- Email: [email protected]
Energy transfer between Pr3+ ions in a borate glass: (B2O3)0.7(CaF2)0.3
Journal of Luminescence 42 (1988) 221-225 North-Holland, Amsterdam
221
ENERGY TRANSFER BETWEEN Pr3~IONS IN A BORATE GLASS: (B203)07(CaF2)03 E.M. PACHECO and Cid B. DE ARAUJO Universidade Federal de Pernambuco, Departamento de Fisica, 50739 Recite, Brazil
Received 9 February 1988 Revised 11 July 1988 Accepted 12 July 19tt~ 3 + -. Pr3 + in a borate glass: (B We measured the energy transfer efficiency of Pr 3203 ± )ions. 0 7(CaF2 A very ) 0.3 large Our analysis energy transfer of the donor rate fluorescence —. iO~s ‘) is transients reportedisfor consistent diluted samples. with a dipole dipole interaction between Pr
1. Introduction Glasses containing rare earth (RE) impurities are of considerable interest for applications in optical technology [1,2]. Such glasses can have sharp electronic absorptions from the near infrared to the UV region and thus may be useful in various kinds of optical devices. These characteristics have attracted the interest of a number of investigators and the research of laser materials stimulate studies of energy transfer in these materials. Although the basic mechanics which govern the energy transfer process between RE ions in glasses have been studied by several authors [3,5] there are not much experimental results related to borate glasses. The research of new hosts for sensitized solid state lasers could benefit from these studies. In the present work3~ions the study in of a energy borate transfer glass is processes between Pr reported. This glass has been shown to be a good host material for basic studies of energy transfer [6].
2. Experimental methods
have been studied. They are prepared by melting the proper amount of reagent-grade compounds (B 203. CaF2. Pr6OH) in an electric furnace. Melting times of 90 nun and melting temperatures in the range of 1200 1300°C were required. The melted glass is cooled to 350°C and annealed for one hour. The obtained samples have a good optical quality and are non-hygroscopic. To investigate the process of energy transfer we performed measurements of the donor fluorescence decay following the resonant excitation of Pr~ions. The excitation source for fluorescence measurements was a 0.3 cm ‘ bandwidth dye laser pumped by the second harmonic of a Nd YAG laser. Emission spectra were obtained by monitoring the signal from a 1.4 m double spectrometer fitted with a 1P28 photomultiplier. A boxcar integrator enhance the measurements. signal-to-noise ratio andwas to used allowtotime-resolved The laser pulse duration (— 10 ns) was short enough so that during the pulse the distribution of excitation is unaffected by the acceptors. For the low temperature experiments the samples were cooled to 18 K in a closed circuit refrigerator. Optical absorption measurements were made with a double beam spectrophotometer. For all
Samples of borate glass (B 203)07(CaF2)03 conmeasurements spectralinewidths. resolution was much 3~ greater than thethe observed taming 0.05, 0.5, 1.0, 2.0, 3.0 and 5.0 wt% of Pr 0022-2313/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
222
E M. Pacheco, C.B. de Araujo
3. Results and discussion The absorption spectra of Pr3~for the studied samples show broad features of about 100 400 A bandwidth which can be easily identified with the corresponding Pr3~levels. For the transition ~H 4 1D 2, for example, the linewidth is 300 A. These large bandwidths result from the site-tosite variation of the crystal field strength. The fluorescence spectra due to the laser excita3H 1D tion of the 4 2 transition exhibit a linewidth which depends not much on the selected pumped region into the inhomogeneous absorption band. The obtained fluorescence linewidths when pumping with different wavelengths does not narrow much because 1D of the multiphonon relaxation between levels 2 and ‘G4 and due to accidental degeneracy which prevents a site-selective excitation [3]. We observed linewidth reduction by a factor 3 as compared with the inhomogeneous linewidth of 300 A. Similar spectra were obtained after focusing the laser beam into different regions of the samples indicating that their composition is homogeneous. This result is in agreement with X-ray diffraction measurements in our samples which show no evidence for crystalline phases. 1D The temporal behavior of the 2 H~emission have been 1D measured for all prepared samples. Firstly, the 2 H4 lifetime was determined at ‘~
—*
—~
—,
0 0.8
~
~
~
3~ 0.05% Pr LASER 5850 A
•~—s~
TIME Fig. 1. Time decay of 1 D
15
