No abstract

The red luminescent composite, achieved by a film casting method, proved to be a promising candidate for applications in UV-LED based lighting devices.

No abstract

This work deals with phosphors suitable for applications in a new generation of Hg-free lamps based on deep ultraviolet (DUV), ultraviolet (UV) and blue light emitting diodes (LEDs). First, two synthesis routes, solid state reaction and Pechini method, have been used for preparing an original red phosphor, Y 3 BO 6 :Eu 3+ . Phase purity was confirmed by XRD analysis for Pechini derived sample after washing the powder with an acidic solution while the synthesis dependence of the morphological and optical characteristics was evidenced by SEM analysis and photoluminescence respectively. Y 3 BO 6 :Eu 3+ powders derived from Pechini process exhibited high photoluminescence quantum efficiency upon excitation at wavelengths corresponding to afore mentioned sources, in comparison with commercial Y 2 O 3 :Eu 3+ red phosphor. Furthermore, the Pechini method was used for elaborating Y 3 BO 6 :Eu 3+ spray-coated thin film. Its structural and optical features were also investigated. Finally, colorimetric simulations have pointed out that Y 3 BO 6 :Eu 3+ could be efficiently combined with blue and green phosphors to produce white light from DUV LEDs. Regarding blue LEDs sources, a mixture constituted of Y 3 Al 5 O 12 :Ce 3+ and Y 3 Al 5 O 12 :Pr 3+ powders has been investigated and resulted in promising results for providing white light with suitable features for indoor or outdoor lighting.

This work focuses on the study of BaMgAl10O17:Eu(2+) (BAM:Eu) nanophosphors prepared by a microwave-assisted combustion procedure and more especially on the polymer/BAM:Eu nanocomposite film suitable for optical devices such as solid-state-lighting. Powder presented a specific nanomorphology, highly friable and thus easily ground into fine particles. They were then homogeneously dispersed into a polymer solution (poly(N-vinylpyrrolidone) or PVP) to elaborate a polymer phosphor nanocomposite. The structural, morphological and optical features of the nanocomposite film have been studied and compared to those of a pristine PVP film and BAM:Eu powder. All the characterizations (XRD, SEM, SAXS, etc.) proved that the blue phosphor nanoparticles are well incorporated into the polymer nanocomposite film which exhibited the characteristic blue emission of Eu(2+) under UV light excitation. Furthermore, the photostability of the polymer/phosphor nanocomposite film has been studied after exposure to accelerated artificial photoageing at wavelengths above 300 nm.

Blue-emitting BaMgAl 10 O 17 :Eu 2þ (BAM:Eu), suitable for applications in a next generation of Hg-free lamps based on UV LEDs, was prepared by a microwave induced solution combustion synthesis, using urea as combustion fuel and nitrates as oxidizers. Purity control of the as-synthesized blue phosphor was undertaken by a washing step followed by a reduction one. Structural and morphological properties of the outcoming phosphors have been considered. Synthesis process allows producing a well-crystallized and nanostructured BAM phase within only few minutes. The influence of reduction treatment on the relative amounts of Eu 2þ /Eu 3þ in our samples has been investigated through an original study by magnetization and M€ ossbauer spectroscopy. Furthermore, a complete optical study has been carried out and allowed us to determine the europium localization in the three possible sites in BAM matrix. The percentage of Eu 2þ increased twofold after the reduction treatment, entailing an increase in the luminescence efficiency upon UV excitation. Finally, temperature-dependent luminescence of combustionderived powders has been studied till 170 C and compared to that of commercial BAM:Eu. MISCSderived phosphors present a higher thermal stability than commercial one: whereas the emission efficiency of this last was reduced by 64%, the one of combustion-derived BAM:Eu experienced an only 12% decline. Furthermore, while commercial BAM suffered from a severe blue-shift with increasing temperature, our phosphors keep its color quality with a good stability of the photometric parameters.

No abstract