Characterization And Improvement Of Basic Parameters In Organic Solid State Cathodoluminescence

Luminescence,a kind of basic phenomenon in the nature,is an embranchment of physics and it can be applied to many kinds of research areas,such as optics,chemistry,mineralogy,archaeology,medicine and biology.In the luminescence, there are five basic important parameters,spectrum,intensity,decay,efficiency and polarization,and the investigation on the dynamics parameters is the basic problem in luminescence.So,in this paper,the solid state cathodoluminescence and its important parameters(spectrum,intensity)are investigated.Additionly,the method to improve the solid state cathodoluminescence,and measure carrier mobility are studied.A.the characterization of spectrum,intensity in solid state cathodoluminescenceSolid state cathodoluminescence is a brand-new kind of luminescence mechanism, as well as an original innovation theory.1.The first(conduction)and secondary(acceleration and multiplication)property of SiO₂,ZnO and ZnS are investigated using organic/inorganic electroluminescence method.The conclusion is that ZnO and ZnS have better conduction property compared to SiO₂ under lower voltage,and SiO₂ possesses better secondary property under higher voltage.The introduction of ZnO and ZnS makes the efficiency enhanced,and the reason is the synergies of electric field and injection barrier2.The solid state cathodoluminescence is characterized by two properties.The first is that it presents two luminescence peak,the long wavelength emission and short wavelength emission,and the intensity of two emissions changes with different applied voltage.The other is the increasing intensity of short wavelength emission is quicker than that of long wavelength.The two properties are connected with the luminescence mechanism and the origin of primary electron.The long wavelength emission is from exciton caused from impact excitation,and the short wavelength emission is from the direct band-band radiative recombination of carriers caused from electric field induced exciton dissociation and direct impact dissociation.The origin of primary electron is from interface state under the lower voltage,and after the voltage is increased,it is from tunneling.3.The mathematical analysis indicates that exciton dissociation under the electric field is the main mechanism for the short wavelength emission.After the voltage is increased,the direct impact dissociation is possible.The mathematical analysis shows that formation cross-section of exciton is larger than that of band-band radiative recombination,and the ratio is 6.B.improvement of decay time and primary electron in solid state cathodoluminescenceThere are two deficiencies in solid state cathodoluminescence,one is longer decay time and the other is the lack of primary electron.In this chapter,they are improved using well structure and field emission cathode array.This is the innovation of structure.1.The luminescence with different luminescence lifetime is studied in frequency domain,and the results show that the frequency has effect on the efficiency,and short luminescence lifetime can help to improve the efficiency.The study on formation cross-section of triplet exciton and singlet exciton indicates that the formation of exciton has effect on the luminescence efficiency.The way to improve the efficiency in frequency domain using the prohibition of triplet exciton luminescence is brought forward based on the investigation on luminescence of singlet and triplet and the advantage of solid state cathodoluminescence.2.The energy transfer in well structure is studied under the light excitation,and the results show that the photoluminescence intensity from well layer in an organic multilayer well structure can be enhanced and adjusted by changing the barrier layer material,the well number,the wavelength of excitation light and the thickness of the well layer.The blue shift with the changing of well thickness is caused from the overlap of spectrum in the well structure.The doped and undoped organic light-emitting diodes are investigated in detail by means of electric-field-induced fluorescence quenching. Results show that the well structure can decrease the exciton quenching.The electroluminescence in well structure is investigated.The results show that the well structure can improve the electroluminescence efficiency.Under the excitation of solid state cathodoluminescence,the emission intensity is enhanced,and the turn-on voltage for the short wavelength emission is lowered.Some new phenomena,such as the appearance of charge transfer exciton emission and blue shift of short wavelength emission,are achieved.3.The ZnO nanorods which present good morphology and crystalline have been fabricated by the hydrothermal decomposition method.The ZnO nanorods possess good field emission property.The turn-on field is 2.8 V/μm at a current density of 1μA/cm². The emission current density can reach 0.67 mA/cm² under the applied electric field 6.4 V/μm.The field emission enhancement factor is 3660.Fluctuating of current density is no more than 25%under electric 4.5 V/μm in 5 hours.The field emission property of SiO₂ thin film indicates that the field emission property of ZnO nanorods is much better than that of SiO₂ thin film.The organic/inorganic hetero-structure LED based on ZnO nanorods presents the broader defect-related visible emission of ZnO centered at 570 nm as well as an excitonic ultraviolet emission at 342 nm.The ultraviolet emission does not correspond to the ZnO band-gap energy(3.37 eV)and it blueshifts,which are interpreted by electron accumulation caused from energy level structure.C.the exploration on new way to measure carrier mobilityIn this chapter the novel method is brought forward,and it is the innovation on methodology and theory.The measurement of the important dynamic parameters, carrier mobility,is investigated in this chapter.The etectroluminescence in frequency domain and the electrochemical impedance spectroscopy are applied to measure the carrier mobility in thin film electroluminescence device.The carrier mobility of MEH-PPV is 1.64×10^-6cm²/V·s under the electric field 8.3×10⁵ V/cm measured by electroluminescence in frequency domain,and it is 1.08×10^-6cm²/V·s under the electric field 7.5×10⁵ V/cm using electrochemical impedance spectroscopy measurement.The results are in accordance with the result measured by time of flight(1.99×10^-6cm²/V·s under 10⁵ V/cm).