Imaging of excitons and free charges in semiconductors by phase modulated light beams

Phase modulation of a CW UV laser is used to modulate the intensity of the laser beam at a single frequency. The intensity modulated beam is used to excite the single crystals of methylammonium lead bromide and cesium lead bromide perovskites. The modulations in the intensity of the photoluminescence are analyzed to show the co-existence of excitons and free charges in the excited crystals. The contributions from the two excited species on the emissions are quantified and imaged over the crystal surfaces.

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