Persistent Spectral Hole-Burning and Zeeman Effect of X-ray-Induced Sm2+ in CaF2:Sm3+ Nanocrystals

We report photoluminescence properties as a function of temperature, Zeeman effects of 4f 5 5d → 4f 6 transitions, and persistent spectral hole-burning measurements in the 4f 6 7 F 0 (A 1g ) → 4f 5 5d (T 1u ) transition of Sm 2+ generated by X-irradiation in CaF 2:Sm 3+ nanocrystals prepared via a coprecipitation method. In the absence of a magnetic field (2–293 K), the luminescence of the dominant electric dipole allowed 4f 5 5d (A 1u ) → 4f 6 7 F 1 (T 1g ) transition at 708.2 nm and the two weak transitions T 1u → A 1g and T 1u → T 1g at 690.2 and 703 nm, respectively, with some vibronic sidebands were observed. The Zeeman splitting of the Zeeman effect of the 7 F 1 level in a magnetic field of 9 T led to an observable, though nonresolved, splitting (5.68 ± 0.11 cm –1 ) into its M J = −1, 0, 1 components yielding a g -factor of 1.35 ± 0.02. The intensity of the symmetry-forbidden A 1u → A 1g -transition at 695.8 nm could be drastically increased by an external magnetic field above 3 T at 2 K, with a quadratic magnetic flux dependence. Spectral holes burned into the A 1g → T 1u transition displayed a Lorentzian line shape and first-order dispersive burning kinetics. The hole-burning rate decreased with an increase of the X-irradiation dose, while an increase was observed with an increase of the Sm concentration. The direct one-phonon relaxation between the T 1u and A 1u levels and the two-phonon Raman scattering process contributed to the hole width. Interestingly, a nonmonotonous temperature dependence was observed for the frequency shift. The hole was relatively stable with less than a 20% reduction in hole area after 1 h and thermal cycling to 25 K. The present results highlight the significance of the Sm 3+ electron traps (type I) in spectral hole-burning of CaF 2:Sm 3+ nanocrystals.