LaF3 : Eu3+ nanocrystal/PNIPAM nanogels: Preparation,thermosensitive fluorescence performance and use as bioprobes for monitoring drug release

Novel core–shell LaF₃ : Eu³⁺ nanocrystals/PNIPAM nanogels were prepared by surface‐initiated living radical polymerization. The microstructure and performance of the LaF₃ : Eu³⁺ nanocrystals and the hybrid nanogels were characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), X‐ray photoelectron spectrometer (XPS), and photoluminescence (PL). The thermosensitive fluorescence behaviors of the core–shell nanogels and the drug release behaviors were investigated by PL at various temperatures. The results suggested that the fluorescence performance of the nanogels was influenced greatly by the ambient temperature, either content of Aspirin absorbed in the nanogels. Compared to other reported systems, our discovery could tell how much the nanogels contain Aspirin by detecting the fluorescence intensity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39930.     

Synthesis and luminescent properties of Sr4−xSi3O8Cl4: xEu3+ red phosphor by hydrothermal method

Sr_4‐xSi₃O₈Cl₄:xEu³⁺ (SSOC:Eu³⁺) phosphors were successfully synthesized by hydrothermal method. The crystallization of this phosphor was analyzed by means of X‐ray diffraction patterns. The size and morphology were recorded using SEM patterns of samples. And the PLE and PL spectra were characterized by a PL spectrophotometer. Excited by 394 nm UV light, the intense red emission is recognized in SSOC:Eu³⁺ phosphor and the main emission peak located at 620 nm. The influences of Eu³⁺ concentration, pH value of reaction solution, and charge compensator on PL spectra of SSOC:Eu³⁺ phosphors were investigated. The results revealed that this red phosphor had potential applications for white LEDs.     

Tracking the local environment of Eu3+ in Eu3+-doped calcium phosphate during hydroxyapatite crystallization and its phase transformation to tricalcium phosphate

We present a study on the crystal structure and luminescence of Eu³⁺-doped calcium phosphate (Eu-CaP) nanoparticles. The sintering treatment on the pristine Eu-CaP leads to its crystallization into hydroxyapatite (HA) and further to biphasic structure that contains both HA and β-tricalcium phosphate (β-TCP). Photoluminescence spectroscopy has been a widely used technique to identify the site occupancy of Eu³⁺ and its thermal-induced migration behavior in pure phase CaP. However, for sintering process that involves the emergence of a second phase or the doped CaP is not luminescent, PL alone is insufficient to characterize how the dopant ions behave during the formation of a biphasic structure. In this work, we utilize X-ray absorption fine structure (XAFS) as an alternative structure probe, targeting the local structure around Eu³⁺, and track the change in the interatomic distance and coordination number of Eu with its neighboring O, P, and Ca atoms. A model describing formation process of a biphasic structure from HA with the presence of Eu³⁺ is proposed.     

A novel scheelite-type LiCaGd(WO4)3:Eu3+ red phosphors with prominent thermal stability and high quantum efficiency

A series of LiCaGd(WO4)3 : xEu³⁺ (0 ≤ x ≤ 1.0) red phosphors with tetragonal scheelite structure were synthesized via the conventional solid-state reaction. Their crystal structure, photoluminescence excitation (PLE), and photoluminescence (PL) spectra, thermal stability and quantum efficiency were investigated. The phosphors exhibit a typical red light upon 395 nm near ultraviolet excitation, and the strongest emission peak at 617 nm is dominated by the ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The PL intensity of the phosphors gradually increases with the increase of Eu³⁺ doping concentration, and the concentration quenching phenomenon is hardly observed. The quantum efficiency and the color purity of the phosphor reach maximum values of about 94.2 and 96.6% at x = 1.0, respectively. More importantly, LiCaGd(WO₄)₃:xEu³⁺ phosphors have prominent thermal stability. The temperature-dependent PL intensity of the phosphors at 423 K is only reduced to 89.1% of the PL intensity at 303 K, which is superior to that of commercial red phosphors Y₂O₃:Eu³⁺. Finally, LiCaGd(WO₄)₃:Eu³⁺ phosphor is packaged with near ultraviolet InGaN chips to fabricate white light emitting diodes, which has a low color temperature (CCT = 4622 K) and a high color rendering index (CRI= 89.6).     

