Efficient Nd^3+→Yb^3+ energy transfer in 08CaSiO_3-02Ca_3(PO_4)_2 eutectic glass

Efficient Nd3+→→→→Yb3+ energy transfer in 0.8CaSiO3-0.2Ca3(PO4)2 eutectic glass

Rolindes Balda1,2,*, Jose Ignacio Peña3, M. Angeles Arriandiaga4, Joaquín Fernández1,2 1Departamento Física Aplicada I, Escuela Superior de Ingeniería, Alda. Urquijo s/n 48013 Bilbao, Spain

2Centro de Física de Materiales CSIC-UPV/EHU and Donostia International Physics Center, Apartado 1072, 20080 San Sebastian, Spain

3 Instituto de Ciencia de Materiales de Aragón (Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas), Facultad de Ciencias, C/ Pedro Cerbuna 12, Zaragoza E-50009, Spain

4Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, Bilbao, Spain

*[email protected]

Abstract: In this work we report the study of energy transfer between Nd3+

and Yb

3+ ions in glasses with the 0.8CaSiO3-0.2Ca3(PO4)2 eutectic

composition at room temperature by using steady-state and time-resolved

laser spectroscopy. The Nd3+→Yb

3+ transfer efficiency obtained from the

Nd3+

lifetimes in the single doped and codoped samples reaches 73% for the highest Nd

3+ concentration. The donor decay curves obtained under pulsed

excitation have been used to establish the multipolar nature of the Nd3+→

Yb3+

transfer process and the energy transfer microparameter. The nonradiative energy transfer is consistent with an electric dipole-dipole interaction mechanism assisted by energy migration among donors. Back transfer from Yb

3+ to Nd

3+ is also observed.

©2010 Optical Society of America

OCIS codes: (160.5690) Rare earth doped materials; (300.6280) Spectroscopy; fluorescence and luminescence.

References and links

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2. J. A. Pardo, J. I. Peña, R. I. Merino, R. Cases, A. Larrea, and V. M. Orera, “Spectroscopic properties of Er3+ and Nd3+ doped glasses with the 0.8CaSiO3–0.2Ca3(PO4)2 eutectic composition,” J. Non-Cryst. Solids 298(1), 23–31 (2002).

3. R. Balda, J. Fernández, I. Iparraguirre, J. Azkargorta, S. García-Revilla, J. I. Peña, R. I. Merino, and V. M. Orera, “Broadband laser tunability of Nd3+ ions in 0.8CaSiO3-0.2Ca3(PO4)2 eutectic glass,” Opt. Express 17(6), 4382–4387 (2009).

4. M. J. Weber, “Optical properties of Yb3+ and Nd3+ -Yb3+ energy transfer in YAlO3,” Phys. Rev. B 4(9), 3153–3159 (1971).

5. C. Lurin, C. Parent, G. Le Flem, and P. Hagenmuller, “Energy transfer in a Nd3+-Yb3+ borate glass,” J. Phys. Chem. Solids 46(9), 1083–1092 (1985).

6. C. Parent, C. Lurin, G. Le Flem, and P. Hagenmuller, “Nd3+→Yb3+ energy transfer in glasses with composition close to LiLnP14O12 metaphosphate (Ln=La, nd, Yb),” J. Lumin. 36(1), 49–55 (1986).

7. W. Ryba-Romanowski, S. Golab, L. Cichosz, and B. Jezowska-Trzebiatowska, “Influence of temperature and acceptor concentration on energy transfer from Nd3+ toYb3+ and from Yb3+ to Er3+ in tellurite glass,” J. Non-Cryst. Solids 105(3), 295–302 (1988).

8. F. Batalioto, D. F. Sousa, M. J. V. Bell, R. Lebullenger, A. C. Hernandes, and L. A. O. Nunes, “Optical measurements of Nd3+/Yb3+ codoped fluorindogallate glasses,” J. Non-Cryst. Solids 273(1-3), 233–238 (2000).

