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Infrared scintillation of Yb(10%):YAG crystal
Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
Infrared scintillation of Yb(10%):YAG crystal P. Antoninia, S. Belogurovb,c,*, G. Bressid, G. Carugnob, D. Iannuzzid,e Dipartimento di Fisica, Universita" di Padova, Via Marzolo 8, 35131 Padova, Italy b INFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy c Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya 25, 117259 Moscow, Russia d INFN, Sezione di Pavia, Via Bassi 6, 27100 Pavia, Italy e Dipartimento di Fisica Nucleare e Teorica, Universita" di Pavia, Via U. Bassi 6, 27100 Pavia, Italy a
Received 16 July 2001; received in revised form 1 October 2001; accepted 1 November 2001
Abstract Ytterbium-doped yttrium aluminum garnets (Yb:YAG) are known as IR laser crystals. Previously, we have shown that they are also fast scintillators in the near UV region. In this work we report on the measurements of IR scintillation properties of Yb(10%):YAG crystal. It emits at room temperature at 1:03 mm with a light yield of ð7978Þ 103 photons=MeV and a decay time of 1:9 ms when excited by 90 keV electrons. With decreasing temperature both light yield and decay time decrease. r 2001 Elsevier Science B.V. All rights reserved. PACS: 07.57.c; 07.77.ka; 29.40.Mc; 78.60.Hk Keywords: Infrared scintillation; Temperature dependence
1. Introduction Recently, we have reported on the measurements of Yb:YAG crystal scintillation properties [1,2]. We observed that *
* *
The spectrum shows a broad line centered about 335 nm: The scintillation time is less than about 20 ns: The light yield at –1501C for a particles is ð872Þ 103 photons=MeV:
The present work extends our study to the IR region. Detectors based on infrared (IR) scintilla*Corresponding author. INFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy. E-mail address: [email protected] (S. Belogurov).
tion could be a promising resource for particle detection and medical imaging [3,4]. Since Yb:YAG crystals are used as laser crystals, emitting at 1:0296 mm [5], we decided to measure the infrared scintillation properties of one of such crystals.
2. Experimental setup A simplified schematics of the experimental setup for the measurements of IR scintillation properties of the crystal is shown in Fig. 1. We excited a sample with a beam from the electron gun described elsewhere [6], used in pulse mode. For measurements of temperature dependencies, the sample was placed inside a dewar and
0168-9002/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 2 1 6 4 - 7
800
P. Antonini et al. / Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
B
e beam
R
C S
F
Fig. 1. Experimental setup for the measurement of IR scintillation properties of Yb:YAG crystal: BFfocalizing magnet; CFcopper cold finger filled with liquid nitrogen; SFsample under investigation; FFfilter; R–optical readout unit.
Yb (10%):YAG IR spectrum 0.4
Intensity (a. u.)
cooled down by means of a copper cold finger filled with liquid nitrogen. The temperature was controlled by a platinum thermoresistor attached to the crystal. Measurements at room temperature were performed without the dewar. To discriminate visible and UV scintillation light when necessary the filter Oriel 57539 was used. Transmittance of the filter is 9575% at 1:03 mm: This filter is not transparent to wavelengths below 700 nm: Three different configurations were used for optical readout. For spectral measurements we used a Bruker Equinox 55 spectrophotometer, equipped with an InGaAs photodiode, which is sensitive from 0.7 to 1:8 mm; and whose quantum efficiency is above 80% from 0.95 to 1:55 mm: For measurements of decay time a PMT (Hamamatsu R632-01) also sensitive in the IR range was used. Its quantum efficiency at 1:03 mm is 0.1%. The PMT fed a digital oscilloscope coupled to 50 O: Measurements of light yield were done by means of a silicon photodiode (Hamamatsu S13371010BQ), sensitive in the range 300–1100 nm: The photodiode was inversely biased to 30 V; through a resistor of 10 MO and readout by digital oscilloscope coupled to 1 MO through a capacitor of 9:4 nF: The sample was an Yb(10%):YAG crystal provided by FEE GMBH, disk shaped with 9 mm diameter, 2 mm thick, not well polished. For relative measurement a reference CsI(Tl) crystal of the same size and level of treatment was used.
0.3
0.2
0.1
0 0.9
0.95
1
1.05 1.1 Wave length (m)
1.15
1.2
Fig. 2. IR spectrum of Yb(10%):YAG crystal excited by 90 keV electrons, at room temperature.
