2-PHOTON EXCITATION OF THE LOWEST 4F2-]4F5D NEAR-ULTRAVIOLET TRANSITIONS IN PR3+-Y3AL5O12

Two-photon transitions from the H-3(4) = ground-state manifold of the 4f2 configuration to the lowest state of the 4f5d configuration of Pr3+ in Y3Al5O12 have been studied with a tunable dye laser as a function of the excitation wavelength, intensity, temperature, and focusing geometry. The two-photon excitation spectrum is vibronic in nature and covers the 555-615-nm excitation wavelength range. Both the direct nonresonant and the resonantly enhanced transitions are observed. The measured two-photon-absorption cross section varies over 3 orders of magnitude with a maximum of 1 x 10(-51) cm4 s at the peak of the resonantly enhanced transition at 581 nm. The parity selection rule which forbids these two-photon transitions in a free ion is relaxed by odd-parity crystal-field mixing of the wave functions, making these transitions possible. Two-photon excitation measurements are complemented by one-photon-absorption and -emission measurements.