for various laser intensities provide essentially the same results. A computer fitting of the intensity decay gives a lifetime of 24 ~is. Multiphonon transitions is expected to be the important 1Gmechanism for relaxation from the ‘D2 to the 4 levels. A multiphonon decay rate of about iO~~s is expected in comparison with other studied borate glasses [3]. The other samples with 0.5 5 wt% of Pr~ present a fluorescence decay which will be discussed below. For all studied samples the temporal behavior of the fluorescence can be described by the expression 1(t)
exp~
P(t)~,
(1)
T0
where P(t) assumes different forms according to the sample concentration and time range. In fig. 1 the behavior of P(t) for all studied samples is shown. A theoretical framework which allows an interpretation of the obtained results has been developed by several authors [3 5]. Based on those models one expects, in the limit of low donor concentrations, P(t) to be given by P(t) = [CAJX(R) (2) where CA represents the acceptor concentration,
dRIt,
a U-
10
18 K for the sample with 0.05 wt% of Pr3t As shown in fig. 1 this sample exhibits an exponential time decay which is not influenced by the excitation wavelength. Measurements of the lifetime at 18 and 300 K
with a relative distance equal to R. Thus, at short times we expect from eqs. (1) and (2) an exponen•
5
ions in borate glass
X( R) is the energy transfer rate between two ions
04 0.2
0
+
181< 0.6
0
Pr
20
25
30
(~ssec)
3
2 —~ 3H4. The fluorescence line corresponds at 6020 to A the for the sample withof0.05 wt%exponential of Pr best fitting a pure curve with ~ — 23 jzs.
lifetime tial decay of the excited state with a characteristic For the sample with 0.5 wt% of Pr3~we observed a linear behavior of P(t) which indicates that the energy transfer occurs only to the nearest acceptors during the studied time range. Deviation of this linear behavior occur for 1> 30 ~.ts.For the sample with 1% of Pr3~ the linear behavior of P(t) occurs for t < 10 j.ts. For longer times we observed a ~1 2 decay for P(t). This behavior can
E.M. Pacheco, C.B. deAraujo
________________________
~
7 6
05%
-
-
Z
~
°
~ °
~
1%
5%3 I
~
~: 10
~‘
0
5
15
20
25
30
TIME (ii sec) . Fig. 2. P(t) as a function of the sample concentrations. Excitation and fluorescence wavelengths as in fig. 1.
be understood assuming an electronic multipolar interaction between donors and acceptors. Thus, according to the Inokuti Hirayama theory [4], the decay function of donor fluorescence is given by 3 / 3 \ ~ 3 s P(t) 3 ° C~T’~1 (3) 41TR =
)
—
223
borate glass
function of concentration. The fluorescence behavior corresponds to a fast exponential decay which indicates that the non-radiative relaxation is influenced by possible effects of energy migration on donors In this case P(t) wt where w is the rate of migration limited relaxation [7 8] Accord ingly, fig. 2 shows a linear behavior of P(t) for the 5wt%ofPr3~samp1ewithcc’=3.6X105s I (2) The for rate the of initial energy (W= transfer dP/dtl is obtained ~) analogously from eq. to the case of crystalline samples [3 5], we obtain
:~%
2
/ Pr3~ ions in
,
S
where T0 is the decay constant theparameter sensitizer of in the absence of an acceptor; s isofthe the multipolar interaction, s 6, 8, 10 for dipole dipole, quadrupole dipole and quadrupole quadrupole interactions, respectively; CA is the acceptor concentration and R 0 is the distance at which the energy transfer rate for an isolated ion pair is equal to the internal decay rate of the donor (the transfer rate for a donor acceptor separation R is proportional to R Accordingly, eqs. (1) and (3) predict an initial fast decay which is mainly due to donors with acceptors nearby, while the slower portion comes from the more nearly isolated donors. 3~,fig. 3 Thus, the the sample 1% of Pr P(t) can shows thatforafter initialwith 10 ~ss interval, be described by a ~I 2 curve which indicates that the dipole dipole interaction is dominant. Also from the best fitting of eq. (3) to the experimental points of fig. 3 we obtain the critical distance R 0 30.2 A. with higher rate concentrations (2 a5 wt%Forof samples Pr3~)the observed decay is also =
W given by C~fX( R) d R. The behavior of W is presented in fig. 4 which displays the results obtained from fig. 2. The linear dependence with the Pr3~concentration is in agreement with the above expression for W. Other studies of concentration quenching of Pr3~in solids have been presented in ref. [9]. Those authors pointed out that the ion ion energy transfer is the more important nonradiative channel. In our samples of (B 203)07(CaF2)0 we believe that the ion ion energy transfer operates through different pathways. The more efficient one is the process which makes an ion in the iD 2 state relax nonradiatively by transferring part of 3~ion. Further its energy occurs to a neighboring Pr relaxation through nonradiative emission of phonons or radiative decay (down-conversion fluorescence). The other possibility is a weaker process involving a pair of excited ‘D 3 ions 2 Pr +
*
7
4)~
36
u.