3. Measurements of IR scintillation properties of Yb:YAG crystals 3.1. Emission spectrum The emission spectrum is expected to be peaked at 1:030 mm; because this is the laser emission line. The interferogram measured by the spectrophotometer at room temperature was analyzed with Fourier Transform software (OPUS 3.0.3). The spectrum, peak at 1:03 mm; is presented in Fig. 2. 3.2. Pulse shape and scintillation time The measurements were done by means of the PMT. IR emission was selected by the optical
P. Antonini et al. / Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
801
Fig. 3. IR signal of Yb:YAG crystal excited by 90 keV electrons, at room temperature. (Time scaleF2 ms/division.)
filter. Average signal at room temperature is shown in Fig. 3. The signal has exponential behavior. The decay time is t ¼ 1:970:1 ms: The same measurement was performed at the temperature of 1591C: The result is shown in Fig. 4. The plot was fitted with a double exponential. It shows a fast component of t1 ¼ 0:270:1 ms and a slow component of t2 ¼ 1:070:1 ms: The second one could be compared to the lifetime of the excited level in Yb:YAG laser system at 77 K : 1:0 ms [5]. Relative intensities of fast and slow components are 0.43 and 0.57, respectively. 3.3. Light yield and its dependence on temperature The light yield for electron excitation was measured at room temperature. The light yield was calculated comparing the integral of the Yb(10%):YAG signal (filtered as described in Section 3.2) with the integral of the signal from a CsI(Tl) crystal, whose absolute light yield is known [7] as LYCsI:Tl ¼ ð64:873:2Þ 103 photons=MeV: The signals from the two crystals were detected with a photodiode. The quantum efficiency of the photodiode at the wavelength of maximum emission of CsI:Tl (540 nm) is QECsI:Tl ¼ 6673%; and at the wavelength of maximum emission of Yb:YAG (1030 nm) is QEYb:YAG ¼ 43:573%: The photodiode is blind
to Cs(Tl) IR emission, peaked at 1:6 mm: For the ratio of integrals of the signals from CsI(Tl) and Yb:YAG we found QCsI:Tl ¼ 1:3170:02: QYb:YAG So, for the IR line of the Yb(10%):YAG we find QYb:YAG 1 QECsI:Tl LYIR ¼ LYCsI:Tl QCsI:Tl Tr QEYb:YAG ¼ ð7978Þ 103 photons=MeV: In the equation above Tr means transmittance of the filter. Solid angles seen by the photodiode are equal in both cases as the refractive indices of the crystals are equal. The light yield was measured also at different temperatures. The result is shown in Fig. 5. At 1301C the light yield is about one-half of the room-temperature signal.
4. Conclusions We have measured IR scintillation properties of an Yb(10%):YAG crystal excited by 90 keV electrons. We get at room temperature a light yield of ð7978Þ 103 photons=MeV; decay time of 1:9 ms; and wavelength of maximum emission of 1:03 mm: With decreasing temperature both
P. Antonini et al. / Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
802
Fig. 4. IR signal of Yb:YAG crystal excited by 90 keV electrons, at 1591C: (Time scaleF2 ms/division.)
Light Yield (a. u.)
1.2
energy resolution, notwithstanding its long decay time. We suggest that X-ray imaging and CT scan techniques should be possible with these crystals.
Light Yield vs Temperature
1 0.8 0.6 0.4
References
0.2 0 -140 -120 -100 -80 -60 -40 Temperature (oC)
-20
0
Fig. 5. Dependence on temperature of the IR signal of Yb:YAG crystal excited by 90 keV electrons.
light yield and decay time decrease. IR scintillation of Yb:YAG crystals is interesting because of the very high light yield, which should allow good
[1] G. Bressi, et al., Nucl. Instr. and Meth. A 461 (2001) 361. [2] P. Antonini, et al., Nucl. Instr. and Meth. A 460 (2001) 469. [3] S. Belogurov, et al., Nucl. Instr. and Meth. A 452 (2000) 381. [4] S. Belogurov, et al., IEEE Trans. Nucl. Sci. NS-47 (2000) 1791. [5] A.R. Reinberg, et al., Appl. Phys. Lett. 19 (1971) 11. [6] S. Belogurov, et al., Nucl. Instr. and Meth. A 449 (2000) 254. [7] J.D. Valentine, et al., IEEE Trans. Nucl. Sci. NS-40 (1993) 1267.
