Quantum cutting through downconversion in rare-earth compounds by crystal-field control

根据通过稀土离子对（例如Gd^3+-Eu^3+）的下转换的量子切割的概念，对于具有最佳稀土离子浓度的稀土基氟化物中的VUV激发，具有高于100%的量子效率的可见量子切割在理论上是可能的。在本研究中，所获得的结果总结如下。（1）在真空紫外光激发下，在KGd_3F_7：Eu^&lt;3+&gt;、KGd_2F_7：Eu^&lt;3 +&gt;、KLiGdF_5：Eu^&lt;3+&gt;中观察到Gd^&lt;3 +&gt;-Eu^&lt;3 +&gt;对的下转换可见光量子剪裁（每个吸收的光子发射两个可见光光子）<10>。由于Eu^&lt;3+&gt;的^5D_0 -^7F_J跃迁，这可以导致量子效率高于100%的可见光发射。本文还从电子跃迁几率的角度，讨论了可见光量子剪裁所需的交叉弛豫效率与Eu^&lt;3+&gt;浓度和晶体结构的关系 关于我们 能量传递是稀土原子间距离的函数。KGd_3F_<10>：Eu^&lt;3+&gt;在这四种氟化物的交叉弛豫步骤中表现出最高的效率。当KGd_3F_2掺杂量为2at.%时，交叉弛豫阶跃效率最高，为0.65<10>Eu ~（3+）。如果假设没有由于能量迁移到猝灭中心而引起的非辐射损失，则量子效率为165%。KLiGdF_5：Eu^&lt;3+&gt;，CsGd_2F_7：Eu^&lt;3+&gt;和KGd_2F_7：Eu ^&lt;3 +&gt;，CsGd_2F_7：Eu^&lt;3+&gt;的最大交叉弛豫效率分别为0.40，0.15，0.05。根据Eu^&lt;3+&gt;的^5D_0发射的临界浓度猝灭和最近邻稀土离子的数目，评价了在KGd_3F_7<10>：Eu^&lt;3+&gt;、KGd_2F_7：Eu^&lt;3 +&gt;、CsGd_2F_7：Eu^&lt;3+&gt;和KLiGdF_5：Eu^&lt;3+&gt;中，受激Gd^&lt;3+&gt;离子可以将能量转移到第三近邻Eu^&lt;3+&gt;。(2)We研究了KGd_3F_7<10>：Eu^&lt;3+&gt;、KLiGdF_5：Eu^&lt;3+&gt;和CsGd_2F_7：Eu^&lt;3+&gt;晶体中量子剪裁的动力学行为。用<10>ArF准分子激光器真空紫外激发Gd^&lt;3+&gt;，研究了KGd_3F_5：Eu ^&lt;3+&gt;、KLiGdF_5：Eu^&lt;3+&gt;和CsGd_2F_7：Eu^&lt;3 +&gt;的Eu^&lt;3 +&gt;发射的时间分辨光谱。在衰变曲线中，^5Do发射的上升较早，而^5D_1发射的上升较晚。这些结果表明，在真空紫外激发下，Gd^&lt;3+&gt;的^6G_J能级发生量子剪裁，这是通过交叉弛豫从Gd^&lt;3+&gt;到Eu^&lt;3+&gt;的两步能量转移（下转换）以及随后剩余的激发能通过Gd^&lt;3+&gt;亚晶格迁移而实现的。(3)UV对新发现的Ce^&lt;3+&gt;掺杂黄长石晶体Ca_2Al_2SiO_7和Eu^&lt;3+&gt;掺杂Ba_2SiO_4和Ba_3SiO_5晶体进行可见光激发，除了本征发光外，Ce^&lt;3+&gt;或Eu^&lt;2+&gt;离子还在蓝/绿色和黄色区域产生长余辉磷光。在时间域中积分的长余辉发光强度的温度依赖性的结果表明，由紫外或可见光激发产生的电子和空穴通过热跳跃和/或隧穿运动回到晶体中的Ce^&lt;3+&gt;或Eu^&lt;2+&gt;位置，并在Ce^&lt;3+&gt;或Eu^&lt;2+&gt;处辐射复合。少

In accordance with the concept of quantum cutting through downconversion for the rare-earth ion couple, -for example Gd^<3+>-Eu^<3+>, visible quantum cutting with a quantum efficiency of higher than 100% is theoretically possible for VUV excitation in rare earth based fluorides with an optimal rare-earth ion concentration. In this research the results obtained are summarized as follows.(1)Upon VUV excitation of Gd^<3+>, visible quantum cutting (the emission of two photons of visible light per absorbed photon) through downconversion is observed for the Gd^<3+>-Eu^<3+> couple in KGd_3F_<10> : Eu^<3+>, KGd_2F_7: Eu^<3+>CsGd_2F_7 : Eu^<3+>, and KLiGdF_5 : Eu^<3+>. This can result in visible emission due to the ^5D_0 -^7 F_J transition of Eu^<3+> with a quantum efficiency higher than 100%. The dependence of the efficiency of cross-relaxation required