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Room temperature persistent spectral hole burning of Sm2+ in fluorohafnate glasses
LUMINESCENCE
Journal of Luminescence 55 (1993) 217—219
JOURNALOF
Room temperature persistent spectral hole burning of Sm2 + in fluorohafnate glasses K. Hirao, S. Todoroki and N. Soga Department of Industrial Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606-01, Japan Received 23 December 1992 Revised 12 March 1993 Accepted 18 March 1993
Persistent spectral hole burning of Sm2 + in a glass system at room temperature was observed. The hole was burned at 680.3 nm with 230 mW laser light and was observed via the excitation spectrum. In this system a photochemical process is likely to be dominant because of the absence ofan anti-hole adjacent to the hole.
1. Introduction There has been considerable activity on persistent spectral hole burning (HB), because of its importance for the application to frequency domain optical storage as an ultra-high density memory device [1]. Sm2 -doped halide crystals are of interest because they show photon-gated photochemical HB [2—6]. Recently, room temperature HB has been observed for this system [7,8]. There is, however, no report of HB in an inorganic glass system above liquid helium temperature although a glass system is expected to be advantageous because of its much larger inhomogeneous line width due to a broad distribution of sites of Sm2 unlike a crystal system, and the easier preparation of large sample. In the present letter, we report the success2 -doped fluorohafful observation of HB in Sm nate glasses at room temperature. +
~,
+
were mixed thoroughly and melted in a glassy carbon crucible and in strongly reducing atmosphere in order to reduce Sm3~to Sm2~.Transparent brown colored glass was obtained whose dimension was 30 mm in diameter and 4 mm in thickness. This coloring is due to the strongly absorbing f d(4f6’~F~ —. 4f55d) transition of Sm2 ~ which is shown in fig. 1. The fluorescence spectrum of the sample, however, showed that some Sm3~ remained (see also fig. 1). The measurement of the HB effect was carried out as follows. The sample was mounted between the two rotating blades of a chopper (5 kHz) and irradiated with a tunable dye laser (DCM dye, 1.33 cm’ in line width) pumped by an Ar laser. The dye laser wavelength was tuned so as to resonate with the 5D ‘~F~ line. The excitation spectra for the 5D0 7F 0 2 fluorescence around 718.3 nm were measured before and after the irradiation with the laser beam for 900 s. —~
+
*—
—~
2. Experimental The glass was prepared using HfF4. A1F3. LaF3. BaF2, NaF and SmF3 as starting matenals, which
3. Results and discussion
Correspondence to: Dr. K. Hirao, Department of Industrial Chemistry, Faculty of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-01, Japan.
Fig. 2 shows the excitation spectra obtained at room temperature, where the intensity of the burning light and probing light were 230 and
0022-2313/93/S06.00
©
1993
—
Elsevier Science Publishers B.V. All rights reserved
218
K. Hirao et al.
HBLAN:Sm
/ Room
2 ~ in fluorohafnate glasses
temperature persistent spectral hole burning of Sm
678 00K
‘~
EX: 400nm
~
C (0
cti
Wavelength (nm) 680 682 Sm2~ 684
_
C ‘-
0
‘‘—I +
E
Sm2~
(0 C
I
400 600 Wavelength I nm
200
C 0
800
Fig. 1. (a) Absorption spectrum and (b) fluorescence spectrum of thesample at room temperature. The exciting wavelength for (b) is 400 nm.
—40
0
40
I
I
14720 14660 14600 Wave number (cm 1)
Fig. 3. Excitation spectra and hole profiles for three other experiments using different burning laser frequencies whose positions are designated by the arrows. The experimental conditions are the same as those in fig. 2
Frequency (cm1) —
14780
~
lID) I IC .~ii~
-40
Frequency (cm
9
—20
El Ic ~I 10 .oI
1)
20
5D
CjS~2+7~
0
0 (0
LU
C
14750
14700
14650
14600
Wave number (cm-’)
U) U)
Fig.2~-doped 2. Bottom: excitation at room temperature the of fluoride glassspectra obtained by monitoring ‘D 7F~emission before and after irradiation with a DCM Sm dye0 laser. — Burning time was 900 s. Persistent hole burning was observed. Top: the difference signal magnified by a factor of 2. The solid line represents a fitted single Lorentzian curve. Inset: energy level diagram of Sm2 ~.
