To break through the bottle-neck of quantum yield in upconversion(UC) core-shell system, we elucidated that the energy transfer efficiency in core-shell system had an evident contribution from the charge transfer of interface with related to two factors:(1) band offsets and(2) binding energy area density. These two variables were determined by material intrinsic properties and core-shell thickness ratio. We further unraveled the mechanism of non-radiative energy transfer by charge transfer induced dipole at the interface, based on a quasi-classical derivation from F?rster type resonant energy transfer(FRET) model. With stable bonding across the interface, the contributions on energy transfer in both radiative and non-radiative energy transfer should also be accounted together in Auzel's energy transfer(ETU) model in core-shell system. Based on the discussion about interface bonding, band offsets, and formation energies, we figured out the significance of interface bonding induced gap states(IBIGS) that played a significant role for influencing the charge transfer and radiative type energy transfer. The interface band offsets were a key factor in dominating the non-radiative energy transfer, which was also correlated to core-shell thickness ratio. We found that the energy area density with related to core/shell thickness ratio followed the trend of Boltzman sigmoidal growth function. By the physical trend, this work contributed a reference how the multi-layered core-shell structure was formed starting from the very beginning within minimum size. A route was paved towards a systematic study of the interface to unveil the energy transfer mechanism in core-shell systems.
A novel tridentate ligand N-(6-(diphenylphosphoryl)pyridin-2-yl)-2,2,2-trifluoroacetamide(DPPOPFA) was designed and synthesized. Crystal structure of the ligand revealed the "keto" form of ligand in solid state other than the "enol" one, and it was also found that two kinds of molecules with different conformations were connected by hydrogen bonding between amide N–H and phosphoryl P=O. This ionic ligand was used to coordinate a variety of lanthanide ions, forming neutral 3:1 complexes. Absolute overall quantum yields of these complexes in solid states were 36% for Eu(Ⅲ), 29% for Tb(Ⅲ) and 3% for Dy(Ⅲ) with lifetimes of 1.1, 1.1 and 0.087 ms, respectively. The complexes had excellent thermal stability and did not decompose till 370 °C. And they could sublimate in vacuum(1×10^(–4) Pa) at 330 °C due to the weak molecular interaction.
Luminescent lanthanide complexes have been widely investigated as light emitting materials in bio-imaging and sensing, solid state lighting and display, anti-fake tags and light conversion films, due to their characterized photophysical properties including large Stokes shift, long lifetime, and sharp emission spectrum, arising from the sensitized f-f transitions. In this review, we summarize the most recent advances in luminescent lanthanide complexes and their applications from 2015 to August 2017 concerning of general concepts to potential applications. We first introduce the basic concept of sensitized luminescence of lanthanide complexes and the strategies used for highly luminescent complexes. Then recent varieties of luminescent lanthanide complexes and their hybrid materials are presented. Finally, applications are discussed in detail.
Pd-capped Mg_(78)Y_(22) thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated.It is found that rising substrate temperature to 60 ℃ can coarsen the surface of thin film,thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to ~1725 mAh·g^(-1).Simultaneously,the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature.In addition,the specimen exhibits a very long and flat discharge plateau at about —0.67 V,at which nearly 60%of capacity is maintained.The property is favorable for the application in metal hydride/nickel secondary batteries.The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.
Yanyan WangGongbiao XinChongyun WangHuiyu LiWei LiJie ZhengXingguo Li
