Two excitation pathways of Pr3+ ion emission in HfO2:Si:Pr films depending on crystalline phase transformations in annealing
Résumé
The impact of annealing on the emission and transformation of the crystalline phases in Si rich HfO 2 :Pr films was investigated by analyzing the morphology, chemical composition, structure, and photoluminescence (PL) characteristics. Films were prepared by RF magnetron sputtering and monitored as-prepared and after annealing at 1000 • C for 5-60 min. Emission through host HfO 2 defects has only been detected in spectra of as-prepared Si rich HfO 2 :Pr films. Heat treatment for 30 min stimulates a phase transformation together with the appearance of a tetragonal HfO 2 phase and Si quantum dot (QDs). This last process is accompanied by appearance of bright emission of rare earth (RE) ions Pr 3+ related to the transitions in the 4f energy levels. Additional annealing for 60 min stimulates the complete oxidation of the Si QDs with the formation of the SiO 2 phase along with partial destruction of a tetragonal HfO 2 phase. This last process is accompanied by the significant increase of the intensity of Pr 3+ ion emission. Two forms of luminescence excitation in 4f energy levels of Pr 3+ ions are discussed, related to energy transfer to Pr 3+ ions, first from Si QDs and then from host defects in HfO 2. These changes in the excitation pathways of Pr 3+ ion emissions are stimulated by the transformations of the crystalline phases in the thermal treatment together with the generation of host HfO 2 defects. Hafnia-based materials doped with RE elements are interesting for telecommunication technology and applications in waveguides and optoelectronic devices.
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