2.3 mW, respectively. The hole width is about 25 cm’ whereas the line width of the 5D 7F 1. The position0 of the0 transition about according 50 cm to the laser frequency burnt hole is changed -+
LU
14750
14700
14650
14600
Wave number (cm1) Fig. 4. Excitation spectra and hole profiles at 80 K. The experimental conditions are the same as those in fig. 2
as shown in fig. 3. Even 1 h after the burning, the hole was clearly observed. The athole measurement was also carried out 80 K burning (see fig. 4, where the hole width is about 5 cm 1). -
K. Hirao et al. I
I
I
/
I
2 ~ in fluorohafnate glasses
Room temperature persistent spectral hole burning of Sm I
I
I
system. Thus, the burning efficiency may be enhanced by using a gating light of shorter wavelength as found in Sm2 ~-doped halide crystal systems [3 8].
I
300K
0
-
-
‘.0
~0
219
inhomogeneous Since the hole linewidth, width is very thislarge material compared can hardly with be applied to high density memory device. Instead,
10
=
it can be applied to photorefractive devices used for holography. Moreover, it is advantageous because an AlGaInP laser diode having the wavelength of
• 2C— o I
I
I
I
300
I
I
I
I
600
900
Burning time (sec)
Fig. 5. The burning time dependence of the persistent hole depth obtained by monitoring the 5D 7F 0 —~ 2 emission in the presence of burning irradiation of a DCM dye laser.
—~680 nm is available as the burning light source. Further studies are necessary to clarify the actual HB mechanism and to control both the hole width and the inhomogeneous line width by changing the
composition of host glass matrix. 4. Conclusion
No “anti-hole”, or increased was observed around the burnt holeemission as shownpeak, in fig. 2. An anti-hole would indicate a photo-induced redistribution of Sm2* ions within the inhomogeneous line width. Therefore, it is suggested that the dominant burning mechanism in this system is not photo-physical such as
2~ in a glass matrixspectral at roomhole temperature observed Persistent burning was of Sm for the first time to our knowledge. In this system, a photochemical process is likely to be dominant because of the absence of an anti-hole adjacent to the hole. For practical applications, hole burning in glass systems is superior to hole burning in other
Sm~~
materials such as organic or crystal, because of their high chemical and thermal stability and ease of preparation.
hw
~
(1)
where the light energy of hw is resonant with Sm~ but not with Sm~4.In other words, the photochemical HB is likely to be dominant, where this photo-ionization reaction is described as Sm2~+ (trap)
Sm3~+ (trap)
.
(2)
The dominant electron trap in the present material can be Hf4~or Sm3~.Or, if F~molecular ions and F°defects are present in the present strongly reduced glass, these are likely to be the dominant traps. These defects are reported to be stable at 180 K in X-irradiated fluoride glasses [9]. Fig. 5 shows the burning time dependence of the hole-depth. A 5% hole depth was attained in the first 140 s. Note that the burning light is one color. The ionization via excited-state absorption of a second resonant photon is expected to occur in this
References [1] W.E. Moerner (ed), Persistent Spectral Hole-Burning: Science and Applications (Springer-Verlag, Berlin, 1988) pp.
1—15.
[2] R.M. Macfarlane and R.M. Shelby, in: Persistent Spectral Hole-Burning: Science and Applications, ed. W.E. Moerner (Springer-Vedag, Berlin, 1988) pp. 127 151.
[3] A. Winnacker, R.M. Shelby and R.M. Macfarlane, Opt. Lett. 10 (1985) 350. [4] C. Wei, S. Huang and J. Yu, J. Lumin. 43 (1989) 161. [5] A. Oppenländer, F. Madeore, J.-C. Vial and i-P. Chaminade, J. Lumin. 50 (1991) 1. [6] C. Wei, K. Holliday, A.J. Meixner, M. Croci and UP. Wild, J. Lumin. 50 (1991) 89. [7] R. Jaaniso and H. Bill, Europhys. Lett. 16 (1991) 569. [8] K. Holliday, C. Wei, M. Croci and UP. Wild, J. Lumin. 53
(1992) 227.
[9] R. Cases, D.L. Griscom and D.C. Tran, J. Non-Cryst. Sol. 72 (1985) 51.
