The luminescence emission of a thermographic phosphor based on trivalent chromium doped ZGO (ZnGa2O4) bulk as well as nanoparticles is here reported. This material has a strong temperature dependence on the optical features such as ratio of their emission bands, bandwidths, bands position as well as the lifetime decay of the Cr3+. This makes this material well suitable as temperature sensor. ZnGa2O4 (ZGO), a normal spinel, exhibits a high brightness persistent luminescence, when doped with Cr3+ ions and shows an emission spectrum centered at 695 nm. At the nanometric scale, ZGO is used for in vivo imaging with a better signal to background ratio than classical fluorescent NIR probes. In this work we investigate the ability of the host to be a new thermographic phosphor. Several optical features are investigated in a broad temperature range (10 K-700 K). A comparison between bulk material and nanoparticles is introduced. The obtained results could be used to determine the optimal design parameters for sensor development.