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