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Upconversion luminescence from magnetron-sputtered Er3+-doped TiO2 films: Influence of deposition- and annealing temperatures and correlation to decay times

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The optical properties of radio-frequency magnetron sputtered TiO2 thin films doped with Er3+ are strongly influenced by the deposition and post-annealing temperatures. This has an impact on the applications of the material for upconversion, i.e., the merging of two low-energy photons to one photon of higher energy. Maximum upconversion luminescence (UCL) yield is obtained using a deposition temperature of 350 degrees C without post-annealing. Motivated by the possibilities that become available by sequential depositions (several layers), the effect of post-annealing is systematically investigated. In general, post-annealing treatments reduce the UCL; however, for the lowest deposition temperatures, post-annealing has a positive impact on the UCL provided that the samples are not exposed to ambient air prior to the annealing step. These observations are further analyzed using time-resolved photoluminescence spectroscopy for determining the characteristic decay times of the Er3+ energy levels in the different samples. It is found that the UCL yield scales to a good approximation linearly with the product of the decay times of the two lowest-lying Er3+ excited energy levels (I-4(11/2) and I-4(13/2)). The combined data provide strong evidence that the reduction in UCL is due to the opening of non-radiative decay channels from the Er3+ excited levels. Structural measurements show no change of the amorphous samples upon annealing, so these decay channels are most likely related to energy transfer between Er3+ and defect states in the TiO2 bandgap. The non-radiative decay could possibly be related to the loss of hydrogen termination of dangling bonds or related to the oxygen vacancies in TiO2. Published by AIP Publishing.

Original languageEnglish
Article number163105
JournalJournal of Applied Physics
Number of pages7
Publication statusPublished - 28 Oct 2018

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