A study was made of the feasibility of increasing the efficiency of fluorescent lamps at high powers by increasing the Hg 2537-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.
T. J. Hammond and C. F. Gallo, "Effects of Argon Atoms on the Self-Absorption and the Intensity of Hg 2537-Å Radiation in Hg + Ar Discharges," Appl. Opt. 10, 58-64 (1971)