Pressure Optical Sensors for Diamond Anvil Cell
Jesús GonzálezCENTRO DE ESTUDIOS DE SEMICONDUCTORES
Facultad de Ciencias, Departamento de Física, Universidad de Los Andes – Mérida, Venezuela
Alfa Meeting Highfield Vienne 26th to 30th April 2004
A Slice of DAC
An open DAC
The pressure changing machine
Shematic optical set-up
Argon laser
PrimaryObjective
DAC with lightfocussed on ruby
SecondaryObjective
Neon lamp
Exit lens
Beam splitter
Eyepiece
Screen
Focussinglens
Modulator
Ruby luminiscence Spectra
Photo luminiscence of Ruby at 300 K
RUBI (Al2O3:Cr3+), luminiscence , R1-R2splittingλ (R1) = 6942 A0 Γ= 6 A0
Lineal variation as compare with the equation of state of Decker
for NaCl, valid up to 30 GPa∆λ/∆P = 0.365 A0 Kbar-1 ∆λ/∆P = -0.753 cm-1 Kbar-1
Fixed Point scale
Criostat for pressure measurements at low
temperatures
Low temperature photoluminiscence spectra of
ruby
4800 4850 4900 4950 5000 5050 5100 5150 52000
3000
6000
9000
77 K 296 K
Al2O3: Cr3+
Phot
olum
inis
cenc
e (A
.U)
wave number (cm-1)
Ruby at Low Temperatures : in-situ termometer
10 < T < 100 K, T=A/ln(ηI1/I2)
A = ∆/ K= 41.86 K
∆ = 29.1 cm-1 between 10 and 100 K (splitting between R1 and R2 ruby lines)
K Boltzmann´s constant
η= quantum efficiency between R2 and R1, transition η= 0.625
Under hydrostatic conditions the calibration was done up to 12 GPa. The relative error in T is less than 10% between 12 and 25 GPa.
The pressure is given by the shift of the ruby line R1
P (GPa) = 380.8[(σ0/σ)5-1]
σ0 = 14425 cm-1, T< 108 K
Range 108< T < 300 K
∆T (K) = [A1-A2/ 1+(T-T0)p]+ A2
A1= -897.0977, A2=2.11313, p=1.188, T0=1.966
The pressure is given by
P (GPa) = 380.8[(σ0/σ)5-1]
σ0 is not constant in this range and is given by:
σ0(cm-1) = 14425-0.043(T-108)- 0.0003(T-108)2
Equations for pressure measurements
Under cuasi-hydrostatic conditions, for pressure bigger than 30 GPa:P (Mbar) = 3.808[(∆λ/6942+1)5-1] ∆λ (nanometers)
In He:P (GPa) = 0.274x λR1(0)/7.665[{λR1(P)/ λR1(0)}7.665 – 1]λ (nanometers)
Major drawbacks of Ruby
The R1 line belongs to a doublet and its line width is very sensitive to nonhydrostatic stress and to temperature. In the presence of one or both factors, the doublet broadens, which results in the overlapping of the two lines and the formation of a broad asymmetrical band. The accuracy of the pressure measurement is then significantly reducedThe signal-to-background ratio of the fluorescence rapidly decrease above 700 K. A similar effect is observed in nonhydrostatic environments, making the measurements difficult above 100 GPaThe R1 line presents a relatively large wavelength shift with temperature and any error in the temperature measurement will directly contribute to an erroneous determination of the pressure
Fig 24: Rubi Lumenescense at 5 kbar
Wavelength / nm688 690 692 694 696 698 700 702
Lum
ines
cens
e / A
rbrit
ary
units
0
500
1000
1500
2000
2500
3000
3500
25ºC75ºC125ºC175ºC225ºC
275ºC x 10
325ºC x 10
Fig 25: Samarium Luminescence at 40kbar
Wavelength / nm685 686 687 688 689
Lum
ines
cenc
e / A
rbitr
ary
units
0
1000
2000
3000
4000
5000
85ºC125ºC175ºC225ºC275ºC325ºC400ºC
SAMARIUM (SrB4O7:Sm2+)
λ 0-0 = 6854.1 A0 Γ= 1.4 A0
