Fabrication and optical characterization of near UV-laser crystals using low-symmetry crystal field

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We have grown CeィイD13+ィエD1-doped fluorides [BaMgFィイD24ィエD2, CaNaYFィイD26ィエD2] and oxides [melilite-type crystals AィイD22ィエD2BィイD23ィエD2OィイD27ィエD2(A=Ca, Y ; B=Al, Si)] which are candidates for tunable laser materials in the near UV and violet regions. In order to widely spread phosphors in the UV and visible regions, we have studied the optical characterization of these crystal and the effects of the strength and low-symmetry of the crystal field in the associated anion coordination polyhedron. The results of this study are summarized as follows.1. The lowest energy and the center of the gravity of the ィイD12ィエD1D excited state energy levels may be explained by the nephelauxetic effect, lowering symmetry caused by distortion, and size of the annion-coordinate polyhedra of the CeィイD13+ィエD1 in fluoride and oxide crystals.2. Broad photoluminescence in the near UV and violet regions is observed in CeィイD13+ィエD1-doped melilite CaィイD22ィエD2AlィイD22ィエD2SiOィイD27ィエD2 and CaYAlィイD23ィエD2OィイD27ィエD2. The p … More hotoluminescence spectra for these crystals are inhomogeneously broadened by the substitutional disorder. The lowest peak energies of the absorption bands of CeィイD13+ィエD1 in those crystals are coincident with the third harmonic (355nm) of a YAG laser. A new phosphor CeィイD13+ィエD1-doped BaMgFィイD24ィエD2 crystal was grown. The different optical spectra of CeィイD13+ィエD1 in the UV region are assigned to be due to regular and perturbed CeィイD13+ィエD1 site in the crystal. The energy level of the lowest 5d excited state of CeィイD13+ィエD1 in the BaMgFィイD24ィエD2 crystal is coincident with the fourth harmonics (266nm) of a Nd : YAG laser.The BaMgFィイD24ィエD2 : CeィイD13+ィエD1 and CaィイD22ィエD2AlィイD22ィエD2SiOィイD27ィエD2 : CeィイD13+ィエD1 crystals are expected to be new laser materials with a high gain and wide tuning range between the UV and near UV regions.3. UV excitation or infrared femtosecond laser excitation of CeィイD13+ィエD1-doped melilite crystals CaィイD22ィエD2AlィイD22ィエD2SiOィイD27ィエD2 and CaYALィイD23ィエD2OィイD27ィエD2 produces long-lasting phosphorescence besides intrinsic CeィイD13+ィエD1 luminescence with short lifetime (40ns). The phosphorescence persists for not less than 1 h after removal of the irradiating light. The long-lasting phosphorescence may be explained by a model of electron-hole recombination at CeィイD13+ィエD1 sites caused by hopping motion, which occurs by a thermally activated process. This is first observation of long-lasting phosphorescence of CeィイD13+ィエD1. This new optical function will be useful in the fabrication of spontaneously disappearing image pattern and time-limited three-dimensional optical memory devices. Less