Morphology Control And Photoluminescence Properties Of Dopeing Ai₂O₃

In recent years, a great deal of research on rare-earth and transition metalion doped materials has been focused to find their potential uses in photonicapplications, such as solid state lighting, medical labeling, imaging, andradiation detection. Alumina is considered to be a suitable host for rare earthmaterial because it offers a large transparency window from the short ultravioletto the near infrared frequencies and has excellent mechanical properties andgood chemical stability. In this paper, Eu³⁺, Tb³⁺, Cr³⁺doped Al₂O₃sampleswere synthesized with different raw materials and methods, and characterizedby XRD, SEM and luminescence spectroscopy. Effect of morphology andannealing temperature on the luminescence intensity was discussed. Optimumconcentration and critical distance of doped ions in the Al₂O₃were alsosystematically discussed.Using AlCl3·6H2O and Eu（NO3）3·6H2O as raw materials, Eu³⁺doped Al₂O₃red phosphors materials were prepared by microwave hydrothermal. Resultsindicated that Eu³⁺doped sample was γ-Al₂O₃; the particles of Al₂O₃+3:Euwerea spherical shape packaged by nanosheets; photoluminescence displayed thatthe main emission peaks of Al₂O₃:Eu³⁺could be assigned to the magic dipoletransition5D70→F1（594nm） and394nm was the best excitation wavelength.Electric dipole5D70→F2intensity of the sample could increase with the contentof Eu³⁺. When the content of Eu³⁺was up to0.09mol%, electric dipole⁵D₀→⁷F₂intensity locating at618nm briefly increased.Using AlCl3·6H2O and Tb（NO3）3·6H2O as raw materials, Al₂O₃:Tb³⁺greenphosphors were synthesized via a microwave solvothermal and thermaldecomposition route. These phosphors exhibiting green emission inherit theshapes of the AlOOH:Tb³⁺microspheres which are hierarchicallynanostructured microspheres packaged by nanosheets. The PLE spectrum is dominated by a broad band due to the4f-4f5d transition of Tb³⁺ion. For allfabricated samples, the⁵D₄→⁷F₅（545nm） electric dipole transition is the mostintensive. From the luminescence study the optimum concentration ofluminescence is found to be0.7mol%.Using AlCl₃·6H₂O and CrCl₃·6H₂O as raw materials, α-Al₂O₃:Cr+powderswere synthesized via a microwave solvothermal method followed by heattreatment. The obtained α-Al₂O₃based powders were microspheres with anaverage diameter about1-2μm. As seen from the PLE spectrum monitored at696nm, two strong broad absorption bands with peak positions at around399and552nm, corresponding to spin-allowed⁴A₂（⁴F）→⁴T₁（P） and⁴A₂（F）→⁴T₂（⁴F） transitions of Cr³⁺ions on the octahedral sites of α-Al₂O₃. From the PLspectrum, well-known narrow R lines at696nm, ascribed to the²E→⁴A₂transition of isolated single Cr³⁺ions, were observed. From the luminescencestudy the optimum concentration of luminescence was found to be0.3mol%.Using Al（NO₃）₃·9H₂O and Tb（NO₃）₃·6H₂O as raw materials,NH₃+4Al（OH）₂CO₃:Tb³⁺microfibers were successfully synthesized through ahydrothermal method and Al₂O₃:Tb³⁺microfibers with different crystallinephases were also obtained by postannealing the resulting precursors at varioustemperatures. The average length of Al32O3:Tb+microfibers is about6-8μm,and the diameter is around300nm. These phosphors exhibiting green emissioninherit the shapes of the NH₄Al（OH）₂CO₃:Tb³⁺microfibers. The PLE spectrumis dominated by a broad band due to the4f-4f5d transition of Tb³⁺ion. For allfabricated samples, the⁵D₄→⁷F₅（545nm） electric dipole transition is the mostintensive. From the luminescence study the optimum concentration ofluminescence is found to be2.0mol%.Using Al（NO₃）₃·9H₂O and Cr（NO₃）₃·9H2O as raw materials,NH₄Al（OH）₂CO₃:Cr³⁺microfibers were prepared via a hydrothermal methodand then were calcined to produce α-Al₂O₃:Cr³⁺microfibers. The averagediameter of Al₂O₃:Cr³⁺microfibers was about100-300nm, and the length wasaround2-5μm. As seen from the PLE spectrum monitored at696nm, twostrong broad absorption bands with peak positions at around400and553nm,corresponding to spin-allowed⁴A₂（⁴F）→⁴T₁（⁴P） and⁴A₂（4F）→⁴T₂（4F）transitions of Cr³⁺ions on the octahedral sites of α-Al₂O₃. From the PL spectrum, well-known narrow R lines at696nm, ascribed to the²E→⁴A₂transition ofisolated single Cr³⁺ions, are observed. From the luminescence study theoptimum concentration of luminescence is found to be0.3mol%.