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

We report photoluminescence properties as a functionof temperature,Zeeman effects of 4f(5)5d & RARR; 4f(6) transitions,and persistent spectral hole-burning measurements in the 4f(6 7)F(0) (A(1g)) & RARR; 4f(5)5d (T-1u) transition of Sm2+ generated by X-irradiation in CaF2:Sm3+ nanocrystals prepared via a coprecipitationmethod. In the absence of a magnetic field (2-293 K), the luminescenceof the dominant electric dipole allowed 4f(5)5d (A(1u)) & RARR; 4f(6 7)F(1) (T-1g) transitionat 708.2 nm and the two weak transitions T-1u & RARR; A(1g) and T-1u & RARR; T-1g at 690.2 and703 nm, respectively, with some vibronic sidebands were observed.The Zeeman splitting of the Zeeman effect of the F-7(1) level in a magnetic field of 9 T led to an observable, thoughnonresolved, splitting (5.68 & PLUSMN; 0.11 cm(-1)) intoits M- J = -1, 0, 1 components yieldinga g-factor of 1.35 & PLUSMN; 0.02. The intensity ofthe symmetry-forbidden A(1u) & RARR; A(1g) -transitionat 695.8 nm could be drastically increased by an external magneticfield above 3 T at 2 K, with a quadratic magnetic flux dependence.Spectral holes burned into the A(1g) & RARR; T-1u transition displayed a Lorentzian line shape and first-order dispersiveburning kinetics. The hole-burning rate decreased with an increaseof the X-irradiation dose, while an increase was observed with anincrease of the Sm concentration. The direct one-phonon relaxationbetween the T-1u and A(1u) levels and the two-phononRaman scattering process contributed to the hole width. Interestingly,a nonmonotonous temperature dependence was observed for the frequencyshift. The hole was relatively stable with less than a 20% reductionin hole area after 1 h and thermal cycling to 25 K. The present resultshighlight the significance of the Sm3+ electron traps (typeI) in spectral hole-burning of CaF2:Sm3+ nanocrystals.