4
~
9-
2
0.Swt% 8K
-.
E I
0
5
tO 15 20 TIME (~t sec)
25
30
. 1 2 depenFig. 3. Experimental P(t) for a sample of (B203)07(CaF2)01 with 0.5 wt% of Pr~dence and for theoretical fiiting with ~ t> 10 ~s.
224
E.M. Pacheco, C.B. de Araujo +4
(xIO
)
40 35
Ui
•
25
~2O 5 ~ Ui
10
Ui
5
z
ions in borate glass
absorption and emission bands for the ‘D2 —s ~ H4 transition is quite large. Therefore, a strong electric dipole dipole transfer probability is expected because of the large overlap between the lineshape functions of donors and acceptors. The values obtained for the energy transfer rate in (B203)07 (CaF2)03 are very large which makes this material
~ 30 ~
/ Pr
a good candidate to be used as a sensitized laser host [1].
•
• S
Acknowledgements I
0
2
3
4
5
3+
3 + concentration Pr CONCENTRATION (wf %) Fig. 4. Energy transfer for allrate theasstudied a function samples. of pr
which exchange energy resulting in an up-conversion emission (3P 0 ~H4). This effect 3~and CaF has been 3~in studied in detail for present LaF2: Pr 2 fluoresPr refs. [10,11]. In the case, the blue cence ~H 4 was observed for all samples and further experiments are being performed to get a better understanding of the process. Finally a comparison our results glass with 3 between in fluorozirconate others for hosts Pr [12] andobtained crystalline such as YAG [13] and LiYF 4 [14] is appropriate. As shown in table 1, the energy transfer rates obtained in the present work are larger than in those materials. It is well known that the energy level structure of the rare earth ion and the inhomogeneous broadening of its transitions play an important role in determining the energy transfer efficiency in any system. In the 3~ studied borate glass the overlap of the Pr —*
available histotechniques of glass preparation and We wish thank Gilberto F. de Sá for making for useful discussions. The technical assistance of J.C. Albuquerque and Margarete Fernandes is also acknowledged. This work was partially supported by Conselho Nacional de Desenvolvimento CientIfico de e Tecnologico (CNPq)(FINEP). and Financiadora Nacional Estudos e Projetos
—
+
Table 1 Energy transfer rates from level 1D 3 * doped materials 2 for various Pr _____________________________________________________ Material Energy Ref transfer rate (s 1) YAG:Pr3 (1%) LiYF 3~(1%) ZBLAglass:Pr3~(1%) 4: Pr Borate glass: Pr3~(1%)
i03 6.8x10~ 5.5 X i0~
[13] [14] [12] this work
References [1] A.M. Prokhorov, Usp. Fiz. Nauk. 148 (1986) 7 (Soy. Phys. Usp. 29 (1986) 3). [2] 0. Blasse, J Less-Common. Met. 112 (1985) 1; Mat. Chem. Phys. 16 (1987) 201. [3] See, for example: Laser Spectroscopy of Solids, Vol. 49, Topics in Applied Physics, eds. W.M. Yen and P.M. Selzer (Springer, Berlin, 1981); J. Lumin. 36 (1987) Special Issue on Optical Linewidth in Glasses; R.T. Brundage and W.M. Yen, Phys. Rev. B 34 (1986) 8810; K. Tanimura, M.D. Shinn, W.A. Sibley, MG. Drexhage and R.N. Brown, Phys. Rev. B 30 (1984) 2429; C.B. Layne, W.H. Lowdermilk and M.J. Weber, Opt. Commun. 18 (1976) 174; G.S. Dixon, R.C. Powell and X. Gang, Phys. Rev. B 33 (1986) 2713. [4] M. Inokuti and F. Hirayama, J. Chem. Phys. 43 (1965) 1978. [5] D.L. Huber, Phys. Rev. B 20 (1979) 2307. [6] O.L. Malta, P.A. Santa-Cruz, G.F. de Sá and F. Auzel, J. Lumin. 33 (1985) 261; Rev. Bras. Fis. 17(1987)145. [7] Yu K. Voronko, T.G. Mamedov, V.V. Osiko, A.M. Prokhorov, V.P. Sakum and IA. Schcherbakov, Zh. Eksp. Teor. Fiz. 71(1976) 478 [Soy. Phys. JETP 44 (1976) 251)]. [8] A.A. Kaminskii, Laser Crystals (Springer, Berlin, 1981).
