The 0.255 Å/kbar linear pressure shift of the intense, narrow, and well-isolated 5D0-7F0 (named 0-0) emission line of SrB4O7:Sm2+ (at 6854.1 Å in ambient conditions) is proposed as a new optical pressure gauge for the diamond anvil cell. The pressure determinations can be made with the same experimental devices as those currently used for the ruby sensor. The good accuracy results from the singlet character and a small linewidth which is no more than 2.5 Å up to 200 kbar in a 4:1 methanol:ethanol mixture, provided the linewidth is ‘‘relaxed’’ through thermal cycles. Such a process can probably be of general interest for this purpose. In nonisostatic media, a similar pressure coefficient and a broadening of ∼0.1 Å/kbar are obtained. This broadening does not greatly disturb the pressure measurements, at least up to 200 kbar. High-pressure determinations up to 400 °C are also shown to be more accurate than with the ruby, owing to the very limited temperature effect on the wavelength (−0.001 Å/°C) and linewidth (∼0.005 Å/°C) of the 0-0 line. The other characteristics of the emission spectrum of SrB4O7:Sm2+ are promising for (a) simultaneous measurements of pressure and temperature (at least up to 400 °C) using this same material and (b) further research on other rare-earth-doped compounds. The possibility of pressure coefficients larger than that of the R1 ruby line is shown by the 0.45 Å/kbar value measured for another emission line of SrB4O7:Sm2+.

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The previously determined optical properties of SrB4O7 ;Sm2+ make this compound a possible better pressure calibrant than ruby, particularly when used at elevated temperatures. Moreover, it can be used with the same experimental devices. In fact, SrB4O7 ;Sm2+ displays an intense emission line which is a nondegenerated singlet, 5D0−7F0, at 685.41 nm in the same spectral range as ruby, 694.22 nm. In the present study, its shift with pressure has been calibrated with the shift of the ruby R1 line up to 60 GPa and has also been recorded to over 100 GPa. No phase transition of SrB4O7 ;Sm2+ was found at least up to 108 GPa. The pressure profiles in the diamond anvil cell have been established at 60 and 105 GPa. In addition, the bulk modulus of SrB4O7 ;Sm2+, B0=170 GPa, has been determined from x-ray diffraction experiments up to 27 GPa. An analytical expression for the shift of the wavelength with pressure is derived and applications to ruby and strontium borate are given.

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