Search

The synthesis and characterization of novel luminescent amorphous POSS-based polysilsesquioxanes (PSQs) with Tb3+ and Eu3+ ions directly integrated in the polysilsesquioxane matrix is presented. Two different Tb3+/Eu3+ molar ratios were applied, with the aim of disclosing the relationships between the nature and loading of the ions and the luminescence properties. Particular attention was given to the investigation of site geometry and hydration state of the metal centers in the inorganic framework, and of the effect of the Tb3+ → Eu3+ energy transfer on the overall optical properties of the co-doped materials. The obtained materials were characterized by high photostability and colors of the emitted light ranging from orange to deep red, as a function of both the Tb3+/Eu3+ molar ratio and the chosen excitation wavelength. A good energy transfer was observed, with higher efficiency displayed when donor/sensitizer concentration was lower than the acceptor/activator concentration. The easiness of preparation and the possibility to finely tune the photoluminescence properties make these materials valid candidates for several applications, including bioimaging, sensors, ratiometric luminescence-based thermometers, and optical components in inorganic or hybrid light-emitting devices. [ABSTRACT FROM AUTHOR]

Tuning the emissive color changes of lanthanide (Ln) complexes is an important and appealing project for promoting the applications of Ln-complexes. A solvothermal reaction of 4-cyano-3-methylbenzoic acid (HL) and Ln(NO3)3·6H2O affords three isostructural Ln-complexes [Eu(L)3(H2O)2]n (1-Ln) (Ln = Eu, Gd and Tb) with one-dimensional chain structures. 1-Eu and 1-Tb show bright red and green emissions with absolute quantum yields of 3.06% and 11.96%, respectively, and the energy transfer was analyzed in detail through combined calculations. Interestingly, a series of heterometallic doped 1-TbxEu1−x coordination polymers were also obtained by mixing different ratios of Eu3+ and Tb3+ ions, which possess continuous luminescent color changes from green to yellow, orange and red. In addition, 1-Eu exhibits high quenching efficiency and low detection limit (∼10−4 M) for the simultaneous sensing of MnO4−, CrO42− and Cr2O72− ions in water. [ABSTRACT FROM AUTHOR]

Tb 3 + and Eu 3 + single- and double-doped barium borate glasses are analyzed for their temperature-dependent luminescence and energy transfer properties. The glasses are investigated in the temperature range from 15 K to 700 K. The Tb 3 + doped glass has a higher temperature stability than the Eu 3 + doped one. Increasing the temperature leads to an enhanced energy transfer from Tb 3 + to Eu 3 + in the double-doped glass. The energy transfer mechanism is investigated in detail. [ABSTRACT FROM AUTHOR]

The europium (Eu) and ytterbium (Yb) co-doped SiO 2 –Al 2 O 3 –MF 2 (M = Ca, Sr) oxyfluoride glasses were prepared by the melting-quenching method, in which the partial reduction of Eu 3+ ions during high temperature fabrication in air atmosphere was explained by optical basicity model. In this system, the near-infrared emission of Yb 3+ at 974 nm can be observed upon the excitation of both Eu 3+ and Eu 2+ , as well as charge transfer state absorption of Yb 3+ . The steady and time-resolved luminescence spectra measurements were carried out to further prove the energy transfer from Eu 3+/2+ ions to Yb 3+ . Based on the measured luminescence decay of Eu 3+ and Eu 2+ , the energy transfer efficiency and the quantum efficiency are much higher in the glass containing SrF 2 due to the efficient energy transfer from both Eu 3+ and Eu 2+ to Yb 3+ . [ABSTRACT FROM AUTHOR]