Infrared scintillation of Yb(10%):YAG crystal P. Antoninia, S. Belogurovb,c,*, G. Bressid, G. Carugnob, D. Iannuzzid,e Dipartimento di Fisica, Universita" di Padova, Via Marzolo 8, 35131 Padova, Italy b INFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy c Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya 25, 117259 Moscow, Russia d INFN, Sezione di Pavia, Via Bassi 6, 27100 Pavia, Italy e Dipartimento di Fisica Nucleare e Teorica, Universita" di Pavia, Via U. Bassi 6, 27100 Pavia, Italy a
Received 16 July 2001; received in revised form 1 October 2001; accepted 1 November 2001
Abstract Ytterbium-doped yttrium aluminum garnets (Yb:YAG) are known as IR laser crystals. Previously, we have shown that they are also fast scintillators in the near UV region. In this work we report on the measurements of IR scintillation properties of Yb(10%):YAG crystal. It emits at room temperature at 1:03 mm with a light yield of ð7978Þ 103 photons=MeV and a decay time of 1:9 ms when excited by 90 keV electrons. With decreasing temperature both light yield and decay time decrease. r 2001 Elsevier Science B.V. All rights reserved. PACS: 07.57.c; 07.77.ka; 29.40.Mc; 78.60.Hk Keywords: Infrared scintillation; Temperature dependence
1. Introduction Recently, we have reported on the measurements of Yb:YAG crystal scintillation properties [1,2]. We observed that *
* *
The spectrum shows a broad line centered about 335 nm: The scintillation time is less than about 20 ns: The light yield at –1501C for a particles is ð872Þ 103 photons=MeV:
The present work extends our study to the IR region. Detectors based on infrared (IR) scintilla*Corresponding author. INFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy. E-mail address: [email protected] (S. Belogurov).
tion could be a promising resource for particle detection and medical imaging [3,4]. Since Yb:YAG crystals are used as laser crystals, emitting at 1:0296 mm [5], we decided to measure the infrared scintillation properties of one of such crystals.
2. Experimental setup A simplified schematics of the experimental setup for the measurements of IR scintillation properties of the crystal is shown in Fig. 1. We excited a sample with a beam from the electron gun described elsewhere [6], used in pulse mode. For measurements of temperature dependencies, the sample was placed inside a dewar and
0168-9002/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 2 1 6 4 - 7
800
P. Antonini et al. / Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
B
e beam
R
C S
F
Fig. 1. Experimental setup for the measurement of IR scintillation properties of Yb:YAG crystal: BFfocalizing magnet; CFcopper cold finger filled with liquid nitrogen; SFsample under investigation; FFfilter; R–optical readout unit.
Yb (10%):YAG IR spectrum 0.4
Intensity (a. u.)
cooled down by means of a copper cold finger filled with liquid nitrogen. The temperature was controlled by a platinum thermoresistor attached to the crystal. Measurements at room temperature were performed without the dewar. To discriminate visible and UV scintillation light when necessary the filter Oriel 57539 was used. Transmittance of the filter is 9575% at 1:03 mm: This filter is not transparent to wavelengths below 700 nm: Three different configurations were used for optical readout. For spectral measurements we used a Bruker Equinox 55 spectrophotometer, equipped with an InGaAs photodiode, which is sensitive from 0.7 to 1:8 mm; and whose quantum efficiency is above 80% from 0.95 to 1:55 mm: For measurements of decay time a PMT (Hamamatsu R632-01) also sensitive in the IR range was used. Its quantum efficiency at 1:03 mm is 0.1%. The PMT fed a digital oscilloscope coupled to 50 O: Measurements of light yield were done by means of a silicon photodiode (Hamamatsu S13371010BQ), sensitive in the range 300–1100 nm: The photodiode was inversely biased to 30 V; through a resistor of 10 MO and readout by digital oscilloscope coupled to 1 MO through a capacitor of 9:4 nF: The sample was an Yb(10%):YAG crystal provided by FEE GMBH, disk shaped with 9 mm diameter, 2 mm thick, not well polished. For relative measurement a reference CsI(Tl) crystal of the same size and level of treatment was used.
0.3
0.2
0.1
0 0.9
0.95
1
1.05 1.1 Wave length (m)
1.15
1.2
Fig. 2. IR spectrum of Yb(10%):YAG crystal excited by 90 keV electrons, at room temperature.
