This paper reports on the spectroscopic properties of the 3H4 and 3F4 Tm3+ levels in a TZN glass host with a concentration range from 0.82 to 22 × 1020 cm−3. Precise refractive index measurements are performed on five different wavelengths by the prism coupling method. Judd–Ofelt intensity parameters have been determined in order to obtain transition rate, branching ratio and radiative lifetime. Spectroscopic measurements show the most promising concentration for the1.8 µm short cavity laser emission at 6.84 × 1020 cm−3 Tm3+ with a 24% quantum efficiency and upper limit concentration of 11 × 1020 cm−3 Tm3+. Energy transfer microparameters and critical ion distance are determined for both emission levels within the framework of diffusion-limited regime and dipole–dipole interaction.