Geneviève Chadeyron

Ce-Doped YAG Nanophosphor and Red Emitting CuInS2/ZnS Core/Shell Quantum Dots for Warm White Light-Emitting Diode with High Color Rendering Index

In this work, we report the solvothermal synthesis of Ce-doped YAG (YAG:Ce) nanoparticles (NPs) and their association with a free-Cd CuInS2/ZnS (CIS/ZnS) core/shell QDs for application into white light emitting diode (WLED). 1500 °C-annealed YAG:Ce NPs and CIS/ZnS core/shell QDs exhibited intense yellow and red emissions band with maxima at 545 and 667 nm, respectively. Both YAG:Ce nanophosphor and CIS/ZnS QDs showed high photoluminescence quantum yield (PL QY) of about 50% upon 460 nm excitation. YAG:Ce nanophosphor layer and bilayered YAG:Ce nanophosphor-CIS/ZnS QDs were applied on blue InGaN chip as converter wavelength to achieve WLED. While YAG:Ce nanophosphor converter layer showed low color rendering index (CRI) and cold white light, bilayered YAG:Ce nanophosphor-CIS/ZnS QDs displayed higher CRI of about 84 and warm white light with a correlated color temperature (CCT) of 2784 K. WLED characteristics were measured as a function of forward current from 20 to 1200 mA. The white light stability of bilayered nanophosphor-QDs-based WLED operated at 200 mA was also studied as a function of operating time up to 40 h. Interestingly, CRI and CCT of such device tend to remain constant after 7 h of operating time suggesting that layer-by-layer structure of YAG:Ce phosphor and red-emitting CIS/ZnS QDs could be a good solution to achieve stable warm WLED, especially when high current density is applied.

Luminescence of the orthoborate YBO3:Eu3+. Relationship with crystal structure

Abstract Pseudo-vaterite structure of YBO3 has been determined from X-Ray data taken from a single crystal. This orthoborate crystallizes in the P6 3 m space group. The structure exhibits two types of [YO8] polyhedra due to the existence of two environments for the yttrium ions. The Eu3+ luminescence in this compound corroborates fairly well the structural determination by identification of two crystallographic sites both showing a C3 symmetry.

Eu-Doped BaTiO3 Powder and Film from Sol-Gel Process with Polyvinylpyrrolidone Additive

Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders revealed spherical and rod shape morphology. The optical quality of films showed a predominant band at 615 nm under 250 nm excitation. A preliminary luminescent test provided the properties of the Eu3+ doped BaTiO3.

Rapid synthesis of Ce3+-doped YAG nanoparticles by a solvothermal method using metal carbonates as precursors

Solvothermal methods to synthesize cerium-doped YAG nanoparticles (YAG:Ce3+ NPs) generally require relatively long heating times (th ≥ 1 h) and temperatures close to 300 °C. In this work, we report a rapid solvothermal synthesis (th = 5 min) leading to well-crystallized and highly monodisperse YAG:Ce3+ NPs of about 30 nm diameter by heating mixed yttrium, aluminium and cerium carbonate precursors in an autoclave at 300 °C using a 1,4-butylene glycol–water mixture as solvent. The as-prepared YAG:Ce3+ NPs showed a broad emission band in the green–yellow range having maximum intensity at 550 nm upon blue or UV excitation. The effect of heating time and Ce3+ concentration on structural, morphological and optical properties of YAG:Ce3+ NPs has been systematically studied by X-ray powder diffraction, transmission electron microscopy, FT-IR spectroscopy, energy dispersive spectroscopy and room temperature photoluminescence experiments. The combination of low Ce3+ doping concentration and short heating time plays a crucial role in the good optical properties of the obtained YAG:Ce3+ NPs. The particles hold good potential to be applied in solid-state lighting or used as coating for display system applications.

Luminescent Nanocomposites Made of Finely Dispersed Y3Ga5O12:Tb Powder in a Polymer Matrix: Promising Candidates for Optical Devices

This paper reports the initial results of an original and simple method to elaborate flexible, self-standing, and thick luminescent films suitable for optical devices. PVP/Y(3)Ga(5)O(12):Tb(3+) nanocomposite films have been successfully achieved from a sol-gel derived Y(3)Ga(5)O(12):Tb(3+) powder and an alcoholic solution of poly-N-vinylpyrrolidone (PVP). The structural, morphological, and optical properties of these nanocomposite films have been studied and compared to those of a pristine PVP film and Y(3)Ga(5)O(12):Tb(3+) powder. The nanocomposite films were characterized by infrared and Raman spectroscopies as well as scanning and transmission electron microscopies (SEM and TEM) and demonstrated good dispersion of the phosphor particles within the polymer matrix via an alveolar mesostructure. The optical properties of these nanocomposites were fully characterized, and both their excitation and emission spectra and decay curves were recorded. Furthermore, photostability of the nanocomposite films and of the luminescent raw powder has been studied after exposure to an accelerated artificial photoageing at wavelengths higher than 300 nm. The elaboration process used is both tunable and applicable to a large variety of powders and polymers because it does not require any additive to form homogeneous and easily shapeable phosphor/polymer nanocomposites applicable in a large variety of optical devices such as solid-state-lighting.