9. D. F. de Sousa, F. Batalioto, M. J. V. Bell, S. L. Oliveira, and L. A. O. Nunes, “Spectroscopy of Nd3+ and Yb3+ codoped fluoroindogallate glasses,” J. Appl. Phys. 90(7), 3308–3313 (2001).

10. D. Jaque, M. O. Ramirez, L. E. Bausá, J. García-Solé, E. Cavalli, A. Speghini, and M. Bettinelli, “Nd3+→Yb3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal,” Phys. Rev. B 68(3), 035118 (2003).

11. F. Liégard, J. L. Doualan, R. Moncorgé, and M. Bettinelli, “Nd3+→Yb3+ energy transfer in a codoped metaphosphate glass as a model for Yb3+ laser operation around 980 nm,” Appl. Phys. B 80(8), 985–991 (2005).

12. R. Balda, J. Fernández, I. Iparraguirre, and M. Al-Saleh, “Spectroscopic study of Nd3+/Yb3+ in disordered potassium bismuth molybdate laser crystals,” Opt. Mater. 28(11), 1247–1252 (2006).

#128191 - $15.00 USD Received 10 May 2010; revised 8 Jun 2010; accepted 9 Jun 2010; published 11 Jun 2010(C) 2010 OSA 7 June 2010 / Vol. 18, No. 13 / OPTICS EXPRESS 13842

13. U. Caldiño, D. Jaque, E. Martín-Rodríguez, M. O. Ramírez, J. García Solé, A. Speghini, and M. Bettinelli, “Nd3+/Yb3+ resonant energy transfer in the ferroelectric Sr0.6 Ba0.4 Nb2O6 laser crystal,” Phys. Rev. B 77(7), 075121 (2008).

14. Z. Jia, A. Arcangeli, X. Tao, J. Zhang, C. Dong, M. Jiang, L. Bonelli, and M. Tonelli, “Efficient Nd3+→Yb3+ energy transfer in Nd3+,Yb3+:Gd3Ga5O12 multicenter garnet crystal,” J. Appl. Phys. 105, 083113 (2009).

15. A. Lupei, V. Lupei, A. Ikesue, and C. Gheorghe, “Spectroscopic and energy transfer investigation of Nd/Yb in Y2O3 transparent ceramics,” J. Opt. Soc. Am. B 27(5), 1002–1010 (2010).

16. M. J. Weber, D. C. Ziegler, and C. A. Angell, “Tailoring stimulated emission cross sections of Nd3+ laser glass: Observation of large cross sections for BiCl3 glasses,” J. Appl. Phys. 53(6), 4344–4350 (1982).

17. A. I. Burshtein, “Hopping mechanism of energy transfer,” Sov. Phys. JETP 35, 882–885 (1972).

1. Introduction

Eutectic structures are a paradigm of composite materials with a fine microstructure whose characteristics are controlled by the solidification conditions. Rapid solidification of some eutectic systems opens up the possibility of fabricating glass. The favorable conditions of eutectic mixtures to produce glasses with a low number of components are also remarkable from the point of view of their photonic applications. A good optical quality glass can be produced by fast directional solidification of the CaSiO3/Ca3(PO4)2 binary eutectic system. This eutectic presents two non-conventional and interesting properties: firstly, the degenerated lamellar structure of the system favors the biological transformation of the tricalcium phosphate phase into hydroxiapatite, giving rise to a biological material with a microstructure similar to that of human bone. Secondly, it is possible to form a eutectic glass of this composition with excellent optical properties [1]. Regarding the optical properties of this system, it was found that the lifetimes and emission cross-sections of the 1.06 µm (Nd

3+) and

1.5 µm (Er3+

) emissions in this glass are equivalent to those of the best commercially used alkaline-silicate glasses [2]. More recently, we have demonstrated laser emission under pulsed pumping which shows a behavior close to a Q-switch operation. Wavelength-resolved pump excitation of Nd

3+ ions in this glass allows for a broad band tunability (10 nm) of the laser

emission which is related with the variety of quasi-isolated crystal field site distributions of Nd

3+ ions in this glass matrix [3].

