Luminescence in sulfides : a rich history and a bright future

Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles

Hybrid fluorescent layer emitting polarized light

Semiconductor nanorods have anisotropic absorption and emission properties. In this work a hybrid luminescent layer is produced based on a mixture of CdSe/CdS nanorods dispersed in a liquid crystal that is aligned by an electric field and polymerized by UV illumination. The film emits light with polarization ratio 0.6 (polarization contrast 4:1). Clusters of nanorods in liquid crystal can be avoided by applying an AC electric field with sufficient amplitude. This method can be made compatible with large-scale processing on flexible transparent substrates. Thin polarized light emitters can be used in LCD backlights or solar concentrators to increase the efficiency

Optical properties of SOI waveguides functionalized with close-packed quantum dot films

It is shown that dipolar coupling between neighboring quantum dots enhances the absorption of light in close packed monolayers of colloidal quantum dots. Based on this concept, the experimentally determined losses in planarized waveguides coated by a quantum dot monolayer can be successfully simulated. These simulations rely on replacing the quantum dot layer by an effective medium with a dielectric function determined by dipolar coupling and use the dielectric constant of the quantum dot host medium as the only adjustable parameter. This leads to a generic approach for the simulation of optical materials including close packed quantum dot layers

Ultrafast exciton dephasing in PbS colloidal quantum dots

In this work, we have measured the ground state excitonic dephasing in PbS QDs of sizes from 3.7nm to 5.7nm diameter in the temperature range from 5K to 100K by transient degenerate four-wave mixing (FWM) using 100fs pulses. A combination of heterodyne and k-selection detection was implemented to increase sensitivity and enable 4 orders of magnitude dynamic range in the FWM field detection