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Effect of pressure on the ruby fluorescence lifetime
Volume 155, number 3
CHEMICAL PHYSICS LETTW
3 March 1989
EFFECT OF PRESSURE ON THE RUBY FLUORESCENCE LIFETIME V. UROSEVIC, B. PANIC’, B. JOVANIC, Lj. ZEKOVIC ’ Institute of Physics, P.O. Box 57, IIOOIBelgrade, Yugoslavia
and P. SAVIC Serbian Academy of SciencesandArts. 11000 Belgrade, Yugoslavia Received 26 October 1988
The pressure dependence of the fluorescence- lifetime of ruby has.been measured in the O-1 18 kbar pressure range. A linear increase of emission lifetime t is found with a slope Ar/m=0.03 12 ms/kbar (for the RI line). This increase can be correlated with the pressure dependence of the crystal field strength.
1.
Introduction
The pressure dependence of spectral properties (positions, widths, intensities and lifetimes of electronic transitions and their vibrational sidebands) of ionic impurities in solids has been studied by many authors. One of the most known examples is the redshift of ruby (A1203:Cr3+) fluorescence lines, used for high-pressure measurements in diamond anvil cells [I]. The change of lifetime with increasing pressure has been observed in different materials. Webster and Drickamer [ 21 found for Eu3+ ( ‘D,d7F3) in La202S : Eu a very fast increase in T between 0 and 30 kbar, followed by a practically constant lifetime up to 80 kbar, similar behaviour has been obtained for the 5D3 level, while the 5D1 lifetime was essentially independent of pressure, but very sensitive to Eu concentration. A simultaneously observed quick pressure rise in radiation intensities of the first two levels was explained by the decrease in the rate of quenching of these levels to the charge-transfer state, but this. model did not fit the lifetime data. Highpressure studies of lifetimes in alkali halides doped
with Cut and Ag+ [3] gave, with two exceptions, a rise of Tby a factor of 1.1-2.6 between 0 and 20 kbar. The authors attributed this rise to the change of intrinsic radiative lifetime with increasing pressure. Some calculations based on the Kubo-Toyozawa configuration coordinate model for phonon-assisted transitions [ 4 1, which predicts that pressure will decrease the phonon assistance, are in fair agreement with the experiment. Me&e et al. [ 51 found for Nd3+(4F3,2+419,2) in NdXYr_-xP5014a decrease of 7 with increasing pressure, attributed to the increase of the interaction between Nd3+ ions leading to fluorescence quenching. The same authors investigated the change of the fluorescence lifetime of ruby R-lines with pressure. Despite the relatively large scatter in the data, an increase in the lifetime with increasing pressure was demonstrated. In this work the emission lifetime of the ruby RI line has been measured in the 0- 118 kbar pressure range, giving a linear rise of r with increasing pressure. This increase can be correlated with the pressure dependence of the crystal field strength in this pressure range.
’ Also at: Faculty of Physics, P.O. Box 550, 11001 Belgmde, Yugoslavia.
325
Volume 155, number 3
CHEMICAL, PHYSICS LETTERS
3 March 1989
2. Experimental details
For pressure generation a diamond anvil cell of the NBS type [6] with l/3 carat stones has been used. Small (~30 pm) chips of ruby (~0.1% Cr) were put in an 0.3 mm hole of a preindented stainless-steel gasket, together with a methanol-ethanol (4: 1) mixture which served as pressure medium. The pressure was determined by the red-shift of the RI line [ 1] using a double optical monochromator with 0.6 nm spectral resolution and a photon counter with multiscaler. The RI and RI1 lines were well separated in. the whole pressure range, without measurable change (at the spectral resolution used) of linewidths. Decay curves have been measured at the maximum (for given pressure) of the RI line with the same spectral resolution, using the method described by Klick et al. [ 3 ] _For this measurement the ruby was excited by green light of a xenon flash or by the chopped beam of a cw Ar* laser at 1= 515 nm. In both cases the illumination lasted about 1 ms, the time resolution was 40 or 80 ps per channel, and the total measuring time (for one scan) 20 or 40 ms. The data collected by the multiscaler after 103-lo4 excitation pulses were transferred to a personal computer in order to obtain the exact shape of the decay curve, the lifetime value and the standard deviation (always less than 2%).
