Optical-absorption and photoionization measurements from the excited states of Ce/sup 3+/:Y3Al5O/sub 12/

The optical transitions in Ce/sup 3+/:Y3Al5O/sub 12/ from the lowest 5d excited state of the Ce/sup 3+/ ion to the host conduction band have been investigated. Two spatially overlapped and time-sequenced laser pulses were used to observe directly the excited-state absorption (ESA) and the two-step photoionization of the cerium ions. The peak cross section of the ESA transition is (1.0 +- 0.3) x 10/sup -17/ cm2 at 700 nm. The ESA spectrum was measured from 600 to 880 nm and is used to construct an energy-level diagram for the Ce/sup 3+/ ions relative to the energy-band states of the Y3Al5O/sub 12/ host. The energy gap between the lowest relaxed 5d state and the conduction-band edge is estimated to be 10 000 cm/sup -1/. Strong-probe saturation measurements indicate a slow and inefficient back-transfer of excitation to the cerium ions following the ESA. Photoconductivity measurements were used to confirm the two-step photoionization of the cerium ions