Effect Of Rare Earth And Transition Metals Coating On The Photoluminescence Of Al₂O₃ Thin Film

Since the anodic aluminium oxide membrane synthesized by a two-step electrochemical anodizing process has excellent physical properties and optical properties, it was widely used in electronic, optoelectronic, nanoscience technology and other fields. However, because it’s wider bandgap leads the lowness in the visible light rate, we can only use ultraviolet excitation. Just because of these reason, we intend to improve its range of spectral response with the rare earth elements(Ce) and transition elements(Cr).In this paper, we use the reflux impregnation method to modified the amorphous Al2O3 thin films, and preparae the Al2O3 films with coating containing rare earth element(Ce) and transition element(Cr). The results of field emission scanning electron microscope(FESEM) show that the morphology of modified thin films is changed, and the results of the x-ray dispersive energy spectrum(EDS) show that the portion of Ce and Cr in the corresponding films increase with the increase of concentrations of solution. There exist Ce3+ ions and Cr3+ in the modified thin films as shown by XPS measurement.(1) The photoluminescence(PL) emission and excitation spectrum of thin films Al2O3:Ce are different from unmodified films at room temperature, and the emission spectrum of Al2O3:Ce has two peaks, centered at 380 nm and 400 nm, respectively.And this is in accordance with the theoretical characteristics of the bimodal structure of Ce3+. The formation of the two photoluminescence peak is from Ce3+ de-excited luminescence from the 2D5/2 excited state to the split ground state level 2F5/2 and 2F7/2( 2D5/2â†'2F5/2 and 2D5/2â†'2F7/2). In addition, we prepared Al2O3:Ce films under different concentration of doped solution. From the PL emission spectra of Al2O3:Ce films, we find that the intensity of PL firstly increases with the increase of concentrations of Ce(NO3)3 solution then decreases with a further increase of concentrations of solution and reaches a maximum value at 0.2 mol.(2) The photoluminescence(PL) emission and excitation spectrum of Al2O3:Cr thin films are different from unmodified films. There is no any R-line near the 694 nm in the doped film, but the emission peak appeared in 705 nm and 878 nm. By the analysis we conclude that the emission peak of 705 nm was derived from some patterned groups of Cr3+ions, the electronic of Cr3+ions from the transition of4T2 state to 4A2 state, and the emission peak of 878 nm was attributed to introduce the chromium ion in the process of modification, leading to increase the amount of(CrO6)9-in the Al2O3 thin films. In addition, we prepared Al2O3:Cr films under different concentration of solution. From the PL emission spectra of Al2O3:Cr films,we find that the intensity of PL firstly increases with the increase of concentrations of solution, then decreases with a further increase of concentrations of solution and reaches a maximum value at 0.5 mol.