Persistent luminescent materials are present in several recent studies on new applications and novel properties. In this work, we demonstrate, for the first time, the production of translucent flexible persistent composites based on Sr2MgSi2O7:Eu2+,Dy3+ (SMSO) into cellulose ether matrix film. The composite was successfully prepared through a new optimized route of co-precipitation and microwave-assisted annealing followed by (3-aminopropyl)triethoxysilane (APTES) coating and dispersion in hydroxypropyl methylcellulose (HPMC). The SMSO@APTES/HPMC films show persistent luminescence emission at 475 nm (blue) and high transmittance in the visible range. To understand the fine distribution of the nanoparticles in the matrix, we have investigated their structure and dispersion by using Synchrotron Radiation X-ray fluorescence mapping and Scanning Transmission X-ray Microscopy. This innovative composite could bring new perspectives for the class of persistent luminescence materials, enhancing technologies in progress throwing light on new applications never perceived.