  Materials with both low absorption of incoming solar radiation and high
emittance in mid-infrared band can be applied for daytime radiative cooling.
Current state-of-the-art materials for passive radiative cooling often utilize
a combination of solar reflector and infrared emitter by different structures,
or even by expensive nanofabricated photonic structures, which limits the
applications in practice. In this study, possessing these two specified
radiative properties, pure Y2Ce2O7 is demonstrated with a performance of
passive radiative cooling. With a bandgap at 375.7 nm, the prepared Y2Ce2O7
shows a high solar reflectance of 91%, while with lattice strain and distortion
of various bonds (e.g., Y-O, Ce-O), it also shows a high emittance of 0.96 in
MIR band. More attracting, the aesthetics performance of Y2Ce2O7 can be
modified by doping Fe3+ ions to change its color from ivory white to light
yellow or red with high NIR reflection and MIR emission, indicating that the
Y2Ce2-xFexO7 shows a better cooling performance than a common paint with a
similar color. According to the field demonstration of cooling performance at
noon time, the Y2Ce2O7 and Y2Ce1.9Fe0.1O7 paints are 2.2 K and 1.8 K lower than
the common white and umber paints, respectively, while at night, all paints are
2.3 K lower than the ambient air. If applied on the envelop of a building, the
simulation shows that the Y2Ce2O7 and Y2Ce1.9Fe0.1O7 paints save 54.45% and
21.14% energy consumption compared with a common white and umber paints,
respectively, in a hot season. The demonstrated Y2Ce2-xFexO7 holds potentials
for energy-saving applications in hot climates.
