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Fabrication and characterization of upconverting RF magnetron sputtered ytterbium-erbium silicate thin films

Çodur, Muhammed Mustafa
Upconversion is a growing research topic as it can be utilized in various applications extending from traditional fields, such as solar cells, and infrared sensing to novel fields, including bioimaging and 3D displays. However, heavy halides, which are frequently used as upconversion host matrices in the literature, exhibit unstable chemical, mechanical, and thermal properties. Oxides with high stability can be used as an alternative to heavy halides, but their high phonon energy reduces upconversion efficiency. In this study, we aimed to enhance the efficiency by increasing the number of luminescence centers (i.e. erbium ions) in the host matrix by utilizing erbium ions as constituents of the compound instead of doping ions. This thesis is dedicated to the improvement of upconversion properties of erbium-ytterbium disilicate (ErxYb2-xSi2O7) compounds as an upconversion material with stable properties. Herein, sputtering was preferred as the fabrication method not only for its uniform deposition capability but also for its compatibility with the silicon technology. In this thesis, we demonstrated erbium-ytterbium disilicate thin films that convert infrared photons with a wavelength from around 1540 nm into a wavelength of around 980 nm. Moreover, the effects of annealing temperature and, erbium and ytterbium concentrations on the upconversion efficiency were investigated. Noteworthy, we present upconversion from erbium-ytterbium silicates as thin as 110 nm. All films fabricated in this work show pure NIR-NIR upconversion, which is considered to be more favorable in various applications where precision is more requisite than high conversion efficiency in the literature, such as bioimaging and fingerprint detection. They can also be the sought-after material for new applications, for instance, coupling them with a cheap silicon detector to detect photons beyond 1.1 μm. In addition, we enhance a method to measure PL lifetimes of samples. This method combines square wave excitation and a lock-in amplifier and allows real-time lifetime measurements.