Core-shell Phosphors Research Articles

A Eu3+doped functional core-shell nanophosphor as fluorescent biosensor for highly selective and sensitive detection of dsDNA

Lanthanide-doped core-shell nanomaterials have illustrated budding potential as luminescent materials, but their biological applications have still been very limited due to their aqueous solubility and biocompatibility. Here, we report a simple and cost-effective approach to construct a water-stable chitosan-functionalized lanthanoid-based core shell (Ca-Eu:Y2O3@SiO2) nanophosphor. The as-synthesized Ca-Eu:Y2O3@SiO2-chitosan (CEY@SiO2-CH) nanophosphor has been characterized for its structural, morphological, and optical properties, by employing different analytical tools. This sensing platform is suitable for dsDNA probing by tracing the “turn on” fluorescence signal generated by CEY@SiO2-CH nanophosphor with the addition of dsDNA. The ratio of fluorescence intensity enhancement is proportional to the concentration of dsDNA in the range 0.1–90 nM, with the limit of detection at ⁓16.1 pM under optimal experimental conditions. The enhancement in fluorescence response of functionalized core-shell phosphor with dsDNA is due to the antenna effect. Additionally, response of probe has been studied for the real samples displaying percent recovery in between 101 and 105, maximum RSD% upto 5.23 (n = 3). This outcome can be applied to the selective sensing of dsDNA through optical response. These findings establish the CEY@SiO2-CH a simple, portable, and potential candidate as a sensor for rapid and analytical detection of dsDNA.

Self-Luminous Wood Coatings with Carbon Dots/TiO2 Grafted Afterglow SrAl2O4: Eu, Dy Core-Shell Phosphors for Long-Lasting Formaldehyde Removal.

Long-term relief of indoor volatile pollution has become a competitive issue worldwide in both visible and dark environments. A novel self-luminous wood coating with carbon dots (CDs)/titanium dioxide (TiO2) nanomaterial coated SrAl2O4: Eu2+, Dy3+ (CDs/TiO2@SAO) composite was prepared for the long-term degradation of formaldehyde through a simple sol-gel method. The microstructure, chemical composition, ultraviolet-visible (UV-vis) spectra, and long-lasting fluorescence of the CDs/TiO2@SAO photocatalyst were analyzed to illustrate the mechanism for degrading formaldehyde. The obtained CDs with a particle size of ~2-7 nm have a good graphite structure and presented good absorption in visible light. In addition, owing to the synergistic effect of the CDs/TiO2 nanomaterial coating layer and the long-afterglow luminescence of the SAO phosphor, the CDs/TiO2@SAO composite can absorb a part of the visible light for photocatalytic degradation and store luminous energy efficiently at daytime so as to give out visible luminescence continuously for a few hours in the darkness. Furthermore, the functional wood coatings with CDs/TiO2@SAO composite presented continuous and efficient photocatalytic activity in the presence and absence of light exposure. The current research could provide a new strategy for designing an efficient photocatalyst for degrading formaldehyde pollution in the daytime with a visible light supply and in an indoor dark environment without an external light source.

Novel Dual-Excitation and Dual-Emission Materials: Eu2+,Pb2+ Co-doped Core-Shell-Structured CaS@CaZnOS Phosphors and Their Application for Highly Efficient Photosynthesis of Plants.

Eu2+,Pb2+-doped core-shell-structured CaS@CaZnOS phosphors were synthesized by a two-step high-temperature solid-phase method. The as-synthesized CaS:Eu2+,Pb2+@CaZnOS:Pb2+ phosphors possess excellent dual-excitation and dual-emission (DE2) luminescent properties, which give rise to red emission peaking at 650 nm under green excitation, derived from the core CaS:Eu2+,Pb2+, and blue emission peaking at 424 nm, originating from the shell CaZnOS:Pb2+, under ultraviolet (UV) excitation. In addition, tunable red/blue emission can be achieved by changing the doping concentration of Pb2+ in the CaZnOS shell. The red/blue dual emission of core-shell DE2 phosphors under excitation of UV and green light significantly matches with the absorption spectrum of chlorophyll (a, b); hence, the as-prepared phosphors are excellent solar spectral conversion (SSC) auxiliaries of plastic films or laminated glass for greenhouses and provide ideas for creating more efficient and practically valuable SSC auxiliaries. The DE2 properties are described, and the energy transfer mechanism from Pb2+ to Eu2+ in the core is proposed and discussed in detail.

