We demonstrate high-efficiency excitonic emission with deep-ultraviolet (DUV) light of 235 nm at room temperature for a (111)-oriented diamond p-i-n junction light-emitting diode (LED) by introducing a thick i-layer. Significant enhancement in excitonic emission efficiency of over 500 times was observed for a diamond LED by increasing the i-layer thickness from 0.1 to 14 μm. Maximum output power and external quantum efficiency of excitonic emission for the LED without any specific device structure were 0.1 mW and 0.006%, respectively, under pulsed-current injection. We also demonstrate the sterilization of Escherichia coli by irradiation with DUV light from the diamond LED.

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