To provide a fluorescent substance having a high emission intensity, and obtained by using an oxide solid solution emitting light of each color of RGB by a single parent body by using a solid phase reaction or a sol-gel reaction which are general methods for producing ceramics.

The invention is completed by making an oxide solid solution represented by the formula: Li_1+x-yTa_1-x-3yTi_x+4yO₃:RE (x and y satisfy 0.04≤x≤0.333 and 0≤y≤0.09; and the percentage of added RE₂O₃ is 0.5-5.0 wt.%) obtained by forming a solid solution of titanium in lithium niobate activated with a rare earth, and finding out that the emission intensity thereof is higher.