IR-to-visible up-conversion mechanisms in Pr3+-doped ZBLAN fluoride glasses and fibers

The infrared-to visible up-conversion in Pr3+-doped ZBLAN fluoride glasses has been investigated for different activator concentrations and for different type-materials, either bulk or fiber. Single beam experiments using continuous wave (CW) laser excitation and pulsed laser excitation allow to point out different up-conversion mechanisms, namely excited state absorption (ESA) and energy transfer up-conversion (ETU). The 2.8th power dependence of the blue fluorescence from the P-3(0) State under CW resonant pumping of the (1)G(4) State indicates a dominant three-photon mechanism involving the D-1(2) state. Pulsed laser excitation shows that an ETU process is occurring. When the excitation wavelength is resonant with an ESA transition from the (1)G(4) state, a two-photon process is pointed out. Concerning the red fluorescence issued from D-1(2) state, under CW excitation of the (1)G(4) state, it is attributed to an ETU process which is greatly enhanced by ESA of the 1.3 mu m signal, in the amplification regime in fibers. The influence of the Stark splitting and subsequent transition probabilities on the optical spectra is discussed, enlightening a behavior particular to Pr3+ ion as compared to other rare earth ions.