Laser operation has been demonstrated in Tm3+-doped optical fibres at several useful wavelengths, including 2.3μm, 2μm, 1.47μm and 800nm, and visible upconversion fluorescence observed in silica and ZBIAN hosts. The ground-state Stark structure is ∼600cm−1 wide, resulting in broad tuning ranges for the lasers studied so far. As several of these laser are operated quasifour level using the ground state multiplet, the structure of this multiplet influences the laser transitions significantly. We Ipresent site-selective line-narrowed fluorescence studies of thulium in ZBLAN1 and silica-based hosts at low temperatures, which show detail of Stark levels not present in the room-temperature luminescence spectrum. Comparison of these data for Tmi: ZBLAN with the performance of fibre lasers and amplifiers based on the 800nm transition explains aspects of the laser performance such as tuning range, and optimum pump wavelength for amplifiers. In addition these data give information about the site-to-site disorder within the inhcmogeneous line.