A non-intrusive laser diagnostics technique has been developed for simultaneous meas-urements of velocity and gas temperature in optically accessible internal combustion engines.</br> The technique, thermographic PIV (T PIV) combines phosphor thermometry and particle image velocimetry (PIV) and offers the possibility of simultaneous meas-urement of gas temperature and velocity.</br> Suitable phosphor materials were selected by testing three commercially available phosphors: BAM:Eu2+, ZnO and ZnO:Zn. The lumi¬nescence emission and the spectral response to various parameters including temperature were measured yielding a tem-perature-dependent calibration curve to be used for signal interpretation in engine ex-periments.</br> The ZnO:Zn phosphor shows the highest sensitivity to temperature allowing higher temperature precision. Therefore, ZnO:Zn phosphor was chosen as the suitable candidate for engine measurements.</br> Measurements were performed in an internal combustion engine at a speed of 1200 rpm with a sampling rate of 10 Hz between 180 and 540°CA under motored conditions. The temperature and velocity fields were meas-ured successfully at various times through-out the compression and the exhaust stroke. The obtained temperature fields are com-pared with simulated bulk-gas temperatures from a 0D model-based simulation showing a temperature deviation of around 1% (200°CA) to 14% (480°CA) from the model.</br> The measurement accuracy was found to be 55 K (18%) at 300 K and 2 K (0.3%) at 614 K for the 200-cycles average.</br> The potential of the diagnostics was tested also in in cylinder post-combustion gases. In this case, the diagnostics was failing proba-bly due to the characteristics of the phos-phor used, which does not seem to resist to high combustion temperatures degrading its luminescence properties.</br> The potential of T-PIV in post-combustion gases remains under the conditions of finding more resistant phosphor particles.