KLuS 2 single crystals doped with divalent europium and co-doped with trivalent praseodymium, samarium or cerium were synthesized in the form of crystalline hexagonal platelets as interesting candidates for white LED solid state lighting. Luminescence characteristics in UV/Vis, including radioluminescence, photoluminescence excitation and emission spectra and photoluminescence decays, were measured in the broad concentration and temperature interval revealing presence of thermally stable emission features of both Eu 2+ and co-dopants in a single KLuS 2 host. Energy transfer from Eu 2+ to Pr 3+ , Sm 3+ and Ce 3+ is identified. CIE xy -coordinates are used to compare effects of dopants on resulting spectrum. The application potential in white LEDs phosphors is discussed. [ABSTRACT FROM AUTHOR]

Eu 3+ and Gd 3+ ions co-doped amorphous silica nanorods were prepared using a simple sol–gel method, and their luminescent properties were studied under the excitation of ultraviolet light. X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared spectrum (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), and Photoluminescence (PL) spectra were employed to characterize the products in detail. The nanorods are uniform and their diameters and lengths are in the range of 200–300 nm and 500–700 nm, respectively. Energy transfer process in Gd 3+ and Eu 3+ co-doped silica, where a ground state of Gd 3+ , 8 S 7/2 , was selectively excited to a 6 I J state under the excitation of 274 nm, was studied in terms of luminescence spectra, which indict that the energy transfer of Gd 3+ –Eu 3+ is efficient. The mechanism of energy transfer from Gd 3+ to Eu 3+ is a resonant transfer, in which electric dipole–dipole interaction plays a leading role. Furthermore, the doping concentration-dependence of Eu 3+ ions on the energy transfer efficiency was also investigated. [ABSTRACT FROM AUTHOR]

Abstract: Europium-doped lanthanum fluoride (LaF3:Eu3+) nanoparticles were synthesized using a solvothermal method, and they were then capped with benzoic acid (BA) ligands to form LaF3:Eu3+–BA hybrid nanostructures. The LaF3:Eu3+–BA hybrid nanostructures showed strong luminescence as a result of energy transfer from BA to the Eu3+ ions of the LaF3:Eu3+ nanoparticles. The dominant excitation band for the LaF3:Eu3+–BA hybrid nanostructures ranged from 200nm to 300nm. It has been shown that the luminescence of LaF3:Eu3+–BA hybrid nanostructures strongly depends on the pH value and content of benzoic acid used in the preparation of the hybrid nanostructures. An X-ray diffraction technique, transmission electron microscopy, luminescence spectroscopy, Fourier transform infrared spectroscopy and a UV–vis spectrophotometer were used to characterize the products. [Copyright &y& Elsevier]

Eu and Mn singly doped and codoped Na(Sr,Ba)PO phosphors were synthesized, and their luminescent properties were investigated. A broad blue emission and a broad orange emission band were observed in Na(Sr,Ba)PO:Eu, Mn phosphor. The resonant-type energy transfer from Eu to Mn was demonstrated, and the energy transfer efficiency was also calculated according to their emission spectra. Based on the principle of energy transfer, the emission intensity ration of Eu and Mn could be appropriately tuned by adjusting the contents of activators. Due to the strong absorption in the 250-400 nm range, Na(Sr,Ba)PO:Eu, Mn phosphor could be used as a potential candidate for near-UV white light-emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

Abstract: La2TeO6 nanocrystals doped with Eu3+ ions have been prepared by the Pechini sol–gel process. A total of seven samples obtained with different Eu3+ concentrations (1–7%). The Eu3+ ions are usually taken as probe ions to test the local structure of the lanthanide in solids. Analyzing the luminescence has been shown two different sites for the Eu3+ ions (in good agreement with the crystallographic analysis). Moreover, the luminescence properties have been analyzed as function of the Eu3+ doping concentration in order to study the interaction between these ions. Under direct excitation into the 5D0 level (at 578nm) the corresponding decay curves show a pure exponential character independently of the Eu3+ concentration. However, the decay curves obtained for the 5D1 level becomes non-exponential for the higher doped nanocrystals samples indicating that the energy transfer processes are important. [Copyright &y& Elsevier]

