Compact fluorescent lamps contain mercury gas which generates ultraviolet radiation. A thin powder layer
constituted of rare-earth oxides is coated inside the glass tube. The role of this layer is to convert the inside
ultraviolet radiation into outside visible radiation. We focus here on a particular powder layer, constituted by
phosphor grains. The phosphor layer has to achieve two distinct goals. On the one hand the grains have to absorb
the maximum amount of ultraviolet radiation in order to generate visible light, and on the other hand the
transmission of visible light has to be maximized in order to optimize the efficiency of the compact fluorescent
lamp. Here, we study the influences of grain size, grain shape, density of packing powder, and thickness of the
phosphor coating. Such a study is a first step towards a better understanding of the conversion efficiency of
ultraviolet radiation into visible radiations, and can eventually, help to improve the production line of compact
fluorescent lamps. All the presented simulations were performed with the commercial software LightTools®
using a ray tracing method.
Lanthanide-ion doped oxide nanoparticles were functionalized for use as fluorescent biological labels. These nanoparticles are synthesized directly in water which facilitates their functionalization, and are very photostable without emission intermittency. Nanoparticles functionalized with guanidinium groups act as artificial toxins and specifically target sodium channels. They are individually detectable in cardiac myocytes, revealing a heterogeneous distribution of sodium channels. Functionalized oxide nanoparticles appear as a novel tool particularly well adapted to long-term single-molecule tracking.
The synthesis and the emission properties of colloidal YVO4:Ln nanocrystals (8nm in diameter) are investigated, where Ln = Eu, Nd, Yb, Er. The nanoparticles synthesized here are constituted of a (Y,Ln)VO4 crystalline core and stabilized by a lanthanide-citrate complexing shell. Surface derivatization of the particles can be achieved through the controlled growth of a silicate shell using a functionalized silane, with elimination of the citrate shell. The luminescence of the Eu3+ -doped YVO4 colloids is studied in details and compared to the bulk material. Chemical treatments are achieved in order to explain the observed differences. Improvement of the emission quantum yield after the transfer of the colloidal particles into D2O shows that surface OH groups act as efficient quenchers of the Eu3+ emission. The growth of a silica shell around the particles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate ions. Moreover, site selective excitation spectroscopy seems to prove the coexistence of core sites and surface sites for the europium ions. Finally, colloidal nanoparticles exhibit an emission yield of about 25%, which appears already suitable for some applications.