Laser spectroscopy of alkaline earth flouride crystals doped with trivalent samarium and europium ions
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Alkaline earth fluoride crystals doped with Sm3+ and Eu3+ ions have been investigated by polarised laser selective excitation, Zeeman infrared and optical absorption. These studies identify four main centres for CaF2:Sm3+ and CaF2:Eu3+ crystals. They are a single RE3+ -F- pair having C4v symmetry, a near-cubic symmetry centre with a non-local charge compensator and two cluster centres. In CaF2:Sm3+ crystals, the cluster centres are entirely non-radiative due to efficient cross-relaxation processes between the constituent Sm3+ ions. These centres have been investigated by codoping with additional RE3+ ions. Efficient 4G 5/2 (Sm3+)→5D0(Eu3+) energy 2 transfer has been observed for the heterogeneous cluster centres in CaF2:Sm3+: Eu3+. In SrF2 crystals doped with Sm3+ and Eu3+ ions, the dominant centre consists of a single RE3+ -F- pair of C4v symmetry. In SrF2: Eu3+ a weak C3v symmetry centre has been observed which is analogous to the dominant centre in BaF2: Eu3+ crystals. Upconversion fluorescence has been observed for the dominant spectroscopic centres in CaF2, SrF2 and BaF2 crystals doped with Eu3+. This is assigned as a sequential absorption process with 5D0 as the intermediate state. Enhancement of the upconverted fluorescence is observed for excitation of the 7F1 →5D0 transitions at room temperature. High-resolution infrared absorption has been employed to study hyperfine structure of sharp absorption lines in CaF2 and SrF2 crystals doped with Pr3+, Tb3+ and Ho3+. An interesting hyperfine pattern is observed for CaF2:Ho3+ in which the hyperfine structure of a doublet state has been perturbed by the presence of two nearby singlet states. This pattern has been successfully analysed using the hyperfine interactions between these excited states.