SEMINAR: Fluorescent Materials for Cool Colored Roofing
The Egyptian blue pigment (CaCuSi4O10) has been known for over 4,000 years. About 20 years ago studies of ancient artifacts and paintings revealed that it fluoresces in the near infrared (~900 nm) when excited by visible light (500-700 nm). This year, we reported that the maximum quantum yield is not ~10%, as had been believed, but ~100%. This fluorescence permits the fabrication of cool blue roofing that emits about 150 W m-2 in sunlight. Thus, the material remains cooler than comparable blues. With the use of co-pigments, we can also fabricate fluorescent green and black colors; further, the use of ruby pigment gives us access to pink/red.
The high quantum yield of Egyptian blue is likely to lead to other applications, not the least of which is the luminescent solar concentrator strategy for photovoltaic conversion.
Two recent papers by Berdahl, Boocock, G. Chan, S. Chen, Destaillats, Kirchstetter, Levinson, and Zalich:
- High quantum yield of the Egyptian blue family of infrared phosphors (MCuSi4O10, M = Ca, Sr, Ba). J. Appl. Phys. 123, 193103 (2018). https://doi.org/10.1063/1.5019808
- Fluorescent cooling of objects exposed to sunlight – The ruby example. Sol. Energy Mater. & Sol. Cells 157, 312-317 (2016). https://doi.org/10.1016/j.solmat.2016.05.058
Affiliate, Building Technology Department, Building Technology & Urban Systems Division
Paul is a physicist who received his Ph. D. from Stanford University in theoretical physics. Most of his research is in the areas of applied solid-state physics, and in environmental physics. Paul is affiliated with the Heat Island Group of our Division's Energy Analysis Program.
Current research interests include:
- Fluorescent pigments that re-radiate solar radiation, for cool roofing
- Combustion synthesis of mixed metal oxides
- Spectral and angular optical properties of rough and soiled surfaces
- Calorimetric measurements using sunlight
Recently, Paul has investigated how surface roughness reduces the solar reflectance of materials, the soiling and weathering of roofing materials and the destruction of air pollutants by photocatalytic oxidation using the semiconductor TiO2.
Prior to Paul's (semi-) retirement in 2005, he worked on synthesis of high-temperature superconducting YBa2Cu3O7 tapes (with R. Russo and R. Reade). World record critical current values were achieved in 1992. Other topics were infrared luminescence of the semiconductor InSb, infrared radiative cooling, longwave radiative transfer in the atmosphere, and the availability of the solar radiation resource.