TRANSIENT ABSORPTION STUDY OF VIBRATIONALLY EXCITED YB2-[CN-](N)-COMPLEXES IN ALKALI-HALIDES()

In alkali halides co-doped with Yb2+- and CN--impurities, complexes wi th Yb2+ and various numbers of molecular neighbors (Yb2+-[CN-](n)) are formed which exhibit strong mutual interaction effects, especially an efficient (E-V) energy transfer from the electronically excited Yb2into the CN-stretch-mode. We used this E-V transfer process to produce CN--molecular excitation under laser irradiation and studied the indu ced transient change in the electronic absorption (EA) of the Yb2+-nei ghbor. In these transient absorption spectra strong new EA bands on th e low-energy side of the regular absorption are found. By careful eval uation of the time-dependent spectral data under variation of excitati on wavelength, temperature and host material we assigned the effect to Yb2+ with excited CN--neighbors. It appears that otherwise forbidden transitions become strongly enhanced by the vibrating CN--molecule. Th is effect is most pronounced while high vibrational levels are populat ed. (C) 1998 Elsevier Science B.V. All rights reserved.