Abstract

The Vacuum Ultraviolet (VUV) and Ultraviolet (UV) absorption and excitation spectroscopic characteristics of the rare-earth (RE) ions [1], activated in the wide band gap of fluoride dielectric crystals, are due to transitions from the levels of the 4fⁿ single configuration of the trivalent lanthanide ion, to the levels of the 4f^n-1 5d mixed configuration. The 4fⁿ → 4^f-1 5d transitions are characterized by strong Frank-Condon factors and they are responsible for the broad-band absorption and emission spectra in the VUV and UV. The use of VUV radiation to excite a common RE impurity, in different dielectric fluoride hosts, allows one to study the excitation mechanisms and to extract all the necessary information for the structure of the levels of the 4f^n-1 5d configuration of the trivalent RE ions. In this communication, we report on the interconfigurational 4f²5d → 4f³ VUV and UV fluorescence characteristics of the Nd³⁺ ion in LiCaAlF₆ single crystal hosts, as it is excited with the laser radiation from the fluorine (F₂) pulsed discharge molecular laser at 157.6 nm. This pumping arrangement, has the advantage that it populates the levels of the 4f²5d configuration directly from the ground level of the RE trivalent ion via one photon transition only. The subsequent deexcitation mechanism of the 4f²5d levels, efficiently populates the levels of the 4f³ single configuration of the Nd³⁺ ion. The absorption spectrum was also recorded at room temperature, using a hydrogen lamp in the VUV with stabilized longitudinal discharge. The absorption characteristics of the crystal samples in the VUV region, are due to transitions from the ⁴I_9/2 ground level of the Nd³⁺ ion of the 4f³ configuration to the Stark components of the levels of the 4f²5d mixed configuration. The number and the spacing of the components depend on the symmetry and the intensity of the crystal field.

© 1998 IEEE