proper selection of excitation wavelength can lead to tunable emissions of Y2SiO5:Bi(3+) between blue and green, which is partially due to the energy transfer among the Bi centers. As a red emission center Eu(3+) is codoped into Y2SiO5:Bi(3+), energy transfer has been confirmed happening from Bi(3+) to Eu(3+) via an electric dipole-dipole (d-d) interaction. Our experiments reveal that it is easily realizable to create the white or tunable emissions by adjusting the Eu(3+) content and the excitation schemes. Moreover, a single-phased white light emission phosphor, X2-type Y1.998SiO5:0.01Eu(3+),0.01 Bi(3+), has been achieved with excellent resistance against thermal quenching and a QE of 78%. At 200 °C, it preserves >90% emission intensity of that at 25 °C. Consequent three time yoyo experiments of heating-cooling prove no occurrence of thermal degradation. A WLED lamp has been successfully fabricated with a CIE chromaticity coordinate (0.3702, 0.2933), color temperature 4756 K, and color rendering index of 65 by applying the phosphor onto a UV LED chip.

Luminescent hollow CaWO4 microspheres: template-free synthesis, characterization and application in drug delivery

Luminescent hollow structural CaWO₄ microspheres prepared by a template-free method show a sustained-release property for IBU.

Sunlight-activated Eu2+/Dy3+ doped SrAl2O4 water resistant phosphorescent layer for optical displays and defence applications

Demonstration of a high brightness, strong green emitting, water resistant and flexible phosphorescent layer for display and defence applications.

Calcination-free micropatterning of rare-earth-ion-doped nanoparticle films on wettability-patterned surfaces of plastic sheets

We demonstrate a patterning technique of rare-earth-ion-doped (RE) nanoparticle films directly on wettability-patterned surfaces fabricated on plastic sheets in one step. Self-assembled monolayers consisting of silane-coupling agent with hydrophobic groups were fabricated on plastic sheets. UV-ozone treatments were performed through a metal mask to selectively remove the self-assembled monolayers in a patterned manner, resulting in the formation of wettability-patterned surfaces on plastic sheets. Using a water dispersion of Er(3+) and Yb(3+)-codoped Y2O3 nanoparticles at a diameter of 100 nm, RE-nanoparticle films were fabricated on the wettability-patterned surfaces by a dip-coating technique. By adjusting the concentration of RE-nanoparticle dispersion, withdrawal speed, and withdrawal angle, amount of RE-nanoparticles, we were able to control the structures of the RE-nanoparticle films. Fluorescence microscope observations demonstrate that visible upconversion luminescence and near-infrared fluorescence were emitted from the RE-nanoparticle films on the wettability-patterned surfaces. This technique allows for the fabrication of flexible emitting devices with long-operating life time with minimized material consumption and few fabrication steps, and for the application to sensors, emitting devices, and displays in electronics, photonics, and bionics in the future.

Efficient luminescence of long persistent phosphor combined with photonic crystal

In this paper, the luminescence properties of the long persistent phosphor (LPP) were apparently improved by combining with photonic crystal (PC). An optimized PC can double the afterglow intensity and prolong 1.7 times of the afterglow time of SrAl2O4: Eu, a commercially available LPP, without any dopants. These results were ascribed to the stopband effect of the PC. The PC combined LPP structure was beneficial for the applications of LPP in emergency indication which called for brighter afterglow intensity and longer afterglow time.

Self-assemblies of luminescent rare earth compounds in capsules and multilayers

This review addresses luminescent rare earth compounds assembled in microcapsules as well as in planar films fabricated by the layer-by-layer (LbL) technique, the Langmuir-Blodgett (LB) method and in self-assembled monolayers. Chemical precipitation, electrostatic, van der Waals interactions and covalent bonds are involved in the assembly of these compounds. Self-organized ring patterns of rare earth complexes in Langmuir monolayers and on planar surfaces with stripe patterns, as well as fluorescence enhancement due to donor-acceptor pairs, microcavities, enrichment of rare earth compounds, and shell protection against water are described. Recent information on the tuning of luminescence intensity and multicolors by the excitation wavelength and the ratio of rare earth ions, respectively, are also reviewed. Potential applications of luminescent rare earth complex assemblies serving as biological probes, temperature and gas sensors are pointed out.

Is BiPO4 a better luminescent host? Case study on doping and annealing effects

Metal phosphates have been popularly regarded as excellent luminescence hosts of lanthanide ions, while such an issue is challenged by the ignorance about the structural stability that may originate from the different chemical nature between the framework and the dopant lanthanide ions. Here, we choose BiPO(4) as a model compound to study. A detailed investigation of the effects of Eu doping and annealing on the structures and related luminescence properties of Bi(1-x)PO(4):Eu(x) (x = 0-0.199) has been carried out. A monoclinic phase (denoted as LTMP) was obtained for the undoped sample, which gradually transformed to a hexagonal phase (HP) with increasing doping level of Eu(3+) to x = 0.068. Further, it is also found that annealing had an obvious impact on the structures of the resulted samples. With increasing the annealing temperature up to 400 °C a phase transformation from HP to LTMP happens, which is opposite to that with doping. The above phase transformation behaviors were further confirmed by performing structural studies of doping with Dy(3+) ions and annealing undoped BiPO(4). The structural evolution had a great influence on the luminescent properties. Initially a significant decrease in Eu(3+) luminescence intensity and quantum efficiency was observed when LTMP transformed to HP. Afterward, a converse situation, increasingly enhanced luminescence performance, appeared when HP transformed to LTMP. Therefore, whether metal phosphates could be taken as better luminescence hosts must take into account their structural changes caused by the different chemical natures between framework and dopant ions, which may provide an important reference for designing new luminescent materials.

Biomimetic engineering of a generic cell-on-membrane architecture by microfluidic engraving for on-chip bioassays

We develop a biomimetic cell-on-membrane architecture in close-volume format which allows the interfacial biocompatibility and the reagent delivery capability for on-chip bioassays. The key concept lies in the microfluidic engraving of lipid membranes together with biological cells on a supported substrate with topographic patterns. The simultaneous engraving process of a different class of fluids is promoted by the front propagation of an air-water interface inside a flow-cell. This highly parallel, microfluidic cell-on-membrane approach opens a door to the natural biocompatibility in mimicking cellular stimuli-response behavior essential for diverse on-chip bioassays that can be precisely controlled in the spatial and temporal manner.