Abstract : This work is a presentation of a newly developed scanning thermal technique which uses a fluorescent nanoparticle as a thermal sensor. The particle is settled at the end of an atomic force microscope tip. The contact with a surface or a heated device makes the fluorescence of the particle change and gives the temperature. The particle is made of rare earth ions (erbium and ytterbium) which have some fluorescent lines in thermal equilibrium. The measurement of the intensity ratio of these lines allows determining the absolute temperature of the particle and the sample in contact with it. This technique has been applied to observe aluminum and nickel stripes heated by DC currents. In the case of the aluminum stripe, a lateral resolution of 250nm has been found, which is close to the size of the uorescent particle. Then we applied the technique to observe stripes heated by AC currents. This mode allows observing highly localised temperature variations but can not determine the temperature of the sample. We used it to observe heated stripes with a width of 200 nm. Finally tip approach/retraction curves have been made to study the different thermal transfer mechanisms between the tip and the sample. In the case of a submicrometer stripes, the direct thermal transfer by contact is more efficient then all the others.