Resonant diffractive optical elements can be used to create the desired spatial
and angular distribution of scattered light in a narrow wavelength range.
Exciton resonance could help to make such elements active. Here an exciton
diffraction grating made from fully inorganic CsPbBr3 halide perovskite is
demonstrated. Spatial modulation of excitonic properties of the single crystal
is achieved using local defect formation by 30 keV Ga+ focused ion irradiation
with low irradiation dose 1014 cm−2. Such a low dose prevents the appearance
of non-resonant diffraction since no sample milling occurs. The observed
diffraction reflex has a maximum efficiency of 2.3 × 10−3 at the free exciton
resonance and 1.7 meV spectral width. The temperature, angular, and spectral
properties of resonant diffraction are studied. The possibility of creating
exciton diffraction gratings based on halide perovskites is one more confirmation
of their applicability as a new material for information photonics.