3 1.0 0.5 0.0 Fluorinert FC70/77 R.T  77K  (a)  1st.  2nd.  1st. 2nd. 1.0 0.5 0.0 FWHM (nm) Daphne7373 R.T 77 K  (b) 1.0 0.5 0.0 10 5 0 Pressure (GPa)  NaCl R.T 77 K  (c) FIG. 2: (Color online)Pressure dependence of full-width at half maximum (FWHM) of the ruby R$_{1}$ fluorescence line at room temperature and 77 K for (a)Fluorinert FC70/77, (b) Daphne 7373, and (c) NaCl. Guide lines in the figures are fitted curves of the pressure dependences of the FWHMs with polynomial functions. A. Group I: 1:1 mixture of Fluorinert FC-70 and FC-77, Daphne 7373, NaCl, silicon oil (polydimethylsiloxane) and Vaseline with the media. The pressure dependence was studied several times with independent settings for each of the media. The guide lines in the figures are fitted curves of the pressure dependences of the FWHMs with poly- nomial functions. The open circles and squares indicate the FWHMs at room temperature in the first and sec- ond runs, respectively. The open up and down-pointing triangles indicate the FWHMs at 77 K in the first and second runs, respectively. The solid triangles indicate the FWHMs at 4.2 K. The nonhydrostatic effects are discussed from the value of ΔFWHM( P ) (= FWHM( P )- FWHM(0)). Here, FWHM( P ) and FWHM(0) are the line widths of the ruby R 1 line at high pressure and am- bient pressure, respectively, obtained by the analyses of the ruby profile with the Voigt function where the instru- mental resolution was taken into account. Depending on the size of the additional broadening ΔFWHM at 5 GPa and 77 K, the media are classified into three groups (I, II and III). Fluorinerts and Daphne 7373 have been widely used in high pressure studies using piston cylinder type high- pressure cells because the media have the advantage of being chemically inert [25–27]. The hydrostatic-limit pressures (solidification pressures) of Flourinert FC70/77 and Daphne 7373 at room temperature were determined to be 1.2 and 2.4 GPa, respectively. Figures 2 (a) and (b) show the pressure dependences of the FWHMs for Fluorinert FC70/77 and Daphne 7373. At room temperature, the FWHMs start to increase above the solidification pressures. The value of FWHMs for the media is about 1.1 nm at 10 GPa, indicating strong nonhydrostatic effects. A strong broadening ef- fect was also observed at 77 K. The value of ΔFWHMs for the media is about 0.7 nm at 10 GPa. The present results suggest that they are not suitable media in the higher-pressure region. Figure 2 (c) shows the pressure dependences of the FWHMs for the solid medium of NaCl at room temper- ature and 77 K. The FWHMs at both temperatures in- crease non-linearly in the lower pressure region below 1 GPa and show a tendency to saturate at the high pres- sure region above 5 GPa. The pressure dependence is quite different from those of liquid media. The value of ΔFWHM at 10 GPa is about 0.5 nm at 77 K. It is sug- gested that the hydrostatic pressure is realized in a very small pressure region even at room temperature. The results of the NaCl medium are compared with those of previous studies that reported the pressure dis- tribution inside a sample chamber filled with the NaCl medium becomes spatially inhomogeneous above 4 GPa at room temperature [10]. It should be noted, however, that the observed broadening effect in the present study reflects both the uniaxial stress and inhomogeneous pres- sure distribution inside the chamber, as mentioned in the previous section. This suggests that uniaxial stress is the main cause of the broadening effect in the low-pressure region. We show the experimental results with the silicon oil and Vaseline. Silicon oils such as polydimethylsil- ioxane, polyethylsiloxane and hexamethyldisiloxane have been accepted as good media for a long time [28– 30]. Polydimethylsilioxane ((CH 3 ) 3 SiO-[SiO(CH 3 ) 2 ]$_{n}$- (CH 3 ) 3 Si) with a kinematic viscosity of 1 mm $^{2}$· s − 1 was tested. Vaseline (petroleum jelly or petrolatum) has been occasionally used in high-pressure experiments [31, 32].