Tm-doped ZBLAN and Tm-doped silica glass are compared spectroscopically and the fiber lasing of the Tm 3F4 →3H6 transition around 1.9 μm in ZBLAN and silica fibers is compared. The spectroscopy of these materials indicates that Tm:ZBLAN possesses advantages over Tm:silica glass due to the lower phonon energies. The phonon energy in these glass hosts influences both the pump manifold lifetime, the Tm 3H4, and the upper laser manifold lifetime, the Tm 3F4. The maximum phonon energy in Tm:ZBLAN, ∼500 cm-1 , compared to Tm:silica, ∼1100 cm-1, leads to better Tm–Tm self quenching towards populating the Tm 3F4, as well as better Tm 3F4→3H6 quantum efficiency. A spectroscopic analysis using the Judd–Ofelt theory and measured lifetimes are used to assess the merits of Tm:ZBLAN over Tm:silica as a fiber laser material. Diode-pumped fiber lasing experiments show that Tm:ZBLAN possesses advantages over Tm:silica that are believed to be due to a lower phonon energy. Data is presented for launched pump energy versus laser energy, fiber length versus slope efficiency, and output mirror reflectivity versus slope efficiency. Tm:ZBLAN is demonstrated to possess higher slope efficiencies and lower thresholds, than Tm:silicate. A grating tuned Tm:ZBLAN laser is also demonstrated for tunable operation between 1.893 μm and 1.955 μm.