The photoluminescence and photoluminescence excitation spectra of a series of ZnS_{1- x}Te_x alloys at various temperatures have been studied. We have observed a strong enhancement in the luminescence intensity as compared to the ZnS and ZnTe compounds, a large broadening in the luminescence peak range from 350nm to 750nm which cover the whole visible range. The PLE spectra show that the Edge State E_D exists in the samples when doped with Al, either due to the N-type doping of Al or the Al induced defect states. The Te₁ center density is very sensitive to the change of composition near 2.2%. The PL peak of Te₁ can be observed clearly at composition below 2.2%. However, the Te₁ peak intensity decreases quickly once the x value is above 2.5%. Al doping increases the PL intensity for low x val...[ Read more ]

The photoluminescence and photoluminescence excitation spectra of a series of ZnS_{1- x}Te_x alloys at various temperatures have been studied. We have observed a strong enhancement in the luminescence intensity as compared to the ZnS and ZnTe compounds, a large broadening in the luminescence peak range from 350nm to 750nm which cover the whole visible range. The PLE spectra show that the Edge State E_D exists in the samples when doped with Al, either due to the N-type doping of Al or the Al induced defect states. The Te₁ center density is very sensitive to the change of composition near 2.2%. The PL peak of Te₁ can be observed clearly at composition below 2.2%. However, the Te₁ peak intensity decreases quickly once the x value is above 2.5%. Al doping increases the PL intensity for low x value alloys, but decrease the PL intensity and makes the overall crystal quality worse for high x value alloys.

The PL intensity is strongly dependent on temperature and at different temperature, different Te_n dominate the PL emission. The Te_n centres are not in thermal equilibrium with one another. Rather, at low temperatures, the radiationless resonance energy transfer is dominated, and at high temperatures, the energy transfer by exciton migration dominates. The peak position energies are linearly dependent on temperature in most of our case. However, the temperature coefficient for each peak is in general different, even within the same sample, an evidence of the complicated electronic properties of the iso-electronic centers.

Quantum Confinement effect of iso-electronic centres in quantum wells has been observed in our samples QW 70 and QW 71. The photon energy is much higher than those ZnSTe with the same x value in the well. That is the first time the iso-electronic centres in quantum well structures are studied.

Photoluminescence and photoluminescence excitation are very good techniques and non-destructive ways to study the optical properties of the ZnSTe alloys. The ZnSTe alloy is potentially an important material system for short wavelength optoelectronic applications.