C. Barthou

Mn2+ Concentration Effect on the Optical Properties of Zn2SiO4 : Mn Phosphors

The optical properties of manganese-activated zinc silicate Zn 2(1-x) Mn 2x SiO 4 are investigated using pulse selective photon excitation. The light response due to the 4 T 1g - 6 6A 1g transition is directly linked to the relative concentration of isolated Mn 2+ and Mn 2+ pairs in this structure. The decay curves can be fitted by a diffusion-limited relaxation mechanism by considering two types of centers with radiative lifetimes no equal to 15 and 1.75 ms, respectively

Nanomaterials containing rare-earth ions Tb, Eu, Er and Yb: preparation, optical properties and application potential

This paper focuses on preparation, optical properties and application potential of some nanomaterials based on Y2O3:Eu,Tb,Er,Yb and SiO2–TiO2 and SiO2–ZiO2 doped with Er and Yb. Y2O3 nanophosphors are prepared by the combustion method with different doped concentrations. The nanocrystal size of Y2O3:Eu is from 4.4 to 72.2 nm depending on the technology condition. The luminescent spectra, up-conversion and lifetimes were measured and compared. The influence of the technological conditions on the luminescent properties was investigated in detail. The energy transfer effect was studied by the luminescent spectra and the lifetimes in the temperature dependence for the samples with rare-earth concentrations of 5 mol%, The relative concentration between Eu and Tb is 8/2 for energy transfer from Tb to Eu. The SiO2–TiO2 and SiO2–ZiO2 thin films containing Er rare-earth ion were prepared by the sol–gel technique. Optical properties were investigated and the influence of the Er concentration on the luminescent spectra as well as the influence of the Ti concentration on the refractive index of thin films was presented.

Luminescence, energy transfer, and upconversion mechanisms of Y 2 O 3 nanomaterials doped with Eu 3+ , Tb 3+ , Tm 3+ , Er 3+ , and Yb 3+ Ions

Luminescence, energy transfer, and upconversion mechanisms of nanophosphors (Y2O3:Eu3+, Tb3+, Y2O3:Tm3+, Y2O3:Er3+, Yb3+) both in particle and colloidal forms were studied. The structure, phase, and morphology of the nanopowders and nanocolloidal media were determined by high-resolution TEM and X-ray diffraction. It was shown that the obtained nanoparticles have a round-spherical shape with average size in the range of 4 to 20nm. Energy transfer was observed for Y2O3:Eu3+, Tb3+ colloidal and powders, upconversion transitions were observed for both Y2O3:Er3+ and Y2O3:Er3+, Yb3+ nanophosphors. The dependence of photoluminescence (PL) spectra and decay times on doping concentration has been investigated. The infrared to visible conversion of emission in Y2O3:Er3+, Yb3+ system was analyzed and discussed aiming to be applied in the photonic technology.

Radiative Properties of the Blue BaAl2S4 : Eu2 + Phosphor

The optical properties of BaAl 2 S 4 doped with Eu 2+ were investigated. The synthesis was performed in evacuated and sealed quartz ampul at 1000°C during 1 h, then at 840°C during 20 h. With absorption, excitation, and emission spectra we have determined the crystal-field splitting, the redshift, the influence of the lattice vibration properties, and the thermal quenching of the luminescence. The crystal-field splitting of Eu 2+ in BaAl 2 S 4 was estimated on the order of 8000 to 10 000 cm -1 and the Huang-Rhys parameter S = 5 ± 1 corresponds to an intermediate electron-phonon coupling regime. The mean phonon energy for BaAl 2 S 4 was evaluated by optical and Raman methods, and the obtained values were 32 ± 5 and 40 meV, respectively. These results confirm the very interesting properties of this blue BaAl 2 S 4 :Eu 2+ phosphor, the most important being the very slight thermal quenching of the luminescence.

