The fluorescence evolution along Tm³⁺-doped ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) optical fibers, as well as amplified spontaneous emission in the UV-IR region with emphasis on 350 nm, 365 nm, and 450 nm, is studied, estimating optimal fiber lengths for amplification within the region. The fibers were diode-pumped with single and double lines (687 and/or 645 nm). Double-line pumping presents a quite superior efficiency for producing UV-blue signals with the benefit of requiring very short fibers, around 20 cm, compared to single-line pumping requiring more than 50 cm. A virtual cycle in which the pumps enhance each other’s absorption is the key to these systems.