A new silicate phosphor MgGd₄Si₃O₁₃:Ce³⁺,Tb³⁺ was successfully synthesized with the objective of application in ultraviolet-excited light emitting diodes (LEDs) and field emission displays (FEDs). The structural and photoluminescence (PL) properties of un-doped MgGd₄Si₃O₁₃ were studied. The PL properties and the energy transfer from Gd³⁺ to Tb³⁺ and Ce³⁺ to Tb³⁺ in Ce³⁺ and Tb³⁺ singly- and co-doped MgGd₄Si₃O₁₃ were discussed. Ce³⁺ occupying two different crystalline sites show diverse PL properties and distinct energy transfer efficiencies to Tb³⁺. The cathodoluminescence (CL) spectra, depending on the accelerating voltage and probe current, were also studied. Excellent degradation resistance properties with good colour stability were obtained with continuous low-voltage electron-beam excitation.