The intensity of Raman lines of small crystals can be appreciably enhanced by placing them in a liquid with equal, or nearly equal, refractive index. This technique usually gives better results than the hollow-cone method used with powders, especially with optically isotropic samples, provided small crystals (2–4 mm in size) can be obtained. In certain cases, the results are comparable to those obtained with much larger single crystals.
R. SAVOIE and J. TREMBLAY, "Raman Spectra of Crystals Immersed in Liquids," J. Opt. Soc. Am. 57, 329-332 (1967)