Light Determines Crystal Phase

Chemists at Polytechnic University in New York and Illinois Institute of Technology in Chicago have used infrared radiation to produce crystalline phases that depend on the polarization of the light. The phenomenon may offer a "green" industrial process for controlling the production of polymorphs and lead to the discovery of unknown phases.

In work described in the Oct. 21 issue of Physical Review Letters, they irradiated solutions of glycine and water for one minute with 9-ns polarized pulses from a Q-switched 1064-nm Nd:YAG. Eight of the 18 samples that were exposed to circularly polarized radiation nucleated, all forming α-glycine, and 22 of the 46 exposed to linearly polarized pulses nucleated, all forming the γ-phase.