UV emitting Gd incorporated LiBaB9O15 phosphors: An ESR and photoluminescence investigation

Abstract

An effort was made to get an idea regarding the correlation between structure and radiative properties of Gd incorporated LiBaB9O15 matrix. The samples were synthesized via a combustion route and characterized using X-ray diffraction (XRD). Photoluminescence (PL) experiments were carried out in order to understand the radiative properties and local site symmetry of ‘Gd’ ions in the sample. The site occupancy of the rare earth ions were also evaluated through electron spin resonance (ESR) measurements. The PL data suggested the emanation of UV light from the system with emission maxima at 307 and 311 nm. Both these peaks belong to the UV-B region which has many useful applications in phototherapy. The nature of the peaks suggested the stabilization of the ion predominantly in asymmetric geometry making the electric dipole transitions more prominent. It was observed that the maximum radiative or luminescence intensity could be obtained for the 0.048 mol ‘Gd’ doped sample. Beyond this, concentration quenching reduced the PL intensity. Based on the energy transfer model it was evaluated that ‘Foster’ type mechanism was responsible for the observed concentration quenching. From the ESR data it could be inferred that the rare earth ion stabilises at two different sites with differing geometries. At lower doping levels, it was seen that the Gd3+ ions predominantly existed at relatively more distorted Ba2+ sites and at higher concentrations, the ions are at the distorted sites as well as at Ba2+ sites with less distorted environment.