Energy transfer between Bi3+ → Eu3+, Bi3+ → Sm3+ and UO2+2 → Eu3+ in oxide glasses

Journal of Luminescence 12/13 (1976) 749—75 3 © North-Holland Publishing Company

ENERGY TRANSFER BETWEEN Bi3~ Eu3~,Bi3~ Sm3~ AND UO~ Eu3~IN OXIDE GLASSES * -~

-~

-~

R. REISFELD, N. LIEBLICH, L. BOEHM The Hebrew University of Jerusalem, Israel

and B. BARNETT Soreq Nuclear Research Center, Yavne, Israel

Probabilities and etficiencies of energy transfer from Bi3+ to Eu3+, Bi3+ to Sm3+ in borax and germanate glasses, and from UO~to Eu3+ in phosphate glass were measured. Enhancement of acceptor fluorescence by two orders of magnitude was achieved as a result of energy transfer. From the decrease of donor fluorescence lifetime the energy transfer from

2+

U0

2

3+

to Fu

was found to be nonradiative.

Energy transfer (ET) from ions having allowed transitions to rare earth ions (RE) is important for the increase of the excited population of the REis [11. 1~ andstate Eu3~in phosphate glass presented in The evidence for ET between UO~ fig. 1 in which the excitation spectra of Eu3~and Eu3~+ UO~~ are compared. Similarly, evidence for ET from Bi3~to Eu3~in germanate glass is presented in fig. 2. In both cases the fluorescence of Eu3~was monitored at 5D transition 3~ at 612 nm. ET from Bi3~to Sm3~in germanate glass0is—~ presented in fig. of 3 Eu monitored at -÷ transition of Sm3~at 605 nm and in borax glass monitored at 4G 3~at 645 nm is presented in fig. 4. 512 -+ were obtained transitionbyof[2] Sm ET efficiencies 1

(1)

?7d’77~‘

where i~ is the efficiency ot the pure donor and i~dis that of the donor in presence of the acceptor.

ET probabilities were calculated as follows: p_(l/rd)(r~/r~d 1),

(2)

where Td is the lifetime of donor without acceptor. The lifetime of the Bi3~ion consists of two components, the longest of which is *

Partially supported by US Army Contract No. DAERO-75-6-029.

749

750

R. Reisfeld et al. / Energy transfer from ions to RE ions in oxide glasses

PHOSPHATE

GLASS

/

3~

4

Eu

4

Eu~.1

uo;~

/ 525

485

445

365

405

.1

325

285

245

nm

~3+ l~ig.1. Excitation spectra of Lu3+ and Lu

+

U0 2+. 2 in phosphate glass.

3S0 nsec in germanate and 333 ns in borax [3]. These values were used for calculating ET probabilities.The probabilities so obtained are presented in table 1. In the same table the increase of acceptor fluorescence is also given. An enhancement of two 3~and Sm3~ doped germanate glass orders of magnitude in the fluorescence of Eu

/

10/, Eu~ ÷ 0/0 Bi ~ ~

GERMANATE GLASS

~

440

360

280

250 240

)~(nm)

Fig.

2.

Fxcitation spectra of Lu3~and Eu3~+ Bi3~in germanate glass.

R. Reisfeld et al.

/ Energy

751

transjer from ions to RE ions in oxide glasses

GERMANATE GLASS 1 1

—~

3 Sm Sm3.

1

Bi3

0

z

!~. 450

500

400

300

350

250

A,nm Fig.

3. Fxcitat ion spectra of Sm3+ and Sm3+

+

Bi3+ in germanate glass.

is observed. The greater increase in the acceptor fluorescence in germanate as compared to borax is due to the higher quantum efficiency of Bi3~ion in the former glass [31. Since the probabilities of transfer depend on the matrix elements of the transition between the ground and excited states of the donor and acceptor ions, we conclude that lIT occurs between the 3P 3~and 5L 5D 3~or the 1 level of Bi 6 and 3 of Eu xlO

~ 500

\~m~27o

450

400

250

350

30(3

A,nm Fig. 4. Excitation spectra of Sm3+ and Sm3+

+

Bi3+ in borax glass.