Design of core–shell phosphors with tunable luminescence and improved thermal stability by coating with g-C3N4

We propose and demonstrate a novel methodology of coating g-C3N4 on phosphors by a vapor deposition method to synthesize core–shell phosphors with tunable luminescence and improved thermal stability.

Multicolor tunable luminescence and energy transfer of core-shell structured SiO2@Gd2O3 microspheres co-activated with Dy3+/Eu3+ under single UV excitation.

Optimizing structure and varying doped ions are two main strategies to obtain excellent luminescence performance. Spherical morphology is considered to be the most ideal phosphor structure due to the least surface defects. Herein, a series of spherical and monodispersed Dy3+/Eu3+ co-activated SiO2@Gd2O3 core-shell phosphors with multicolor tunable luminescence were successfully prepared via a facile urea assisted precipitation method. Related chemical reactions and the possible growth mechanism of Gd2O3:Ln3+ directional deposition on the surface of SiO2 microspheres were put forward. Upon 273 nm UV radiation excitation, SiO2@Gd2O3:Dy3+ and SiO2@Gd2O3:Eu3+ samples exhibited characteristic yellow (4F9/2-6H13/2) and blue (4F9/2-6H15/2) emissions of Dy3+ and red (5D0-7F2) emission of Eu3+, respectively. Meanwhile, multicolor emissions (warm white, yellow and orange) could be easily obtained by modulating the relative content of Dy3+ and Eu3+ in SiO2@Gd2O3:Ln3+ samples under a single excitation wavelength. Moreover, it was confirmed that Dy3+ could transfer energy to Eu3+ in the form of quadrupole-quadrupole interaction and further improved the luminescence intensity of Eu3+ by comparing experimental data with theoretical calculations. These results imply that tunable luminescence Dy3+,Eu3+ co-doped SiO2@Gd2O3 microspheres have great potential applications in multicolor displays and biolabeling fields.

Full spectrum core-shell phosphors under ultraviolet excitation.

Ce/MgY4Si3O13:Ce-Y2O3:Eu core-shell structure was designed and accomplished via a urea homogeneous precipitation method. The as prepared phosphors can emit photons with a broad range of wavelengths from 340 nm to 700 nm under excitation light of 330 nm. The internal quantum efficiency can reach up to 68%.

Investigation of undoped ZnO@SiO2 core–shell phosphors with green luminescence

In this study, ZnO nanoparticles (NPs) with the structure of hexagonal prisms and different diameters (20–45 nm) and lengths (80–320 nm) were used as a precursor with tetraethyl orthosilicate to fabricate ZnO@SiO2 core–shell NPs. After SiO2 was coated on the surfaces of the ZnO NPs as the shell, the ZnO@SiO2 core–shell NPs were heated at temperatures of 900–1300 °C. The zinc orthosilicate (α-Zn2SiO4) phase was observed as the ZnO@SiO2 core–shell NPs were heated at temperatures of 800–1300 °C. Analysis of the X-ray diffraction patterns showed that at 900 °C, unknown or secondary phases were observed in the ZnO@SiO2 core–shell NPs. When the temperature exceeded 900 °C, no secondary or unknown phases were observed. The effect of calcining temperature on the luminescence properties of the ZnO@SiO2 core–shell phosphors was readily observable. We found two important novelties in the synthesized ZnO@SiO2 (or undoped α-Zn2SiO4) powders. First, the fabricated ZnO@SiO2 phosphors could emit green light with no activators. Second, measurement of the decay time of the ZnO@SiO2 phosphors revealed a long decay time.

Synthesis and luminescence properties of Al2O3@YAG: Ce core–shell yellow phosphor for white LED application

A monodispersed Al2O3@YAG: Ce core-shell phosphor has been synthesized by coating Y2O3: Ce film on Al2O3 particle. The phosphor has particles size of 60–120 nm and shows high dispersity due to the high dispersed Al2O3 particles prepared by nonaqueous precipitation method. The core-shell structured phosphor consists of a corundum core and a YAG shell. The Al2O3@YAG: Ce core-shell yellow phosphor presents high yellow emission. The light-emitting diode (WLED) based on this yellow phosphor and InGaN blue chip displays high white purity. This Al2O3@YAG: Ce core–shell phosphor can be viewed as a promising candidate yellow phosphor for white LEDs.