E. M. Pacheco, C. B. de A raujo
[91MR.
Brown, J.S.S. Whiting and W.A. Shand, J. Chem. ~ 43 (1965) 1; J. Hergarty, D.L. Huber and W.M. Yen, Phys. Rev. B 25 (1983) 5638. [10] R. Buisson and J.C. Vial, J. de Phys. Lett. 42 (1981) LilS; J.C. Vial and R. Buisson, J. de Phys. Lett. 43 (1982) L339. [11] A. Lezama, M. Oriá, J.R. Rios Leite and Cid B. de Araujo, Phys. Rev. B 32 (1985) 7139;
/ Pr3
*
ions in borate glass
225
A. Lezama, M. Oriá and Cid B. de Araujo, Phys. Rev. B 33 (1986) 4493. [121 J.L. Adam and WA. Sibley, J. Non-Cryst. Solids 76 (1985) 267. [13] V. Lupei, A. Lupei, S. Georgescu and C. lonescu, Opt. Commun. 60 (1986) 59. [14] J.L. Adam, W.A. Sibley and DR. Gabbe, J. Lumin. 33 (1985) 391.
221
ENERGY TRANSFER BETWEEN Pr3~IONS IN A BORATE GLASS: (B203)07(CaF2)03 E.M. PACHECO and Cid B. DE ARAUJO Universidade Federal de Pernambuco, Departamento de Fisica, 50739 Recite, Brazil
Received 9 February 1988 Revised 11 July 1988 Accepted 12 July 19tt~ 3 + -. Pr3 + in a borate glass: (B We measured the energy transfer efficiency of Pr 3203 ± )ions. 0 7(CaF2 A very ) 0.3 large Our analysis energy transfer of the donor rate fluorescence —. iO~s ‘) is transients reportedisfor consistent diluted samples. with a dipole dipole interaction between Pr
1. Introduction Glasses containing rare earth (RE) impurities are of considerable interest for applications in optical technology [1,2]. Such glasses can have sharp electronic absorptions from the near infrared to the UV region and thus may be useful in various kinds of optical devices. These characteristics have attracted the interest of a number of investigators and the research of laser materials stimulate studies of energy transfer in these materials. Although the basic mechanics which govern the energy transfer process between RE ions in glasses have been studied by several authors [3,5] there are not much experimental results related to borate glasses. The research of new hosts for sensitized solid state lasers could benefit from these studies. In the present work3~ions the study in of a energy borate transfer glass is processes between Pr reported. This glass has been shown to be a good host material for basic studies of energy transfer [6].
