It is interesting to investigate the characteristics of luminescence in GaP crystals doped with two kinds of isoelectronic impurities Bi and N.In the present paper

the experimental evidence for exciting energy transfering from N-and NNi-traps to Bi-traps is presented for the first time.Photo- luminescence measurement had been carried out for GaP epilayers under the excitation of 4880A radiation from an Ar-ion laser in the temperature range of 4.2-147K.The PL spectrum were presented which were recorded from GaP:Bi at 4.2K phonon sidebands of the BBi-line

and there were not ABi-line

its phonon sidebands

and the BBi-line.The 4.2K spectra of many GaP-crystals doped with N and Bi were similar to that of GaP-crystal doped with Bi alone.Although the crystals used in these measurements contained nitrogen with a concentration of about 1×10

18

cm

-3

in general the AN-line and NNi-lines were hardly seen in the 4.2K spectra.In the temperature range of 50-77K these lines could only be recorded by radiation detecting system with a higher sensitivity for most of the samples.On the other hand

the EL spectra of LEDs of GaP:(Bi

N) at room temperature showed both N-green emission band (peak) and Bi-emission band (shoulder).Therefore it is reasonable to suggest that there is an exciting energy transfering from N-NNi-traps to Bi-traps to Bi-traps at low temperatures.Based on the experimental results a dynamical model was proposed.The intensity of Bi-emission band iswhele

G is a constant depending on the number of Bi atoms in GaP:(Bi

N)

and excitation density.The termrepresents the energytransfer from N and NNi-pair centres to Bi centres due to tunneling and thermal dissociation.The competition between radiative transition and thermal quenching are represented by 1 and Ae-Ea/kT in denominator.It was pointed out that the energy transfer due to exciton tunneling from N centres and NNi-pair (

i

≥3) traps to Bi traps was predominant at temperatures below 40K and the energy transfer from N and NNi-pair centres to Bi centres due to thermal dissociation predominated above 40K.Above a certain temperature both the two kinds of energy transfer decreased

so that the intensity of AN and NNi-line in the spectra increased with the temperature for the ability of Bi centres to bind excitons had dropped.This formula was used for explaining the temperature dependence of the ratio of the intensity of Bi-emission band in GaP:(Bi

N) samples to that in GaP:Bi sample.