230

210

250

752

R. Reisfeld et al.

/ Energy

transfer from ions to RE ions in oxide glasses

Table 1 3~and Sm3~fluorescence, fla/fl~,energy transfer probabilities p and transfer eltiIncrease of I u cienc~s~in borax and germanate glasses a) Matrix and Xex borax glass excit. at 305 nm

1% Eu3~

germanate glass excit. at 333 nm

~

1.13

47.6

1)

0.5% Eu3~

p(106s ~a’~

0.18 6.4 1.67

0.20 7.2 176.0

1)

1% Sm3~

p(105s ~a’~a p(lO5s

i)

0.50 34.5 2.55 0.19 6.9

0.29 11.4 55.0 0.43 21.3

0.5% Sm3~

~a’~a

2.60

117.5

0.31 p(105s

0.28

30.8

i)

6.30

a) Bi’~concentration 1 wt%.

group 4F

6P

4K

3~.The energies which are in rehighest.

4M

1112, to 2112 sonance, 712, arid the312, absorption theselevels levelsofareSm the

The increase of Eu3~fluorescence in the presence of ~ ET efficiencies and probabilities are given in table 2. The transfer probabilities are found to be linear with the square of the acceptor ion concentration. The decay curve of the fluorescence of the UO~ion deviates from a single exponent. This behavior may be due to several fluorescent sites [4]. From a nonlinear Table 2 Increase of Eu3+ fluorescence 31a/fl~,energy transfer probabilities p and transfer efficiency ~. in phosphate glass a) Ion concentration wt~ 0.5’~lu 1~(Eu 1.5~(Eu 2% Lu 2.5%Fu 3%Fu 3.5% Eu 4% Eu “)

uo~concentration

~

~t

P (s

180 146 127 119 113 107

0.330 0.381 0.436 0.492 0.549 0.603 0.658 0.713

988 1215 1552 1939 2421 3030 3850 4989

I wt~’.

R. Reisfeld et al.

/ Energy transfer from ions to RE ions in oxide glasses

753

list square fitting to the decay lifetime curve of UO~~ in phosphate glass. the long component was found to be 0.5 ms. This value was used in the calculation of ET probabilities given in table 2. From the shortening of UO~fluorescent lifetimes as a function of Eu3+ concentration, we conclude that lIT is nonradiative. Recently, it was shown that the quantum number of the fluorescent state of the UO~1~ ion is ~2 = 4 [5]. Since the energy transfer is efficient, we suggest that ET occurs between level ~2= 4 of UO~and a group of Eu3~levels having high absorption probabilities, 5D 5D 2, 3 and ~L6. Some of these levels are situated at higher energies than ~ 4, and may be reached by a phonon assisted process.

References [I] R. Reisfeld, Properties of rare earth doped inorganic glasses as related to their lasing ability, in: Lasers in Physical Chemistry and Biophysics, ed. J. Joussot-Dubien (Flsevier, Amsterdam, 1975) p. 77. [2] R. Reisfeld, Structure and Bonding 13 (1973) 53. [3] R. Reisfeld and L. Boehm,J. Non-Crystalline Solids 16(1974)83. [4] H.D. Burrans and T.J. Kemp, Chem. Soc. Rev. 3 (1974) 139. 151 C.K. JØrgensen and R. Reisfeld, Chem. Phys. Letters 35 (1975) 441.

Discussion J.L. Sommerdijk: In the case of energy transfer, decay curves are expected to be non-exWhat is the form of your decay curves and how did you determine the transfer prob-

ponential.

abilities from them? R. Reisfeld: According to the theory of Inokuti and I-Iirayama non-exponential decay curves should be observed, and from the curvature of the curves the type of multipolar interaction may be determined. In the case where the energy diffuses between the donor ions prior to the transfer to the acceptor ions, a theory of Yokota and Tanimoto predicts non-exponentiality at very short times followed by linear behaviour thereafter. Such behaviour was observed in our case, indicating that at least to some extent our transfer is governed by the diffusion mechanism. E. Grillot: 1. You present the energy transfer here in donor acceptor terms. Don’t you think that the role of Bi must be better understood 3+ is alone, in terms its of main sensitizer? emission corresponds to the transition from when Bi3+ is present 5D 3 levels play an im2.and In one example, when Eutoo, the excited 5D portant role. Don’t you believe that quadupolar interactions 1 and perhaps between 2 Eu Bi3 and Fu3+ can much better explain the energy transfers at long distances, as was the case in the paper presented by Mrs. Bancie-Grillot yesterday in CdF 3~and R. Reisefeld: 2 crystals between Er 1. The sensitizer activator terminology was replaced in chemical literature by donor—acceptor. In energy transfer the meaning is different to the donor acceptor in semiconductors. 2. We believe that dipole quadrupole interaction and dipole dipole interaction are mostly responsible for the transfer, however, one should not disregard the exchange interaction at that

distances. Note that the macroscopic properties measured reflect the overall processes.