[en] A study on the effect of ambient oxygen pressure maintained during deposition and its variation on the structural, electrical and optical properties of Eu doped ZnO thin film is presented. The films were grown by the pulsed laser deposition technique wherein the 4th harmonic of Nd:YAG laser at 266 nm (pulse duration t_p = 7 nsec) was used. 1% Eu doped ZnO target (Zn_0.99Eu_0.01O) was synthesized by the standard solid state ceramic route using high purity ZnO and Eu₂O₃ powders taken in their stoichiometric proportions. The X-ray diffraction (XRD) studies of the synthesized pellet revealed the formation of single phase, polycrystalline Zn_0.99Eu_0.01O. This pellet was ablated in the deposition chamber to deposit the thin films. The films were deposited on SiO_x/Si(100) substrates under different oxygen pressure conditions viz. 10^-6 (vacuum), 10^-5, 10^-4 and 10^-3 Torr. X-ray diffraction studies reveal the growth of highly c-axis oriented, single phase Zn_0.99Eu_0.01O thin films on SiO_x/Si(100) substrate. The in-plane stress of the Zn_0.99Eu_0.01O films was observed to be extensive which increased with the increase in oxygen pressure. With the increase in oxygen pressure the crystalline quality of Zn_0.99Eu_0.01O showed slight improvement. The average roughness of the films was observed to reduce with the increase in ambient oxygen pressure. Eu doped ZnO thin films deposited in vacuum showed low resistive, however it was observed to increase with the increase in oxygen pressure. The charge carrier concentration was commensurately observed to reduce with the increase in oxygen pressure. The photoluminescence spectra showed significant variation in the intensity of the band edge emission of ZnO and also the ⁵D₀ → ⁷F₂ transition at 612 nm corresponding to Eu³⁺ ions. It was seen that the intensities of the band edge emission and that of the ⁵D₀ → ⁷F₂ transition in case of thin films deposited at 1 x 10^-5 Torr was much higher than that of other samples. Attempt is made to explicate these observations in correlation with the oxygen ambient pressure. (author)