Structural and luminescence properties of undoped,Nd3+ and Er3+ doped TiO2 nanoparticles synthesized by flame spray pyrolysis method

Bulk and thin film forms of titanium dioxide (TiO₂) have been studied many times due to its very promising optical properties. In this study, low-cost flame spray pyrolysis (FSP) synthesis of Nd³⁺/Er³⁺doped TiO₂ nanoparticles has been reported for the first time. The produced particles were post-annealed after FSP process at 550 °C in order to obtain crystalline structure. The phase and elemental analysis of the produced materials were performed by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS), respectively. The surface morphology, accurate size and specific surface area of the primary particles were identified using scanning electron microscopy (SEM) and particle size analyser. Luminescent properties of the produced nanoparticles were investigated by steady state and time resolved fluorescence spectra. Doping of TiO₂ nanoparticles with the rare earths of Nd³⁺and Er³⁺resulted in visible and near-infrared light emission when excited at 364 nm. The utilized nanoparticles yielded bi-and tri-exponential decay curves. Additionally, they exhibited typical upconversion luminescence when radiated by 810 nm.     

Study on luminescence properties of co-doped nanoparticles Gd2O3:Tb3+, Eu3+ synthesized by polyol route

Spherical-like Tb³⁺ and Eu³⁺ co-doped Gd₂O₃ nanoparticles with a particle size around 5.5 nm were synthesized by a polyol route. The optimized luminescence property was obtained when 5 mol% Tb³⁺ and 2 mol% Eu³⁺ were co-doped. The influence of different polyalcohol solvents (DEG/PEG) on particle size and luminescence properties was investigated. The results show that the nanoparticles Gd₂O₃:5%Tb³⁺ prepared in PEG presented greater particle size (around 79 nm) and higher luminescence intensity.     

EDTA-assisted hydrothermal synthesis of KLa(MoO4)2:Eu3+ microcrystals and their luminescence properties

Monoclinic KLa(MoO₄)₂:Eu³⁺ microarchitectures with different morphologies were synthesized by an EDTA-assisted hydrothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and photoluminescence (PL) spectrometer. It was found that the amounts of EDTA and the pH values of precursor solution have crucial influences on the structure, morphology and size of the obtained samples, respectively. Under 270 nm excitation, Eu³⁺ doped KLa(MoO₄)₂ samples showed red emission centered at 618 nm which attributed to ⁵D₀→⁷F₂ transition of Eu³⁺. The dependence of luminescence intensity on different morphologies were discussed in detailed. With further annealing treatment, the emission intensities of peanut-like samples increased amazingly. Moreover, the lifetime of the annealed samples were calculated. The significantly enhanced photoluminescence performances indicate that the as-annealed samples are promising phosphors which can be used for white light-emitting diodes (WLEDs).     

Eu3+ doped KYF4 nanocrystals: synthesis, electronic structure, and optical properties

Monodisperse cubic-phase KYF(4)?:?Eu(3+) nanocrystals (NCs) were synthesized via a modified thermal decomposition method. The optical properties of Eu(3+) in KYF(4) NCs including multiple luminescence centers, site symmetry, luminescence dynamics, as well as crystal-field levels of Eu(3+) were investigated in detail based on high-resolution photoluminescence (PL) spectroscopy at low temperature (10 K). Different from Eu(3+) in bulk counterparts, multiple sites of Eu(3+) in KYF(4) NCs were revealed by using the luminescence of Eu(3+) as a sensitive structural probe. The highest site symmetry of Eu(3+) at new near-surface site was deduced to be distorted from O(h) to D(2) (or C(2v)). Due to a small filling factor (0.45) of NCs, the PL lifetime of (5)D(0) of Eu(3+) in KYF(4) NCs was much longer than that in bulk counterparts, which was found to be significantly affected by the surrounding medium around the NCs.     

