The Study On Luminescence Of ZnO Nano-particles Loaded Into Porous Alumina Hosts

ZnO is a wide band-gap semiconductor material, suitable for laser diodes andoptoelectronic devices operating in blue-green spectral region. The porous aluminafilms can be used to fabricate assembles of many kinds of nano-materials. In thispaper, we studied the mechanism of growth of anodic alumina and the characteristicsof photoluminescence of ZnO nano-particles loaded into porous anodic alumina hosts. Through the measurements of Al₂O₃ films by scanning electron microscopy (SEM)and X-ray diffraction, it was found that the Al₂O₃ template we prepared is anamorphous film, with the parallel-sided hexagonal pores ordering in a scale of a fewmicrometers. Our work was focused on the dependence of the growth and propertiesof Al₂O₃ film on relative parameters, such as volt, the kinds of electrolyte, temperatureand anodic time. The main results are (1) Both pore distance and size increase linearlywith the anodic voltage;(2) Al₂O₃ templates appeared different colors whendeveloped by different electrolyte. The Al₂O₃ templates made in oxalic acid are yellow,while those prepared in phosphoric or chromic acid appeared baby blue-purple;(3)The longer anodic time is, the more periodic the pore arrangements appear and thethicker Al₂O₃ films become;(4) The anodizing temperature needs as low as possible.The surface of Al₂O₃ films will appear frothy when the temperature goes beyond morethan 20℃.The ZnO nano-particles were grown in porous alumina templates by sol-gel method,meanwhile the effects of porous nanoholes on the luminescence of ZnO nano-particleswere studied by photoluminescence (PL) spectra. The main results and analyses are asfollows:(1) An intensive blue PL emission peak around 484 nm has been observed in Al₂O₃template. The 484 nm peak was attributed to the singly ionized oxygen vacancies (F+centers) in ZnO nano-particles loaded in PAA hosts.(2) An intensive blue PL emission peak around 472 nm appears when the Al₂O₃template was annealed lower than 500℃. This "blue shift" comes from the annealingreduces the stress in alumina membranes. The intensity of the Al₂O₃ template isdecreased with the increase of the temperature, because of the decrease of oxygenvacancy concentration due to the composite of oxygen diffusing from air with theoxygen vacancy in template. The luminescence is diminished when annealingtemperature went beyond 500℃, because the oxygen defects were diminished.(3) For the luminescence of ZnO/PAA composite system, the "blue shift" of PLpeak continually shifts to 445nm when the annealing temperature is lower than 500℃.However , the PL peak contrastively moves to red region when the temperatures arehigher than 500℃. Both the "continual blue shift" and the "red shift" are contributedto the quantum confinement effect of ZnO nano-particles. The intensity of the PL ofZnO/PAA composite system arrive to maximum when annealed in 700℃.