Nanocrystalline CaYAlO4:Sm3+ phosphors were synthesized by a citrate-based sol–gel method. After annealing at 1000 °C, the closely packed particles with pure tetragonal crystalline structure were observed. The photoluminescence spectra exhibited the emission peaks of 565 nm (4G5/2 → 6H5/2), 600 nm (4G5/2 → 6H7/2), and 650 nm (4G5/2 → 6H9/2) under an excitation wavelength of 409 nm. The optimum concentration of CaYAlO4:Sm3+ phosphors was found to be 2 mol%. The lifetimes were measured to analyze the effect of Sm3+ concentration in CaYAlO4 host lattice. And similar emissions of cathode-luminescence (CL) spectra were also observed. By increasing the accelerating voltage from 1 to 5 kV, the CL intensity was linearly increased.