Effect of Crystallite Size and Crystallinity on Photoluminescence Properties and Energy Transfer of Y6MoO12:Eu

The phosphors Y₆MoO₁₂:Eu³⁺ have been synthesized via citrate complexation method at different calcination temperatures. The evolutions of the crystal structure and the photoluminescence (PL) properties were characterized by means of powder X‐ray diffraction (XRD), Raman and PL spectra, respectively. It was revealed that a red emission could be obtained via three excitation channels, namely f–f transition of Eu³⁺ ions, charge‐transfer transition from O² to Eu³⁺, and interband transition (IBT) of MoO₆ groups. The PL spectra and their temporal decay character of Eu³⁺ ions depended on both crystal structure and excitation channel. The emission reduced with the crystallite size when Eu³⁺ ions were excited directly, but the emission evolved in a different model with the host lattices were excited. The effect of grain boundary and other lattice defect on the energy transfer and dissipation within the phosphors were discussed.     

Monodisperse nanospheres of yttrium oxysulfide: Synthesis,characterization, and luminescent properties

A red long-lasting phosphorescent material, monodisperse Y₂O₂S: Eu³⁺, Mg²⁺, Ti⁴⁺ nanospheres have been prepared successfully. Y(OH)(CO₃): Eu³⁺ nanospheres were firstly synthesized via an urea-based homogeneous precipitation technique to serve as the precursor. Nanospheres long-lasting phosphors Y₂O₂S: Eu³⁺, Mg²⁺, Ti⁴⁺ were obtained by calcinating the precursor in CS₂ atmosphere. XRD investigation shows a pure phase of Y₂O₂S, indicating no other impurity phase appeared. SEM observation reveals that the structures are nanosphere. The Y₂O₂S: Eu³⁺, Mg²⁺, Ti⁴⁺ nanospheres with particle size about 100–150 nm show uniform size and well-dispersed distribution. After irradiation by ultraviolet radiation with 325 nm for 5 min, the phosphor emitted red color long-lasting phosphorescence corresponding to typical emission of Eu³⁺ ion. The main emission peaks are ascribed to Eu³⁺ ions transition from ⁵D_J (J = 0, 1, 2) to ⁷F_J (J = 0, 1, 2, 3, 4). Both the PL spectra and luminance decay revealed that this phosphor had efficient luminescent and long-lasting properties. It was considered that the red-emitting long-lasting phosphorescence was due to the persistent energy transfer from the traps to the Ti⁴⁺ and Mg²⁺ ions.     

Monitoring the t → m Martensitic Phase Transformation by Photoluminescence Emission in Eu3+‐Doped Zirconia Powders

In this work, we demonstrate that the martensitic t → m phase transformation of ZrO₂ powder stabilized with Eu³⁺ and Eu³⁺/Y³⁺ ions, can be effectively monitored by photoluminescence (PL) spectroscopy. As the luminescent properties of Eu³⁺ from within a host lattice are strongly influenced by the coordination geometry of the ion, we used the emission spectrum to monitor structural changes of ZrO₂. We synthesized Eu³⁺‐doped and Eu³⁺/Y³⁺‐codoped samples via the coprecipitation method, followed by calcination. We promoted the martensitic transformation by applying mechanical compression cycles with an increasing pressure, and deduced the consequential structural changes from the relative intensities of the ⁵D₀ → ⁷F₂ hypersensitive transitions, centered, respectively, at 606 and 613 nm whether the Eu³⁺ is in the eightfold coordinated site of the tetragonal phase or in the sevenfold coordinated site of the monoclinic phase. We suggest that the unique emission profile for Eu³⁺ ions in different symmetry sites can be exploited as a simple analytical tool for remote testing of mechanical components that are already mounted and in use. The structural changes observed by PL spectroscopy were corroborated by X‐ray powder diffraction (XRPD), with the phase compositions and volume fractions being determined by Rietveld analysis.     

Improved Photoluminescence Property of YBO3:Eu3+ Phosphor by Structure Tailoring

YBO₃:Eu³⁺ microspheres were synthesized by a hydrothermal method. Size and surface morphology of the spheres were tailored by ion‐adding. Phase identification, morphology observation, and photoluminescence (PL) performance of the YBO₃:Eu³⁺ microspheres were characterized byX‐ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), and PL spectrophotometer, respectively. Moderate particles with enlarged size and perfect surface were achieved by adding Li⁺ ion or/and Mg²⁺ ion. PL emissions of such YBO₃:Eu³⁺ phosphors were enhanced. Significantly improved PL intensity was achieved when 1% Li⁺ ion and 5% Mg²⁺ ion were added, which was nearly doubled compared with the reference sample.     

