NEW LUMINESCENT COMPOSITION*)

The reviewed work indicates a method for obtaining an interesting luminescent composition.

Potassium sulfate (\(\mathrm{K_2SO_4}\)) is heated for several minutes in an atmosphere conducive to a reduction reaction. The degree of purity of the potassium sulfate is not important; heating may be carried out with a gas burner. By cooling \(\mathrm{K_2SO_4}\), one can obtain several fairly large pieces of the solidified melt.

If the reduction reaction has proceeded for a sufficiently long time and not too violently, then these pieces (sometimes as transparent as glass) give a remarkable red fluorescence when excited by long-wave ultraviolet. Irradiation with short-wave ultraviolet (for example, the Hg 2537 Å line) produces blue fluorescence. The same blue luminescence is excited by electrons whose velocity is equal to several thousand volts. The clearly expressed dependence of the character of luminescence on the wavelength of the exciting light can be successfully demonstrated to a large audience.

In the course of the reduction reaction, potassium sulfide is formed, which, in all probability, being incorporated into the crystal lattice of potassium sulfate, is responsible for the observed luminescence. The possibility of the influence of activating metals is excluded: potassium sulfate of various degrees of purity and of various origin was investigated, yet the observed luminescence remained unchanged in all cases.

) H. Gobrecht, Phys. Blätter* No. 2 (1949).

Several substances related to potassium sulfate were investigated. Potassium sulfide, when irradiated with long-wave ultraviolet, gives the same red fluorescence as potassium sulfate. The fluorescence spectrum of potassium disulfate and potassium bisulfate differs somewhat from the fluorescence spectrum of potassium sulfate.

If sodium sulfate or sulfide is treated in the indicated manner, a substance can be obtained that, upon excitation with long-wave ultraviolet, gives a yellow glow. From this one may conclude that the cation affects the character of the fluorescence. This circumstance is still more pronounced for the salts of alkaline-earth metals. Barium sulfate, after the corresponding treatment, when excited by the light of a mercury lamp gives a whitish-yellow glow; strontium sulfate, a green glow; calcium sulfate, a blue glow.

Cooling to the temperature of liquid air does not affect the fluorescence. The fluorescence spectrum consists of a broad continuous band.

The work under review has the character of a preliminary communication and, unfortunately, contains no indications concerning the numerical value of the yield or the duration of the glow. It is only noted that these characteristics are smaller than in ordinary luminous compositions. Judging from the fact that the author of the reviewed work speaks of fluorescence, the duration of the glow is short.

V. Bredel