Structure and luminescence of core-shell phosphor aluminate-boron oxide

Long-afterglow phosphor SrAl2O4: 0.01Eu2+, 0.01Dy3+ (SAO) requires a high sintering temperature of 1400 °C even when boric acid is added as flux via a solid-state reaction. The aluminum source NaAlO2 behaved as a good mineralizer in the designed hydrothermal process to achieve a large surface-to-thickness ratio of SAO. The flower-like shape of hydrothermally prepared hSAO without B2O3 after annealing at 1100 °C/4 h transformed into a rod-like plate phosphor with nano-thickness. Such a small rod-like plate exhibited higher photoluminescence (PL) intensity than large-grained B2O3-added bSAO prepared via a solid-state reaction. The annealed hSAOs inherited the morphology of the as-hydrothermally prepared aluminates. A nano-thick sheet of annealed aSAO containing B2O3 further enhanced the PL significantly and indicated a blue shift independent of the grain size. Furthermore, the nano-thick sheet of phosphors exhibited the same afterglow as the conventional tens-of-micrometers-sized phosphors. Fourier-transform infrared spectroscopy and X-ray diffraction results showed that the BO4 bond may substitute AlO4 in the structure and the BO3 bond is in a flux outside the annealed aSAO and bSAO grains. The molten flux formed a thin layer on the surface of the SAO particles to be a core-shell of the SAO-B2O3 structure, behaving as a diffusion-assistant medium and environmental protection layer against acid and humidity.

Improved optical properties of YVO4:Eu3+ nano–layers on silica spheres

In this research, silica spheres with uniform size of 400 nm were successfully prepared by modified Stöber process. Then, the surface of the synthesized silica particles was coated with several layers of YVO4:Eu3+ using properly adjusted ethanol/water mixture ratio by an optimized sol–gel process. The obtained phosphor nanostructures were characterized precisely using X–ray diffraction, Fourier transform infrared, field emission scanning electron microscope, and transmission electron microscope instruments. The photoluminescence properties of SiO2@YVO4:Eu3+ phosphors were analyzed after the formation of YVO4:Eu3+ layers. When the calcination temperature was adjusted at 800 °C, the synthesized core–shell phosphors showed the highest luminescent properties. This method produces designed SiO2@YVO4:Eu3+ phosphor nanostructures with favourable photoluminescence properties having low–cost fabrication due to the partial substitution of precious rare earth elements by inexpensive SiO2 spheres while presenting comparable luminescence properties with the pure YVO4:Eu3+ phosphors.

Core-shell-core heterostructural engineering of Y2O3:Eu3+/MCM-41/YVO4:Eu3+ for enhanced red emission and tunable, broadened-band response to excitation

For the first time, a hierarchical phosphor Y2O3:Eu3+/MCM-41/YVO4:Eu3+, with a core–shell-core heterostructure, is presented in this study. Synergistically bridging the phosphors Y2O3:Eu3+ (as an inner core) and YVO4:Eu3+ (as an outer core) by amorphous SiO2, i.e., MCM-41 (with ordered mesoporous channels) leads to the generation of the core–shell-core heterostructure with enhanced red emission and tunable, broadened-band response to excitation. The novel structure of the core–shell-core hierarchical material is clarified through various characterization methods including X-ray diffraction analysis, transmission electron microscopy, selected-area electron diffraction and N2 adsorption–desorption measurements. Significantly, through temperature-dependent fluorescence investigation, it is found that our core–shell phosphor (Y2O3:Eu3+/MCM-41) exhibits impressive fluorescence stability against temperature variation (27–227 °C) due to the protective effect resulting from MCM-41. By contrast, lowered stability can be noted for the core–shell-core phosphor (Y2O3:Eu3+/MCM-41/YVO4:Eu3+), especially when the temperature is higher than 100 °C, owing to the outer core (YVO4:Eu3+ nanoparticles) that is directly exposed to heat. Such a kind of luminescent materials holds substantial promise for labeling the organisms that are vulnerable to short-wavelength UV light irradiation. Additionally, potential intelligent systems can be expected to be designed on the basis of the fluorescence mutation as triggered by the temperature of 100 °C.

Synthesis and Characterization of SiO2@Y2MoO6:Eu3+ Core-Shell Structured Spherical Phosphors by Sol-Gel Process.

