Yb3+/Tm3+ co-doped NaNbO3 nanocrystals as three-photon-excited luminescent nanothermometers

•Nanocrystals as high resolution three-photon excited luminescent nanothermometers.•Pump induced local heating as self-referenced photo-thermal agent.•Outstanding applications in the development of controlled hyperthermia.•Tm/Yb:NaNbO3 nanoparticles as self-monitored photo-thermal agents.

In this paper we report on Thulium/Ytterbium codoped sodium niobate (NaNbO3) colloidal nanocrystals as high resolution luminescent nanothermometers operating under three-photon excitation. The spectral shape of the Thulium (1G4→3H6) luminescence band at 480 nm after 980 nm (Ytterbium) excitation has been analyzed in detail in the biophysical temperature range. It has been found that the population re-distribution among the thermally coupled stark levels could be successfully used for ratiometric thermal sensing. The thermal sensitivity of the three photon excited luminescence has been successfully used to evaluate, in a single-beam experiment, the light induced thermal loading taking place in 940 nm excited NaNbO3:Tm3+/Yb3+ nanocrystals.