Tailored for optical applications

Nov 09, 2007

When a calcite crystal is placed onto a printed page, the letters appear doubled. This is the result of a property called birefringence. Scientists at the Simon Fraser University in Canada have now developed a material that is among the most birefringent solids ever observed. As described in the journal Angewandte Chemie, this material is not a mineral, but rather a coordination polymer.

Refraction is the change in direction of a wave of light when it passes from air into water or a crystal. It is caused by a local change in the speed of propagation. In the case of birefringence, the light is divided into two perpendicularly polarized beams, which move at different speeds and exit the material shifted relative to each other. The source of this effect is a crystal lattice that has different optical properties along its various axes (anisotropy).

Birefringent optical components are usually made of calcite. The critical value for these applications is the difference in the refractive index of light in two directions in the crystal, the birefringence, which is 0.17 for calcite.

The team led by Daniel B. Leznoff and Zuo-Guang Ye has now produced a highly birefringent coordination polymer. Coordination polymers are one-, two-, or three-dimensional bridged metal complexes. The advantage to this type of compound is the limitless number of design possibilities: The individual components—metal center, chelating ligands, and bridging ligands—can be selected and combined almost at will to get the desired material properties.

Leznoff’s team, spearheaded in the lab by Michael J. Katz, decided to use a “terpy” ligand, a flat ring system consisting of three pyridine units (six-membered aromatic rings with one nitrogen atom), and lead as the metal center. The complexes are linked by linear bridging ligands made of a central silver or gold ion and two cyanide groups to form two-dimensional layers. If the central lead atom is replaced with manganese, one-dimensional ladder-like structures are formed. Within their crystals, however, the lead and manganese polymers have analogous arrangements: the terpy molecules are piled up plane-to-plane, perpendicular to the axis of crystal growth. This is clearly the crucial factor leading to the high birefringence, which reaches values from 0.43 to just under 0.4, significantly higher than those of the numerous inorganic birefringent materials.

Improved optical data storage and data transfer in communications technology are possible applications for such highly birefringent materials.

Source: Wiley

Explore further: Chemists use high speed camera to fully explain high school explosion demonstration

add to favorites email to friend print save as pdf

Related Stories

Plasmon-enhanced Polarization-selective filter

Jul 17, 2014

As we all know, some optical devices can only work with a certain incident polarization direction. In this case, a polarizer is necessary to shift the polarization direction of linearly polarized light. A ...

Scientists make huge strides in imaging science

Jun 02, 2014

(Phys.org) —University scientists have developed a rapid new technique involving X-ray imaging that allows clear images to be obtained displaying the orientational properties of molecules in solid materials.

Recommended for you

Micropore labyrinths as crucibles of life

4 hours ago

Water-filled micropores in hot rock may have acted as the nurseries in which life on Earth began. An LMU team has now shown that temperature gradients in pore systems promote the cyclical replication and ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.