Optical properties of Eu3+/Pr3+ doped Zn4O(BO2)6 synthesized by solid-state reaction

Zn₄O(BO₂)₆ based on the [B₂₄O₄₈] sodalite-cage structure fixed by the inside [Zn₄O₁₃] clusters is expected to be a new class of solid-state lighting material with perfect thermal and mechanical stability. Herein, in the current work, we have respectively introduced non-equivalent rare-earth cations Eu³⁺ and Pr³⁺ into Zn₄O(BO₂)₆ host to design white and green emission materials by a novel solid-phase sintering method at lower temperatures. Zn₂B₆O₁₁ replacing B₂O₃ or H₃BO₃ as raw materials can effectively avoid the impure products caused by the uncontrollable volatilization of B₂O₃ or H₃BO_3. The newly designed light-emitting materials of Zn_4(1-x)O(BO₂)₆: xRe³⁺ (ReEu or Pr), including Zn₄O(BO₂)₆ host, have good absorption capacity in the ultraviolet region. Under ultraviolet irradiation, Zn₄O(BO₂)₆, Zn_4(1-x)O(BO₂)₆: xEu³⁺and Zn_4(1-x)O(BO₂)₆: xPr³⁺ emit the blue, white and green lights, respectively. In addition, all these materials can effectively degrade methylene blue, in which Zn_4(1-x)O(BO₂)₆: xPr³⁺ has the highest efficiency. The luminescence and degradation mechanisms of Zn₄O(BO₂)₆, Zn_4(1-x)O(BO₂)₆: xEu³⁺and Zn_4(1-x)O(BO₂)₆: xPr³⁺ have been adequately explained by their electronic structures based on the first principle calculations. The current study confirms that the doping of Eu³⁺/Pr³⁺ in Zn₄O(BO₂)₆ can broaden its applications as photoluminescent and photocatalytic materials.     

Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

It was unusual for Bi³⁺ ions to enhance the emission intensity of phosphors via nonsensitization. Here, La₂MoO₆:Eu³⁺, Bi³⁺ phosphors were successfully synthesized by a high temperature solid-state reaction method in air atmosphere. As the increase of doping concentration of Bi³⁺, the emission spectra of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors had obvious shifts, splits and the enhancement of intensities, which indicated that the characteristics of the phosphors were modified. To analyze these phenomena, the crystal structure refinements, spectral characteristic analyze and Judd-Ofelt theoretical calculation were mainly performed. Bi³⁺ ions played the role of the nonsensitizer and affected the distortion of the crystal, the sites of Eu³⁺ ions, the field splitting energy and the internal quantum yield. Moreover the nephelauxetic effects of Bi³⁺ ions and the ET process caused synergistically the life times of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors to increase and then gradually decrease. The CIE coordinates of phosphors changed within a small range. This study might be instrumental in promoting the further application of Bi³⁺ ions in rare earth luminescent materials.     

Structure and luminescent properties of oxyfluoride glass-ceramics with YF3:Eu3+ nanocrystals derived by sol-gel method

In this paper, the transparent oxyfluoride glass-ceramic materials containing YF₃:Eu³⁺ nanocrystals were fabricated via controlled ceramization of precursor xerogels at relatively low temperature T = 350 °C. The formation of YF₃ nanocrystalline phase from Y(CF₃COO)₃ was verified based on X-ray diffraction (XRD) measurements as well as high-resolution transmittance electron microscopy (HR-TEM). Based on IR-ATR spectroscopy the functional groups inside sol-gel structures were identified. The optical properties of Eu³⁺ ions in fabricated sol-gel samples were investigated based on photoluminescence excitation and emission spectra as well as luminescence decay analysis of the ⁵D₀ excited level. Upon excitation at near-UV illumination, λ_exc = 393 nm, the series of 4f⁶-4f⁶ photoluminescence bands of Eu³⁺ ions in reddish-orange light area were recorded. The Stark splitting of photoluminescence bands, double-exponential character of decay curves and long-lived emission for fabricated glass-ceramic samples clearly evidenced the partial substitution of Y³⁺ by optically active Eu³⁺ ions in precipitated YF₃ nanocrystals. Indeed, it was identified that applied annealing conditions resulted in significant, almost 34-fold prolongation of luminescence lifetime from 0.24 ms (Eu³⁺ ions in xerogel host) up to 8.14 ms (Eu³⁺ ions incorporated into YF₃ nanocrystals). It was also observed a clear correlation between identified phonon energies from IR measurements and luminescence behavior of Eu³⁺ ions.     