for visible quantum cutting on the Eu^<3+> concentration and crystal structure is and evaluated and discussed in terms of the probability of e … More nergy transfer as a function of the rare-earth interatomic distance. KGd_3F_<10> : Eu^<3+> exhibits the highest efficiency in the cross-relaxation step of these four fluorides. The highest efficiency of the cross-relaxation step, 0.65, is obtained for the KGd_3F_<10> doped with 2 at.% Eu^<3+>. If it is assumed that there are no non-radiative losses due to energy migration to quenching centers, the quantum efficiency is 165%. The highest cross-relaxation efficiency for KLiGdF_5 : Eu^<3+>, CsGd_2F_7 : Eu^<3+>, and KGd_2F_7 : Eu^<3+>, CsGd_2F_7 : Eu^<3+> are 0.40, 0.15, 0.05, respectively. From the critical concentration quenching of the ^5D_0 emission of Eu^<3+> and number of nearest-neighbor rare-earth ion, it was evaluated that in KGd_3F_<10> : Eu^<3+>, KGd_2F_7 : Eu^<3+>, CsGd_2F_7 : Eu^<3+>, and KLiGdF_5 : Eu^<3+> an excited Gd^<3+> ion can transfer its energy to third-nearest Eu^<3+> neighbors.(2)We have examined dynamical behavior of quantum cutting in KGd_3F_<10> : Eu^<3+> KLiGdF_5 : Eu^<3+> and CsGd_2F_7 : Eu^<3+> crystals. Time resolved spectra of emissions Eu^<3+> for KGd_3F_<10> : Eu^<3+>, KLiGdF_5 : Eu^<3+>, and CsGd_2F_7 : Eu^<3+> have been studied upon VUV excitation of Gd^<3+> using an ArF excimer laser. The ^5Do emission has an earlier rise in the decay profiles, while the ^5D_1 emission has a later rise in the profiles. It was clarified from the these results that upon VUV excitation in the ^6G_J levels of Gd^<3+> quantum cutting occurs through a two-step energy transfer (downconversion) from Gd^<3+> to Eu^<3+> by cross-relaxation and sequential the remaing excitation energy migration via the Gd^<3+> sublattice.(3)UV or visible excitation for newly discovered Ce^<3+>-doped melilite crystals Ca_2Al_2SiO_7 melilite and Eu^<3+>-doped Ba_2SiO_4 and Ba_3SiO_5 crystals produces long-lasting phosphorescence in the blue/green and yellow regions from Ce^<3+> or Eu^<2+> ions in addition to the intrinsic luminescence. The results of the temperature dependence of the long-lasting phosphorescence intensities integrated in a time domain suggest that electrons and holes produced by UV or visible excitation move back to Ce^<3+> or Eu^<2+> sites in the crystals though thermal hopping and/or tunneling and recombine radiatively at Ce^<3+> or Eu^<2+>. Less