The

Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapp ...

Fluorescence Pressure Scale is an

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

method to measure pressure within a sample chamber of a

Diamond Anvil Cell A diamond anvil cell (DAC) is a high-pressure device used in geology, engineering, and materials science experiments. It enables the compression of a small (sub-millimeter-sized) piece of material to extreme pressures, typically up to around ...

apparatus. Since it is an optical method, which fully make use of the

transparency Transparency, transparence or transparent most often refer to: * Transparency (optics), the physical property of allowing the transmission of light through a material They may also refer to: Literal uses * Transparency (photography), a still ...

of diamond anvils and only requires an access to a small scale

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

generator, it has become the most prevalent pressure gauge method in high pressure sciences.

Principles

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and h ...

-dopped corundum (Al₂O₃). The Cr³⁺ in corundum

lattice Lattice may refer to: Arts and design * Latticework, an ornamental criss-crossed framework, an arrangement of crossing laths or other thin strips of material * Lattice (music), an organized grid model of pitch ratios * Lattice (pastry), an ornam ...

formed an octahedra with surrounding oxygen ions. The octahedral

crystal field Crystal field theory (CFT) describes the breaking of degeneracies of electron orbital states, usually ''d'' or ''f'' orbitals, due to a static electric field produced by a surrounding charge distribution (anion neighbors). This theory has been used ...

together with spin-orbital interaction results in different energy levels. Once 3d electrons in Cr³⁺ is energized by lasers, the excited electrons would go to ⁴T₂ and ²T₂ levels. Later they will return to ²E levels and the R₁, R₂ lines come from luminescence from ²E levels to ⁴A₂ ground level. The energy difference of ²E levels are 29 cm⁻¹, corresponding to the splitting of R₁, R₂ lines 1.39 nm.

Development

Ruby fluorescence spectra has two strong sharp lines, R₁ and R_2. R₁ refers to the stronger intensity and lower energy (longer wavelength) excitation and is used to gauge pressure. Pressure is calculated as:

P(GPa)=\frac left ( \frac \right )^b-1 /math>, where λ

₀ is the R₁ wavelength measured measured at 1atm, a and b are constants. (e.g. a = 1904, b = 5) Since first demonstrated by Forman and colleagues in 1972, many scientists have contributed to the establishment of accurate ruby pressure scale in various experimental conditions. A likely incomplete summary of is given below: {, class="wikitable" , + !Year !First Author !a !b !Primary pressure standard used !Temperature !Pressure range !Pressure transmitting medium !References , - , 1972 , R. A. Forman , - , -, linear , Transitions of CCl₄, H₂O, C₂H₅Br, ''n''-C₇H₁₆ , Room temperature , 2.2 GPa , See standards used , , - , 1978 , H. K. Mao , 1904 , 5 , Ag, Cu, Mo, Pd , Room temperature , 6 - 100 GPa , M-E, H₂O , , - , 1986 , H. K. Mao , 1904 , 7.665 , Cu, Ag, Ar , Room temperature , 80 GPa , Ar , , - , 2004 , A. Dewaele , 1904 , 9.5 , Al, Cu, W , Room temperature , 153 GPa , Helium , , - , 2005 , A. D. Chijioke , 1876(6.7) , 10.71(0.14) , Au, Pt , Room temperature , 150 GPa , Helium, Hydrogen, Ar , , - , 2008 , S.D Jacobsen , 1904 , 10.32(7) ,

MgO Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ion ...

, Room temperature , 118 GPa ,

Helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

, , - , 2012 , H. Yamaoka , 1762*ln(λ/λ₀) , , Ruby R₁ , Low temperature to 16K , 26 GPa , M-E, Silicone oil , , - , 2020 , G. Shen , 1870 , 5.63(3) , MgO, Mo, Cu,

Diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...

, Room temperature , 150 GPa ,

, {{Cite journal, last=Shen, first=Guoyin, last2=Wang, first2=Yanbin, last3=Dewaele, first3=Agnes, last4=Wu, first4=Christine, last5=Fratanduono, first5=Dayne E., last6=Eggert, first6=Jon, last7=Klotz, first7=Stefan, last8=Dziubek, first8=Kamil F., last9=Loubeyre, first9=Paul, last10=Fat’yanov, first10=Oleg V., last11=Asimow, first11=Paul D., date=2020-07-02, title=Toward an international practical pressure scale: A proposal for an IPPS ruby gauge (IPPS-Ruby2020), url=https://www.tandfonline.com/doi/full/10.1080/08957959.2020.1791107, journal=High Pressure Research, language=en, volume=40, issue=3, pages=299–314, doi=10.1080/08957959.2020.1791107, issn=0895-7959

References

High pressure science Optics Applied and interdisciplinary physics