Laser action in the infrared region from Yb3+

ions presents several advantages if compared to Nd

3+ ions due to the energy level scheme of Yb

3+ with only two levels

2F7/2 and

2F5/2. This

avoids some problems such as excited-state absorption, cross-relaxation, and upconversion. Moreover, the longer lifetime of Yb

3+ allows greater energy-storage efficiency with diode

laser pumped schemes and broader absorption and emission bands which is promising for the generation of shorter light pulses. However, the simple energy level scheme of Yb

3+ ions

limits the pump wavelength region around 980 nm. The use of Nd3+

ions as sensitizer allows to use a wide range of excitation wavelengths due to the Nd

3+ absorption bands. Efficient

energy transfer between Nd3+

and Yb3+

ions has been demonstrated both in glasses and crystals, e.g [4–15].

In this work we report the study of energy transfer between Nd3+

and Yb3+

ions in 0.8CaSiO3-0.2Ca3(PO4)2 eutectic glasses at room temperature by using steady-state and time-resolved laser spectroscopy. The transfer efficiency has been obtained from the lifetimes in the single doped and codoped samples as a function of Nd

3+ concentration. The donor decay

curves obtained under pulsed excitation have been used to establish the multipolar nature of

the Nd3+→Yb

3+ transfer process and the energy transfer microparameter.

2. Experimental details

Ceramic precursor rods, 3 mm in diameter and 50-100 mm in length, were prepared from the powder mixture of wollastonite (CS)-tricalcium phosphate (TPC) with the eutectic composition (80CaSiO3 + 20Ca3(PO4)2 in mol%) by pressureless sintering at 1200 °C for 10 h. Nd2O3 and Yb2O3 were added to the precursors to obtain the doped and codoped samples. Glass rods were then produced from the precursors by the laser floating zone method [2]. This inverted glass with a high content of CaO modifier presents a highly transparent optical window from 0.35 to 4 µm and is not hygroscopic. Its refractive index is 1.65 [2]. The glasses were doped with 0.5, 1, 2, and 3 wt% of Nd2O3 which correspond to 0.53x10

20, 1.05x10

20,


2.08x1020

, and 3.18x1020

Nd3+

ions/cm3 respectively and codoped with 2 wt% of Yb2O3

(1.78x1020

Yb3+

ions/cm3). Single doped samples with 0.5, 1, 2, and 3 wt% of Nd2O3 and a

single doped sample with 2 wt% of Yb2O3 were also prepared. The room temperature absorption spectra in the 300-2500 nm spectral range were recorded

by using a Cary 5 spectrophotometer. The steady-state emission measurements were made by

using a Ti-Sapphire ring laser (0.4 cm−1

linewidth) in the 780-920 nm range. The fluorescence was analyzed with a 0.22 m SPEX monochromator, and the signal was detected by a Hamamatsu R7102 photomultiplier and finally amplified by a standard lock-in technique. Lifetime measurements were performed by exciting the samples with a Ti-sapphire laser, pumped by a pulsed frequency doubled Nd:YAG laser (9 ns pulse width), and detecting the emission with a Hamamatsu R7102 photomultiplier. Data were processed by a Tektronix oscilloscope.

3. Results and discussion

3.1 Absorption and emission spectra

The room temperature absorption spectra were obtained for all samples in the 300-2500 nm range with a Cary 5 spectrophotometer. As an example, Fig. 1 shows the absorption spectrum of the codoped glass with 3 wt% Nd2O3 and 2 wt% Yb2O3. The inhomogeneously broadened bands are assigned to the transitions from the

4I9/2 ground state to the excited states of Nd

3+

ions and to the 2F7/2→

2F5/2 optical transition corresponding to Yb

3+ ions. The spectra obtained

for the other codoped samples are similar, except for the band intensities, which are dependent on the Nd

3+ concentration. The integrated absorption coefficient for different absorption bands

shows a linear dependence on concentration, which indicates that the relative concentrations of Nd

3+ are correct.