3. Measurements of IR scintillation properties of Yb:YAG crystals 3.1. Emission spectrum The emission spectrum is expected to be peaked at 1:030 mm; because this is the laser emission line. The interferogram measured by the spectrophotometer at room temperature was analyzed with Fourier Transform software (OPUS 3.0.3). The spectrum, peak at 1:03 mm; is presented in Fig. 2. 3.2. Pulse shape and scintillation time The measurements were done by means of the PMT. IR emission was selected by the optical
P. Antonini et al. / Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
801
Fig. 3. IR signal of Yb:YAG crystal excited by 90 keV electrons, at room temperature. (Time scaleF2 ms/division.)
filter. Average signal at room temperature is shown in Fig. 3. The signal has exponential behavior. The decay time is t ¼ 1:970:1 ms: The same measurement was performed at the temperature of 1591C: The result is shown in Fig. 4. The plot was fitted with a double exponential. It shows a fast component of t1 ¼ 0:270:1 ms and a slow component of t2 ¼ 1:070:1 ms: The second one could be compared to the lifetime of the excited level in Yb:YAG laser system at 77 K : 1:0 ms [5]. Relative intensities of fast and slow components are 0.43 and 0.57, respectively. 3.3. Light yield and its dependence on temperature The light yield for electron excitation was measured at room temperature. The light yield was calculated comparing the integral of the Yb(10%):YAG signal (filtered as described in Section 3.2) with the integral of the signal from a CsI(Tl) crystal, whose absolute light yield is known [7] as LYCsI:Tl ¼ ð64:873:2Þ 103 photons=MeV: The signals from the two crystals were detected with a photodiode. The quantum efficiency of the photodiode at the wavelength of maximum emission of CsI:Tl (540 nm) is QECsI:Tl ¼ 6673%; and at the wavelength of maximum emission of Yb:YAG (1030 nm) is QEYb:YAG ¼ 43:573%: The photodiode is blind
to Cs(Tl) IR emission, peaked at 1:6 mm: For the ratio of integrals of the signals from CsI(Tl) and Yb:YAG we found QCsI:Tl ¼ 1:3170:02: QYb:YAG So, for the IR line of the Yb(10%):YAG we find QYb:YAG 1 QECsI:Tl LYIR ¼ LYCsI:Tl QCsI:Tl Tr QEYb:YAG ¼ ð7978Þ 103 photons=MeV: In the equation above Tr means transmittance of the filter. Solid angles seen by the photodiode are equal in both cases as the refractive indices of the crystals are equal. The light yield was measured also at different temperatures. The result is shown in Fig. 5. At 1301C the light yield is about one-half of the room-temperature signal.
4. Conclusions We have measured IR scintillation properties of an Yb(10%):YAG crystal excited by 90 keV electrons. We get at room temperature a light yield of ð7978Þ 103 photons=MeV; decay time of 1:9 ms; and wavelength of maximum emission of 1:03 mm: With decreasing temperature both
P. Antonini et al. / Nuclear Instruments and Methods in Physics Research A 486 (2002) 799–802
802
Fig. 4. IR signal of Yb:YAG crystal excited by 90 keV electrons, at 1591C: (Time scaleF2 ms/division.)
Light Yield (a. u.)
1.2
energy resolution, notwithstanding its long decay time. We suggest that X-ray imaging and CT scan techniques should be possible with these crystals.
Light Yield vs Temperature
1 0.8 0.6 0.4
References
0.2 0 -140 -120 -100 -80 -60 -40 Temperature (oC)
-20
0
Fig. 5. Dependence on temperature of the IR signal of Yb:YAG crystal excited by 90 keV electrons.
light yield and decay time decrease. IR scintillation of Yb:YAG crystals is interesting because of the very high light yield, which should allow good
[1] G. Bressi, et al., Nucl. Instr. and Meth. A 461 (2001) 361. [2] P. Antonini, et al., Nucl. Instr. and Meth. A 460 (2001) 469. [3] S. Belogurov, et al., Nucl. Instr. and Meth. A 452 (2000) 381. [4] S. Belogurov, et al., IEEE Trans. Nucl. Sci. NS-47 (2000) 1791. [5] A.R. Reinberg, et al., Appl. Phys. Lett. 19 (1971) 11. [6] S. Belogurov, et al., Nucl. Instr. and Meth. A 449 (2000) 254. [7] J.D. Valentine, et al., IEEE Trans. Nucl. Sci. NS-40 (1993) 1267.