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A color developed by the Egyptians thousands of years ago also has a modern application: the pigment can increase energy efficiency by cooling roofs and walls, but can also allow the production of 39, electricity of solar origin via windows.
Egyptian blue, derived from the silicate of copper and calcium, was commonly used on ancient representations of the gods and royalty. Previous studies have shown that when Egyptian blue absorbs visible light, it then emits light in the near infrared. A team led by researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) of the Ministry of Energy confirmed that the fluorescence of the pigment could be 10 times stronger than expected.
By measuring the temperature of surfaces coated with Egyptian blue and related compounds exposed to the sun, Berkeley Lab researchers have found that fluorescent blues can emit nearly 100% of the number of photons absorbed. The energy efficiency of the emission process can reach 70% (infrared photons carry less energy than visible photons).
This discovery adds to the information on the most effective colors for cooling roofs and facades in sunny climates. Although white is the most conventional and effective choice for keeping a building cool by reflecting sunlight and reducing energy consumption for air conditioning, building owners often need colors that are not white for aesthetic reasons. For example, bright white asphalt shingles are almost never used on roofs of sloping houses.
Berkeley Lab scientists measured the temperature rise above the observed air temperature in full sun for five pigment-coated samples, each of 75 square millimeters. The white and black samples show low and high temperatures. Credit: Berkeley Lab
Berkeley Lab researchers have already shown that ruby red fluorescent pigments can be an effective alternative to white; This idea about Egyptian blue adds refreshing color choices to the menu. In addition, they discovered that green and black fluorescent colors can be produced with yellow and orange co-pigments. The new discoveries have recently been published in the Journal of Applied Physics.
In addition to its cooling potential for buildings, the fluorescence of Egyptian blue could also be useful in the production of solar energy. Used on blue-tinted windows, the photovoltaic cells on the edges can convert fluorescent near-infrared energy into electricity.
Over the years, Berkeley Lab's Heat Island group has conducted extensive research that has shown that reflective walls and roofs can cool buildings and cars. This reduces the need for air conditioning and mitigates the effect of urban heat island. By reflecting the sun 's rays in space, these cold materials also release less heat into the atmosphere, thus cooling the planet and offsetting the warming effects of significant greenhouse gas emissions. .
Explore further:
Fluorescent ruby red roofs remain as cool as white
More information:
Paul Berdahl et al. High quantum yield of the family of Egyptian blue infrared phosphors (MCuSi4Oten, M = Ca, Sr, Ba), Journal of Applied Physics (2018). DOI: 10.1063 / 1.5019808
Sarah Michaud. The quantum yield of Egyptian blue IR phosphors is calculated using the temperature changes of sunlight, Scilight (2018). DOI: 10.1063 / 1.5040060
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