Effect of the Cu+ concentration on the curve of thermoluminescence of ZnS:Cu electroluminescent material

In the paper, five ZnS:Cu electroluminescent material specimens were prepared by adding 0.05%, 0.10%, 0.15%, 0.20% and 0.25% Cu+ to ZnS. From the sample's thermoluminescence curve and luminance, the authors can see that with the variation of Cu+ concentration, the peak of thermoluminescence curve changed correspondingly. At first with the increase of Cu+ concentration, the peak of thermoluminescence curve rised gradually. When the Cu+ concentration was 0.05%, the peak of thermoluminescence curve was 124.15 which attainded max, when the Cu+ concentration was 0.25%, the peak of the curve of thermoluminesence forther decreased to 51. But the temperature corresponding to the peak of the curves of thermoluminesence, didn't change, which means that the depth of electron trap did not vary. The authors therefore conclude that excessive Cu+ results in a decline of luminance because the energy of trapped electrons turns into the transition without radiation, though the probability of trapping electrons increases and the life of photoelectrons shortens as the luminescence center increases. In this way, there is an optimal value for Cu+ concentration, which leads to the peak of the curves of thermoluminesence and the maximum of luminance.