Excitation Mechanism of SrS Thin-Film Electroluminescence Devices Studied by Excitation Spectra of Photo-Induced Transferred Charge

稀土掺杂碱土硫化物作为多色和全色薄膜电致发光(EL)显示面板的发光材料受到了人们的极大关注。研究发现，掺杂Eu^&lt；2+&gt；和Ce^&lt；3+&gt；发光中心的CaS薄膜，由于(4f)&lt；n-1&gt；(5d)-(4f)^n跃迁而发光，表现出高效的电致发光。根据几个实验结果，认为这些过程起着重要的作用，首先发生发光中心的电离，然后与电子复合，最后产生发光。然而，在新发现之前，还没有观察到发光中心电离的直接证据。在这项工作中，我们研究了Eu^&lt；2+&gt；和Ce^&lt；3+&gt；掺杂的CaS和SRS薄膜EL器件的光致转移变化，为发光中心的电离提供了直接的证据。实验结果描述如下：1。光电…的光谱响应研究了Eu^&lt；2+&gt；和Ce^&lt；3+&gt；掺杂的CaS和SRS薄膜EL器件中更多的感生转移电荷Delta Q。对于掺Eu^&lt；2+&gt；的EL器件，在400-600 nm的宽波范围内观察到了增量Q的增加。对于Ce^&lt；3+&gt；掺杂的器件，在440 nm附近观察到增量Q的增加。结果表明，光致转移电荷的激发光谱与光致发光的激发光谱一致。这一结果表明，当Eu^&lt；2+&gt；或Ce^&lt；3+&gt；发光中心被激发到(4f)^&lt；n-1&gt；(5d)激发态时，其发光中心被电场电离。电致发光的动力学由发光中心的场相关电离和电离中心的场相关陷阱控制，而不是由发光中心的碰撞激发所控制。我们计算了发光中心的电离几率随电场的变化。在1×10~(-6)V/cm以上的强电场作用下，Eu~(2+)和Ce~(2+)发光中心发生电离，而不是发光跃迁。该激发模型很好地解释了这些器件的电致发光特性。较少

Rare-earth doped alkaline-earth sulfides have been receiving a great deal of attention as a phosphor materials for malti- and full-color thin-film ElectroLuminescent (EL) display panels. It has been found that CaS thin-films doped with Eu^<2+> and Ce^<3+> luminescent centers, which give rise to luminescence due to (4f)^<n-1>(5d)-(4f)^n transitions, Show the efficient EL. Based on several experimental results, it has been argued that the processes play an important role in that the ionization of luminescent centers first occurs, subsequent recombination with electrons follows, and finally luminescence arises. However no direct evidence of the ionization of luminescent centers has been observed until new. In this work, we studied the photo-induced transferred change in Eu^<2+> and Ce^<3+> doped CaS and SrS thin-film EL devices, which give us direct evidence of ionization of luminescent centers. The experimental results are described in the following.1. The spectral response of the photo- … More induced transferred charge DELTA Q in Eu^<2+> and Ce^<3+> doped CaS and SrS thin-film EL devices has been studied. For the Eu^<2+> doped EL devices, the increase in DELTA Q is observed for wide wave region from 400 to 600 nm. For the Ce^<3+> doped devices, the increase in DELTA Q is observed at around 440 nm.2. It is found that the excitation spectra of the photo-induced transferred charge agree with those of photoluminescence. This results implies that Eu^<2+> or Ce^<3+> luminescent centers are ionized by electric field when the centers are excited to the (4f)^<n-1>(5d) excited state. The dynamics of the EL emission is controlled by field dependent ionization of the luminescent centers, and by field-dependent trapping at the ionized centers rather than impact excitation of the luminescent centers.3. We have calculated the ionization probability of the luminescent centers as a function of electric field. The ionization of the Eu^<2+> or Ce^<3+> luminescent centers takes place rather than luminescent transition under the strong electric field over 1X10^6 V/cm. EL characteristics of these EL devices are well explained by this excitation model. Less