World’s first warm white LED to use
single phosphor with single emitting center
Breakthrough could lead to widespread use of
LEDs for indoor lighting
University of Georgia researchers have published
a report that details the fabrication of the world’s
first light emitting diode (LED) to emit a warm white light using a
single light emitting material (phosphor) with a single emitting
center for illumination.
The University of Georgia’s
Zhengwei Pan, center, an associate professor of physics and
engineering, holds a prototype of what is thought to be the
world’s first single-phosphor,
single-emitting-center-converted LED that emits a warm white light
while the UGA College of Engineering’s Feng Liu, left,
and Xufan Li look on. (Credit: John Paul Gallagher/UGA)
“Right now, white LEDs are mainly used
in flashlights and in automotive lamps, but they give off a bluish,
cool light that people tend to dislike, especially in indoor
lighting,” said senior author Zhengwei Pan, an associate
professor in the department of physics in the UGA Franklin College
of Arts and Sciences and in the College of Engineering.
“Our material achieves a warm color temperature while at
the same time giving highly accurate color rendition, which is
something no single-phosphor-converted LED has ever been shown to
How they did it
In a majority of today’s LED bulbs,
warm white light is achieved by using a blue LED chip coated with
phosphors to create what’s aptly referred to as
phosphor-based white LEDs. Combining these source materials in an
exact ratio, however, can be a costly, time consuming endeavor.
What’s more, the resulting color typically varies due to
the fact that the materials respond differently to temperature
To overcome these hurdles, Pan and his UGA team
created a new phosphor that combined minute quantities of europium
oxide with aluminum oxide, barium oxide, and graphite powders. They
then heated these powders at 2,642 F (1,450 C) in a tube furnace.
The vacuum of the furnace then pulled the vaporized materials onto
a substrate, at which point they were deposited as a yellow
luminescent compound in a bulb and illuminated by a blue LED
The result: warm white light.
Making sure the light meet expectations
There are two main variable used to assess the
quality of artificial light. First is correlated color temperature,
which measures the coolness or warmth of the light. Temperatures
less than 4,000 kelvins are considered ideal for indoor lighting,
while those above 5,000 kelvins give off more of a bluish
The other consideration is the ability of the
light source to replicate natural light. A value of more than 80 is
considered ideal for indoor lighting; lower values result in colors
that seem unnatural.
Tests that Pan and his UGA colleagues performed
indicate that the material they developed meets both thresholds,
with a correlated color temperature less than 4,000 kelvins, and a
color rendering index of 85.
While the future might look bright for this new
technology, there is still some work to do before it can be put to
actual use. For one, the efficiency of the material is much lower
than any of the bluish white LEDs on the market today. Also,
scaling the production to an industrial scale will be a major
challenge, given the fact that even the slightest variations in
temperature and pressure in the phosphor synthesis process can have
an adverse effect on the materials.
The team is presently working to discern how the
ions in the compound are arranged in hopes that a better
understanding of the compound at an atomic level will eventually
lead to an improvement in its efficiency.
“We still have more work to
do,” Pan said, “but the color temperature and
rendition that we have achieved gives us a very good starting
The material is described in detail in the
current edition of the Nature Publishing Group journal
“Light: Science and Applications.” It is
available for download below. ■
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