Fig. 1. The dependence of ruby fluorescence lifetime (RI line) on pressure: ., this work, x Merkle’s [ 51measurement; full line, ccl. (1).
It seems that the observed rise in fluorescence lifetime can be attributed to the diminution of the *Ed4A2 transition probability of individual Cr’+ ions, The other possible high-pressure effects on lifetime, such as the change of non-radiative decay rate of each Cr3+ ion or the increase in the interaction between neighbour Cr3+ pairs, are expected to produce the opposite influence on the radiation lifetime, or are too small in the observed pressure range. For an electric dipole transition of a localized luminescent center in a solid of refractive index n, the transition probability is given by [ 91
3. Results and discussion
1/r=(4eZ/9C3fi4)(n2+2)n(Av)3M2,
All observed decay curves were single-exponential. In the investigated pressure range (P=O-118 kbar) we found for the RI line a linear increase in emission lifetime r with increasing pressure P,as presented in fig. 1. The experimental points can be interpolated by a straight line,
where AYis the photon energy at the emission peak, and M is the dipole matrix element, or
r (ms)=3.04+0.0312P
(kbar) ,
(1)
the cornelation factor being 0.995. The commonly measured room-temperature and zero-pressure value is ro= 3.0 ms [ 7 1, which is in agreement with our P=O value (3.04 ms), showing the absence of both temperature rise by laser illumination and self-absorption of fluorescence [ 8 1. Preliminary measurements for the RI1 lines gave a similar behaviour. 326
z -= b
(n;+Z)nd(fiv,)3M; (n2+2)n(hv)3W
’
(2)
(3)
where ro, no, vo,MOare atmospheric-pressure values. For the ruby RI line and P= 100 kbar the ratio ( ft v,/ Rv)3= 1.016 [ 1 ] which cannot explain the rise of T by a factor ~2. As for the ratio ($,+2)&J (n2+2)n, a decrease of n to 0.7no at 100 kbar is needed to obtain the measured rise in z, and this is improbable. So, a decrease of M with increasing pressure is expected. Taking into account that R lines are genuine nophonon lines, it seems that the model used in ref. [ 3 ] is not applicable to this case. We suppose that the
Volume 155, number 3
CHEMICAL PHYSICS LETTERS
observed rise in 7 could be connected with the increase of the crystal field strength with increasing pressure. Using the conception of the expansion of the electron radial wavefunction of Cr3+ under compression, Ma et al. [lo] were able to calculate the pressure-induced shifts of ruby spectra and the change of ligand field strength (Dq) as a function of the linear compression ratio K= R/Ro, where R and R. are interionic ( W+-02) distances at high and zerc pressure, respectively. On the other hand, there is experimental evidence indicating that the l.igand field strength greatly influences the lifetime of Cr3+ R lines in different host materials, as shown in table 1. In the last two materials in table 1 non-radiative quenching processes also can play an important role. Ruby Dq data given in ref. [ lo] can be approximated by a fourth-order equation, Dq= 1810t l.l0254P-
3 March 1989
Table 2 Measured and calculated lifetimes and A(&) different pressures Pressure (kbar)
0 14.0 19.0 25.5 29.6 35.5 54.5 73.0 87.1 92.7 98.6 106.0 118.0
A(&) (cm-‘)
0 15 20 27 31 37 54 71 82 86 91 96 105
Measured lifetime (ms) 3.04 3.4s 3.70 3.90 3.94 4.18 4.84 5.33 5.62 5.87 6.01 6.37 6.86
values of ruby at
Calculated lifetime (ms) eq. ( 1)
eq. (5)
3.04 3.48 3.63 3.84 3.96 4.15 4.74 5.32 5.76 5.93 6.12 6.35 6.72
3.04 3.53
3.10 3.93 4.06 4.26 4.82 5.38 5.75 5.88 6.04 6.21 6.5 1
1.95154x 10-3P2
+1.31686x10-6P3+4.87713x10-‘oP4
4. Conclusion
(forP=O-500 kbar) ,
(4)
but at low P values the change of Dq with increasing pressure is nearly linear. So, for the pressure range used in this experiment we assume the following relation between A(Dq) =Dq-Dqo and E T (ms) =3.04+0.033A(Dq)
(cm-‘) ,
(5)
Table 2 shows a comparison between the measured lifetime values and those calculated from eqs. ( 1) iind (5) ; A(Dq) for given pressures was calculated using eq. (4). The mean deviation of the calculated lifetime values from the measured ones is about 1,5%, which is within the experimental uncertainty, but for higher pressures an important deviation from eq. ( 1) is expected and perhaps from eq. (5), too.
