Directionally solidified eutectics (DSEs) in Al2O3-based systems have been studied as high-temperature structural ceramics, also recently attracting attention as a phosphor screen for high-resolution radiation imaging. However, it is difficult to obtain uniform and thinly processed DSE in large areas. Here, we report a chemically deposited eutectic (CDE) of Lu3Al5O12 (LuAG)–Al2O3 using a laser-assisted chemical vapor deposition method. The Ce3+-doped LuAG lamella were epitaxially grew with an α-Al2O3 matrix on an r-cut sapphire substrate. The Ce3+:LuAG–α-Al2O3 CDE film exhibited green emissions due to the 5d–4f transitions of the Ce3+ center under UV light and α-/X-ray irradiations. The α-ray dose in the Ce3+:LuAG phase was estimated with Monte Carlo simulations to study a scintillation light yield of the CDE film. The X-ray radiograph of the semiconductor storage device was successfully obtained using a 15-μm-thick Ce3+:LuAG–α-Al2O3 CDE film as an X-ray phosphor screen.