Fluorescence of line 7D0-5F0
∆λ0-0(P)= 0.248 P + 8.9x 10-4 P2Up to 120 GPa at 300K
Luminescence spectra of (a) ruby
and (b) of the Samarium at 108.4 Gpa in helium. The laser power was 10
mW and the accumulation time,
10 s. The star indicate the plasma lines from Ar+ laser
Luminiscence spectra of the Samarium compound and of ruby in ice (H2O). The stars indicate the plasma lines
from the Ar+ laser. (a) Ruby at 95 Gpa. The laser power
(P1) was 13 mW and the accumulation time (tacc),
10s; (b) Samarium at 95 Gpa (Pt=13mW, tacc=10 s) and, in the inset, at 130 Gpa (Pt=13
mW, tacc=20 s)
SAMARIUM
∆λ0-0 (T> 500)= 1.06x10-4(T-500)+1.5x10-7(T-500)2
Pressure and temperature In-Situ measurements with both sensors
T=300+137(∆λR1-1.443∆λ0-0)
Calibration of the wavelength shift of the 7D0-5F0 line of samarium and he R1 line of ruby with temperature
at ambient pressure.Solid line: linear fit to the ruby data from 300 to 600 K (∆λR1/∆T=7.3x10-3 nm/K); dashed line: quadratic fit to
the ruby data between 600 and 800 K
Calibration of the 7D0-5F0 line wavelength shift with
pressure in helium. Squares and up-triangules: incresing prresure runs; circles and
down-triangules: drecrease pressure run; the solid line is
a numerical fit to the experimental data:
The dotted line is the linear fit (P=∆λ0.255 obteined by Lacam et al. In 4:1 M-E mixture up to 20 GPa
λλλ
∆×+∆×+
∆= −
−
2
3
1032.211029.91032.4P
High Temperatures
External Resistive Furnaces up to900 K in the air, and up to 1400 K in the vacum or inert gas.
Ruby: 300< T< 600 K lineal law∆λR1/∆T= 7.3x10-3 nmK-1
600< T < 1300 K∆λR1= 2.22+ 7.7x10-3∆T+5.5x10-6∆T2
∆T=T-600
External Heater
High Temperature Setup
Diamond Types
Type Ia = contains nitrogen in clusters (aggregates)
Type IaA contains predominantly A-aggregates (pair of nitrogen atoms, forms at lower geological temperatures) Type IaB contains predominantly B-aggregates (four nitrogen atoms surrounding a vacancy, forms at higher geological temperatures)
Many type Ia diamonds contain similar amounts of A- aggregates as well as B-aggregates and are the called type laA/B. In these stones one can frequently detect a certain amount of N3 centers, which cause the light yellow coloration of "cape" diamonds. Nitrogen may also be present in platelets which have a large extent and low thickness and which represent probably a structure of carbon and nitrogen atoms
Type Ib = contains mostly isolated substitutional nitrogen (i.e. one nitrogen atom substitutes one carbon atom)
Type IIa = does not show any impurity-related absorption in the UV, visible or infrared parts of the spectrum (the optically most transparent diamonds)Type IIb = contains boron as an isolated substitutional impurity, is therefore electrically conductive and always has a gray to blue color.Stones with a very low boron content may appear near colorless Type IIc = type II diamonds which contain hydrogenas a substitutional impurity with a dominating absorption around 2900cm-1 in the infrared
INFRARED ABSORPTION OF DIFFERENT TYPES OF
DIAMOND
Firts Order Raman
Second Order Raman
Raman Sintetic Diamond
FTIR Diamond IIa
FTIR diamonds Ia, IIaand IIb