  We report that two rotated layers of blue phosphorene behave as a direct band
gap semiconductor. The optical spectrum shows absorption peaks in the visible
region of the spectrum and in addition the energy of these peaks can be tuned
with the rotational angle. These findings makes twisted bilayer blue
phosphorene a strong candidate as a solar cell or photodetection device. Our
results are based on ab initio calculations of several rotated blue phosphorene
layers.
