UV laser induced photochromic centers in cerium doped calcium fluoride
Technical Report
·
OSTI ID:6947592
The optical excitation of the lowest 4f to 5d transition in Ce/sup 3 +/:CaF/sub 2/ by the 308 mm output of a Xe-Cl excimer laser results in strong coloration. The centers created were found to be divalent cerium ions at cubic sites. The system exhibits photochromic properties; the crystal can be returned to the original transparent state by illuminating it with light which is absorbed by the divalent cerium ions. The creation process for these photochromic centers involves a resonant two-photon transition from the 4f ground state of the cerium ion to the conduction band of the CaF/sub 2/ host. The lowest 5d level of the cerium ion serves as the real intermediate state for this transition. The photoionized electron can be trapped by another trivalent cerium ion at a site of cubic symmetry. These impurity sites with O/sub h/ symmetry result when the charge compensator associated with the rare earth ion is somewhat removed from the cerium ion site. The charge compensator is needed to maintain charge neutrality in the crystal when a trivalent rare earth is substituted for a Ca ion in the host lattice. The absence of a local charge compensator at a Ce/sup 3 +/ site with O/sub h/ symmetry, provides a net positive Coulombic potential, which aids in the trapping of electrons from the conduction band. The capture of an electron by a cerium ion at cubic site, changes the valence state of the ion to Ce/sup 2 +/ which accounts for the coloration of the crystal after illumination with uv laser light. A model for the production of the photochromic centers is presented.
- Research Organization:
- Connecticut Univ., Storrs (USA)
- DOE Contract Number:
- FG02-84ER45056
- OSTI ID:
- 6947592
- Report Number(s):
- DOE/ER/45056-3; ON: DE87005359
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
360603* -- Materials-- Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
CALCIUM COMPOUNDS
CALCIUM FLUORIDES
CALCIUM HALIDES
CERIUM ADDITIONS
CERIUM ALLOYS
COLOR CENTERS
COLORATION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
D STATES
DOPED MATERIALS
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
IONIZATION
MATERIALS
PHOTOCHROMIC MATERIALS
PHOTOIONIZATION
POINT DEFECTS
RADIATIONS
RARE EARTH ADDITIONS
RARE EARTH ALLOYS
ULTRAVIOLET RADIATION
VACANCIES
360603* -- Materials-- Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
CALCIUM COMPOUNDS
CALCIUM FLUORIDES
CALCIUM HALIDES
CERIUM ADDITIONS
CERIUM ALLOYS
COLOR CENTERS
COLORATION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
D STATES
DOPED MATERIALS
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
IONIZATION
MATERIALS
PHOTOCHROMIC MATERIALS
PHOTOIONIZATION
POINT DEFECTS
RADIATIONS
RARE EARTH ADDITIONS
RARE EARTH ALLOYS
ULTRAVIOLET RADIATION
VACANCIES