Maximized vertical photoluminescence from optical material with losses employing resonant excitation and extraction of photonic crystal modes

Optical losses of a host material together with the total internal reflection phenomenon can significantly reduce photoluminescence external quantum efficiency of embedded light-emitters. This is not only the case for light-emitting color centers in thin layers of nanocrystalline diamond, but also for silicon nanocrystals in silica dioxide matrices and for some types of perovskite materials. Here, we show that a significant boost (more than 100-fold enhancement) of the directional light emission efficiency from light-emitters in diamond can be achieved by using two-dimensional photonic crystal slabs (PhCs) to extract the light emission into vertical direction (resonant extraction) and at the same time to couple the excitation beam into the structure (resonant excitation). We have further shown that this so-called resonant extraction and excitation scheme provides the highest enhancement when the overlap between the electric field distribution of extraction leaky mode and the region of the excited light-emitters is maximized. This can be achieved by using the same type of the photonic mode for both extraction and excitation, and by optimizing the thickness of a diamond layer. The usage of the same type of modes appears to be more significant than tuning of the Q-factors of the excitation and extraction leaky modes individually. The results of our measurements are supported by the outputs of computer simulations. Our findings may be helpful in designing future PhCs for extraction of luminescence originating from various optoelectronic and sensor devices making use of the unique properties of the diamond. Moreover, our concept can be easily extended to other light-emitting materials with optical losses.