The equivalent or hetervalent substitution strategy is an efficient way to stimulate photoluminescence tuning or to optimize the luminescence performances of phosphor materials. Garnet-type compounds receive much attention as phosphor hosts due to their flexible structural frameworks. Herein, a garnet-type broadband-emitting Lu 2 MgAl 4 SiO 12 :Eu 2+ phosphor is firstly explored with the two-site occupation via varying the Eu 2+ content. Two host substitution approaches to control the luminescence behavior of Lu 2 MgAl 4 SiO 12 :Eu 2+ phosphor is implemented. Based on the cation substitution strategy of Ca 2+ for Mg 2+ , it achieves continuously tunable emission from 463 nm to 503 nm together with broadening emission bands in Lu 2 Mg 1-y Ca y Al 4 SiO 12 :Eu 2+ phosphors. Moreover, chemical unit cosubstitution of [Ca 2+ -Ge 4+ ] replacing [Lu 3+ -Al 3+ ] results in Lu 2-z Ca z MgAl 4-z Ge z SiO 12 :Eu 2+ phosphors, which induces a red-shift of the emission peak of about 60 nm and a broadening in the emission spectra with an increasing Ca 2+ and Ge 4+ concentration. The possible photoluminescence tuning mechanism is ascribed to the coordination sphere variation in the EuO 8 polyhedron depending on the changing neighboring cations. The proposed approaches on equivalent or hetervalent substitution can contribute to the developing of Eu 2+ -activated garnet-type phosphors with regulating luminescence performance and further initiate research discovering new phosphors for white light-emitting diodes.
The reactive power compensation of converter station plays an important role in the design of HVDC project. Reactive power configuration for HVDC converter station is introduced in this paper. The regulation and control of reactive power and devices are considered from both steady-state and dynamics aspects. The performance of various reactive power configuration methods are compared and summarized. The principle, characteristics and application of shunt and series reactive power compensation device and a brief description of the reactive power support capacity of AC system are given. The adjustment of transformer tap changer and firing angle can also affect reactive power level. It comes to a conclusion that proper reactive compensation devices should be chosen carefully in converter station, and AC system reactive support capacity and the behavior of HVDC system must be fully taken into consideration when the comprehensive configuration of reactive power of converter station is determined.
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