Assessing the key parameters for efficient sensitized infrared emission from erbium-doped SnO2 films

Erbium -doped SnO2 films (Er:SnO2) combine the properties of Er3+ and SnO2, providing an avenue for developing unique luminophores with sensitized infrared emission. In such a system, Er3+ luminescence evolves over doping-concentration and thermal-treatment shifts, where low-temperature-annealed or highly-doped Er:SnO2 exhibits degraded emission. To fully exploit the potential of Er:SnO2, a deep understanding of the underlying physical process is required. This paper discusses the parameters determining the intensity of sensitized Er3+ emission and their evolution with doping concentration and thermal treatment. The observation of temperatureindependent decay of Er3+ luminescence excludes the nonradiative interaction of the Er3+ 4I13/2 -> 4I15/2 transition with defects in SnO2. Moreover, despite the loss of Er3+ optical activity observed in highly-doped or lowtemperature-annealed samples, the sensitized emission intensity doesn't scale linearly with it. Instead, the most prominent parameter determining the sensitized emission intensity is found to be the energy transfer efficiency from SnO2 to Er3+, which highly depends on the crystallinity of SnO2. The presence of defects in low-crystallinity SnO2, that is, highly-doped or low-temperature-annealed ones, would deteriorate the energy transfer efficiency, which could be healed by high-temperature annealing. This work negates the traditional consensus of concentration quenching in Er:SnO2 and provides an important insight into developing efficient Er:SnO2 based infrared luminophores.