A novel fluorescent substance for a light-emitting diode, emitting light of any one of three primary colors by excitation of an ultraviolet light-emitting diode. Alternatively, a novel fluorescent substance for a light-emitting diode, emitting light in a red region of a spectrum by excitation of a blue light-emitting diode. Na2SrSi2O6 is doped with Eu3+. Preferably, Eu3+ is added so as to account for 1 to 80 mol % in concentration in a host crystal, while sites of Si4+ in Na2SrSi2O6. are replaced by Al3+ and/or Ga3+. Alternatively, Ca3Si2O7 is doped with Ce3+ and Tb3+. Preferably, Ce3+ and Tb3+ are added so as to account for 0.1 to 80 mol % and 0.1 to 20 mol % in concentration in a host crystal, respectively. Still alternatively, Ca3Si2O7 is doped with Eu2+. Preferably, Eu2+ is added so as to account for 0.5 to 10 mol % in concentration in the host crystal.