@article{27911,
  keywords = {Al2O3, Cr, Fluorescent cooling, Quantum efficiency, Ruby},
  author = {Paul H Berdahl and Sharon S Chen and Hugo Destaillats and Thomas W Kirchstetter and Ronnen M Levinson and Michael A Zalich},
  title = {Fluorescent Cooling of Objects Exposted to Sunlight - The Ruby Example},
  abstract = {<p>Particularly in hot climates, various pigments are used to formulate desired non-white colors that stay cooler in the sun than alternatives. These cool pigments provide a high near-infrared (NIR) reflectance in the solar infrared range of 700–2500&nbsp;nm, and also a color specified by a reflectance spectrum in the 400–700&nbsp;nm visible range. Still cooler materials can be formulated by also utilizing the phenomenon of fluorescence (photoluminescence). Ruby, Al<sub>2</sub>O<sub>3</sub>:Cr, is a prime example, with efficient emission in the deep red (~694&nbsp;nm) and near infrared (700–800&nbsp;nm). A layer of synthetic ruby crystals on a white surface having an attractive red color can remain cooler in the sun than conventional red materials. Ruby particles can also be used as a red/pink pigment. Increasing the Cr:Al ratio produces a stronger (darker) pigment but doping above ~3&nbsp;wt% Cr<sub>2</sub>O<sub>3</sub> causes concentration quenching of the fluorescence. The system quantum efficiency for lightly doped ruby-pigmented coatings over white is high, 0.83±0.10.</p>},
  year = {2016},
  journal = {Solar Energy Materials and Solar Cells},
  volume = {157},
  pages = {312-317},
  doi = {10.1016/j.solmat.2016.05.058},
}