350 450 550 650 750 850 950 1050

Wavelength (nm)

0

2

4

6

8

10

Absorp

tio

n C

oeff

icie

nt (c

m-1

)

4F3/2

4G5/2,2G7/2

2P1/2

T=295 K

4F5/2

4F7/2

4G7/2,9/2

4F9/2

2F5/2

Fig. 1. Room temperature absorption spectrum of a codoped sample with 3 wt% of Nd2O3 and 2 wt% of Yb2O3.

The steady-state emission spectra were performed by exciting at 805 nm in the 4I9/2→

4F5/2

absorption band. For all samples the spectra are characterized by inhomogeneously broadened bands. Figure 2 shows the emission spectra for all codoped samples together with the emission spectrum of the single doped glass doped with 3 wt% of Nd2O3 normalized to the

Nd3+

emission at around 880 nm (4F3/2→

4I9/2). As can be seen the codoped samples show a

broad emission due to the superposition of Nd3+

(4F3/2→

4I9/2,

4I11/2) and Yb

3+ (

2F5/2→

2F7/2)

emission bands. It can be also observed that the Yb3+

emission increases with Nd3+

concentration. The presence of the Yb3+

(2F5/2→

2F7/2) emission clearly indicates the existence

of an efficient Nd3+→Yb

3+ energy transfer. After excitation in the

4F5/2 level of Nd

3+, the

4F3/2


level is populated by fast nonradiative relaxation and the energy is transferred to the 2F5/2

emitting level of Yb3+

.

800 850 900 950 1000 1050 1100 1150

Emission Wavelength (nm)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Inte

nsity (

arb

. un

its)

4F3/2→4I9/2

4F3/2→4I11/2

2F5/2→2F7/2

Nd3-Yb2

Nd0.5-Yb2

Nd3

Nd1-Yb2Nd2-Yb2

Fig. 2. Room temperature emission spectra of Nd3+ and Yb3+ in the codoped samples together with the emission spectrum of Nd3+ ions in a single doped glass. The spectra are normalized to the 880 nm emission of Nd3+.

The absorption and emission cross-section spectra of Yb3+

ions in the single doped glass are shown in Fig. 3. The absorption cross-section was calculated from the absorption spectrum whereas the emission cross section was calculated by using the Fuchtbauer-Landeburg (F-L) equation [16]. The form of this equation is,

( )( )

4

p

se 2

R

λ Iσ

8πn c τ I d

β λ

λ λ=

∫ (1)

where λp is the peak fluorescence wavelength, β is the branching ratio for the transition, n is the refractive index of the host matrix, c the velocity of light, τR the radiative lifetime of the emitting level, and I(λ) the emission intensity. The radiative lifetime can be calculated from the expression [4],

( )2

2 2

R 0

1 8 cn

N

f

i

gd

g

α λπλ

τ λ λ= ∫ (2)

were gf, and gi are the degeneracies of the initial (2F5/2) and final (

2F7/2) states, λ0 is the mean

wavelength of the 2F5/2→

2F7/2 electronic transition, n is the refractive index, N is the Yb

3+

concentration, and α is the absorption coefficient of the 2F7/2→

2F5/2 transition. The calculated

lifetime is 0.81 ms.


800 850 900 950 1000 1050 1100 1150

Wavelength (nm)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Cro

ss s

ection (

10

-20cm

2)

2F7/2→2F5/2

2F5/2→2F7/2

Fig. 3. Absorption and emission cross section of Yb3+ in the single doped sample.

