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

根据稀土离子对(如Gd^&lt；3+&gt；-Eu^&lt；3+&gt；)的下转换量子切割的概念，在具有最佳稀土离子浓度的稀土基氟化物中，量子效率高于100%的可见量子切割在理论上是可能的。(1)在真空紫外光激发下，观察到KGd_3F；10&gt；：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Gd^&lt；3+&gt；和KLiGdF_5：Eu&lt；3+&gt；。这可以导致Eu^&lt；3+&gt；的^5D_0-^7 F_J跃迁产生可见光发射，量子效率高于100%。用e-…几率计算和讨论了可见量子切割所需的交叉弛豫效率与Eu~(2+)浓度和晶体结构的关系更多的能量转移是稀土原子间距离的函数。在这四种氟化物的交叉驰豫步骤中，KGd3F&lt；10&gt；：Eu^&lt；3+&gt；表现出最高的效率。对于掺杂2 at.%Eu^&lt；3+&gt；的KGd_3F_&lt；10&gt；，其交叉驰豫效率最高，为0.65。如果假设没有能量迁移到猝灭中心的非辐射损失，则量子效率为165%。KLiGdF_5：Eu^&lt；3+&gt；，CsGd_2F_7：Eu^&lt；3+&gt；，KGd_2F_7：Eu^&lt；3+&gt；，CsGd_2F_7：Eu^&lt；3+&gt；的最高交叉驰豫效率分别为0.40，0.15，0.05。从Eu5D0发射的临界浓度猝灭和最近邻稀土离子个数两个方面评价了KGd3F；10&gt；：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；(2)研究了KGd_3F_&lt；10&gt；：Eu^&lt；3+&gt；KLiGdF_5：Eu^&lt；3+&gt；和CsGd_2F_7：Eu^&lt；3+&gt；晶体中量子切割的动力学行为。用ArF准分子激光真空紫外光激发，研究了KGd_3F；10&gt；，KLiGdF_5：Eu^&lt；3+&gt；和CsGd_2F_7：Eu^&lt；3+&gt；的时间分辨发射光谱。^5Do辐射在衰变剖面中具有较早的上升，而^5D_1发射在剖面中具有较晚的上升。这些结果表明，在真空紫外光激发下，Gd^&lt；3+&gt；的6G_J能级通过两步能量转移(下转换)发生量子切割。(3)新发现的Ce^&lt；3+&gt；黄长石和Eu^&lt；3+&Gt；的紫外光或可见激发。掺杂的Ba2SiO4和Ba3SiO5晶体除了本征发光外，还在Ce^&lt；3+&gt；或Eu^&lt；2+&gt；离子的蓝/绿和黄色区域产生了长时间的磷光。在时间域积分的长余辉发光强度随温度变化的结果表明，由紫外光或可见光激发产生的电子和空穴通过热跳跃和/或隧道传输回到晶体中的Ce^&lt；3+&gt；或Eu^&lt；2+&gt；位，并在Ce^&lt；3+&gt；或Eu^&lt；2+&gt；处辐射复合。较少

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