In allusion to the problems existing in the defect-related luminescent materials, a series self-activated light emitting semiconductors of Li3AlN2: R (R=0, Na+, Mg2+, Si4+, Tb3+, Eu3+) have been successfully synthesized by sample-pressure sintering. Under the excitation at 422 nm, a yellow light peaked at 580 nm have been observed in the host lattice of Li3AlN2. The crystal structure and the electron structure of Li3AlN2 have been measured to investigate the defect-related luminescent properties of Li3AlN2 using the Rietveld refinement on the basic of X-ray diffraction data and the density functional theory (DET). The results show that Li3AlN2 crystallizes in cubic phase with full filled edge-shared (Al/Li)N-4 tetrahedrons and is a wide-bandgap semiconductor. The impurity defects produced by ions substitution have also been investigated, which leads to the red-shift of the emission peak. Finally, the photoluminescence excitation (PLE) spectrum of Li3AlN2 with two excitation bands peaked at 300 nm and 422 nm has been detected, and the latter matches well with near-UV LED chips. The thermal stability shows that integral intensity of Li3AlN2 at 150 degrees C still has 60% of the initial intensity at room temperature. The results indicate their potential applications as the LED used phosphors.