It is worthy to mention that in contrast with other glasses [5–9,11] and crystals [10], the energy mismatch between the lowest Stark of

4F3/2 (Nd

3+) and the highest Stark of

2F5/2 (Yb

3+)

levels is only about 260 cm−1

. This short energy gap indicates that no thermal assistance is needed to have an efficient energy transfer. A similar situation was found in molibdate

crystals [12] with an energy mismatch around 300 cm−1

and in strontium barium niobate laser

crystals [13] (636 cm−1

). On the other hand, a comparison of the energy gap and the spectral

overlap between the Nd3+

emission (4F3/2→

4I9/2) and the Yb

3+ absorption (

2F7/2→

2F5/2) for

different glasses and crystals showed that as the energy gap decreases the spectral overlap increases [13]. Figure 4 shows the spectral overlap between the Nd

3+ emission and Yb

3+

absorption in the eutectic glasses. The Nd3+

emission cross-section has been calculated from Eq. (1). This unusual overlap can be related with the variety of quasi-isolated crystal field site distributions of rare-earth ions in this glass matrix [3]. Therefore, these eutectic glasses can be

considered as promising hosts for an efficient Nd3+

→Yb3+

energy transfer.

800 850 900 950 1000 1050 1100

Wavelength (nm)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Cro

ss s

ection (

10

-20cm

2) 2F7/2→

2F5/2

4F3/2→4I9/2

Fig. 4. Spectral overlap between Nd3+ emission and Yb3+ absorption in the single doped samples.

3.2 Lifetimes

The lifetime of the 4F3/2 level has been obtained in the single doped and codoped samples by

exciting at 805 nm, at the center of the 4I9/2→

4F5/2 absorption band, and collecting the

luminescence at 890 nm (4F3/2→

4I9/2 emission). The decays of the

4F3/2 level of Nd

3+ in the

single doped glasses were found to be exponential for all concentrations. As an example, Fig.


4(a) shows the decays for the samples doped with 0.5% and 3%. As concentration increases, they remain single exponential but a decrease from 258 to 248 µs is observed when the concentration increases from 0.5 to 3% which indicates the presence of nonradiative energy transfer processes. This behaviour could be associated to a rapid energy diffusion among Nd

3+

ions. The fluorescence lifetime of the 4F3/2 level for a sample doped with 0.07% at low

temperature (10K) measured under laser excitation at 805 nm, is 330 µs, which is close to the calculated radiative lifetime (340 µs) [2].

The lifetimes of the 4F3/2 level are affected by the presence of Yb

3+ ions. The decays of the

4F3/2 level in the codoped samples exhibit a non-exponential behavior and a shortening of the

lifetime if compared with the single doped samples, because of the additional relaxation probability by nonradiative energy transfer to Yb

3+ ions. The time dependent behavior of the

Nd3+

fluorescence from the codoped samples is shown in Fig. 4(b). The values of the Nd3+

emission lifetimes, monitored at 890 nm as a function of concentration are shown in Fig. 5, which also includes the lifetime of single doped samples for comparison.

0.0 0.5 1.0 1.5 2.0Time (ms)

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

Ln I(t

) (a

rb. units)

4F3/2→4I9/2T= 295 K

Nd3+

0.5%

3%

0.0 0.5 1.0 1.5 2.0

Time (ms)

-12

-10

-8

-6

-4

-2

0

Ln I(t

) (a

rb. units)

4F3/2→4I9/2T= 295 K

Nd3+3%-Yb3+2%

Nd3+0.5%-Yb3+2%

(a) (b)

Fig. 4. Logarithmic plot of the fluorescence decays of the 4F3/2→4I9/2 emission as a function of Nd3+ concentration in (a) single doped and (b) codoped samples.

