Preparations And Optical Properties Of Cr³⁺, Ho³⁺ Doped Powders And Films

As the first used laser medium material, Al₂O₃has been made into a variety of lasermedium materials and is widely used in manufacturing, medical and scientific fieldsbecause of its good mechanical properties, corrosion resistance and optical properties.Cr³⁺doped ruby laser is still one of the main media to prepare high-power lasers today;At present, Ti doped sapphire femtosecond lasers still can’t be replaced in medicalapplications. To prepare a laser medium which can produce high-quality, high-powerlaser in different bands is still a main research field in the development of lasertechnology. In this paper, Cr³⁺、Ho³⁺doped Al₂O₃powders and films with differentdoping concentrations have been prepared by ball milling method and by pulsed laserdeposition method. The experimental contents and the results are as follows:1. Cr³⁺doped Al₂O₃powder were prepared by high energy ball milling, andannealed in1200℃for2hours. The samples exhibit hexagonal α-Al₂O₃structure, andits particle size is between22and25nm. Using the excitation source with a wavelengthof579nm, the emission spectra of the samples exhibit emission peaks at469nm,482nm and492nm caused by the F⁺color centers of Al₂O₃. The emission peak appearing at694nm is asctibed to the transition of Cr³⁺ions’ electronics from2A to4A₂and the0.3%Cr³⁺doped sample shows the greatest fluorescence emission intensity. As thedoping concentration increases, Cr³⁺concentration quenching occurs, resulting in areduction of the light intensity.2. Cr³⁺:Al₂O₃thin films were grown on Si （100） by pulsed laser deposition method,and the samples show cubic γ-Al₂O₃structure. The SEM image reveals that the filmshave an average grain size of250nm. The electron energy spectrum show that the thinfilms almost remained the same ratio of the elements in the target，with a great deal ofoxygen vacancies generated. Compared with the Al₂O₃powders，the emission peakintensity of the Al₂O₃thin films at320nm and386nm has been greatly enhanced. This can be ascribed to an increase of oxygen vacancies generated during the process ofdepostion，As a consequence, more and more F2and F₂⁺color centers, caused bydouble-oxygen-vacancy absorbing electrons, appear, which makes the fluorescenceintensity increase.1wt%Cr³⁺ions doping Al₂O₃thin film shows two new emissionpeaks at694nm and646nm caused by the of transition of Cr³⁺ions’ electronics from2A to4A₂.3. Ho³⁺doped Al₂O₃powders were prepared by high energy ball milling, and thenannealed in1200℃for2hours. The samples were hexagonal α-Al₂O₃detected byXRD, and its particle size is between35and36nm. The UV absorption spectroscopy ofthe samples show absorption peaks at454nm and540nm caused by⁵I₈�'⁵G₆（⁵F₂,³K₈,⁵F₁） and⁵I₈�'⁵F₄（5S2） of Ho³⁺.4. Ho³⁺doped Al₂O₃thin films were grown on Si （100） by pulsed laser depositionmethod, and the samples show cubic γ-Al₂O₃structure. Using the excitation source witha wavelength of579nm, in addition to the Al₂O₃color center emission peaks, noemission peak caused by Ho³⁺ions was observed, which can be ascribed to theSuppression of color centers in the Al₂O₃.