Site construction of Eu2+ and sensitized luminescence of Eu3+ in LaF3:Eu nanophosphor

LaF₃:Eu nanophosphors were prepared by a traditional hydrothermal method with citric acid as a reducing agent. X-ray diffraction, scanning electronic microscopy, and luminescence spectroscopy were used to study the nanophosphors. The formation of three different luminescence centers of Eu²⁺ and two different luminescence centers of Eu³⁺ is attributed to the existence of abundant surface defects in this nanophosphor. Eu³⁺ is effectively excited by energy transfer from Eu²⁺ to Eu³⁺. The excitation wavelength of Eu³⁺ covers a broad spectral range from 250 to 480 nm. The nanophosphor shows a tunable luminescence color varying from blue to white and then to red, which is explained from three aspects of Eu concentration, energy transfer, and concentration quenching. Utilizing the surface defect of nanoparticles to control the reduction of Eu³⁺ is considered a promising strategy for exploring Eu²⁺ and Eu³⁺ codoped phosphor suitable for the lighting and display application.     

Structural and luminescence properties of silica powders and transparent glass‐ceramics containing LaF3:Eu3+ nanocrystals

In this work, silica powders and transparent glass‐ceramic materials containing LaF₃:Eu³⁺ nanocrystals were synthesized using the low‐temperature sol‐gel technique. Prepared samples were characterized by TG/DSC analysis as well as X‐ray diffraction and IR spectroscopy. The transformation from liquid sols toward bulk powders and xerogels was also examined and analyzed. The optical behavior of prepared Eu³⁺‐doped sol‐gel samples were evaluated based on photoluminescence excitation (PLE: λ_em = 611 nm) and emission (PL: λ_exc = 393 nm, λ_exc = 397 nm) spectra as well as luminescence decay analysis. The series of luminescence lines located within reddish‐orange spectral scope were registered and identified as the intra‐configurational 4f⁶‐4f⁶ transitions originated from Eu³⁺ optically active ions (⁵D₀ → ⁷F_J, J = 0‐4). Moreover, the R/O‐ratio was also calculated to estimate the symmetry in local framework around Eu³⁺ ions. The luminescence spectra and double‐exponential character of decay curves recorded for fabricated nanocrystalline sol‐gel samples (τ₁(⁵D₀) = 2.07 ms, τ₂(⁵D₀) = 8.07 ms and τ₁(⁵D₀) = 0.79 ms, τ₂(⁵D₀) = 9.76 ms for powders and glass‐ceramics, respectively) indicated the successful migration of optically active Eu³⁺ ions from amorphous silica framework to low phonon energy LaF₃ nanocrystal phase.     

Preparation and luminescence properties of Eu2O3 doped glass-ceramics containing NaY(MoO4)2

Eu₂O₃ doped transparent glass-ceramics containing NaY(MoO₄)₂ crystalline phase were prepared via melting-crystallization. The optimum heat treatment condition (660℃/3h) was determined by DSC, XRD, SEM and transmittance curves. The transmittance of glass-ceramic can reach 80 % in the visible region. The emission spectra of Eu₂O₃ doped glass-ceramics consist of Eu³⁺ ions characteristic emission peaks at 591nm (⁵D₀→⁷F₁) and 614nm (⁵D₀→⁷F₂). The optimal doping concentration of Eu₂O₃ in the glass-ceramics is 0.9 mol%, and fluorescence lifetime is 1.37042ms. The change of the ratio of red emission intensity to orange emission intensity leads to the shift of chromaticity coordinates from orange to red region, and the chromaticity coordinate (0.6337, 0.3635) of 0.9 mol% Eu₂O₃ doped glass-ceramic is closest to the standard red light coordinate. The results show that this kind of glass-ceramic is expected to be good red emission material.     

Polychromatic tunable luminescence of Eu3+ doped CsPbBr3 quantum dot glass ceramic induced by mechanical crystallization

Nowadays, inorganic perovskite quantum dots (QDs) glass has become a hot topic in the field of new optical materials. In this work, the Eu³⁺ doped CsPbBr₃ QDs phosphate glass has been successfully prepared. Different from the traditional heat treatment method, the CsPbBr₃ QDs were prepared by mechanical crystallization. When the QDs glass was ground at different times, due to the synergistic effect of red emission (Eu³⁺) and green emission (CsPbBr₃ QDs), the prepared QDs glass can produce the red-yellow-green polychromatic luminescence phenomenon. Benefit from the dual-emission centers of CsPbBr₃ QDs and Eu³⁺ which do not interfere with each other, the relative sensitivity of the temperature sensing is up to 2.11% K^-1, proving that the prepared Eu³⁺ doped QDs glass has practical application in the field of temperature sensing. The glass material obtained in this way not only has tunability and favorable sensitivity but also provides an effective way for the preparation of QDs.     