For the pressure range O-l 18 kbar a linear increase of ruby fluorescence lifetime with increasing pressure has been found. It seems that this increase is connected with the pressure dependence of the crystal field strength, but additional measurements at higher pressures ( 2 500 kbar) and in different host materials with different C?+ concentrations are needed to establish this correlation. The results obtained are interesting from the point of view of possible high-pressure solid-state lasers. It is also possible to use relation ( 1), up to x 100 kbar, for high-pressure measurements in diamond anvil cells, instead of the wavelength shift method, with greater sensitivity (about 100% of the change in Tat 100 kbar) and, in principle, higher accuracy of time measurement as compared with wavelength measurement.
Table 1 Ligand iield strength Dg and emission lifetime r of Cr3+ (*E) in various materials at normal pressure
Acknowledgement Material
Dq (cm-‘)
r(p)
ruby alexandrite glass ceramics glasses
1810 1740 a 1600-1700 * 1450-1580
3000 [7] 260 [II] >200 [ 121 17 [13]
The authors are grateful to Professor D. Curie, from the University Paris VI, for high interest in this work and to Mr. B. PetroviC for precious technical assistance.
327
Volume 155, number 3
CHEMICAL PHYSICS LE-l-l-ERS
References [l] G.P. Piermarini, S. Block, J.D. Barnett and R.A. Forman, J. Appl. Phys. 46 ( 1975) 2774. [2] G. Webster andH.G. Drickamer, J. Chem. Phys. 72 (1980) 3740. [3] D.I. Klick, K-W. Bieg and H.G. Drickamer, Pbys. Rev. B 16 (1974) 4599. [4] R. Kubo and Y. Toyozawa, Progr. Theoret. Phys. 13 (1955) 160. [S]L.D. Merkle, I.L. Spain and R.C. Powell, J. Phys. C 14 (1981) 2027. [6] G.J. Pie& and S. Block, Rev. Sci. Instr. 46 (1975) 973.
328
3 March 1989
/7] V. Evtuhov and J.K. Neeland, in: Lasers - a series of advances, ed. AK Levine (Dekker, New York, 1966) p. 15. [S ] D.F. Nelson and M.D. &urge, Phys. Rev. 137 (1965) A1117. [9] W.B. Fowler, in: Physics of color centers, ed. W.B. Fowler (Academic Press, New York, 1968) ch. 2. [ 1OlD.P. Ma, J.R. Chen and Z.Q. Wang, Phys. Letters A 126 (1988) 377. [ 111B.A. Lengyel, Lasers ( Wiley-Interscience, New York, 197I). [ 12 ] N. Karayamis. D.E. Wortman and H.P. Jenssen, 1. Phys. Chem. Solids 37 (1976) 675. [ 131 A. Yariv, Introduction to optical electronics (Halt, Reinhart and Winston, New York, 1971).
