A study was made of the feasibility of increasing the efficiency of fluorescent lamps at high powers by increasing the Hg 237-Å resonance radiation through a reduction of self-absorption. Specifically, we attempted to reduce the Hg 2537-Å self-absorption by introducing a higher pressure of a foreign gas (argon) to alter the Hg 2537-Å absorption line shape and width by collision broadening. The intensity of the Hg 2537-Å line in Hg + Ar discharges was measured as an independent function of mercury pressure (0.7 mTorr to 27 mTorr), argon pressure (5 Torr to 400 Torr), and dc input power (5.5 W to 97 W). A detailed theoretical analysis indicates that there are four ways that additional argon reduces the Hg 2537-Å self-absorption: (1) The Hg 2537-Å line gets broader simply because the additional argon atoms increase the Hg–Ar collision frequency; (2) adding argon causes the gas temperature to rise and this drives the Hg–Ar collision frequency still higher; (3) the rise in gas temperature also causes an increase in the Hg 2537-Å doppler width; (4) the additional argon changes the Hg 2537-Å line shape from doppler dominated to a collision dominated profile. The experiments demonstrate, however, that no gain is achieved in the Hg 2537-Å intensity with the addition of extra argon in spite of the beneficial effect on the self-absorption escape rate. This advantage is apparently offset by the argon’s reduction of the electron energy which leads to fewer mercury atoms excited to the Hg 63P1 state.
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