Stimulated emission of ultraviolet radiation by benzoxazoles

It is shown that the lasing ability of benzoxazoles depends on the structure of different types of their electronic energy levels. Compounds with $T_{\pi\pi^*}$, $S^*_{\pi\pi^*}$, $T_{n\pi^*}$ and $S^*_{n\pi^*}$ lower levels emit radiation. Stimulated emission was obtained from solutions of 2-phenylbenzoxazole derivatives in the shortest wavelength range of 319-360 nm and from solutions of 4-(benzoxazole-2-yl)-4'-phenylstilbene derivatives in the 426-446 nm range. A nonselective resonator pumped by $\lambda_p=308$ nm radiation from a pulse-periodic excimer laser was used. The laser action was achieved in two bands corresponding to the vibrational structure in the gain spectrum.