CHEMICAL PHYSICS LETTW
3 March 1989
EFFECT OF PRESSURE ON THE RUBY FLUORESCENCE LIFETIME V. UROSEVIC, B. PANIC’, B. JOVANIC, Lj. ZEKOVIC ’ Institute of Physics, P.O. Box 57, IIOOIBelgrade, Yugoslavia
and P. SAVIC Serbian Academy of SciencesandArts. 11000 Belgrade, Yugoslavia Received 26 October 1988
The pressure dependence of the fluorescence- lifetime of ruby has.been measured in the O-1 18 kbar pressure range. A linear increase of emission lifetime t is found with a slope Ar/m=0.03 12 ms/kbar (for the RI line). This increase can be correlated with the pressure dependence of the crystal field strength.
1.
Introduction
The pressure dependence of spectral properties (positions, widths, intensities and lifetimes of electronic transitions and their vibrational sidebands) of ionic impurities in solids has been studied by many authors. One of the most known examples is the redshift of ruby (A1203:Cr3+) fluorescence lines, used for high-pressure measurements in diamond anvil cells [I]. The change of lifetime with increasing pressure has been observed in different materials. Webster and Drickamer [ 21 found for Eu3+ ( ‘D,d7F3) in La202S : Eu a very fast increase in T between 0 and 30 kbar, followed by a practically constant lifetime up to 80 kbar, similar behaviour has been obtained for the 5D3 level, while the 5D1 lifetime was essentially independent of pressure, but very sensitive to Eu concentration. A simultaneously observed quick pressure rise in radiation intensities of the first two levels was explained by the decrease in the rate of quenching of these levels to the charge-transfer state, but this. model did not fit the lifetime data. Highpressure studies of lifetimes in alkali halides doped
with Cut and Ag+ [3] gave, with two exceptions, a rise of Tby a factor of 1.1-2.6 between 0 and 20 kbar. The authors attributed this rise to the change of intrinsic radiative lifetime with increasing pressure. Some calculations based on the Kubo-Toyozawa configuration coordinate model for phonon-assisted transitions [ 4 1, which predicts that pressure will decrease the phonon assistance, are in fair agreement with the experiment. Me&e et al. [ 51 found for Nd3+(4F3,2+419,2) in NdXYr_-xP5014a decrease of 7 with increasing pressure, attributed to the increase of the interaction between Nd3+ ions leading to fluorescence quenching. The same authors investigated the change of the fluorescence lifetime of ruby R-lines with pressure. Despite the relatively large scatter in the data, an increase in the lifetime with increasing pressure was demonstrated. In this work the emission lifetime of the ruby RI line has been measured in the 0- 118 kbar pressure range, giving a linear rise of r with increasing pressure. This increase can be correlated with the pressure dependence of the crystal field strength in this pressure range.
’ Also at: Faculty of Physics, P.O. Box 550, 11001 Belgmde, Yugoslavia.
325
Volume 155, number 3
CHEMICAL, PHYSICS LETTERS
3 March 1989
2. Experimental details
For pressure generation a diamond anvil cell of the NBS type [6] with l/3 carat stones has been used. Small (~30 pm) chips of ruby (~0.1% Cr) were put in an 0.3 mm hole of a preindented stainless-steel gasket, together with a methanol-ethanol (4: 1) mixture which served as pressure medium. The pressure was determined by the red-shift of the RI line [ 1] using a double optical monochromator with 0.6 nm spectral resolution and a photon counter with multiscaler. The RI and RI1 lines were well separated in. the whole pressure range, without measurable change (at the spectral resolution used) of linewidths. Decay curves have been measured at the maximum (for given pressure) of the RI line with the same spectral resolution, using the method described by Klick et al. [ 3 ] _For this measurement the ruby was excited by green light of a xenon flash or by the chopped beam of a cw Ar* laser at 1= 515 nm. In both cases the illumination lasted about 1 ms, the time resolution was 40 or 80 ps per channel, and the total measuring time (for one scan) 20 or 40 ms. The data collected by the multiscaler after 103-lo4 excitation pulses were transferred to a personal computer in order to obtain the exact shape of the decay curve, the lifetime value and the standard deviation (always less than 2%).
