Reliable surface thermometry of stored nuclear waste containers is essential for both health monitoring and corrosion modelling. In this paper we investigate the feasibility of using phosphor thermometry for long-term temperature monitoring of nuclear waste containers and storage racks. Two strands of research were conducted. Firstly, two thermographic phosphors (ruby and manganese-doped magnesium fluorogermanate [MFG]), mixed with six different binders were coated onto stainless steel (316L) substrates and exposed for one month to gamma radiation (γ-ray) and sodium hydroxide (NaOH) solution. Secondly, a hybrid fibre-optic phosphor thermometer, capable of measuring these samples, was constructed and tested. The instrument can measure temperatures using both the luminescence decay time and intensity ratio techniques. Following γ-ray and NaOH exposure, no significant degradation in phosphor appearance or performance was observed. The MFG/silicone binder combination gave the best results. The hybrid phosphor thermometer demonstrated for MFG/silicone binder that:•the intensity ratio technique gave the lowest measurement standard deviation (σ(T) < 0.1 °C) but suffered minor drift with thermal cycling.•the decay time technique (650 nm emission) did not show any drift and was capable of a measurement standard deviation of σ(T) ≤ 0.3 °C.