Arizona State University researchers have created a
new compound crystal material that promises to help produce advances in a range
of scientific and technological pursuits.
The newest material, called erbium chloride silicate,
can be used to develop the next generations of computers, improve the
capabilities of the internet, increase the efficiency of silicon-based photovoltaic
cells to convert sunlight into electrical energy, and enhance the quality of
solid-state lighting and sensor technology.
Ning's research team of team of students and
post-doctoral degree assistants help synthesize the new compound in ASU's
Nanophotonics Lab in the School of Electrical, Computer and Energy Engineering,
one of the university's Ira A. Fulton Schools of Engineering.
The breakthrough involves the first-ever synthesis of
a new erbium compound in the form of a single-crystal nanowire, which has
superior properties compared to erbium compounds in other forms.
Erbium is one of the most important members of the
rare earth family in the periodic table of chemical elements. It emits photons
in the wavelength range of 1.5 micrometers, which are used in the optical
fibers essential to high-quality performance of the Internet and telephones.
Erbium is used in doping optical fibers to amplify the
signal of the internet and telephones in telecommunications systems. Doping is
the term used to describe the process of inserting low concentrations of
various elements into other substances as a way to alter the electrical or
optical properties of the substances to produce desired results. The elements
used in such processes are referred to as dopants.
With the new erbium compound, 1,000 times more erbium
atoms are contained in the compound. This means many devices can be integrated
into a chip-scale system. Thus the new compound materials containing erbium can
be integrated with silicon to combine computing and communication
functionalities on the same inexpensive silicon platform to increase the speed
of computing and internet operation at the same time. Erbium materials can also
be used to increase the energy-conversion efficiency of silicon solar cells.
Silicon does not absorb solar radiation with
wavelengths longer than 1.1 microns, which results in waste of energy -- making
solar cells less efficient. Erbium materials can remedy the situation by
converting two or more photons carrying small amounts of energy into one photon
that is carrying a larger amount of energy. The single, more powerful photon
can then be absorbed by silicon, thus increasing the efficiency of solar cells.
Erbium materials also help absorb ultraviolet light
from the sun and convert it into photons carrying small amounts of energy,
which can then be more efficiently converted into electricity by silicon cells.
This color-conversion function of turning ultraviolet light into other visible
colors of light is also important in generating white light for solid-state
lighting devices.
While erbium's importance is well-recognized,
producing erbium materials of high quality has been challenging. The standard
approach is to introduce erbium as a dopant into various host materials, such
as silicon oxide, silicon, and many other crystals and glasses. One big problem
has been that we have not been able to enough erbium atoms could not be introduced
into crystals and glasses without degrading optical quality, because too many
of these kinds of dopants would cluster, which lowers the optical quality.
What is unique about the new erbium material
synthesized here is that erbium is no longer randomly introduced as a dopant.
Instead, erbium is part of a uniform compound and the number of erbium atoms is
a factor of 1,000 more than the maximum amount that can be introduced in other
erbium-doped materials. Increasing the number of erbium atoms provides more
optical activity to produce stronger lighting. It also enhances the conversion
of different colors of light into white light to produce higher-quality
solid-state lighting and enables solar cells to more efficiently convert
sunlight in electrical energy. In addition, since erbium atoms are organized in
a periodic array, they do not cluster in this new compound. The fact that the
material has been produced in a high-quality single-crystal form makes the
optical quality superior to the other doped materials.
This new erbium compound can be used for various
applications, such as increasing silicon solar cell efficiency and making
miniaturized optical amplifiers for chip-scale photonic systems for computers
and high-speed internet.
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