2. Experimental methods
have been studied. They are prepared by melting the proper amount of reagent-grade compounds (B 203. CaF2. Pr6OH) in an electric furnace. Melting times of 90 nun and melting temperatures in the range of 1200 1300°C were required. The melted glass is cooled to 350°C and annealed for one hour. The obtained samples have a good optical quality and are non-hygroscopic. To investigate the process of energy transfer we performed measurements of the donor fluorescence decay following the resonant excitation of Pr~ions. The excitation source for fluorescence measurements was a 0.3 cm ‘ bandwidth dye laser pumped by the second harmonic of a Nd YAG laser. Emission spectra were obtained by monitoring the signal from a 1.4 m double spectrometer fitted with a 1P28 photomultiplier. A boxcar integrator enhance the measurements. signal-to-noise ratio andwas to used allowtotime-resolved The laser pulse duration (— 10 ns) was short enough so that during the pulse the distribution of excitation is unaffected by the acceptors. For the low temperature experiments the samples were cooled to 18 K in a closed circuit refrigerator. Optical absorption measurements were made with a double beam spectrophotometer. For all
Samples of borate glass (B 203)07(CaF2)03 conmeasurements spectralinewidths. resolution was much 3~ greater than thethe observed taming 0.05, 0.5, 1.0, 2.0, 3.0 and 5.0 wt% of Pr 0022-2313/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
222
E M. Pacheco, C.B. de Araujo
3. Results and discussion The absorption spectra of Pr3~for the studied samples show broad features of about 100 400 A bandwidth which can be easily identified with the corresponding Pr3~levels. For the transition ~H 4 1D 2, for example, the linewidth is 300 A. These large bandwidths result from the site-tosite variation of the crystal field strength. The fluorescence spectra due to the laser excita3H 1D tion of the 4 2 transition exhibit a linewidth which depends not much on the selected pumped region into the inhomogeneous absorption band. The obtained fluorescence linewidths when pumping with different wavelengths does not narrow much because 1D of the multiphonon relaxation between levels 2 and ‘G4 and due to accidental degeneracy which prevents a site-selective excitation [3]. We observed linewidth reduction by a factor 3 as compared with the inhomogeneous linewidth of 300 A. Similar spectra were obtained after focusing the laser beam into different regions of the samples indicating that their composition is homogeneous. This result is in agreement with X-ray diffraction measurements in our samples which show no evidence for crystalline phases. 1D The temporal behavior of the 2 H~emission have been 1D measured for all prepared samples. Firstly, the 2 H4 lifetime was determined at ‘~
—*
—~
—,
0 0.8
~
~
~
3~ 0.05% Pr LASER 5850 A
•~—s~
TIME Fig. 1. Time decay of 1 D
15
for various laser intensities provide essentially the same results. A computer fitting of the intensity decay gives a lifetime of 24 ~is. Multiphonon transitions is expected to be the important 1Gmechanism for relaxation from the ‘D2 to the 4 levels. A multiphonon decay rate of about iO~~s is expected in comparison with other studied borate glasses [3]. The other samples with 0.5 5 wt% of Pr~ present a fluorescence decay which will be discussed below. For all studied samples the temporal behavior of the fluorescence can be described by the expression 1(t)
exp~
P(t)~,
(1)
T0
where P(t) assumes different forms according to the sample concentration and time range. In fig. 1 the behavior of P(t) for all studied samples is shown. A theoretical framework which allows an interpretation of the obtained results has been developed by several authors [3 5]. Based on those models one expects, in the limit of low donor concentrations, P(t) to be given by P(t) = [CAJX(R) (2) where CA represents the acceptor concentration,
dRIt,
a U-
10
18 K for the sample with 0.05 wt% of Pr3t As shown in fig. 1 this sample exhibits an exponential time decay which is not influenced by the excitation wavelength. Measurements of the lifetime at 18 and 300 K
with a relative distance equal to R. Thus, at short times we expect from eqs. (1) and (2) an exponen•
5
ions in borate glass
X( R) is the energy transfer rate between two ions
04 0.2
0
+
181< 0.6
0
Pr
20
25
30
(~ssec)
3
2 —~ 3H4. The fluorescence line corresponds at 6020 to A the for the sample withof0.05 wt%exponential of Pr best fitting a pure curve with ~ — 23 jzs.
lifetime tial decay of the excited state with a characteristic For the sample with 0.5 wt% of Pr3~we observed a linear behavior of P(t) which indicates that the energy transfer occurs only to the nearest acceptors during the studied time range. Deviation of this linear behavior occur for 1> 30 ~.ts.For the sample with 1% of Pr3~ the linear behavior of P(t) occurs for t < 10 j.ts. For longer times we observed a ~1 2 decay for P(t). This behavior can
E.M. Pacheco, C.B. deAraujo
________________________
~
7 6
05%
-
-
Z
~
°
~ °
~
1%
5%3 I
~
~: 10
~‘
0
5
15
20
25
30
TIME (ii sec) . Fig. 2. P(t) as a function of the sample concentrations. Excitation and fluorescence wavelengths as in fig. 1.
