Characterization of substitutional and interstitial Eu+3-positions in CdS lattice

Cd1-xEuxS thin films, with x in the 0 ≤ x ≤ 5 at% range, were prepared by chemical bath at 80 °C on glass substrates. X ray diffraction (XRD) patterns reveal that the samples crystallize in cubic zinc blende phase, with high preferred orientation along the (111) direction. From XRD data the (111) interplanar spacing (IS) and average crystal size (CS) were calculated. IS(111) decreases from 0.3350 nm for x = 0.0–0.3346 nm for x = 1.2 at%, then increases from here to the initial value for x = 3.0 at%, after decreases slightly until x = 5.0 at%. CS follows approximately an inverse behavior of that of IS(111) vs x taking values in the 29.0–31.5 nm range. The vibrational mode 1LO hardens when x decreases and softens when x increases following the opposite behavior of IS(111), as is expected, however, 1TO follows an opposite behavior to that of 1LO. The direct optical band gap Eg reduces when x decreases and the contrary when x rises, which is the opposite to commonly observed. Besides, the photoluminescent (PL) energy-emissions exhibit a contrary dependence on x as that followed by Eg, this behavior is associated with the distortion of the host CdS lattice due to the Eu doping. PL signals from m1Dn1 → m2Fn2 transitions of E2+,3+ ions are also affected by the behavior of IS(111). All the experimental results are discussed based on the relation among the different observations, and those results reported in the literature.