Fiber optic hydrogen gas sensor utilizing surface plasmon resonance and native defects of zinc oxide by palladium

We present an experimental study on a surface plasmon resonance (SPR) based fiber optic hydrogen gas sensor employing a palladium doped zinc oxide nanocomposite (ZnO_(1−x)Pd_x, 0 ≤ x ≤ 0.85) layer over the silver coated unclad core of the fiber. Palladium doped zinc oxide nanocomposites (ZnO_(1−x)Pd_x) are prepared by a chemical route for different composition ratios and their structural, morphological and hydrogen sensing properties are investigated experimentally. The sensing principle involves the absorption of hydrogen gas by ZnO_(1−x)Pd_x, altering its dielectric function. The change in the dielectric constant is analyzed in terms of the red shift of the resonance wavelength in the visible region of the electromagnetic spectrum. To check the sensing capability of sensing probes fabricated with varying composition ratio (x) of nanocomposite, the SPR curves are recorded typically for 0% H₂ and 4% H₂ in N₂ atmosphere for each fabricated probe. On changing the concentration of hydrogen gas from 0% to 4%, the red shift in the SPR spectrum confirms the change in dielectric constant of ZnO_(1−x)Pd_x on exposure to hydrogen gas. It is noted that the shift in the SPR spectrum increases monotonically up to a certain fraction of Pd in zinc oxide, beyond which it starts decreasing. SEM images and the photoluminescence (PL) spectra reveal that Pd dopant atoms substitutionally incorporated into the ZnO lattice profoundly affect its defect levels; this is responsible for the optimal composition of ZnO_(1−x)Pd_x to sense the hydrogen gas. The sensor is highly selective to hydrogen gas and possesses high sensitivity. Since optical fiber sensing technology is employed along with the SPR technique, the present sensor is capable of remote sensing and online monitoring of hydrogen gas. (paper)