Solar driven photocatalytic properties of Sm3+ doped ZnO nanocrystals

ZnO nanocrystals (NCs) doped with different Sm³⁺ concentrations were prepared by sol gel method. XRD analysis showed that the ZnO:Sm³⁺ NCs crystallized in the hexagonal wurtzite structure with a grain size varying from 61.4 nm to 72.6 nm, with Sm³⁺ concentration. Transmission electron microscopy (TEM) images indicated that ZnO NCs adopted a bimodal size distribution. X-ray photoelectron spectroscopy (XPS) revealed that Sm ions existed in trivalent state and substituted at the Zn²⁺ sites in the ZnO lattice. Raman spectra highlighted the presence of the LO mode, confirming the successful substitution of Zn²⁺ by Sm³⁺. Excitation and emission spectra highlighted the typical 4f-4f transitions of Sm³⁺. A photoluminescence (PL) quenching accompanied by a decrease of PL lifetime was observed for Sm³⁺ concentrations above 1.5%. The processes of excitation and de-excitation of the Sm³⁺ ions in ZnO NCs were discussed based on dipolar interactions between the excited ions. The ZnO:Sm³⁺ (1.5%) photocatalyst induced complete and fast photodegradation of RhB under sunlight irradiation. The photocatalytic mechanism is discussed based on the analysis of PL lifetimes. The role of oxygen vacancies on the reduction of Sm³⁺ ions and its impact on the photocatalytic process is also discussed.     

Optical and photostimulated luminescence properties of Eu:BaFBr translucent ceramics synthesized by SPS

Eu:BaFBr translucent ceramics were synthesized by the spark plasma sintering method, and then the crystal structure, optical and photostimulated luminescence (PSL) properties were investigated. The synthesized 0.05–0.5% Eu:BaFBr are translucent, and the optical transmittance is 30–50%. The photoluminescence and PSL spectra consist of an emission band peaking around 390 nm due to the presence of Eu²⁺ ion. The photoluminescence quantum yield and the sensitivity of PSL to X-rays are the highest when the doping concentration is 0.5%, and they are higher than those of the commercial Eu:BaFBr imaging plate (IP). In addition, the spatial resolution of an X-ray image obtained by using the 0.5% Eu:BaFBr translucent ceramic as an imaging plate is higher than the one obtained by using the commercial IP.     

Effects of doping content and crystallite size on luminescence properties of Eu3+ doped fluorapatites obtained from natural waste

In this study, Eu³⁺ doped natural fluorapatites [Ca₁₀(PO₄)₆F₂:xEu³⁺ (x = 0.1, 0.3 and 0.5)] were produced from a natural waste by solid-state powder synthesis, conventional sintering, and spark plasma sintering techniques. The effects of doping content and crystallite size on luminescence properties of fluorapatite were investigated by XRD, SEM, and PL analysis. The obtained results showed that luminescence emission's intensity significantly increased with doping content, but no effect was observed on the density and crystallite size. For the samples produced with different methods, emission intensity was the lowest for sintered samples by SPS (1150 °C, 10 min, 50 MPa) with the smallest crystalline size. In contrast, emission intensity was found much higher for synthesized powders with the largest crystallite size. Furthermore, upon excitation under UV radiation, the Eu doped fluorapatites demonstrated the characteristic ⁵D₀–⁷F₂ and ⁵D₀–⁷F₄ emission lines of Eu³⁺ at 618 nm and 704 nm (red region) with an ultrahigh intensity that has been firstly observed in the literature. Therefore, Eu doped fluorapatites, quickly produced from a natural waste in an eco-friendly and cost-effective way, carry a potential to be used in biological applications and lightning applications.     

Structure and luminescence of Eu doped glass ceramics embedding ZnO quantum dots

Eu³⁺ doped glass ceramics embedding ZnO quantum dots (QDs) were successfully prepared by a sol–gel method. High-resolution transmission electron microscopy (HRTEM) observations revealed that ZnO QDs with size of 3–6 nm precipitated homogeneously among the SiO₂ glassy matrix after thermal treatment of the precursor sample. Such glass ceramics show a high transparency in the visible-infrared range due to the much smaller size of the ZnO QDs than the wavelength of the visible light. The emission and excitation spectra of the samples with various ZnO contents were studied. Based on Judd–Ofelt theory, the intensity parameter Ω₂ was evaluated to investigate the change of the environment around Eu³⁺ in samples with and without QDs.     

