Circularly polarized light emission and detection by chiral inorganic semiconductors

Chiral inorganic semiconductors with high dissymmetric factor are highly desirable,but it is generally difficult to induce chiral structure in inorganic semiconductors because of their structure rigidity and symmetry.In this study,we introduced chiral ZnO film as hard template to transfer chirality to CsPbBr3 film and PbS quantum dots(QDs)for circularly polarized light(CPL)emission and detection,respectively.The prepared CsPbBr_(3)/ZnO thin film exhibited CPL emission at 520 nm and the PbS QDs/ZnO film realized CPL detection at 780 nm,featuring high dissymmetric factor up to around 0.4.The electron transition based mechanism is responsible for chirality transfer.

Dehydration at subduction zones and the geochemistry of slab fluids

Subducting oceanic slabs undergo metamorphic dehydration with the increase of temperature and pressure during subduction.Dehydration is an essential step for element recycling,and slab fluids are critical agents for mediating slab-mantle interaction.Dehydration is mainly controlled by the thermal structure of subduction zones and the stability of hydrous minerals.At fore-arc depths,slab dehydration produces aqueous fluid with dissolved salts such as NaCl.As subduction proceeds deeper,the content of silicate components increases.At sub-arc and post-arc depths,a hydrous silicate melt is likely to form,or a supercritical fluid could arise from complete miscibility between silicates and H_(2)O.The partitioning of elements between slab fluid and the residual solid rock is controlled by the type of fluid,and generally it is the supercritical fluid that is the most capable of mobilizing trace elements,being an effective carrier even for high field strength elements.Understanding the chemistry of slab fluids relies on sophisticated integration of experiments,theoretical computation and investigation of natural rock samples.This contribution focuses on the content and speciation of key volatiles,including carbon,nitrogen and sulfur,in slab fluids as well as important fluid properties such as oxygen fugacity and acidity.The properties of slab fluids show complicated variation under the control of mineral assemblages and T-P conditions.Slab fluids at great depths of subductions have been inferred to be modestly alkaline and not necessarily very oxidizing as often assumed.Further progress in the research of slab dehydration and the chemistry and properties of slab fluids demands urgently the development of innovative experimental and computational technology including in situ analytical methods at high T-P.

Giant enhancement of photoluminescence quantum yield in 2D perovskite thin microplates by graphene encapsulation

The optoelectronic performances of the layered materials are strongly dependent on the thickness of the samples due to the surface effect.As the size of the samples decreases to few nanometers,the surface depletion field and surface defect density are prominent arising from the large surface to volume ratio.For instance,thin two-dimensional(2D)organic-inorganic hybrid perovskite microplates usually exhibit a rather low photoluminescence quantum yield(PLQY),owning to the strong surface effect.Here,we report that the PLQY can be enhanced as large as 28 times in(iso-BA)2Pbl4(BA=C4H9NH3)2D perovskite thin microplates encapsulated by graphene,resulting in that the PLQY is more than 18%for the microplate with a thickness of 6.7 nm at 78 K.As the thickness of the 2D perovskite microplate increases,the enhancement is gradually reduced and finally vanishes.This observation is in striking contrast to that in monolayer transition metal dichalcogenides(TMDs),when the PLQY is quenched by covering a layer of graphene due to the efficient charge transfer.The enhancement of PLQY in 2D perovskites can be mainly ascribed to the reduced quantum confined Stark effect(QCSE)due to the reduced surface depletion field after covering graphene flake,resulting in the enhanced radiative recombination efficiency.Our findings provide a cost-effective approach to enhance the luminescence,which may pave the way toward high performance light emitting devices based on 2D perovskites.

Surface depletion field in 2D perovskite microplates: Structural phase transition, quantum confinement and Stark effect

Surface depletion field would introduce the depletion region near surface and thus could significantly alter the optical,electronic and optoelectronic properties of the materials,especially low-dimensional materials.Two-dimensional(2D)organic—inorganic hybrid perovskites with van der Waals bonds in the out-of-plane direction are expected to have less influence from the surface depletion field;nevertheless,studies on this remain elusive.Here we report on how the surface depletion field affects the structural phase transition,quantum confinement and Stark effect in 2D(BA)2PbI4 perovskite microplates by the thickness-,temperature-and power-dependent photoluminescence(PL)spectroscopy.Power dependent PL studies suggest that high-temperature phase(HTP)and low-temperature phase(LTP)can coexist in a wider temperature range depending on the thickness of the 2D perovskite microplates.With the decrease of the microplate thickness,the structural phase transition temperature first gradually decreases and then increases below 25 nm,in striking contrast to the conventional size dependent structural phase transition.Based on the thickness evolution of the emission peaks for both high-temperature phase and low-temperature phase,the anomalous size dependent phase transition could probably be ascribed to the surface depletion field and the surface energy difference between polymorphs.This explanation was further supported by the temperature dependent PL studies of the suspended microplates and encapsulated microplates with graphene and boron nitride flakes.Along with the thickness dependent phase transition,the emission energies of free excitons for both HTP and LTP with thickness can be ascribed to the surface depletion induced confinement and Stark effect.