be understood assuming an electronic multipolar interaction between donors and acceptors. Thus, according to the Inokuti Hirayama theory [4], the decay function of donor fluorescence is given by 3 / 3 \ ~ 3 s P(t) 3 ° C~T’~1 (3) 41TR =
)
—
223
borate glass
function of concentration. The fluorescence behavior corresponds to a fast exponential decay which indicates that the non-radiative relaxation is influenced by possible effects of energy migration on donors In this case P(t) wt where w is the rate of migration limited relaxation [7 8] Accord ingly, fig. 2 shows a linear behavior of P(t) for the 5wt%ofPr3~samp1ewithcc’=3.6X105s I (2) The for rate the of initial energy (W= transfer dP/dtl is obtained ~) analogously from eq. to the case of crystalline samples [3 5], we obtain
:~%
2
/ Pr3~ ions in
,
S
where T0 is the decay constant theparameter sensitizer of in the absence of an acceptor; s isofthe the multipolar interaction, s 6, 8, 10 for dipole dipole, quadrupole dipole and quadrupole quadrupole interactions, respectively; CA is the acceptor concentration and R 0 is the distance at which the energy transfer rate for an isolated ion pair is equal to the internal decay rate of the donor (the transfer rate for a donor acceptor separation R is proportional to R Accordingly, eqs. (1) and (3) predict an initial fast decay which is mainly due to donors with acceptors nearby, while the slower portion comes from the more nearly isolated donors. 3~,fig. 3 Thus, the the sample 1% of Pr P(t) can shows thatforafter initialwith 10 ~ss interval, be described by a ~I 2 curve which indicates that the dipole dipole interaction is dominant. Also from the best fitting of eq. (3) to the experimental points of fig. 3 we obtain the critical distance R 0 30.2 A. with higher rate concentrations (2 a5 wt%Forof samples Pr3~)the observed decay is also =
W given by C~fX( R) d R. The behavior of W is presented in fig. 4 which displays the results obtained from fig. 2. The linear dependence with the Pr3~concentration is in agreement with the above expression for W. Other studies of concentration quenching of Pr3~in solids have been presented in ref. [9]. Those authors pointed out that the ion ion energy transfer is the more important nonradiative channel. In our samples of (B 203)07(CaF2)0 we believe that the ion ion energy transfer operates through different pathways. The more efficient one is the process which makes an ion in the iD 2 state relax nonradiatively by transferring part of 3~ion. Further its energy occurs to a neighboring Pr relaxation through nonradiative emission of phonons or radiative decay (down-conversion fluorescence). The other possibility is a weaker process involving a pair of excited ‘D 3 ions 2 Pr +
*
7
4)~
36
u.
4
~
9-
2
0.Swt% 8K
-.
E I
0
5
tO 15 20 TIME (~t sec)
25
30
. 1 2 depenFig. 3. Experimental P(t) for a sample of (B203)07(CaF2)01 with 0.5 wt% of Pr~dence and for theoretical fiiting with ~ t> 10 ~s.
224
E.M. Pacheco, C.B. de Araujo +4
(xIO
)
40 35
Ui
•
25
~2O 5 ~ Ui
10
Ui
5
z
ions in borate glass
absorption and emission bands for the ‘D2 —s ~ H4 transition is quite large. Therefore, a strong electric dipole dipole transfer probability is expected because of the large overlap between the lineshape functions of donors and acceptors. The values obtained for the energy transfer rate in (B203)07 (CaF2)03 are very large which makes this material
~ 30 ~
/ Pr
a good candidate to be used as a sensitized laser host [1].