Journal of Luminescence 55 (1993) 217—219
JOURNALOF
Room temperature persistent spectral hole burning of Sm2 + in fluorohafnate glasses K. Hirao, S. Todoroki and N. Soga Department of Industrial Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606-01, Japan Received 23 December 1992 Revised 12 March 1993 Accepted 18 March 1993
Persistent spectral hole burning of Sm2 + in a glass system at room temperature was observed. The hole was burned at 680.3 nm with 230 mW laser light and was observed via the excitation spectrum. In this system a photochemical process is likely to be dominant because of the absence ofan anti-hole adjacent to the hole.
1. Introduction There has been considerable activity on persistent spectral hole burning (HB), because of its importance for the application to frequency domain optical storage as an ultra-high density memory device [1]. Sm2 -doped halide crystals are of interest because they show photon-gated photochemical HB [2—6]. Recently, room temperature HB has been observed for this system [7,8]. There is, however, no report of HB in an inorganic glass system above liquid helium temperature although a glass system is expected to be advantageous because of its much larger inhomogeneous line width due to a broad distribution of sites of Sm2 unlike a crystal system, and the easier preparation of large sample. In the present letter, we report the success2 -doped fluorohafful observation of HB in Sm nate glasses at room temperature. +
~,
+
were mixed thoroughly and melted in a glassy carbon crucible and in strongly reducing atmosphere in order to reduce Sm3~to Sm2~.Transparent brown colored glass was obtained whose dimension was 30 mm in diameter and 4 mm in thickness. This coloring is due to the strongly absorbing f d(4f6’~F~ —. 4f55d) transition of Sm2 ~ which is shown in fig. 1. The fluorescence spectrum of the sample, however, showed that some Sm3~ remained (see also fig. 1). The measurement of the HB effect was carried out as follows. The sample was mounted between the two rotating blades of a chopper (5 kHz) and irradiated with a tunable dye laser (DCM dye, 1.33 cm’ in line width) pumped by an Ar laser. The dye laser wavelength was tuned so as to resonate with the 5D ‘~F~ line. The excitation spectra for the 5D0 7F 0 2 fluorescence around 718.3 nm were measured before and after the irradiation with the laser beam for 900 s. —~
+
*—
—~
2. Experimental The glass was prepared using HfF4. A1F3. LaF3. BaF2, NaF and SmF3 as starting matenals, which
3. Results and discussion
Correspondence to: Dr. K. Hirao, Department of Industrial Chemistry, Faculty of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-01, Japan.
Fig. 2 shows the excitation spectra obtained at room temperature, where the intensity of the burning light and probing light were 230 and
0022-2313/93/S06.00
©
1993
—
Elsevier Science Publishers B.V. All rights reserved
218
K. Hirao et al.
HBLAN:Sm
/ Room
2 ~ in fluorohafnate glasses
temperature persistent spectral hole burning of Sm
678 00K
‘~
EX: 400nm
~
C (0
cti
Wavelength (nm) 680 682 Sm2~ 684
_
C ‘-
0
‘‘—I +
E
Sm2~
(0 C
I
400 600 Wavelength I nm
200
C 0
800
Fig. 1. (a) Absorption spectrum and (b) fluorescence spectrum of thesample at room temperature. The exciting wavelength for (b) is 400 nm.
—40
0
40
I
I
14720 14660 14600 Wave number (cm 1)
Fig. 3. Excitation spectra and hole profiles for three other experiments using different burning laser frequencies whose positions are designated by the arrows. The experimental conditions are the same as those in fig. 2
Frequency (cm1) —
14780
~
lID) I IC .~ii~
-40
Frequency (cm
9
—20
El Ic ~I 10 .oI
1)
20
5D
CjS~2+7~
0
0 (0
LU
C
14750
14700
14650
14600
Wave number (cm-’)
U) U)
Fig.2~-doped 2. Bottom: excitation at room temperature the of fluoride glassspectra obtained by monitoring ‘D 7F~emission before and after irradiation with a DCM Sm dye0 laser. — Burning time was 900 s. Persistent hole burning was observed. Top: the difference signal magnified by a factor of 2. The solid line represents a fitted single Lorentzian curve. Inset: energy level diagram of Sm2 ~.