Preparation and Sustained-Release Property of Triblock Copolymer/Calcium Phosphate Nanocomposite as Nanocarrier for Hydrophobic Drug

The P123/ACP nanocomposite with sizes less than 100 nm consisting of triblock copolymer P123 and amorphous calcium phosphate (ACP) has been prepared by using an aqueous solution containing CaCl₂, (NH₄)₃PO₄, and P123 at room temperature. The P123/ACP nanocomposite is used as the nanocarrier for hydrophobic drug ibuprofen, based on the combined advantages of both amphiphilic block copolymer and calcium phosphate delivery system. The P123/ACP nanocomposite has a much higher ibuprofen loading capacity (148 mg/g) than the single-phase calcium phosphate nanostructures. The drug release percentage of the P123/ACP nanocomposite in simulated body fluid reaches about 100% in a period of 156 h, which is much slower than that of single-phase calcium phosphate nanostructures. It is expected that the P123/ACP nanocomposite is promising for the application in the controlled delivery of hydrophobic drugs.     

Covering the optical spectrum through different rare-earth ion-doping of YAG nanospheres produced by rapid microwave synthesis

In this work, YAG:RE³⁺ (RE = Pr³⁺, Tm³⁺, Tb³⁺, Ce³⁺, Eu³⁺, Nd^3+, and Er³⁺;Yb³⁺) luminescent nanospheres with tunable photoluminescence (PL) emission were prepared by using fast and energy-saving microwave-assisted synthesis (MWAS). The nanopowders were post-annealed at 1100 °C for 3 h to obtain nanocrystalline phosphors. X-ray diffraction (XRD) analysis confirmed the presence of nanocrystals that were well indexed to the cubic YAG phase. Surface chemical groups were detected using Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy (TEM) showed that the synthesized samples consist of nanospheres with an average size of ~ 110 nm. The effect of aluminum precursors on the morphology of synthesized nanoparticles is discussed. The produced nanophosphors showed strong emission at different wavelengths (ultraviolet, visible and near-infrared) corresponding to different RE³⁺ ions. Altogether, the merits of spherical morphology and PL emission at various wavelengths endow rare-earth-doped YAG nanoparticles with suitable characteristic for potential applications in the field of nanomedicine (e.g., bioimaging and nanoscintillators), light display systems, optoelectronic devices, and lasers.     

Phase formation and spectral evolution of (Sr,Ba)2Si(O,N)4:Eu2+ phosphors

Sr_2‐xBa_xSi(O,N)₄:Eu²⁺ (SB_xSON:Eu²⁺) oxynitridosilicate phosphors were prepared via incorporation of N^3?, Eu²⁺, and Ba²⁺ ions into Sr₂SiO₄ (SSO) lattices. X‐ray diffraction patterns of the prepared powders revealed that SB_xSON:Eu²⁺ was a solid‐solution form of SSO. An increase in x values caused a phase transition and an expansion of the unit cell. The photoluminescence excitation (PLE) spectra of SB_xSON:Eu²⁺ were broad, covering the ultraviolet range to the visible range. Corresponding PL emission spectra strongly depended on the excitation wavelengths and consisted of two emission bands, one in the green‐blue region (A‐band) and the other in the red region (B‐band), which were assigned to Eu(I) and Eu(II), respectively. The B‐band resulted from a dramatic red‐shift of the green emission band assigned to Eu(II) of SSO:Eu²⁺, revealing that the nitridation process preferentially affected the Eu(II) sites. This behavior was explained by crystal field splitting, the fluorescence decay time, and thermal quenching. The Ba²⁺ substitution caused evolution of the PL spectra, and its effects on the spectra were discussed under consideration of ionic size and covalence.     

Synthesis of YVO4:Eu3+/YBO3 Heteronanostructures with Enhanced Photoluminescence Properties

Novel YVO₄:Eu³⁺/YBO₃ core/shell heteronanostructures with different shell ratios (SRs) were successfully prepared by a facile two-step method. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the heteronanostructures. Photoluminescence (PL) study reveals that PL efficiency of the YVO₄:Eu³⁺ nanocrystals (cores) can be improved by the growth of YBO₃ nanocoatings onto the cores to form the YVO₄:Eu³⁺/YBO₃ core/shell heteronanostructures. Furthermore, shell ratio plays a critical role in their PL efficiency. The heteronanostructures (SR = 1/7) exhibit the highest PL efficiency; its PL intensity of the ⁵D₀–⁷F₂ emission at 620 nm is 27% higher than that of the YVO₄:Eu³⁺ nanocrystals under the same conditions.     