SiO2@Y2MoO6:Eu3+ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO2@Y2MoO6:Eu3+ core-shell phosphors. The XRD results demonstrated that the Y2MoO6:Eu3+ layers on the SiO2 spheres crystallized after being annealed at 700 °C and the crystallinity increased with raising the annealing temperature. The obtained core-shell phosphors have spherical shape with narrow size distribution (average size ca. 640 nm), non-agglomeration, and smooth surface. The thickness of the Y2MoO6:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (70 nm for four deposition cycles). The Eul+ shows a strong PL emission (dominated by 5D0-7F2 red emission at 614 nm) under the excitation of 347 nm UV light. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

Synthesis and luminescence properties of highly uniform SiO2@LaPO4:Eu3+ core–shell phosphors

Abstract SiO 2 @LaPO 4 :Eu 3+ core–shell phosphors have been successfully synthesized by a one-step and economical wet-chemical route at low temperature. The as-obtained products were characterized by means of photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The SEM, EDS and XPS analysis indicate that SiO 2 @LaPO 4 :Eu 3+ core–shell phosphors can only be synthesized in a pH range of 8–11 and the possible mechanism has been proposed. The XRD results demonstrate that the structure of LaPO 4 :Eu 3+ layers is transferred into monoclinic phase from hexagonal phase after annealing at 800 °C for 2 h. The SiO 2 @LaPO 4 :Eu 3+ phosphors show strong orange–red luminescence under ultraviolet excitation. The relative emission intensity of Eu 3+ increases with increasing the annealing temperature and the number of coating cycles, and the optimum concentration for Eu 3+ was determined to be 5 mol% of La 3+ in SiO 2 @LaPO 4 phosphors.

Synthesis and Photoluminescence Properties of Monodisperse Spherical SiO<sub>2</sub>@Lu<sub>2</sub>O<sub>3</sub>: Eu<sup>3+</sup> Particles with Core-Shell Structure

Spherical submicron SiO2 particles have been coated with luminescent Lu2O3: Eu3+ layers by a Pechini sol-gel process, resulting in the formation of SiO2@Lu2O3: Eu3+ core-shell particles(300, 500 nm). The obtained core–shell phosphors have perfect spherical shape with narrow size distribution, smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (50 nm for four deposition cycles). Under the excitation of ultraviolet, the Eu3+ ion mainly shows its characteristic emissions in the core-shell particles from Lu2O3: Eu3+) shells. The PL intensity of Eu3+ increases with the number of coating cycles.

Synthesis and Characterization of Monodisperse Spherical SiO<sub>2</sub>@Y<sub>2</sub>O<sub>3</sub>: Tb<sup>3+</sup> Particles with Core-Shell Structure

Spherical submicron SiO2 particles have been coated with luminescent Y2O3: Tb3+ layers by a Pechini sol-gel process, resulting in the formation of SiO2@Y2O3: Tb3+ core-shell particles. The obtained core–shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 450 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (35 nm for two deposition cycles). Under the excitation of ultraviolet, the Tb3+ ion mainly shows its characteristic emissions in the core-shell particles from Y2O3: Tb3+) shells. The emission intensity of Tb3+ can be tuned by the annealing temperature and the number of coating cycles.

Preparation and luminescence properties of SiO2@LaBO3:Eu3+ nanoparticles

Spherical SiO2 particles having a LaBO3:Eu3+ shell have been prepared by coating of silica nanoparticles (size around 130–150 nm) with a LaBO3:Eu3+ sol–gel precursor and subsequent calcination. The SiO2@LaBO3:Eu3+ nanoparticles were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, and transmission electron microscopy. The XRD and FTIR results revealed that the LaBO3:Eu3+ layer on SiO2 nanoparticles formed an H-LaBO3 crystal phase when calcination at a temperature up to 700 °C. Both excitation and emission properties were characterized. The strong excitation lines at 393 and 465 nm of SiO2@LaBO3:Eu3+ indicated that the core–shell phosphor matched well with the output wavelength of near-UV (350–400 nm) or blue LED (450 nm) chips in phosphor-converted W-LEDs. The emission spectra of the 5D0 → 7FJ (J = 0, 1, 2, 3, and 4) transitions at blue/near-UV light showed strong emission lines around 615 nm which were attributed to the induced electric dipole transition of 5D0 → 7F2. The coating cycles affected the luminescence of SiO2@LaBO3:Eu3+ nanoparticles and their CIE chromaticity coordinate shifted from orange-red to the deep red zone with the increase in the coating cycles (up to 3). The luminescence lifetime of the Eu3+ ions in SiO2@LaBO3:Eu3+ was 2.32 ms. Such a luminescent material may be useful for display and light applications.

