I've been studying ternary and quaternary quantum dots and noticed that it's much harder to observe the connection between light emission and the size of these quantum dots than traditional binary quantum dots. Ternary and quaternary quantum dots seem to emit only one colour, and while their spectrum changes as they grow, the colour remains constant. In contrast, binary quantum dots make it much easier to perceive size-dependent light emission because the colours change noticeably. Why does this happen?