•
• S
Acknowledgements I
0
2
3
4
5
3+
3 + concentration Pr CONCENTRATION (wf %) Fig. 4. Energy transfer for allrate theasstudied a function samples. of pr
which exchange energy resulting in an up-conversion emission (3P 0 ~H4). This effect 3~and CaF has been 3~in studied in detail for present LaF2: Pr 2 fluoresPr refs. [10,11]. In the case, the blue cence ~H 4 was observed for all samples and further experiments are being performed to get a better understanding of the process. Finally a comparison our results glass with 3 between in fluorozirconate others for hosts Pr [12] andobtained crystalline such as YAG [13] and LiYF 4 [14] is appropriate. As shown in table 1, the energy transfer rates obtained in the present work are larger than in those materials. It is well known that the energy level structure of the rare earth ion and the inhomogeneous broadening of its transitions play an important role in determining the energy transfer efficiency in any system. In the 3~ studied borate glass the overlap of the Pr —*
available histotechniques of glass preparation and We wish thank Gilberto F. de Sá for making for useful discussions. The technical assistance of J.C. Albuquerque and Margarete Fernandes is also acknowledged. This work was partially supported by Conselho Nacional de Desenvolvimento CientIfico de e Tecnologico (CNPq)(FINEP). and Financiadora Nacional Estudos e Projetos
—
+
Table 1 Energy transfer rates from level 1D 3 * doped materials 2 for various Pr _____________________________________________________ Material Energy Ref transfer rate (s 1) YAG:Pr3 (1%) LiYF 3~(1%) ZBLAglass:Pr3~(1%) 4: Pr Borate glass: Pr3~(1%)
i03 6.8x10~ 5.5 X i0~
[13] [14] [12] this work
References [1] A.M. Prokhorov, Usp. Fiz. Nauk. 148 (1986) 7 (Soy. Phys. Usp. 29 (1986) 3). [2] 0. Blasse, J Less-Common. Met. 112 (1985) 1; Mat. Chem. Phys. 16 (1987) 201. [3] See, for example: Laser Spectroscopy of Solids, Vol. 49, Topics in Applied Physics, eds. W.M. Yen and P.M. Selzer (Springer, Berlin, 1981); J. Lumin. 36 (1987) Special Issue on Optical Linewidth in Glasses; R.T. Brundage and W.M. Yen, Phys. Rev. B 34 (1986) 8810; K. Tanimura, M.D. Shinn, W.A. Sibley, MG. Drexhage and R.N. Brown, Phys. Rev. B 30 (1984) 2429; C.B. Layne, W.H. Lowdermilk and M.J. Weber, Opt. Commun. 18 (1976) 174; G.S. Dixon, R.C. Powell and X. Gang, Phys. Rev. B 33 (1986) 2713. [4] M. Inokuti and F. Hirayama, J. Chem. Phys. 43 (1965) 1978. [5] D.L. Huber, Phys. Rev. B 20 (1979) 2307. [6] O.L. Malta, P.A. Santa-Cruz, G.F. de Sá and F. Auzel, J. Lumin. 33 (1985) 261; Rev. Bras. Fis. 17(1987)145. [7] Yu K. Voronko, T.G. Mamedov, V.V. Osiko, A.M. Prokhorov, V.P. Sakum and IA. Schcherbakov, Zh. Eksp. Teor. Fiz. 71(1976) 478 [Soy. Phys. JETP 44 (1976) 251)]. [8] A.A. Kaminskii, Laser Crystals (Springer, Berlin, 1981).
E. M. Pacheco, C. B. de A raujo
[91MR.
Brown, J.S.S. Whiting and W.A. Shand, J. Chem. ~ 43 (1965) 1; J. Hergarty, D.L. Huber and W.M. Yen, Phys. Rev. B 25 (1983) 5638. [10] R. Buisson and J.C. Vial, J. de Phys. Lett. 42 (1981) LilS; J.C. Vial and R. Buisson, J. de Phys. Lett. 43 (1982) L339. [11] A. Lezama, M. Oriá, J.R. Rios Leite and Cid B. de Araujo, Phys. Rev. B 32 (1985) 7139;
/ Pr3
*
ions in borate glass
225
A. Lezama, M. Oriá and Cid B. de Araujo, Phys. Rev. B 33 (1986) 4493. [121 J.L. Adam and WA. Sibley, J. Non-Cryst. Solids 76 (1985) 267. [13] V. Lupei, A. Lupei, S. Georgescu and C. lonescu, Opt. Commun. 60 (1986) 59. [14] J.L. Adam, W.A. Sibley and DR. Gabbe, J. Lumin. 33 (1985) 391.