Design of Eu2+-activated broadband orange-emitting phosphors with excellent luminescent performance for warm WLEDs

We report orange-emitting Sr₈La_0.5Na_0.5Mg_1.5(PO₄)₇:Eu²⁺ (SLNMPO-0.5:Eu²⁺) and Sr₇LaNaMg_1.5(PO₄)₇:Eu²⁺ (SLNMPO-1:Eu²⁺) phosphors with broad emission bands covering from 450 to 800 nm. The phosphors can be excited by n-ultraviolet and blue light efficiently. Their crystal structure, diffuse reflection spectra, photoluminescence (PL) spectra, fluorescence decay curves and thermal stability were investigated systematically. Under the excitation of 365 and 400 nm, SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ both exhibit better PL properties and contain more red emissions than SMPO:Eu²⁺. CIE coordinates of SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ under 365 nm excitation are (0.460, 0.497) and (0.457, 0.494), respectively. Furthermore, high-quality warm white light can be generated by fabricating warm white light-emitting diode (WLED) devices with 370 nm LED chips, BaMgAl₁₀O₁₇:Eu²⁺ commercial blue phosphor and orange-emitting SLNMPO-0.5:Eu²⁺ (or SLNMPO-1:Eu²⁺) phosphor. The correlated color temperature, R_a and color coordinates are 3880 K, 94.05, (0.3895, 0.3922) and 3736 K, 91.73, (0.4005, 0.4078) for the fabricated WLED devices with SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺, respectively. The excellent performances indicate that SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ have great potential to be attractive candidates in the application of warm WLEDs.     

Investigation of Eu2+ luminescence in barium tetraphosphate Ba3P4O13 polycrystalline ceramics

In this paper, Ba₃P₄O₁₃:Eu²⁺ phosphor was synthesized by a solid-state reaction. The photoluminescence (PL) emission spectrum and luminescence decay kinetics confirm that the doped Eu²⁺ ions can occupy two different Ba²⁺ sites. The PL excitation spectrum shows a broad band matching well with the emission of near-UV chip. Ba₃P₄O₁₃:Eu²⁺ is a promising phosphor for near-UV chip excited white LEDs. The doped Eu³⁺ ions can also be reduced to Eu²⁺ ions in air atmosphere at high temperature. Charge compensation mechanism is applied to explain this kind of abnormal reduction.     

Radio-photoluminescence observed in Eu-doped BABF glass-ceramics

Radio-photoluminescence (RPL), which is an infrequent phenomenon observed in phosphor materials where new luminescent centre is generated by interacting with ionizing radiation, was observed in Eu-doped BaAlBO₃F₂ (BABF) glass-ceramics. The as-prepared material shows photoluminescence (PL) only due to the 4f‐4f transitions of Eu³⁺ whereas an additional broad emission band appears around 510?nm, which is due to the 5d‐4f transitions of Eu²⁺. The appearance of the Eu²⁺ as a new emission centre is an evidence of RPL. The RPL in this system is based on intra-valence reduction of Eu ion (Eu³⁺→Eu²⁺), which was confirmed as a decrease of PL intensity by Eu³⁺ and increase of PL intensity by Eu²⁺ as a function of irradiation dose. Moreover, additional RPL centre is observed after heat-treatment of irradiated material, which is seen as a broad PL peak centering around 480?nm. Based on the luminescence features, the latter RPL is characterized to defect-related luminescence.     

Synthesis and photocatalytic activity of Na+ co-doped CaTiO3:Eu3+ photocatalysts for methylene blue degradation

The Na⁺ co-doped CaTiO₃:Eu³⁺ powders were produced through the solution combustion method. The phase structure and optical properties of the synthesized samples were adequately characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and scanning electron microscopy (SEM). The XRD patterns revealed that a low level of Eu³⁺ doping could not cause lattice distortion of CaTiO₃. Photoluminescence (PL) displayed the CaTiO₃:0.5% Eu³⁺ sample synthesized at 900 °C has the weakest PL emission and the low electrons and holes recombination rate. The morphology of the sample was small nanoscale spherical particles. The UV–vis diffuse reflection spectra proved that doping Na⁺ and Eu³⁺ enlarged the absorption region and reduced band energy of pure CaTiO₃. The photocatalytic properties of Na⁺ co-doped CaTiO₃:Eu³⁺ samples were investigated via degrading methylene blue (MB) under ultraviolet light irradiation. The CaTiO₃:0.5% Eu³⁺, 0.5% Na⁺ sample, by contrast, exhibited the greatest photocatalytic property and the degradation rate was as high as 96.62%, which makes it a promising multi-functional material (photocatalytic material and red phosphor) for decreasing organic pollution in water.     

