Among many I-II-VI2 chalcopyrite semiconductors, CuAlS2 is an only prospective candidate for blue LED application. Our recent observation of purple to green photoluminescence in CuAl1-xGaxS2 mixed alloys urges to prepare a heterojunction of p-CuAl1-xGaxS2/n-ZnS by liquid epitaxial growth. After a brief review of luminescence properties and LED fabrication of CuGaS2, photoluminescence properties and possibility of a blue LED of CuAl1-xGaxS2 are described.