Abstract: The Eu and Eu/Tb doped silicate glasses are good candidates for light emitting diode (LED) applications. But the optical performance of these glasses is sensitive to variations in chemical composition. In this paper we report our recent findings about the effect of addition of minor components such as B2O3, Al2O3 and CaF2 on the luminescent properties of the above-mentioned glasses. We explore the role of Eu3+ ions as a structural probe of the glasses by determining the asymmetry factor, i.e., the ratio of the emission intensity of the transition to that of the transition. The results show that the asymmetry factor and luminescence lifetimes of as-prepared materials are dependent on composition. White fluorescence is achieved in Eu/Tb co-doped glasses, which can be attributed to the simultaneous generation of red, green and blue wavelengths from Eu3+ and Tb3+ ions. The variation of the excitation wavelength can tune the emission spectra as well as Commission Internationale de L’Eclairage (CIE) chromaticity coordinates of Eu/Tb co-doped glasses for specific applications. The energy transfer from Tb3+ to Eu3+ ions is investigated by analyzing fluorescence spectra and decay curves. [Copyright &y& Elsevier]

Abstract: Eu3+ doped nano-composites containing CeO2 nano-crystals are fabricated by a sol–gel process. The Stark splitting emissions as well as the low forced electric dipole 5D0 → 7F2 transition of Eu3+ reveals the partition of them into CeO2 nano-crystals. Increasing CeO2 content results in a growth of Eu3+ quantity incorporated in the nano-crystals and therefore the enhancement of Eu3+ photoluminescence. CeO2 nano-crystals not only afford a low phonon energy environment to Eu3+, but also sensitize their emissions and protect them from OH− quenching. [Copyright &y& Elsevier]

Abstract: Eu2+ and Eu2+–Mn2+ codoped (Ba,Sr)Mg2Al6Si9O30 phosphors have been synthesized by solid state reaction, and their luminescent properties are investigated. Under the excitation of 330nm, it is observed that the emission of Eu2+ consists of two emission bands, located at around 370 and 450nm, which are attributed to two Eu2+ centers (Eu2+(I) and Eu2+(II)) ions substituting for two different Ba2+ and Mg2+ sites, respectively. As Sr2+ gradually substitutes Ba2+, the emission bands of Eu2+(I) shift to longer wavelength whereas the emission bands of Eu2+(II) exhibit no change. This phenomenon is discussed in terms of the crystal-field strength. A detail analysis on the energy transfer from Eu2+ to Mn2+ in SrMg2Al6Si9O30 host is presented, which indicates the energy of the red emission of Mn2+ is derived mainly from Eu2+(I). We have also demonstrated that BaMg2Al6Si9O30:Eu2+, Mn2+ exhibits better thermal quenching properties than that of SrMg2Al6Si9O30:Eu2+, Mn2+ because of bigger activation energy. [Copyright &y& Elsevier]

Abstract: Eu3+ doped ZnO nanoparticles are synthesized by solvothermal reaction and following annealing process. When molar ratio of Eu/Zn is increased from 0.01 to 0.03, a small percentage of Eu3+ is slowly separated from host ZnO lattice accompanied by decrease of average particle size. However, the proportion of individual Eu2O3 particles in doped ZnO is extremely low. After doping, a great deal of crystal defects are generated in host ZnO lattice, in which O vacancy, interstitial Zn and interstitial O are involved in energy transfer from host lattice to Eu3+. Among them interstitial O plays an important bridge role in this process. [Copyright &y& Elsevier]

The title phosphor with different concentrations of dopants is prepared by a combustion-assisted method using Eu2O3, MnCO3, Ca(NO3)2, NH4F, and NH4H2PO4 as starting materials, and CO(NH2)2 as the fuel (flowing 5%H2/N2, porcelain boat, 900 °C, 3 h). [ABSTRACT FROM AUTHOR]