The Inductive Effect of Neighboring Cations in Tuning Luminescence Properties of the Solid Solution Phosphors.

Forming solid solutions through cation substitution is an efficient way to improve the luminescence properties of Ce3+ or Eu2+ activated phosphors and even to develop new ones, which is badly needed for phosphor-converted white LEDs. Here, we report new color tunable solid solution phosphors based on Eu2+ activated K2Al2B2O7 as a typical case to demonstrate that, besides crystal field splitting of 5d levels, centroid shift and Stokes shift can be dominant in tuning excitation and emission spectra as well as thermal stability of solid solution phosphors, both of which were previously considered to be negligible. Moreover, a general model involving the inductive effect of neighboring cations is proposed to explain the obvious variations in centroid shift and Stokes shift with cation substitution. Our work is propitious for the construction of more reasonable structure-property relations and thus offers theoretical guidance for designing solid solution phosphors.

Enhanced ∼2 µm Emission of Tm3+ in Lu2O3 by Addition of a Trace Amount of Er3.

Er3+-induced intensity enhancement of ∼2 µm emission is observed in 2 atom % Tm3+ doped Lu2O3 under 782 nm excitation. The maximum enhancement reaches 41.9% with only 0.05 atom % Er3+. Er3+ introduces a new quantum cutting process which is proved to be a Tm3+ → Er3+ → Tm3+ forward-backward energy transfer (FBET) system. The FBET system is observed to work efficiently even at very low Er3+ concentration. Thus, energy loss due to energy migration among Tm3+ ions is suggested to be suppressed by the FBET process. The Tm3+ → Er3+ → Tm3+ FBET system may be a new route to improve the performance of Tm3+ lasers.

Synergetic dielectric loss and magnetic loss towards superior microwave absorption through hybridization of few-layer WS2 nanosheets with NiO nanoparticles.

WS2 nanomaterials have attracted great attention in the field of electromagnetic wave absorption due to their high specific surface area, layered structure, and peculiar electronic properties. However, further improvements on their limited electromagnetic absorbing (EMA) capacity and bandwidth are urgently required for their practical application as EMA absorbents. In this work, WS2/NiO hybrids with heterostructures are prepared by a hydrothermal method and developed into EMA absorbents. The maximum reflection loss of the hybrids with 20% NiO loading could reach -53.31 dB at a thickness of 4.30 mm; the bandwidth with a reflection loss value of less than -10 dB is determined to be 13.46 GHz (4.54-18 GHz) when the thickness of the absorbent is between 3.5 and 5.5 mm. It is found that the enhanced EMA performance of WS2/NiO hybrids is caused by the addition of magnetic NiO, which could result in the interfaces between WS2 and NiO being responsible for the synergetic magnetic loss and dielectric loss in the hybrids. This work provides a new approach for the design of excellent EMA materials for practical applications.

Facile synthesis of highly conductive MoS2/graphene nanohybrids with hetero-structures as excellent microwave absorbers.

Two-dimensional (2D) MoS2/graphene nanosheet (MoS2/GN) hybrids have been demonstrated to be promising microwave absorption (MA) materials due to their unique chemical and physical properties as well as rich impedance matching. However, the reported strategies for preparing MoS2/GN hybrids have limited their application potential due to the complex, high-cost and inefficient preparation processes. On the other hand, it is of note that the main source of graphene is based on converting insulating graphene oxides (GO) back to conductive reduced graphene oxides (RGO). Thus, the MA performance of obtained MoS2/RGO nanohybrids is greatly affected by the conversion process of GO. In this work, we prepared the MoS2/GN hybrids by a facile hydrothermal method with directly introducing highly pure and electroconductive GNs. It is found that the highest reflection loss value of the sample-wax containing 40% MoS2/GN is -57.31 dB at a thickness of 2.58 mm, and the bandwidth of RL values less than -10 dB can reach up to 12.28 GHz (from 5.72 to 18 GHz) when an appropriate absorber thickness between 1.5 and 4 mm is chosen. The excellent MA performances emanate from effective conjugation of MoS2 with GN (Mo-C bond between the interfaces), which provides the dielectric loss caused by multi-relaxation, conductance, and polarization. Taking into account the facile synthesis route and their excellent MA performance, the MoS2/GNs hybrid nanosheets and those composite materials with similar isomorphic hetero-structures are very promising for a wide range of MA applications.