It is well known that if donor-donor transfer can be omitted

the energy transfer between donors and acceptors can be described by static model

[1

2]

. In this case the decay of the donor fluorescence can be expressed by F(t)=exp(-γt)f(t)=exp(-γt)exp[ΣIn(1-C

A

+C

A

exp(-X

0

t))]

(2) where γ is the intrinsic decay rate of the donor

C

A

is the concetration of the acceptor

X

0n

is the transfer rate between the donor at the origin and the acceptor at the site

n

the summation is taken over all cells. With the approximation of isotropic contineous medium and C

A

<

<

1

it was shown

[1

2

3]

for electric multipole interaction lnf(t)=-C

A

(X

0

t)

3/s

Γ(1-3/s)

(4) where X

0

is the D-A transfer rate at the separation R

0

the radius of the Wigner-Seitz sphere. This expression is valid if X0t

>

>

1.If C

A

<

<

1 is invalid

more terms should be taken in the expansion of (2). It is shown in this paper

that (4) must be modified by lnf(t)=-1n(l-C

A

)-A(C

A

)C

A

(X

0

t)

3/s

Γ(l-3/s)

(7).