[OPTICAL REVIEW Vol. 7, No. 6 (2000) 495-498]

Phase-Modulation Fluorometer Using an Ultraviolet Light-Emitting Diode

Tetsuo IWATA,1 Takeshi KAMADA1 and Tsutomu ARAKI2

1Department of Mechanical Engineering, Faculty of Engineering, University of Tokushima, Minami-Jyosanjimacho-2, Tokushima, 770-8506 Japan, 2Department of Systems and Human Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531 Japan

(Received March 27, 2000; Accepted June 25, 2000)

We have constructed a phase-modulation fluorometer using a commercially-available ultraviolet light-emitting diode (UV LED) as an excitation light source. The center wavelength of the UV LED is 370 nm and its spectral bandwidth is 10 nm. A 10 ?�E�?�E�mA?�E�?�E�?�E�?�E�pp?�E�?�E� modulation-current was superimposed on a bias current of 5 mA with a fixed frequency in the range of 1-20 MHz. The average UV power on the sample was 250 μW. The fluorescence signal was detected by a photomultiplier tube and was fed into a versatile digital oscilloscope. The phase difference between the fluorescence signal and the reference signal obtained from a diffusion plate was directly read out using the operational functions of the digital oscilloscope. To demonstrate the system performance, fluorescence lifetimes of 25 ppm rhodamine 6G in ethanol and of 10 ppm quinine sulfate in 0.1 N H2SO4 were measured. The calculated lifetimes of 5.8 ns and 19.1 ns, respectively, agreed with those reported in the literature. The combination of the UV LED and the digital oscilloscope made the fluorometer simple and easy to construct with low cost.

Key words : spectroscopic instruments, fluorescence, ultraviolet light-emitting diode, phase-modulation fluorometer