Time-resolved photoluminescence on ion doped CdWO4 thin films prepared with pulsed laser deposition

Abstract

Samarium-, nickel-, cesium-ion-doped and -undoped ${\mathrm{CdWO}}_4$ thin films are prepared by pulsed laser deposition (PLD) method. Photoluminescence (PL), cathode luminescence (CL), and x-ray excited luminescence (XL) are studied on these thin films. Luminescence spectra are deconvoluted to three luminescence species typically at 2.77, 2.48, and 2.18 eV. Luminescence intensities and the relative contribution of three deconvoluted components are compared with those on the undoped ${\mathrm{CdWO}}_4$ (010) single crystal surface. PL intensity on the undoped thin film can be compared to that on the (010) single crystal surface. Not only CL and XL intensities but also PL intensity drops drastically on ion-doped ${\mathrm{CdWO}}_4$ thin films. However, the emission component at about 2.2 eV is dominant and the relative contribution of 2.77 eV is diminished on the ion-doped PLD thin films. The x-ray diffraction data indicates that the (002) plane is most intense on these films and the peak shifts to lower 2θ value on the ion-doped ${\mathrm{CdWO}}_4$ thin films. These results imply that these films are polycrystalline and the interplane distance is enlarged on the ion-doped ${\mathrm{CdWO}}_4$ thin films. The stress of the crystal structure is associated with the origin of the PL component at about 2.2 eV which has been assigned to oxygen vacancies such as $[{\mathrm{WO}}_5{]}^{\text{4−}}$ moieties in the crystal. Time-resolved PL decay analyses are studied on the PLD thin films at three wavelengths, 440 nm (2.82 eV), 550 nm (2.25 eV), and 650 nm (1.91 eV). The slow and fast decay component can be detected on the PLD thin films with a decay lifetime of 8–10 and 0.6–0.8 μs, respectively. Comparing to the corresponding ${\mathrm{CdWO}}_4$ (010) single crystal surfaces, the decay time of the slow PL component is decreased on PLD thin films. The PL component with fast decay time will be associated with the strain of ${\mathrm{CdWO}}_4$ crystal structure.