Fig. 1. The dependence of ruby fluorescence lifetime (RI line) on pressure: ., this work, x Merkle’s [ 51measurement; full line, ccl. (1).
It seems that the observed rise in fluorescence lifetime can be attributed to the diminution of the *Ed4A2 transition probability of individual Cr’+ ions, The other possible high-pressure effects on lifetime, such as the change of non-radiative decay rate of each Cr3+ ion or the increase in the interaction between neighbour Cr3+ pairs, are expected to produce the opposite influence on the radiation lifetime, or are too small in the observed pressure range. For an electric dipole transition of a localized luminescent center in a solid of refractive index n, the transition probability is given by [ 91
3. Results and discussion
1/r=(4eZ/9C3fi4)(n2+2)n(Av)3M2,
All observed decay curves were single-exponential. In the investigated pressure range (P=O-118 kbar) we found for the RI line a linear increase in emission lifetime r with increasing pressure P,as presented in fig. 1. The experimental points can be interpolated by a straight line,
where AYis the photon energy at the emission peak, and M is the dipole matrix element, or
r (ms)=3.04+0.0312P
(kbar) ,
(1)
the cornelation factor being 0.995. The commonly measured room-temperature and zero-pressure value is ro= 3.0 ms [ 7 1, which is in agreement with our P=O value (3.04 ms), showing the absence of both temperature rise by laser illumination and self-absorption of fluorescence [ 8 1. Preliminary measurements for the RI1 lines gave a similar behaviour. 326
z -= b
(n;+Z)nd(fiv,)3M; (n2+2)n(hv)3W
’
(2)
(3)
where ro, no, vo,MOare atmospheric-pressure values. For the ruby RI line and P= 100 kbar the ratio ( ft v,/ Rv)3= 1.016 [ 1 ] which cannot explain the rise of T by a factor ~2. As for the ratio ($,+2)&J (n2+2)n, a decrease of n to 0.7no at 100 kbar is needed to obtain the measured rise in z, and this is improbable. So, a decrease of M with increasing pressure is expected. Taking into account that R lines are genuine nophonon lines, it seems that the model used in ref. [ 3 ] is not applicable to this case. We suppose that the
Volume 155, number 3
CHEMICAL PHYSICS LETTERS
observed rise in 7 could be connected with the increase of the crystal field strength with increasing pressure. Using the conception of the expansion of the electron radial wavefunction of Cr3+ under compression, Ma et al. [lo] were able to calculate the pressure-induced shifts of ruby spectra and the change of ligand field strength (Dq) as a function of the linear compression ratio K= R/Ro, where R and R. are interionic ( W+-02) distances at high and zerc pressure, respectively. On the other hand, there is experimental evidence indicating that the l.igand field strength greatly influences the lifetime of Cr3+ R lines in different host materials, as shown in table 1. In the last two materials in table 1 non-radiative quenching processes also can play an important role. Ruby Dq data given in ref. [ lo] can be approximated by a fourth-order equation, Dq= 1810t l.l0254P-
3 March 1989
Table 2 Measured and calculated lifetimes and A(&) different pressures Pressure (kbar)
0 14.0 19.0 25.5 29.6 35.5 54.5 73.0 87.1 92.7 98.6 106.0 118.0
A(&) (cm-‘)
0 15 20 27 31 37 54 71 82 86 91 96 105
Measured lifetime (ms) 3.04 3.4s 3.70 3.90 3.94 4.18 4.84 5.33 5.62 5.87 6.01 6.37 6.86
values of ruby at
Calculated lifetime (ms) eq. ( 1)
eq. (5)
3.04 3.48 3.63 3.84 3.96 4.15 4.74 5.32 5.76 5.93 6.12 6.35 6.72
3.04 3.53
3.10 3.93 4.06 4.26 4.82 5.38 5.75 5.88 6.04 6.21 6.5 1
1.95154x 10-3P2
+1.31686x10-6P3+4.87713x10-‘oP4
4. Conclusion
(forP=O-500 kbar) ,
(4)
but at low P values the change of Dq with increasing pressure is nearly linear. So, for the pressure range used in this experiment we assume the following relation between A(Dq) =Dq-Dqo and E T (ms) =3.04+0.033A(Dq)
(cm-‘) ,
(5)
Table 2 shows a comparison between the measured lifetime values and those calculated from eqs. ( 1) iind (5) ; A(Dq) for given pressures was calculated using eq. (4). The mean deviation of the calculated lifetime values from the measured ones is about 1,5%, which is within the experimental uncertainty, but for higher pressures an important deviation from eq. ( 1) is expected and perhaps from eq. (5), too.