2.3 mW, respectively. The hole width is about 25 cm’ whereas the line width of the 5D 7F 1. The position0 of the0 transition about according 50 cm to the laser frequency burnt hole is changed -+
LU
14750
14700
14650
14600
Wave number (cm1) Fig. 4. Excitation spectra and hole profiles at 80 K. The experimental conditions are the same as those in fig. 2
as shown in fig. 3. Even 1 h after the burning, the hole was clearly observed. The athole measurement was also carried out 80 K burning (see fig. 4, where the hole width is about 5 cm 1). -
K. Hirao et al. I
I
I
/
I
2 ~ in fluorohafnate glasses
Room temperature persistent spectral hole burning of Sm I
I
I
system. Thus, the burning efficiency may be enhanced by using a gating light of shorter wavelength as found in Sm2 ~-doped halide crystal systems [3 8].
I
300K
0
-
-
‘.0
~0
219
inhomogeneous Since the hole linewidth, width is very thislarge material compared can hardly with be applied to high density memory device. Instead,
10
=
it can be applied to photorefractive devices used for holography. Moreover, it is advantageous because an AlGaInP laser diode having the wavelength of
• 2C— o I
I
I
I
300
I
I
I
I
600
900
Burning time (sec)
Fig. 5. The burning time dependence of the persistent hole depth obtained by monitoring the 5D 7F 0 —~ 2 emission in the presence of burning irradiation of a DCM dye laser.
—~680 nm is available as the burning light source. Further studies are necessary to clarify the actual HB mechanism and to control both the hole width and the inhomogeneous line width by changing the
composition of host glass matrix. 4. Conclusion
No “anti-hole”, or increased was observed around the burnt holeemission as shownpeak, in fig. 2. An anti-hole would indicate a photo-induced redistribution of Sm2* ions within the inhomogeneous line width. Therefore, it is suggested that the dominant burning mechanism in this system is not photo-physical such as
2~ in a glass matrixspectral at roomhole temperature observed Persistent burning was of Sm for the first time to our knowledge. In this system, a photochemical process is likely to be dominant because of the absence of an anti-hole adjacent to the hole. For practical applications, hole burning in glass systems is superior to hole burning in other
Sm~~
materials such as organic or crystal, because of their high chemical and thermal stability and ease of preparation.
hw
~
(1)
where the light energy of hw is resonant with Sm~ but not with Sm~4.In other words, the photochemical HB is likely to be dominant, where this photo-ionization reaction is described as Sm2~+ (trap)
Sm3~+ (trap)
.
(2)
The dominant electron trap in the present material can be Hf4~or Sm3~.Or, if F~molecular ions and F°defects are present in the present strongly reduced glass, these are likely to be the dominant traps. These defects are reported to be stable at 180 K in X-irradiated fluoride glasses [9]. Fig. 5 shows the burning time dependence of the hole-depth. A 5% hole depth was attained in the first 140 s. Note that the burning light is one color. The ionization via excited-state absorption of a second resonant photon is expected to occur in this
References [1] W.E. Moerner (ed), Persistent Spectral Hole-Burning: Science and Applications (Springer-Verlag, Berlin, 1988) pp.
1—15.
[2] R.M. Macfarlane and R.M. Shelby, in: Persistent Spectral Hole-Burning: Science and Applications, ed. W.E. Moerner (Springer-Vedag, Berlin, 1988) pp. 127 151.
[3] A. Winnacker, R.M. Shelby and R.M. Macfarlane, Opt. Lett. 10 (1985) 350. [4] C. Wei, S. Huang and J. Yu, J. Lumin. 43 (1989) 161. [5] A. Oppenländer, F. Madeore, J.-C. Vial and i-P. Chaminade, J. Lumin. 50 (1991) 1. [6] C. Wei, K. Holliday, A.J. Meixner, M. Croci and UP. Wild, J. Lumin. 50 (1991) 89. [7] R. Jaaniso and H. Bill, Europhys. Lett. 16 (1991) 569. [8] K. Holliday, C. Wei, M. Croci and UP. Wild, J. Lumin. 53
(1992) 227.
[9] R. Cases, D.L. Griscom and D.C. Tran, J. Non-Cryst. Sol. 72 (1985) 51.