Persistent luminescence (PersL) nanoparticles offer attractive capabilities for in vivo imaging applications as an optical excitation of the nanoparticles outside the animal before injection is possible. Therefore, long-lasting emission of light allows performing in vivo imaging with high signal to noise ratio and with high sensitivity. Here we report the development of LaAlO3 (LAO) nano-perovskite doped with Cr3+ and Sm3+, the trivalent chromium cation being the recombination center, while Sm3+ is used to enhance the persistent properties. Nanoparticles are synthesized by co-precipitation method and are tailored to present deep red persistent luminescence at 734 nm due to the Cr3+: 2E(2G) → 4A2(4F) transition after UV excitation. The intense deep red PersL matches well with the first biological window (650–950 nm). These nanoparticles have been successfully functionalized with polyethylene glycol (PEG) and the stealth obtained nanoparticles were tested for the first time for imaging on small animal in order to have access to their in vivo biodistribution.