For the pressure range O-l 18 kbar a linear increase of ruby fluorescence lifetime with increasing pressure has been found. It seems that this increase is connected with the pressure dependence of the crystal field strength, but additional measurements at higher pressures ( 2 500 kbar) and in different host materials with different C?+ concentrations are needed to establish this correlation. The results obtained are interesting from the point of view of possible high-pressure solid-state lasers. It is also possible to use relation ( 1), up to x 100 kbar, for high-pressure measurements in diamond anvil cells, instead of the wavelength shift method, with greater sensitivity (about 100% of the change in Tat 100 kbar) and, in principle, higher accuracy of time measurement as compared with wavelength measurement.
Table 1 Ligand iield strength Dg and emission lifetime r of Cr3+ (*E) in various materials at normal pressure
Acknowledgement Material
Dq (cm-‘)
r(p)
ruby alexandrite glass ceramics glasses
1810 1740 a 1600-1700 * 1450-1580
3000 [7] 260 [II] >200 [ 121 17 [13]
The authors are grateful to Professor D. Curie, from the University Paris VI, for high interest in this work and to Mr. B. PetroviC for precious technical assistance.
327
Volume 155, number 3
CHEMICAL PHYSICS LE-l-l-ERS
References [l] G.P. Piermarini, S. Block, J.D. Barnett and R.A. Forman, J. Appl. Phys. 46 ( 1975) 2774. [2] G. Webster andH.G. Drickamer, J. Chem. Phys. 72 (1980) 3740. [3] D.I. Klick, K-W. Bieg and H.G. Drickamer, Pbys. Rev. B 16 (1974) 4599. [4] R. Kubo and Y. Toyozawa, Progr. Theoret. Phys. 13 (1955) 160. [S]L.D. Merkle, I.L. Spain and R.C. Powell, J. Phys. C 14 (1981) 2027. [6] G.J. Pie& and S. Block, Rev. Sci. Instr. 46 (1975) 973.
328
3 March 1989
/7] V. Evtuhov and J.K. Neeland, in: Lasers - a series of advances, ed. AK Levine (Dekker, New York, 1966) p. 15. [S ] D.F. Nelson and M.D. &urge, Phys. Rev. 137 (1965) A1117. [9] W.B. Fowler, in: Physics of color centers, ed. W.B. Fowler (Academic Press, New York, 1968) ch. 2. [ 1OlD.P. Ma, J.R. Chen and Z.Q. Wang, Phys. Letters A 126 (1988) 377. [ 111B.A. Lengyel, Lasers ( Wiley-Interscience, New York, 197I). [ 12 ] N. Karayamis. D.E. Wortman and H.P. Jenssen, 1. Phys. Chem. Solids 37 (1976) 675. [ 131 A. Yariv, Introduction to optical electronics (Halt, Reinhart and Winston, New York, 1971).