Photoluminescence and optical properties of Eu3+/Eu2+-doped transparent Al2O3 ceramics

Transparent Eu³⁺-doped (0.05–0.15 at. %) alumina ceramics with fine-grained microstructure were prepared and studied in terms of optical properties and photoluminescence (PL). The light transmission through ceramics up to dopant concentrations 0.125 at. % is dominated by birefringence scattering at grain boundaries. As confirmed by HRTEM/EDS element mapping, high photoluminescence intensity was achieved as the result of the dopant segregation at grain boundaries. The PL emission spectra of Al₂O₃:Eu³⁺ ceramics exhibited red light emissions with the highest intensity (394 nm excitation) for material containing 0.125 at. % of Eu³⁺. The luminescence decay was single-exponential with a lifetime ～1.5 ms. The post-sintering reduction of Eu³⁺→Eu²⁺ under an H₂ atmosphere (at 1300 °C) was difficult. Two simultaneously coexisting Eu²⁺ emitting PL centers were identified, one emitting blue light with average decay constant of 150 ns, and the other green light (more intense) with average decay constant of 1.3 μs.     

Photoluminescence Enhancement of SiO2‐Coated LaPO4:Eu3+ Inverse Opals by Surface Plasmon Resonance of Ag Nanoparticles

The surface plasmon resonance of Ag nanoparticles (NPs) and SiO₂ coating had been extensively employed to improve the photoluminescence (PL) intensity of nanomaterials. In the article, the LaPO₄:Eu³⁺ inverse opal photonic crystals were fabricated via combining a self‐assembly process with a sol–gel method. The SiO₂ shells were formed on the skeleton surface of LaPO₄:Eu³⁺ inverse opals and the Ag NPs were added into the voids of LaPO₄:Eu³⁺ inverse opals with the SiO₂ shells. The influence of the SiO₂ shells and Ag NPs on the PL of the LaPO₄:Eu³⁺ inverse opals were investigated. About sevenfold luminescence enhancement of LaPO₄:Eu³⁺ inverse opals was obtained by the coordination action of surface plasmon absorption effects of Ag nanoparticle and silica‐coating effects. The luminescence enhancement mechanisms of LaPO₄:Eu³⁺ inverse opals were discussed.     

Preparation and Luminescence Properties of Blue‐emitting Phosphor Ba2Ca(PO4)2:Eu2+

Using the conventional high temperature solid‐state reaction method Ba₂Ca(PO₄)₂:Eu²⁺ phosphors were prepared. The phase structure, photoluminescence (PL) properties, and the PL thermal stability of the samples were investigated, respectively. Under the excitation at 365 nm, the phosphor exhibited an asymmetric broad‐band blue emission with peak at 454 nm, which is ascribed to the 4f–5d transition of Eu²⁺. It was further proved that the dipole–dipole interactions results in the concentration quenching of Eu²⁺ in Ba₂Ca_1?x (PO₄)₂:xEu²⁺ phosphors. When the temperature turned up to 150°C, the emission intensity of Ba₂Ca_0.99(PO₄)₂:0.01Eu²⁺ phosphor was 59.07% of the initial value at room temperature. The activation energy ΔE was calculated to be 0.30 eV, which proved the good thermal stability of the sample. All the properties indicated that the blue‐emitting Ba₂Ca(PO₄)₂:Eu²⁺ phosphor has potential application in white LEDs.     

A novel tunable green-to-red emitting phosphor Ca4LaO(BO3)3:Tb,Eu via energy transfer with high quantum yield

A novel green phosphor composed of Ca₄LaO(BO₃)₃:Tb³⁺ (CLBO:Tb) has been synthesized by a combustion method with urea. Its crystal structure, temperature-dependent luminescence, and quantum yield (QY) have been characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra with heating device and integrate sphere. No concentration quenching has been observed when all of La³⁺ ions are substituted with Tb³⁺ ions. Green phosphor Ca₄TbO(BO₃)₃ (CTBO) has 200% luminescence intensity of commercially available phosphor LaPO₄:Ce, Tb (LPO:Ce, Tb) under 378 nm excitation. The QY of CTBO is as high as 98%. Through a Dexter energy transfer mechanism, Eu³⁺ ions are efficiently sensitized by Tb³⁺, resulting in an emission with color tunable from green to red under ultraviolet excitation. A possible mechanism of energy transfer from Tb³⁺ to Eu³⁺ has been investigated by PL spectra and decay measurements. The energy transfer efficiency from Tb³⁺ to Eu³⁺ increases linearly with concentration of Eu³⁺ increasing.