Materials - properties and applications

Inhaltsverzeichnis

1. 1.  a) luminescent nanocomposites
      1. ZnS: Mn/PMMA nanocomposites
      2. ZnS: Cu/PMMA thin films
   2.  b) Photorefractive nanocomposites
   3.  c) photochromic nanocomposites

 a) luminescent nanocomposites

ZnS: Mn/PMMA nanocomposites

Luminescent ZnS:Mn-nanoparticles were integrated into polymers using acrylic acid as coordinating monomer. Transparent nanocomposites with strong orange luminescence (30% quantum yield) were obtained. Besides the preparation of PMMA-based bulk polymers, the particle/monomer dispersions can be used for ink-jet printing invisible writings onto transparent substrates. Under excitation with UV light the writings become visible by the particles luminescence.

ZnS: Cu/PMMA thin films

Application: Electroluminescent devices

Thin nanocomposite films embedding ZnS :Cu nanoparticles can be used in a electroluminescent device structure. The nanoparticles are generated via simple arrested co-precipitation method. After a phase transfer they can be dispended in a polymer solution and spin cast on ITO electrode to create nanocomposite films with thicknesses about 60 nm. After contacting with an aluminum counter electrode the EL-device is operated with direct current.

 b) Photorefractive nanocomposites

Ferroelectric nanomaterials have recently attracted considerable attention because of their promising applications in integrated microelectronic devices, especially in nonvolatile memories and microelectromechanical systems. Within this project new methods for the preparation of lead-free ferroelectric nanomaterials were established. The A- site substitution of Bi4Ti3O12 with rare earth cations (as La3+, Pr3+) and the co-substitution with high valence cations (as V5+) was successfully demonstrated using a modified citrate-gel method.

The cosubstitued nanoparticles show improved ferroelectric performances as high remanent polarization without significant decrease even after switching over 108 cycles.

For further applications nanocomposite thin film devices containing ferroelectric nanoparticles were prepared. A TENG-MAN-setup is used to measure the pockels coefficient and to determine the quadratic electro- optic effect.

 c) photochromic nanocomposites

BiOI nanocomposites were prepared via microemulsion polymerization technique. The obtained nanocomposites are sensitive to UV-irradiation, changing the color from yellow to black under UV irradiation and back to yellow after air exposure. Responsible for this photochromic effect is the temporary reduction of Bi3+ to elementary Bi. In this way temporary patterning can be created in the colored composite materials offering a high potential for lithographic structuring.