💎 Sm:YAG Fluorescence Gauge (Sm³⁺ Y-lines ~617 nm) — High-pressure optical scale▾ 
§1 — What is the Sm:YAG gauge?
Samarium-doped yttrium aluminium garnet (Sm:YAG, Y₃Al₅O₁₂) emits a group of sharp Sm³⁺ fluorescence lines — labelled Y1, Y2, Y3… — near 616–618 nm (the ⁴G₅/₂→⁶H₇/₂ multiplet), excited at 514 or 532 nm. The line position shifts reproducibly with pressure (sensitivity ≈ 0.32 nm/GPa, identical to ruby) and serves as an optical pressure gauge in the DAC, well separated from the ruby R1/R2 doublet at 694 nm [Trots et al. 2013].

§2 — Why use it instead of ruby?
The Y-lines are nearly temperature-independent in position — pressure can be read without any thermal correction from 6 to 820 K below 25 GPa [Hess & Schiferl 1990] — so the reading drifts far less with temperature than ruby — valuable in externally-heated and laser-heated DAC work. The Y-band intensity also increases with pressure (unlike ruby R1, which weakens), keeping the gauge readable to very high pressure [Liu & Vohra 1994].

§3 — Primary calibration: Trots et al. 2013 (recommended)
The modern primary scale ties the Y1/Y2 shifts to absolute pressure via a Brillouin + XRD equation of state (V₀ = 1735.15 ų, K₀ = 185 GPa, K′ = 4.18), calibrated to 58 GPa: P = (A/B)·{[1 + Δλ/λ₀]^B − 1} ( Δλ = λ − λ₀ ) Y1 : A = 2089.91 , B = −4.43 ( λ₀ ≈ 617.8 nm ) Y2 : A = 2578.22 , B = −15.38 ( λ₀ ≈ 616.0 nm ) This is the calibration used by the converter above [Trots et al. 2013, doi:10.1002/2013JB010519].

§4 — Other calibrations & high-pressure extensions
ReferenceRangeNotes
Trots et al. 20130–58 GPaPrimary scale, Y1/Y2 power law — recommended
Liu & Vohra 19940–180 GPaHighest-pressure Sm:YAG calibration
Wei et al. 20110–120 GPa, ≤700 KCombined P–T calibration
Yusa et al. 19940–50 GPaEarly Sm:YAG pressure scale
Goncharov 2007 / Datchi 20070–60 GPaLinear quick formulas (Y1/Y2/Y3/Y6)
Linear quick formulas (Goncharov / Datchi 2007, 0–60 GPa): Y1 P = 3.15·(λ−617.7) · Y2 P = 3.29·(λ−615.6) · Y3 P = 3.08·(λ−610.7) · Y6 P = 6.37·(λ−603.1).

§5 — Do not confuse with SrB₄O₇:Sm²⁺
A different samarium gauge, Sm²⁺-doped strontium tetraborate (SrB₄O₇:Sm²⁺), emits its 0–0 line near 685 nm [Datchi, LeToullec & Loubeyre 1997]. It is also temperature-insensitive but is a separate material with its own calibration — it must not be mixed with the 616 nm Sm:YAG Y-lines.

§6 — References
· Trots et al. (2013) — The Sm:YAG primary fluorescence pressure scale, J. Geophys. Res. Solid Earth 118:5805 — Y1/Y2 power-law, 0–58 GPa
· Liu & Vohra (1994) — Sm:YAG pressure sensor to 180 GPa, Appl. Phys. Lett. 64:3386
· Liu & Vohra (1993) — Y2 band, 0.32 nm/GPa to 73 GPa, Solid State Commun. 88:417
· Wei, Dubrovinskaia & Dubrovinsky (2011) — Ruby & Sm:YAG to 120 GPa / 700 K, J. Appl. Phys. 110:043513
· Yusa, Yagi & Arashi (1994) — Sm:YAG to 50 GPa, J. Appl. Phys. 75:1463
· Datchi, LeToullec & Loubeyre (1997) — SrB₄O₇:Sm²⁺ scale (~685 nm), J. Appl. Phys. 81:3333
· Goncharov et al. (2007) — Sm:YAG Y-line linear formulas, J. Appl. Phys. 101:095904
· Datchi et al. (2007) — Optical pressure sensors review, High Press. Res. 27:447
· Hess & Schiferl (1990) — Sm:YAG fluorescence P–T; no thermal correction needed 6–820 K, J. Appl. Phys. 68:1953
Sm:YAG Fluorescence → Pressure
Trots 2013 — Y1: P=(A/B)·[(λ/λ₀)^B−1] A=2089.91 B=−4.43
Trots 2013 — Y2: P=(A/B)·[(λ/λ₀)^B−1] A=2578.22 B=−15.38
Measured λ R (nm)
nm
Ref. λ₀ (nm)
nm
No thermal correction applied — Y-lines are quasi temperature-independent (6–820 K, Hess & Schiferl); the small residual shift at very high T is still debated between studies
0 GPa ~10 GPa ~30 GPa ~60 GPa ~100 GPa
Enter measured λ (608–665 nm)
Sm:YAG P vs λ chart — click to read
Trots Y1
Trots Y2
Ruby Mao H (ref.)
Goncharov 2007 & Datchi 2007 — Sm³⁺:YAG Y2 line (~615.6 nm)
Linear formula: P = 3.29 × (λ − λ₀) — valid 0–100 GPa — Y2 band, quasi-hydrostatic (N₂/H₂)
Goncharov et al. J.Appl.Phys (2007) — Datchi et al. High Pressure Res. 27, 447 (2007)
⚠ Y2 band ≈ 615.6 nm (Sm³⁺:YAG) — a linear quick estimate; cross-check against the Trots 2013 scale above
Measured λ Y2 (nm)
nm
Ref. λ₀ Y2 (nm)
nm
0 GPa ~10 GPa ~28 GPa ~48 GPa ~90 GPa
Enter measured λ Y2 (612–650 nm)
Y1 (0–60 GPa) : P = 3.15 × (λ−617.7)  |  Y3 (0–60 GPa) : P = 3.08 × (λ−610.7)  |  Y6 (0–60 GPa) : P = 6.37 × (λ−603.1)
Note: Sm³⁺:YAG (~616 nm) ≠ Sm²⁺:SrB₄O₇ (~685 nm) — two different samarium-doped materials with distinct calibrations and spectral ranges.