| Summary: | Erbium-doped cadmium selenide thin films grown on 7059 Corning glass by means of a chemical bath at 80 °C were prepared. Doping was performed by adding an aqueous Er(NO3)<sub>3</sub>3·H<sub>2</sub>O dilution to the CdSe growth solution. The volume of Er doping solution was varied to obtain different Er concentration (<i>x</i> at%). Thus, in the Cd<sub>1−<i>x</i></sub>Er<i><sub>x</sub></i>Se samples, the <i>x</i> values obtained were in the 0.0–7.8 at% interval. The set of the CdSe:Er thin films synthesized in the hexagonal wurtzite (WZ) crystalline phase are characterized by lattice parameters (a and c) that increase until <i>x</i> = 2.4% and that subsequently decrease as the concentration of <i>x</i> increases. Therefore, in the primitive unit cell volume (UC), the same effect was observed. Physical parameters such as nanocrystal size, direct band gap (<i>E<sub>g</sub></i>), and optical longitudinal vibrational phonon on the other hand, shift in an opposite way to that of UC as a function of <i>x</i>. All the samples exhibit photoluminescence (PL) emission which consists of a single broad band in the 1.3 ≤ hν ≤ 2.5 eV range (954 ≥ λ ≥ 496 nm), where the maximum of the PL-band shift depends on <i>x</i> in the same way as the former parameters. The PL band intensity shows a singular behavior since it increases as <i>x</i> augments but exhibits a strong decreasing trend in the intermediate region of the <i>x</i> range. Dark d.c. conductivity experiences a high increase with the lower <i>x</i> value, however, it gradually decreases as <i>x</i> increases, which suggests that the Er<sup>3+</sup> ions are not only located in Cd<sup>2+</sup> sites, but also in interstitial sites and at the surface. Different physical properties are correlated among them and discussed considering information from similar reports in the literature.
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