The shape control of nano-and microcrystals has received considerable attention because the morphology, dimensionality, and size of materials are well known to have great effects on their physical and chemical properties, as well as on their applications in optoelectronic devices. Ionic liquids were found to be very advantageous in synthetic nanochemistry, especially as templates and capping agents. Their particular phase behavior and unique physicochemical properties, including complex solvation interactions with organic and inorganic compounds, can provide various growth pathways for nanocrystals with novel morphologies and properties. This chapter gives an overview of existing ionic liquid-assisted hydrothermal method for the synthesis of rare earth luminescence materials. Particular attention is given to synthesis mechanism and the role of ionic liquids in the formation of specific morphology, as well as the effect of morphology on the luminescent properties.