The Nd3+→Yb

3+ energy transfer efficiency has been estimated from the lifetime values in

the single doped and codoped samples according to the expression,

1 Nd Ybt

Nd

τη

τ

−= − (3)

where τNd-Yb and τNd are the Nd3+

lifetimes, with and without Yb3+

ions respectively. The lifetime values for the codoped samples correspond to the average lifetime defined

by0

I(t)dtτ

I= ∫ . Figure 5 also shows the transfer efficiency for the codoped samples as a

function of donor concentration. The transfer efficiency reaches 73% for the highest Nd3+

concentration.


0 1 2 3 4

Nd3+concentration (1020cm-3)

0

50

100

150

200

250

300

Life

tim

e (µs

)

0.2

0.4

0.6

0.8

1.0

Tra

nsfe

r E

ffic

iency

Nd3+

Nd3+-Yb3+

Fig. 5. Lifetimes of the 4F3/2→4I9/2 emission for the single doped samples (black) and codoped samples (pink) and Nd3+-Yb3+ energy transfer efficiency (blue) as a function of Nd3+ concentration.

The presence of nonradiative Nd3+→Yb

3+ energy transfer can be demonstrated by the

time-dependent behavior of the Nd3+

fluorescence from the codoped samples. Figure 4(b) showed an increasing rate for the Nd

3+ decays in the codoped glasses due to the additional

relaxation probabilities and a nonexponential behavior. These decays have been analyzed to

determine the mechanism responsible for the Nd3+→Yb

3+ energy transfer, by considering the

existence of energy migration among donors. The best agreement between experimental data and theoretical fit occurs with the expression corresponding to the Burshtein model [17],

( ) 0

0

expt

I t I t Wtγτ

= − − −

(4)

where τ0 is the intrinsic lifetime of donor ions, γ characterizes the direct Nd3+→Yb

3+ energy

transfer, and W represents the migration parameter. In the case of dipole-dipole interaction, γ

is given by the expression, 3/2 1/24

3DAN Cγ π= , where NYb is the acceptors concentration and

CDA is the energy transfer microparameter. Figure 6 shows the fit for the sample doped with 3% of Nd2O3 and 2% of Yb2O3. The inset shows the same decays but in a semilogarithmic plot. These results indicate that the electronic mechanism of energy transfer is a dipole-dipole

interaction. From the fitting in Fig. 6, the value obtained for the Nd3+→Yb

3+energy transfer

microparameter is 1.6x10−39

cm6/s. Similar values for the energy transfer microparameter are

obtained for the samples codoped with 1 and 2 wt% of Nd2O3, whereas the migration rate

increases from 1467 s−1

(1 wt% of Nd2O3) to 4482 s−1

for the sample doped with 3 wt% of Nd2O3. The value obtained for the energy transfer microparameter is similar to the one found

in metaphosphate glasses (1.6x10−39

cm6/s) [6], lower than those found in tellurite (3.8x10

−39

cm6/s) [7], Pb-ultraphosphate (2.4x10

−39 cm

6/s) [7], and borate glasses (6x10

−39 cm

6/s) [5] and

higher than those found in fluorindogallate glasses (0.34x10−39

cm6/s and 0.45x10

−39 cm

6/s)

[8,9].


0.0 0.2 0.4 0.6 0.8 1.0Time (ms)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Inte

nsity (

arb

. units)

0.0 0.2 0.4 0.6Time (ms)

3F3/2→4I9/2T= 295 K

Fig. 6. Experimental emission decay curve of level 4F3/2 for the codoped sample with 3 wt% of

Nd2O3 and 2 wt% of Yb2O3 at room temperature and the calculated fit with Eq. (4) (solid

line).

3.3 Back transfer

In order to investigate the existence of back transfer from Yb3+

to Nd3+

we have performed emission spectra under excitation at 890 nm where only Yb

3+ ions absorb. The existence of

back transfer can be demonstrated by the presence of the Nd3+

emission. Figure 7 shows the emission spectrum of the codoped sample with 3 wt% of Nd2O3 and 2% Yb2O3 together with the emission spectrum of the Yb

3+ single doped glass normalized to the Yb

3+ emission. As can

be observed, after excitation of Yb3+

ions there is emission around 1064 nm corresponding to

the 4F3/2→

4I11/2 transition of Nd

3+ which indicates the presence of Yb

3+→Nd3+

energy transfer at room temperature.

