Spectroscopy and optical maser action in SrF2: Sm2+

A crystal of SrF2: Sm2+ was operated as a pulsed optical maser at temperatures close to 4.2°K. The 6969 output corresponds to the wavelength of an exceedingly sharp line (<0.6 cm-1) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in CaF2: Sm+2 masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in CaF2: Sm2+ the value of is approximately 1.5×10-6 sec, in SrF2: Sm2+ it has a value of 15 msec. The reason for the large difference in values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable D05 level from which fluorescence occurs. Absorption measurements taken at helium temperatures on SrF2: Sm2+ show that the lowest vibrational level of the lowest lying 4f-5d band lies 600 cm-1 above the position of the D05 level while in CaF2: Sm2+ there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of SrCl2: Sm2+ were also studied in this regard and display an expected close similarity in spectral characteristics to SrF2: Sm2+. The vibrational structure on the 4f-5d bands is much more pronounced, however, than in CaF2: Sm2+ and SrF2: Sm2+, indicating weaker coupling to the lattice in the excited 5d state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of Sm2+ ions is given. © 1962 The American Physical Society.