Fabrication And Applications Of Functional Micro/nano-devices Based On Solid State Luminescent Materials

Organic luminescent materials have attracted wide research concerns in fields of solid-state lighting,light emitting diodes(LEDs),optical sensing and organic luminescent display devices because of the intrinsic merits such as the good luminescence properties,structural modification feasibility and widely tunable spectral range.In terms of practicability,the luminescent materials are more favorably and widely incorporated in the solid-state devices than the solution or dispersion phase.However,most of traditional luminophors suffer from the aggregation-cause quenching(ACQ)effect with sharply luminescence quenching in high-concentration liquids and solid-state films,which limits the practical applications of fabricated devices.In order to reduce the ACQ effect,the luminophors can be uniformly dispersed into a solid matrix or modified with functional groups of large steric hinderance to avoid aggregations,for instance,conjugated organic polymers show high luminescent efficiency in solid state due to their large side chains.Even though the above method can reduce ACQ effect to a certain extent,they never get rid of this phenomenon.The presence of aggregation-induced emission luminogen(AIEgen)fundamentally sovle this problem based on their novel luminescent mechanism(restrictin of intramolecular motions,RIM)and distorted molecular conformation,which show high luminescence efficiency in solid state and open a new door for the development of solid devices.However,the development of AIE materials in solid-state devices is still in the initial stage,and their fabrication techniques and applications are not mature.As reported in the previous literatures,AIE based solid luminescent devices are mainly film devices,and some 1D micro/nanodevices via simple processing techniques,which cannot meet the increasing demand form device variety and performance improvement.Thus,it is of great significance to flexibly construct a variety of AIE solid devices with specific functionality via some mature techniques(e.g.,UV-photolithograph,femtosecond laser direct writing).Our work will focus on the existing problems on luminescent materials and processing techniques,and attempt to solve the problems from some aspects,such as molecular design and synthesis,device fabrication,and practical applications.Specifically,we will investigate the prossibility of some processing methods(like UV lithography,laser direct writing)in micro/nanodevice farbrication,and their applications in optical sensing,microlasers,etc.The research results mainly contain the following four aspects:1.We rationally designed and synthesized three kinds of AIE materials through molecular levels,and further investigated their processability for solid devices.To solve the processing problems caused by the poor film quality of AIE,we obtained the smart composite resists by mixing AIEgens into the epoxy resin SU-8 for device fabrication.The AIEgens exhibit high luminous quantum efficiency in resin matrix,and also high chemical stability,good photostability and thermostability,which is suitable for solid devices.Besides,the oxetane groups are modified on the main AIE structures(AIEoxe)to guarantee the fabricating feasibility of composite resists because of the crosslink property between AIEoxe and SU-8 matrix.Besides,the existance of oxetance improves the miscibility of AIEoxe in SU-8,which eliminate the negative effects of aggragarion on the device morphology.2.We fabricated large-area AIEoxe based microstructure arrays using simple UV lithography technique,and explored their applications in the detection of organic solvents.The fabricated AIEoxe composite micro-arrays have smooth morphologies and various sizes,and emit uniform and strong fluorescence under UV light.We applied the fabricated micro/nano-structures to liquid VOC sensing in consideration of the VOC-stimuli fluorescence response of AIEgens and the excellent organic solvent tolerance of crosslinking structures.Three monochromatic microstructures show different fluorescence response towards acetone,tetrahydrofuran(THF),dimethylformamide(DMF)and ethanol(EtOH).Furthermore,ratiometric sensors were constructed based on three-AIEoxes mixed microstructures because of the inner fluorescence resonance enery transfer process among AIEoxe molecules,which have improved sensitivity as well as anti-interference performance.3.In virtue of femtosecond laser direct writing(FsLDW)technique,we are able to fabricated a variety of complicated 2/3-dimensional microstructures,making up the weakness of UV lithography in 3D device farbrication.We designed and fabricated micro/nanowires with various sizes and smooth morphology(Ra~4.4 nm),and they emit uniform fluorescence under UV excition,showing excellent optical waveguiding property.The fabricated polymeric microwires have very low optical loss thanks to the small self-absorption of AIEoxes,strong fluorescence brightness,as well as smooth surface morphology.The optical loss coefficient of bAIEoxe/SU-8,gAIEoxe/SU-8 and rAIEoxe/SU-8 waveguides was calculated to be 0.0309 dB/?m,0.0274 dB/?m and 0.0412 dB/?m,respectively,which are even lower than the optical loss of some reported organic crystalline micro-rods and organic/inorganic waveguides.We then used the AIE waveguides as optical sensors for the detection of VOCs in aqueous solutions.Because of the amplified quenching effect of AIE microwires,the limit of detection(LOD)of VOCs improves about 10 times above simple microstructures(LOD=0.004 v/v%).4.We also investigated the processing feasibility of UV lithography and FsLDW technique towards the micro/nano-fabrication of some other solid luminescent materials.Taken conjugated semiconducting polymers for example,we choose polyfluorene as research object to investigate their potential applications in photoelectric functional devices.The polyfluorene is modified with crosslinkable oxetane groups(do-PFO)so that they can be fabricated to various microstructures through above orptical processing techniques.The large-area micro-array structures were fabricated using UV-lithography and reactive ion etching technique.And the delicated and complicated microstructures were obtained by FsLDW method.The crosslinked patterns have good chemical stability and optical gain,showing promising application prospects in micro-lasers as well as laser sensors.In summary,we fabricated various functional micro/nanodevices based on some highly efficient solid luminescent materials using mature processing techniques.In combination of the structure's configuration and the materials' special properties,the fabricated micro/nanodevices show promising prospects in microsensing and microlasers,which greatly accelerate the development of solid-state luminescent materials in fuctional micro/nanodives as well as integrated configurations.