800 850 900 950 1000 1050 1100 1150

Emission Wavelength (nm)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Inte

nsity (

arb

. un

its)

4F3/2→4I11/2

2F5/2→2F7/2 Nd3-Yb2

Yb2λexc= 890nm

Fig. 7. Room temperature emission spectra obtained for the codoped sample with 3 wt% of Nd2O3 and 2 wt% of Yb2O3 and the single doped glass with 2 wt% Yb2O3. The spectra are normalized to the Yb3+ emission.

We have also investigated the temporal evolution of Yb3+

emission in the codoped samples obtained by exciting the Nd

3+ ions at 805 nm. As an example, Fig. 8 shows the decays of the

Yb3+

fluorescence in three codoped samples. The decays show an initial rise time with a rate corresponding to excitation by transfer from Nd

3+ ions followed by an exponential decay. The

lifetime value of the codoped sample with 0.5% of Nd2O3 is close to the radiative lifetime (0.81 ms); however, as Nd2O3 concentration increases the Yb

3+ lifetime decreases from 0.82


ms for the sample doped with 0.5% of Nd2O3 to 0.77 ms for the sample with the highest Nd2O3 concentration. This reduction of the Yb

3+ lifetime can be due to the presence of

Yb3+→Nd

3+ back transfer.

0.0 1.0 2.0 3.0 4.0 5.0 6.0Time (ms)

-12

-10

-8

-6

-4

-2

0

Ln I(t

) (a

rb. units)

2F5/2→2F7/2

T= 295 K

Nd3+3%-Yb3+2%

Nd3+2%-Yb3+2%

Nd3+0.5%-Yb3+2%

Fig. 8. Logarithmic plot of the fluorescence decays of the 2F5/2→2F7/2 emission of Yb3+ ions in the codoped samples for three different Nd3+ concentrations.

4. Conclusions

In this work we have demonstrated efficient Nd3+→Yb

3+ energy transfer in 0.8CaSiO3-

0.2Ca3(PO4)2 eutectic glasses from the emission spectra and the decrease of the Nd3+

fluorescence lifetimes in the presence of Yb

3+ ions. In contrast with other glass matrices and

crystals, this energy transfer is non-phonon assisted due to the small energy difference

between the Nd3+

emission (4F3/2→

4I9/2) and the Yb

3+ absorption (

2F5/2→

2F7/2) bands which is

around 260 cm−1

and the important spectral overlap between these bands. The transfer efficiency, which has been studied at room temperature, as a function of donor concentration reaches 73% for the highest Nd

3+ concentration. The analysis of the donor decay curves is

consistent with a dipole-dipole energy transfer mechanism assisted by donor migration. Back transfer from Yb

3+ to Nd

3+ is also observed in the emission spectra of the codoped samples

under excitation of Yb3+

ions and in the small reduction from 0.82 ms to 0.77 ms of Yb3+

ions in the codoped samples. However the efficiency of this process is very low in comparison to

the Nd3+→Yb

3+ energy transfer.

Finally, the efficient Nd3+→Yb

3+ energy transfer obtained for the highest Nd

3+

concentration together with the excellent optical properties of these eutectic glasses suggest that these glasses can be promising materials for the generation of laser action from Yb

3+ ions

under Nd3+

excitation.

Acknowledgments

This work was supported by the Spanish Government under projects MAT2008-05921, MAT2009-14282-C02-02, and Consolider CSD2007-00013 (SAUUL), and the Basque Country Government (IT-331-07).


Efficient Nd^3+→Yb^3+ energy transfer in 08CaSiO_3-02Ca_3(PO_4)_2 eutectic glass

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