The effect of deposition time on the structural, morphological and luminescence properties of Y2O2S:Eu3+ thin films prepared by pulsed laser deposition

Y2O2S:Eu3+ thin films were deposited on Si (100) substrate using pulsed laser deposition technique (PLD) under 20 mTorr oxygen pressure. The effects of deposition time on the structural and photoluminescence properties were studied. X-ray diffraction analysis shows the formation of cubic and hexagonal crystal structures depending on the growth duration. Thin films deposited for 15, 30, 45 and 60 min have cubic phase with impurities of Y2O3, while that grown for 90 min is hexagonal phase. The crystallite size for the cubic phase was observed to increase from 58.4 to 79.2 nm with increase in deposition time. Scanning electron micrographs show the surface morphology comprising spherical particles distributed randomly over the surface with film prepared for longer duration having much larger grain size. Energy-dispersive X-ray spectrum confirms the presence of all the main elements of the Y2O2S:Eu3+ phosphor. Photoluminescence measurements showed blue emission of the films with the most intense peak observed at 452 nm, which is due to the Y2O2S host emission. The band gap values for the cubic phase calculated from absorbance spectra using the Tauc's relation decreased from 4.35 to 4.18 eV with increase in deposition time attributed to change in crystallites size.