Experimental Physics Department, Ural Federal University, 19 Mira Street, Ekaterinburg 620002, Russia.
J Phys Condens Matter. 2012 Oct 10;24(40):405902. doi: 10.1088/0953-8984/24/40/405902. Epub 2012 Sep 18.
The anomalous (τ < 10 ns) luminescence of wide bandgap crystals of lithium-gadolinium orthoborate Li(6)GdB(3)O(9) doped with trivalent cerium ions, has been revealed for the first time and investigated through the low-temperature time-resolved vacuum ultraviolet synchrotron spectroscopy. It was shown that the optical transitions at 6.2 eV are due to electron transfer from the ground 4f(1) states of Ce(3+) ion onto the autoionized states near the conduction band bottom of a crystal. These transitions lead to the formation of impurity-bound excitons in the form of correlated electron-hole pair, in which the hole component is localized at 4f-level of the cerium ion and an electron component is located at the conduction band bottom in the attractive potential of this hole. It is established that the direct radiative recombination of the cerium impurity-bound exciton leads to a fast broadband emission at 4.25 eV. The energy threshold for creation of the impurity-bound excitons was determined on the basis of the obtained spectroscopic data. We calculated the H(k) functions of distribution of the elementary relaxations over the reaction rate constants and explained on this basis the decay kinetics and quenching processes, not only for the anomalous emission at 4.25 eV, but for the ordinary 5d-4f luminescence at 3.0 eV in Ce(3+) ions. The paper discusses the decay channels for the impurity-bound excitons and their influence on the decay kinetics and spectra of luminescence in Li(6)GdB(3)O(9) crystals.
首次揭示并通过低温时间分辨真空紫外同步辐射光谱研究了掺三价铈离子的宽带隙晶体六硼酸锂镓（Li(6)GdB(3)O(9)）的异常（τ < 10 ns）发光。结果表明，6.2 eV 的光学跃迁归因于电子从 Ce(3+) 离子的基态 4f(1) 态转移到晶体导带底部的自电离态。这些跃迁导致以相关电子-空穴对形式形成杂质束缚激子，其中空穴部分定域在铈离子的 4f 能级，电子部分位于该空穴的吸引力势中的导带底部。确定了铈杂质束缚激子的直接辐射复合导致 4.25 eV 的快速宽带发射。基于获得的光谱数据确定了杂质束缚激子的创建的能量阈值。我们计算了反应速率常数上的基本弛豫分布的 H(k) 函数，并在此基础上解释了衰减动力学和猝灭过程，不仅对于 4.25 eV 的异常发射，而且对于 Ce(3+) 离子的 3.0 eV 的普通 5d-4f 发光。本文讨论了杂质束缚激子的衰减通道及其对 Li(6)GdB(3)O(9)晶体中发光衰减动力学和光谱的影响。
