Room-temperature phosphorescence materials from crystalline to amorphous state

Room temperature phosphorescence(RTP)in metal-free organic materials has attracted considerable attention due to its rich excited state properties,high quantum efficiency,long luminescence lifetimes,etc.,showing great potential in organic optoelectronic devices,bioimaging,information anti-counterfeiting,and so forth.The crystals have excellent rigidity and clear molecular packing patterns,which can effectively avoid non-radiative transitions of excitons for phosphorescence enhancement.In the early stages,researchers paid great attention to the regulation of RTP performance in crystalline states.However,due to the complex preparation and poor processability of crystals,amorphous materials with RTP features have become a new research topic recently.This perspective aims to summarize the recent advances of RTP materials from crystalline to amorphous states,and analyze their molecular design strategies and luminescence mechanisms in detail.Finally,we prospect the future research directions of amorphous RTP materials.This perspective will provide a guideline for the future study of advanced RTP materials.

Structural Role of CeO₂in the Modified Borate Glass-Ceramics

A new type of cerium borate glass-ceramic is prepared and studied. The microstructure and crystallization behaviors of the glass samples were investigated by X-ray diffraction (XRD), electron diffraction (ED), and 31P NMR spectroscopy. The microstructures of samples contain <1 mol% CeO2 are amorphous in nature. More addition of CeO2 transforms the glass to glass-ceramics without thermal annealing. The morphological change of the microstructure of these materials was followed by transmission electron microscopy (TEM). The obtained results have revealed that the addition of more than 0.8 mol% CeO2 can promote nucleation and crystallization routes that are combined with the establishment of diverse crystalline phases. Glasses with lower contents of CeO2showed no tendency to crystallization. The crystals of CeO2 containing glasses were spheroid like morphology that was assigned to the three-dimensional fast growth of the well-formed structural species in the boro-apatite phase. In addition, the cerium free glass is characterized by particle-like morphology. Then the growth of spheroid species in three-dimension plays better compatibility and bioactivity behavior than that of the other types of morphology. This is may because the spherical shape has a higher surface area than that of the needle-like morphology. Accumulation and aggregation of small-sized spheres from cerium borate phases played the role of enhancing the hardness of the studied materials.

First-principles study of the co-effect of carbon doping and oxygen vacancies in ZnO photocatalyst

Although tuning band structure of optoelectronic semiconductor-based materials by means of doping single defect is an important approach for potential photocatalysis application,C-doping or oxygen vacancy(Vo)as a single defect in ZnO still has limitations for photocatalytic activity.Meanwhile,the influence of co-existence of various defects in ZnO still lacks sufficient studies.Therefore,we investigate the photocatalytic properties of ZnOx C0.0625(x=0.9375,0.875,0.8125),confirming that the co-effect of various defects has a greater enhancement for photocatalytic activity driven by visible-light than the single defect in ZnO.To clarify the underlying mechanism of co-existence of various defects in ZnO,we perform systematically the electronic properties calculations using density functional theory.It is found that the coeffect of C-doping and Vo in ZnO can achieve a more controllable band gap than doping solely in ZnO.Moreover,the impact of the effective masses of ZnO_(x)C_(0.0625)(x=0.9375,0.875,0.8125)is also taken into account.In comparison with heavy Vo concentrations,the light Vo concentration(x=0.875)as the optimal component together with C-doping in ZnO,can significantly improve the visible-light absorption and benefit photocatalytic activity.

Ultra-strong phosphorescence with 48% quantum yield from grinding treated thermal annealed carbon dots and boric acid composite

Metal-free room-temperature phosphorescence(RTP)materials are of great significance for many applications;however,they usually exhibit low efficiency and weak intensity.This article reports a new strategy for the preparation of a high-efficiency and strong RTP materials from crystalline thermal-annealed carbon dots(CDs)and boric acid(BA)composite(g-t-CD@BA)through grinding-induced amorphous to crystallization transition.Amorphous thermal-annealed CDs and BA composite(t-CD@BA)is prepared following a thermal melting and super-cooling route,where the CDs are fully dispersed in molten BA liquid and uniformly frozen in an amorphous thermal annealed BA matrix after super-cooling to room temperature.Upon grinding treatment,the fracture and fragmentation caused by grinding promote the transformation of the high-energy amorphous state to the lower energy crystalline counterparts.As a result,the CDs are uniformly in situ embedded in the BA crystal matrix.This method affords maximum uniform embedding of the CDs in the BA crystals,decreases nonradiative decay,and promotes intersystem crossing by restraining the free vibration of the CDs,thus producing strong RTP materials with the highest reported phosphorescence quantum yield(48%).Remarkably,RTP from g-t-CD@BA powder is strong enough to illuminate items with a delay time exceeding 9 s.