151Eu Mössbauer study of luminescent Y2O3:Eu3 + core-shell nanoparticles

151Eu Mossbauer spectroscopy was applied to distinguish among different Eu microenvironments and phases in spherical Y2O3:Eu3 + and core-shell Y2O3@Eu3 + phosphor nanoparticles prepared by using homogeneous precipitation method. 151Eu isomer shift revealed that Eu atoms exist only in oxidation state Eu3 + in all spherical and core-shell phosphors. Significant differences have been found between the Mossbauer parameters (isomer shift, principal component of EFG and linewidth) characteristic of spherical Y2O3:Eu3 + and core-shell Y2O3@Eu3 + phosphor nanoparticles. The Mossbauer parameters of spherical Y2O3:Eu3 + were associated with Eu substituting Y in the Y2O3, while Mossbauer parameters of core-shell Y2O3@Eu3 + phosphor were attributed to Eu being in the Eu2O3 shell, proving the structural model and the successful preparation of these phosphors.

Y2Si2O7:Eu/SiO2 core shell phosphor particles prepared by flame spray pyrolysis

This paper reports the synthesis of core shell phosphor particles (Y2Si2O7:Eu/SiO2) produced by flame spray pyrolysis with yttrium and europium nitrates and colloidal silica dispersed precursor solutions. Particles of various structures were produced, including heterogeneous, core shell and non-spherical core shell particles, depending on the synthesis conditions; the ideal core shell structure was obtained under the highest flame temperature and high silicon concentration in the precursor solution. Based on the phase diagram, the formation of the core shell structure was caused by the separation of each component at the liquid phase in the synthesis route. In the energy-dispersive X-ray spectroscopy, yttrium could be detected only at the core part of the particle, while silicon and oxygen could be detected at both the shell and core parts. Under ultraviolet excitation, the ideal core shell particles of Y2Si2O7:Eu showed photoluminescent characteristics. Consequently, it could be concluded that Y2Si2O7:Eu/SiO2 core shell phosphor particles were successfully synthesized by flame spray pyrolysis.

High-Quality White Light Using Core–Shell RE3+:LaPO4 (RE = Eu, Tb, Dy, Ce) Phosphors

Rare-earth (RE = Eu, Dy, Tb, and Ce) ion doped core and core–shell LaPO4 phosphors were synthesized to elucidate the effect of spatial distribution of dopants on the emission spectra. The core–shell architecture was designed as a single particle that can be excited by a single wavelength and yield a balanced white light appearance with long emission lifetimes. Specifically, a multishell architecture was employed to separate the Eu3+ and Tb3+ within the phosphor to circumvent the energy transfer between them, passivate the surface quenching sites, and control Ce3+ doping to sensitize other RE ions. To assess the effectiveness of these core–shell phosphors, the International Commission on Illumination (CIE) coordinates and luminescence lifetimes are quantified as the figures of merit. The Eu3+:LaPO4|Ce3+,Dy3+:LaPO4|Tb3+:LaPO4 layering resulted in CIE coordinates of (0.34, 0.35) using 365 nm excitation, nearly at center of the white light regime at (0.35, 0.35). Finally, the emission lifetimes were measured to be 0.85, 4.34, and 3.26 ms and resulted in a total increase of 31, 36, and 16% over the RE3+:LaPO4 reference phosphors, where RE = Dy, Tb, and Eu, respectively. The synthesized phosphor material has high-quality white light with improved emission lifetimes, suitable for application in white light LED devices.

Facile synthesis of bifunctional silica-coated core–shell Y2O3:Eu3+,Co2+ composite particles for biomedical applications

In the present study, bifunctional silica-coated Y2O3:Eu3+,Co2+ spherical-shaped submicron composite particles were successfully prepared using a facile urea-assisted homogenous precipitation method. Synthesized Y2O3:Eu3+,Co2+ phosphor composites showed both ferromagnetic behaviour and strong visible red luminescence emission. The surface of the Y2O3:Eu3+,Co2+ phosphor composites was modified with a thin silica layer to enhance the luminescent properties and obtain higher biocompatibility of the samples. The composite particles with silica coatings resulted in a small decrease in the viability of L-929 fibroblastic cells at concentrations lower than 25 ppm and allowed cell imaging via internalization and wide distribution into the cells. Overall, these synthesized novel SiO2@Y2O3:Eu3+,Co2+ core–shell phosphor composites with both magnetic and luminescent properties have potential biomedical applications, including bioimaging and diagnosis, and can be also potentially used as MRI contrast agents.