Bi doped LaOCl and LaOF thin films grown by pulsed laser deposition

Thin films of Bi³⁺ doped LaOCl and LaOF phosphors prepared via the pulsed laser deposition (PLD) technique in vacuum and different argon (Ar) pressures were compared in order to assess their luminescence properties. All peaks of the X-ray diffraction patterns of the films were consistent with the tetragonal structure of the LaOCl and LaOF, but in the case of LaOF the signal was weaker and not all peaks were present, suggesting some preferred orientation. Photoluminescence measurements revealed that the films exhibited emission around 344 nm for LaOCl:Bi and 518 nm for LaOF:Bi under excitations of 266 nm and 263 nm, respectively. The luminescence from the LaOF:Bi sample was less intense compared to the LaOCl:Bi sample prepared under the same conditions, which was also the case for the powder samples. The amount of ablated material present on the substrate was much less for LaOF:Bi compared to LaOCl:Bi, which is attributed to the greater bandgap and hence weaker absorption of the laser pulses for LaOF:Bi. Therefore phosphors based on LaOCl as the host material were found to be preferable over LaOF under the PLD conditions used in this study.