Photoluminescence properties of Eu3+-doped stalk-like Al2O3 via a hydrothermal route followed by heat treatment

ABSTRACT

Uniform Al₂O₃:Eu³⁺ samples were successfully fabricated via a hydrothermal method and subsequent thermal decomposition of Eu³⁺-doped precursors. The sample characterisations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectra. XRD results revealed Eu³⁺-doped samples were a pure γ-Al₂O₃ phase after being calcined at 1173?K. SEM results showed that these Eu³⁺-doped Al₂O₃ samples were stalk-like, with an average length of 1.5?μm. Upon excitation at 394?nm, the orange–red emission bands, having wavelengths longer than 580?nm, were to be from ⁵D₀→⁷F_J (J?=?1, 2) transitions. The asymmetry ratio of (⁵D₀→⁷F₂)/(⁵D₀→⁷F₁) intensity is about 0.54, 2.76, 3.29, 2.86, 3.36, 3.13 for Eu³⁺ concentrations of 0.1, 0.4, 0.7, 1.0, 1.5 and 2.0?mol-%, respectively. The optimal doping concentration of Eu³⁺ ions in Al₂O₃ is 1.5?mol-%. According to Dexter's theory, the critical distance between Eu³⁺ ions for energy transfer was determined to be 14?Å.     

Laser synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

A laser melting method has been developed for the synthesis of highly luminescent, long-lasting SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors. The high temperature achieved in high-power density CO₂ laser irradiation of mixtures of SrCO₃, Al₂O₃, Eu₂O₃, and Dy₂O₃ enabled the one-step, fast synthesis of these phosphors in air at atmospheric pressure. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy characterization studies reveal that the produced materials consist of monoclinic SrAl₂O₄ grains extensively surrounded by rare-earth ion-enriched grain boundaries. The photoluminescence properties of laser-produced SrAl₂O₄:Eu²⁺, Dy³⁺ materials are discussed. The results reported here suggest that this laser melting method is a promising route for the synthesis of ceramic phosphors. It is presented as an alternative to the conventional sol–gel and solid-state methods, which require the use of high-temperature furnaces, flux additives, and reducing atmospheres.     

Study of electrical transport properties of Eu+3substituted MnZn-ferrites synthesized by co-precipitation technique

Eu substituted MnZn-ferrites with nominal composition Mn_0.78Zn_0.22Eu_x Fe_(2?x)O₄ (x=0.0, 0.02, 0.04, 0.06, 0.08 and 0.10) were prepared by co-precipitation technique. The effect of Europium substitution on electrical transport properties of Mn–Zn ferrites is reported. XRD analysis reveals fcc phase in all the samples along with few traces of second phase. The lattice constant shows decreasing trend with the substitution of Eu due to partial solubility of Eu-ions in the lattice. Room temperature resistivity both at 10 and 20 V shows on average an increasing trend. This increase in resistivity is attributed to the unavailability of Fe⁺³ ions in the lattice due to Eu-substitution. The dc resistivity decreases with temperature for all the samples at 10 V and 20 V indicating the semiconducting behavior of these samples. Room temperature dc resistivity and activation energies show similar trend both at 10 V and 20 V indicating that the samples with high resistivity have high activation energies and vice versa. The dielectric constant (ε′), complex dielectric constant (ε″) and loss tangent of these samples decreased with the increase of Eu-concentration, following the Maxwell–Weigner model.     

Modifying the luminescence characteristics of Lu2O3:Eu large nanocrystals with polycarbonate host

Lu₂O₃:Eu phosphor fine powder with average size of crystallites of about 100–150 nm was synthesized. TEM images proved only an insignificant agglomeration of the phosphor. Using these fine particles and commercial polycarbonate a composite material was prepared in a form of 2 mm thick plate and its spectroscopic properties were compared to the powder. While the emission and luminescence excitation spectra were found very similar in both types of materials, the decay times of the Eu³⁺ red luminescence appeared to drop from 1.8–2 ms for the powder to 0.9–1 ms for the composite, with the latter value being perfectly the same as for the coarse‐grained sintered translucent ceramics. Since the refractive indices of Lu₂O₃ host and the polycarbonate are 1.935 and 1.582, respectively, such a drastic change in the Eu³⁺ emission kinetics could not be fully explained by the variations of this parameter only. This result is with some disagreement with previously published data. POLYM. COMPOS., 37:1330–1334, 2016. © 2014 Society of Plastics Engineers