Eu2+-doped phosphors Sr2MgSi2O7: xEu2+ (x = 1–5 mol%) with blue color are synthesized by the co-precipitation method. The X-ray diffraction patterns of these phosphors indicate a tetragonal crystal structure. The emission peak centered at 486 nm is attributed to the 4 F7→ 4F65D1 transitions of Eu2+ ions with CIE coordinates of (x = 0.176, y = 0.637). We use Sr2MgSi2O7: 4 mol% Eu2+ phosphors to find latent fingerprints (LFPs) with visible patterns on different surfaces under 337 nm UV light. The results indicate that this phosphor may possess the potential to be used for LFP recognition. Three calculated models mimicking the crystal host, Eu2+ ion-doped phosphor, and Eu2+ ion-doped phosphor with oxygen vacancy are built using CASTEP software to perform density functional theory (DFT) calculations. The geometry optimization results of the Eu2+ doping ion reveal that a coordinate covalent bond is formed by the Eu2+ doping ion with its neighboring oxygen atoms. The oxygen vacancy VO causes obvious changes in the electron orbitals of Si and O atoms as well as the 5d empty orbital of Eu2+ ions.