SEQUENTIAL 2-PHOTON-EXCITED FLUORESCENCE IN A ND3-DOPED BI4GE3O12 CRYSTAL()

Upconverted fluorescences in the UV-blue spectral range in a Nd3+-dope d Bi4Ge3O12 crystal are investigated using pulse laser excitations at wavelengths around 590 nm. The Nd3+ ions excited to the F-4(3/2) level s through the linear absorption from the (4)G(5/2) levels are further excited to the D-4(3/2) levels by the excited state absorption from th e F-4(3/2) to D-4(5/2) levels, followed by the nonradiative transition from the D-4(5/2) to D-4(3/2) levels. The transitions from the D-4(3/ 2) to I-4(9/2), I-4(11/2), I-4(13/2) and I-4(15/2) levels give rise to the upconverted fluorescences at 362 nm, 393 nm, 416 nm and 453 nm, r espectively. The dominant mechanism for the upconverted fluorescences is proven to be the sequential two-photon excitations of the Nd3+ ions .