Abstract
Chromium-doped Y3Al5O12 or YAG thin films emitting at 688 nm due to the 4A2–4E2 transition were synthesized in a combinatorial fashion using reactive sputtering approach. Multilayer YAG and Cr thin films were sputter deposited with a gradient in the Cr thickness and subsequently annealed to diffuse the Cr dopant into the YAG matrix. The combinatorial thin film sputtering technique was used to rapidly determine that ∼0.69 at.% is the optimum chromium concentration for maximum photoluminescence (PL) intensity in YAG. This result was consistent with previous work in YAG:Cr powders. Design of experiments was conducted to determine the effects of various sputter parameters, namely, substrate bias, substrate temperature and oxygen flow rate on PL intensity and crystallinity of co-sputter deposited Cr-doped YAG thin films. The optimum sputtering condition consisted of high substrate bias and low oxygen flow rate and was independent of substrate temperature. The PL temperature dependent behavior of YAG:Cr film was also investigated. Thermal quenching was observed at ∼110 K where the total integrated PL emission intensity was found to rapidly decrease. A non-radiative activation energy of 25.2 meV was determined and is attributed to electron–phonon coupling.
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