Wide band gap fluoride dielectric crystals doped with trivalent rare earthions as optical materials for 157 nm photolithography

We investigate the possibility to use a new class of wide band gap fluoride dielectric crystals as optical elements for 157 nm photolithography. The r are earth doped or non-doped crystals can be used as passive or active opti cal elements in the VUV. Applications are depending on the structure of the levels of the 4f(n-1)5d electronic configuration and the strength of the i nterconfigurational 4f(n)--> 4f(n-1)5d transitions of the trivalent rare ea rth ions in the dielectric fluoride host. The laser induced fluorescence an d the absorption spectra of the pure LiCaAlF6 crystal and the doped with Nd 3+ and Er3+ ions were studied in the VUV region of the spectrum.