Light emitting diode-based nanosecond ultraviolet light source for fluorescence lifetime measurements

A compact pulsed‐light source is devised from an InGaN/AlGaN double heterostructure light‐emitting diode (LED). The LED emits a 450‐nm (blue) light under conventional dc operation below 30 mA. When a current larger than 50 mA is applied, the intensity of the 450‐nm light saturates, but that of the 380‐nm light due to the InGaN component continues to increase. This phenomenon is utilized to realize a nanosecond ultraviolet (UV) light source. Under repetitive, large current pulsing (frequency=10 kHz, pulse width=4 ns, peak current=2 A), the peak LED emission shifts from 450 to 380 nm. Intense light pulses (peak value=40 mW) of 4‐ns duration were generated. To evaluate the potential of the pulsed LED as an excitation source, the fluorescence lifetime of a quinine‐sulfate solution was measured. The observed lifetime characteristics agreed well with the generally accepted behavior.