Jay:
Cubic Zirconia just doesn't sparkle like diamonds do!
And Jewelry is an investment....they would retain their value if I ever need to sell them!
Citrine
Try silicon carbide - higher refractive index than diamond (although slightly softer on the mohs scale). It is doubly refractive due to the combined elemental structure, but I doubt most people could see a difference with close examination even if told.
As for jewelry being an investment? All of my (very limited) second-hand experience has been massive initial depreciation followed by appreciation that significantly lags CD rates.