Engineering of rare-earth Eu³⁺ ions doping on p-type NiO for selective detection of toluene gas sensing and luminescence properties

We present the engineering of various concentrations of rare-earth europium (Eu³⁺) ions in the range of 1–4 wt% doped in p-type NiO for selective detection of toluene prepared utilizing the hydrothermal method. The undoped showed a nanoflake-like, while doped samples displayed the evolution of NiO that was induced by Eu³⁺ dopants. The X-ray diffraction and photoluminescence (PL) findings showed that the Eu³⁺ ions were successfully doped into NiO. The PL emission spectrum upon the excitation of 394 nm and displayed four emission peaks with the maxima at 468, 571, 611, and 665 nm. Among the doped samples, the 3 wt% Eu³⁺ doped NiO displayed improved response (R_g/R_a ≈25 %) towards 60 ppm toluene vapour in the presence of other interfering vapours, such as benzene, ethylene-benzene and xylene at the functional temperature of 100 °C with a bias voltage of 1 V. The 3 wt% Eu³⁺ doped NiO based sensor response was approximately 1.5 higher in comparison to other vapours, with sensitivity and low detection limit of 0.36 ppm⁻¹ and 250 ppb, respectively. Under the bias voltage and exposure time of 2 V and 3 h, respectively, we noticed a massive response of R_g/R_a ≈ 59 %, which is twice higher compared to the initial response Thus, the probability of fine-tuning the gas sensitivity and selectivity of the Eu³⁺ doped NiO based sensor by designing the relative amount of Eu³⁺ in NiO (∼3 wt% Eu) is encouraging for further fabrication of Eu³⁺doped NiO as a potential sensor for toluene detection.