Emission efficiency of the laser and luminescence materials depends directly on the concentration of active centers. In order to obtain a high efficient material

one usually hopes to increase the concentration to as a high level as possible. However

the energy transfer between active ions at a high concentration level often causes fluorescence quenching. Therefore

the study of energy transfer processes including resonant and phonon-assisted processes is important in both theory and practice. The effect of mass difference between ions of the host crystals on the phonon assisted energy transfer rates of activeions in the crystals has been discussed in this paper. Besides that resulted from the change of phonon frequency

this effect can be expressed as a multiplication factor

D

2

for the single-phonon assisted energy transfer and

D

4

for the two-phonon assisted energy transfer. The expressions of factor

D

for the case when the crystal is composed by two kinds of ions

i.e.

n

ions with mass

m

and

n

ions with mass

m

is

<

img style="vertical-align: middle" alt="" order="0" src="http://www.rhhz.net/qikantupian/fgxb-20030202-117-1.gif" /

>

where

n

=

n

+

n

and

m

=

nm

+

nm

. Generally

when the crystal composed by

p

kinds of ion

one have

<

img style="vertical-align: middle" alt="" order="0" src="http://www.rhhz.net/qikantupian/fgxb-20030202-117-2.gif" /

>

It is clear that one can use this equation to take into account the influence of the mass difference on the energy transfer rates.