Study On Fabrication,Structure And Optical Properties Of Porous ZnO Thin Films

High voltage sodium lamp is a kind of high performance electric light source.It has been used in various lighting places because of its higher luminous efficiency,low power consumption and strong ability to penetrate the fog.However,as the key part of high voltage sodium lamp,the alumina transparent ceramics has the lower transmittance,which has limited the luminous efficiency and service life of sodium lamp.Antireflection coatings are deposited on a device in order to Reducing the surface reflection and increasing the transmittance.Among the antireflective materials,ZnO thin film is can be applied as an antireflection layer on alumina transparent ceramics because it has large exciton binding energy,high permeability,high chemical and thermal stability,simple preparation process and suitable for industrial production.This paper aims to fabricate ZnO thin film with high transmittance,which has studied the preparation and mechanisms of porous ZnO thin film and Cr-doped ZnO thin film.The major study contents are as follows.The uniform and transparent sols with different concentrations are prepared by the sol-gel method,and then dipped them on alumina transparent ceramics to obtain porous films.It found that the grain growth orientation and pores structures of films are influenced by sol concentration.When the sol concentration was 0.6 M,the ZnO thin film was preferentially orientated along c-axis.It showed obvious and regular pores structure on the surface of films.Meanwhile,the transmittance of thin film is about 8.5%higher than substrate.The porous ZnO thin films with different molecular weights of PEG have been prepared,which aimed to study the influence of PEG on structure and optical properties of films.The results showed that the crystal structure had little change with the molecular weights of PEG increased from 600 to 4000.However,the grains of films were gradually gathered and finally formed island with the increased molecular weights of PEG.In addition,with the further increase of molecular weights,the pores structures were also gradually disappeared and the transmittance showed a tendency to increased first and then decreased.The porous ZnO thin film has the best optical properties when the porogen was PEG1000.Afterwards,the mechanism of prepare porous ZnO thin films with PEG1000 has been discussed through thermal analysis and FTIR spectra.There was formed ring-like network structure in sols because of the strong interaction between PEG1000 and zinc oligomers under the appropriate conditions,and then the porous thin films will finally be obtained after annealing treatment.The optical properties of porous ZnO thin films have been improved by Cr³⁺doping.The mechanism of Cr-doped ZnO films has been discussed by comparing the changes of the structure and optical properties of the films under different Cr³⁺doping concentration and annealing temperature.When the Cr³⁺doping concentration was 3at.%and the annealing temperature was 500?,the film had the best crystallinity and there were more micropores structures on the surface.Meanwhile,this porous thin film had the highest optical transmittance?>90%at 450-750nm?.