Development of rare-earth-free phosphors for eco-energy lighting based LEDs

Several phosphors without rare-earth elements were synthesized by a simple and practical method. Depending on their wavelength emitting range upon UV excitation, i.e. blue, green or red, they were classified in three groups. The phosphors exhibiting the best performances in optical properties were selected to be incorporated in free-standing silicon films and combined with a 365 nm LED. The thermal quenching of phosphors as well as the photometric parameters of the luminescent composite films were investigated. This white emission of the combination between the rare-earth-free phosphors based silicon film and LED shows a CRI >75 and CCT around 4000 K which can fulfil the requirements for indoor domestic lighting source.

Hydrothermal Synthesis and Characterization of Europium-doped Barium Titanate Nanocrystallites

Barium titanate nanocrystallites were synthesized by a hydrothermal technique from barium chloride and tetrabutyl titanate. Single-crystalline cubic perovskite BaTiO3 consisting of spherical particles with diameters ranging from 10 to 30 nm was easily achieved by this route. In order to study the influence of the synthesis process on the morphology and the optical properties, barium titanate was also prepared by a solid-state reaction. In this case, only the tetragonal phase which crystallizes above 900° was observed. High-temperature X-ray diffraction measurements were performed to investigate the crystallization temperatures as well as the particle sizes via the Scherrer formula. The lattice vibrations were evidenced by infrared spectroscopy. Eu3+ was used as a structural probe, and the luminescence properties recorded from BaTiO3:Eu3+and elaborated by a solid-state reaction and hydrothermal process were compared. The reddish emission of the europium is increased by the nanometric particles.

Structural studies of BaTiO3:Er3+ and BaTiO3:Yb3+ powders synthesized by hydrothermal method

Erbium and ytterbium doped barium titanate nanopowders were prepared using the hydrothermal method. A barium titanate structure doped with rare earth ions manifested new characteristics and improved the field of application of optical devices such as trichromatic tubes, LCD displays, lamps, and infrared lasers. In this work, BaTiO3:Er3+ and BaTiO3:Yb3+ were prepared using barium chloride [BaCl2], titanium butoxide [C16H36O4Ti], erbium chloride [ErCl3] and ytterbium chloride [YbCl3] as precursors. Anhydrous methanol was employed as a solvent. Metallic potassium was used to promote solubility in the system and increase the pH to 13. This method yielded the formation of a predominantly cubic structure in both Er3+ and Yb3+ doped BaTiO3 powders. Characteristic bondings of BaTiO3 were observed with FT-IR spectroscopy. The predominantly cubic structure was confirmed by X-ray diffraction and micro-Raman analyses. The particle size (∼30 nm) was estimated using the Scherrer equation and X-ray diffraction data. The results were presented and discussed.

A thorough spectroscopic study of luminescent precursor solution of Y3Al5O12:Tb3+: influence of acetylacetone

Undoped and Tb3+-doped precursor solutions of Y3Al5O12 (YAG) have been prepared by the sol–gel process using alkoxide precursors stabilized by a chelating agent: acetylacetone (acacH), with various complexation ratios RC = 0, 1, 2 and 3 defined as the ratio between [Al(OPri)3] and [acacH]. Combining in situ UV-visible investigation of the hydrolysis process of these sols with X-ray diffraction study on the powders extracted after water addition to the sols, drying and subsequent heating, an optimal RC value has been determined. It leads to sols stable over a long period of time and resulting in a pure YAG phase. Structural and optical properties of Tb3+-doped precursor sols characterized by RC = 0 (as a reference for the influence of acacH) and RC = 1 (determined optimal value) were studied by means of X-ray Absorption Spectroscopy (XAS) and photoluminescence, respectively. Y K and Tb L3 edges XAS results show the presence of double heterometallic Y or Tb/Al alkoxides for the sol with RC = 1 involving pre-nuclei cluster with YAG structure. Emission and excitation spectra as well as decay curves were recorded and compared. Results revealed that the stabilized sol is much more efficient upon UV excitation than its unmodified counterpart thanks to an efficient energy transfer from acetylacetonate groups to active ions. Upon a 485 nm excitation, acac-modified samples remain the most efficient ones. It could be related to the dissimilar Tb local environments of the sols suggested by both UV-visible and photoluminescence excitation results.

Cerium-activated sol–gel silica glasses for radiation dosimetry in harsh environment

Cerium-doped silica glass has been prepared for ionizing radiation dosimetry applications, using the sol–gel route and densification under different atmospheres. In comparison with the glass densified under air atmosphere, the one obtained after sintering the xerogel under helium gas presents improved optical properties, with an enhancement of the photoluminescence quantum yield up to 33%, which is attributed to a higher Ce3+ ions concentration. Such a glassy rod has been jacketed in a quartz tube and then drawn at high temperature to a cane, which has been used as active material in a fibered remote x-ray radiation dosimeter. The sample exhibited a reversible linear radioluminescence intensity response versus the dose rate up to 30 Gy s−1. These results confirm the potentialities of this material for in vivo or high rate dose remote dosimetry measurements.