Abstract

When zinc silicate with a violet luminescence peaked at 370 nm is doped with gallium in concentrations of 1).001 2).005 3).2 4)1.0 mol % gallium oxide a new emission band with a maximum at 420 nm is established as shown in Fig. 1. The separation of both superimposed emission bands is possible because of their different luminescent decay times. By such doping additional traps are introduced as could be proved by the thermal glow curves for the 1) 0 2). 01 3) .2 mol % gallium oxide concentrations after a 4 minute excitation with 220 nm and a heating rate of 14 K/min as shown in Fig. 2. The doped samples are distinguished by an increased light sum and photoconductivity. The red shift of the time-resolved emission spectra for zinc silicate doped with .8 mol % gallium oxide at 20 K as shown in Fig. 3 allows to assume that radiating donator-acceptor-pair transitions i.e. radiating tunneling processes between shallow traps and excited activator centers are involved in the charge recombination process. This is in agreement with the results shown in Fig. 4a, where the time dependence of the temperature (1) and the luminescence (2) of the doped sample after excitation with 250 nm at 100 K are compared. Below 50 K a remarkable increase in luminescence intensity is observed. The number of electrons thermally released from the shallow traps is certainly small at these low temperatures. This behaviour is also seen in Fig. 4b, where the cooling process has been interrupted by short periods of heating. In the range between 45 K and 60 K the decay of the luminescence is temperature independent, which demonstrates that no thermally stimulated recombination occurs. The additional luminescence can therefore be explained only by electron tunneling from shallow traps to excited activator centers.

© 1984 Optical Society of America