Cerium Concentration and Temperature Dependence of the Luminescence of SrGa2 S 4 : Ce , Na , a Blue‐Emitting Material for Electroluminescent and High Current Density Cathodoluminescent Displays

The cerium concentration and temperature dependence of the spectral distribution, quantum yield, and lifetime of the Ce 3+ photoluminescence has been investigated in powders having the composition Sr, 2r Ce , Na r Ga 2 S 4 (x < 0.5). With increasing cerium concentration the emission shows a strong shift to longer wavelengths caused mainly by changes in the ligand field. Despite a relatively small Stokes shift (2000 cm -1 ), the emission shows a low concentration quenching up to x = 0.10. Because of the size differences between the Ce 3+ , Na + , and Sr 2+ ions, cerium ions possess various environments. Energy migration to defects is impeded by the transfer of the excitation energy to the ions having the lowest emitting states, whose emission exhibits reduced overlap with the absorption of other ions. As a result of the small Stokes shift, at low Ce concentration the luminescence is not affected by the thermal quenching up to 500 K. The low concentration quenching and the high thermal stability are favorable characteristics for use of this phosphor in electroluminescence and high current density CL screens.

Quantitative analyses and crystallographic studies of Zns:Mn thin films prepared by r.f. magnetron reactive sputtering

Abstract ZnS: Mn thin films prepared by r.f. magnetron reactive sputtering were examined by electron probe microanalysis and X-ray diffraction. The necessity of producing reactive sputtering by adding H 2 S gas to the argon discharge was established. The best crystallinity with only cubic structure and a strong preferred orientation of the (111) plane parallel to the substrate was obtained for a low substrate temperature of 100 °C and a high pressure of 6 Pa during the sputtering. The presence of 0.2–0.5 at.% argon atoms incorporated in the ZnS: Mn films was found.

Excitation efficiency in thin‐film electroluminescent devices: Probe layer measurements

The study of the excitation efficiency ηexc on thin‐film electroluminescent devices with special semiconductor layer—a very thin probe‐doped layer located at different part of the pure ZnS layer—has proved that ηexc is not homogeneous across the active layer. Moreover, this variation of ηexc depends on the amount of the transferred charge. At high excitation range, ηexc decreases continuously from the cathode toward the anode of the active layer. This behavior of ηexc is related to a space charge located in some part of the ZnS layer and generated by the energetic electrons. This space charge reduces the total efficiency of a conventional device when operating at high excitation range.

Photoluminescence and cathodoluminescence properties of green emitting SrGa2{S}4 : Eu2+ thin film

Photoluminescence and cathodoluminescence properties of SrGa2S4 : Eu2+ thin films prepared by reactive RF magnetron sputtering are investigated. Luminescence performances of the phosphor in the thin film form are compared to those of powder samples: the brightness efficiency of thin films is found to be about 30% of the efficiency of powder at low current density. A ratio higher than 40% is expected at higher current density. Thin film screens for FEDs will become a positive alternative to powder screens provided that film quality and light extraction could be improved by optimization of thickness and deposition parameters.

Energy transfers between Eu2+ and Er3+ in EuGa2S4:Er3+

The photoluminescence properties of EuGa2S4:Er polycrystals under 337.1 and 976 nm laser excitations versus temperature (78–500 K) are presented. Under 337.1 nm excitation wavelength, a wide emission band corresponding to Eu2+ ions in the visible range and emission lines of Er3+ in the visible and near infrared were observed. These emissions were also observed under 976 nm excitation wavelength with a two-photon absorption accompanied by a phonon assisted energy transfer to Eu2+ ions. According to experimental conditions, energy transfers from Eu2+ to Er3+ and from Er3+ to Eu2+ are highlighted.

Structural and luminescent properties of green emitting SrGa2S4:Eu thin films prepared by RF-sputtering

Green emittingSrGa 2S4:Eu thin films have been prepared by reactive RF magnetron sputtering. Electron Probe MicroAnalysis, X-ray diffraction, Micro-Raman spectroscopy and roughness measurements were used to study the growth of SrGa2S4:Eu and to determine the effects of the post-deposition heat treatment on the morphological and structural properties. The post-deposition annealingis a necessary step for the layer crystallisation, it influences the film composition and the structural properties leadingto the improvement of luminescence performances. Photoluminescence properties as a function of annealingparameters are reported. r 2003 Elsevier B.V. All rights reserved.