Chameleon for optoelectronics

July 13, 2007

This release is also available in German.

A liquid that changes its color "on demand" and can take on any color of the rainbow one desires" A research team headed by Yadong Yin at the University of California, Riverside (USA) has now shared the secret of their wonderful liquid with the journal Angewandte Chemie: Nanoscopic particles made of tiny magnetic crystals coated with a plastic shell self-assemble in solution to form photonic crystals--semiconductors for light. When a magnetic field is applied, the optical properties of the crystals change, allowing their color to be very precisely adjusted through variation of the strength of the field.

The crystals involved here are no "conventional" lattices of ions or molecules like the one we are familiar with for salt; instead they are colloidal crystals, periodic structures that form from uniform solid particles that are finely dispersed in a liquid. Colloidal crystals can be produced at little cost and on a large scale--and can be used as photonic crystals. Photonic crystals are the optical analogue of electronic semiconductor materials. Like their electronic counterparts, they have photonic band gaps, forbidden energy levels, or wavelengths, at which the photonic crystal does not transmit light. These optical properties depend on the spatial relationships within the crystal.

Current research is concerned with photonic crystals whose forbidden bands are variable and can be adjusted quickly and precisely in response to an external stimulus. These requirements have been impossible to meet until now.

One stimulus that could be used is a magnetic field, if the crystals are made of magnetic materials, such as iron oxide. The problem with this is that the magnetization is maintained when the particles grow into larger domains (ferromagnetism). Yin and his team have found a solution: They coated nanoscopic iron oxide particles with a plastic called polyacrylate. This results in separate clusters of nanocrystals, which self-assemble in solution to form colloidal photonic crystals. The forces of the magnetic field affect every individual cluster, changing the cluster-to-cluster distances within the crystal lattice. Depending on the distance from the magnet and thus the field strength, the color of the colloidal crystal changes right across the whole visible spectrum. This response is rapid and fully reversible because the nanocrystals in clusters are so small that they lose their magnetism when the magnetic field is shut off (superparamagnetism). Potential applications for these switchable "optical semiconductors" include novel optoelectronic components for telecommunications, displays, and sensors.
-end-
Author: Yadong Yin, University of California, Riverside (USA),
http://www.chem.ucr.edu/index.html?main=faculty&facsort=profile&faculty=yin
Title: Highly Tunable Superparamagnetic Colloidal Photonic Crystals
Angewandte Chemie International Edition, doi: 10.1002/anie.200701992

Wiley

Related Magnetic Field Articles from Brightsurf:

Investigating optical activity under an external magnetic field
A new study published in EPJ B by Chengping Yin, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Magnetic field with the edge!
This study overturns a dominant six-decade old notion that the giant magnetic field in a high intensity laser produced plasma evolves from the nanometre scale.

Global magnetic field of the solar corona measured for the first time
An international team led by Professor Tian Hui from Peking University has recently measured the global magnetic field of the solar corona for the first time.

Magnetic field of a spiral galaxy
A new image from the VLA dramatically reveals the extended magnetic field of a spiral galaxy seen edge-on from Earth.

How does Earth sustain its magnetic field?
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles.

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.

Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.

Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.

Read More: Magnetic Field News and Magnetic Field Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.