Audrey Potdevin

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.

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.

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.

In situ synthesis of a highly crystalline Tb-doped YAG nanophosphor using the mesopores of silica monoliths as a template

This report describes the first synthesis of a highly crystalline YAG:Tb nanophosphor inside the pores of a mesoporous silica monolith (MSM). A simple wet impregnation procedure using a YAG:Tb sol and a MSM platform prepared by a sol–gel method was adopted to prepare highly homogeneous MSM–YAG:Tb luminescent composites. The morphological, structural and luminescence properties of in situ generated YAG:Tb nanocrystals, investigated using XRD, TEM, HRTEM, EDS, FTIR, nitrogen gas sorption and photoluminescence measurements, were compared to those of the bulk YAG:Tb phosphor. The specific surface area and the pore volume of the MSM host material were found to be lower when YAG:Tb nanoparticles were grown in the pores of the MSM material. The particle diameter of the nano-sized YAG:Tb phosphor was estimated to be about 23 nm. The MSM–YAG:Tb composite exhibited a strong green fluorescence emission with the characteristic main emission band of Tb3+ located at 548 nm. The prepared composite also showed a shorter photoluminescence (PL) lifetime and excitation bands shifted to lower wavelengths compared to the neat YAG:Tb phosphor. The as-prepared MSM–YAG:Tb material could be integrated into optoelectronic devices and holds good potential to be applied in decorative lighting.