Trivalent europium in x-irradiated NaCl: Eu

In the present paper evidence has been gathered to show for the first time that the room-temperature x irradiation of an europium-doped NaCl crystal produces the conversion of doubly valent europium ions to the tripositive state. This conversion occurs in both well-aged and fast-quenched samples. However, it is considerably enhanced in the former crystals in which precipitates with the Eu${\mathrm{Cl}}_2$ structure are present before irradiation. If one takes advantage of this fact, the optical absorption, emission, and excitation spectra of the ${\mathrm{Eu}}^{3+}$ ions can be obtained. In particular, transitions between the different Stark levels of the various ${}_{}{}^7{}_{}{}^{}F$ manifolds and the excited levels ${}_{}{}^5{}_{}{}^{}D_2^{}{}_{}{}^{}$, ${}_{}{}^5{}_{}{}^{}D_1^{}{}_{}{}^{}$, and ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}$ of ${\mathrm{Eu}}^{3+}$ have been identified in the visible region of the absorption, emission, and excitation spectra of the x-irradiated samples.