(NB: Etsy link is not available)
Most synthetic gemstones are flawless.
A good light effect needs some imperfections in the stone, but not too much. Need to find a good balancing (same situation than a laser that need smoke or dust particles in the air to be visible).
For instance, there is a very clear and flawless small Quartz crystals called "Herkimer". These quartz won't fit for a crystal chamber while basic crystals can be awesome.
Note : Aqua-aura is articial light-blue colored quart, amethyst is natural purple quartz, citrin is a yellow/brown quartz too (either natural, or artificial heated)
For other colors, I'm still looking for alternatives cheaper than emerald, spinel or tourmaline...
Moreover, depending on the stone, the polish can be mirror-like and so, the light effet will not be satisfying.
Sapphire/Ruby (same familly "corundum"), quartz have good reflexion properties to be polished, while garnet and zircon (same property than diamond) probably may not have.
Sorry, my english is not good enough to speak about gems and jewelry. I hope to be understandable...