UP-CONVERSION AND RELAXATION OF HIGH-LYING STATES IN RARE-EARTH-DOPED ZBLAN BULK AND FIBERS

Upconversion pumping of fluorescence of Nd3+-, Tm3+- and Pr3+-doped and Pr3+-Yb3+ co-doped samples of ZBLAN in bulk and fiber form was measured using cw and pulsed laser excitation. It is shown that single-laser-beam excited fluorescence is very sensitive to the resonance between the photon energy and an excited state transition frequency. Such resonance in the ESA mechanism can be associated with avalanche absorption in crystals and suggests the possibility of observing similar effects in these glasses, but it could be two-step absorption given the broad bands of glasses. It is concluded that the fiber configuration, as compared with bulk, is the best suited for achieving efficient upconversion lasers.