Spectroscopic properties and Judd–Ofelt analysis of Eu3+ doped GdPO4 nanoparticles and nanowires

Abstract Eu 3+ doped GdPO 4 orthophosphates with hexagonal and monoclinic crystal structures were prepared by a solvothermal process at 160 °C. Nanoparticles (NPs) and nanowires (NWs) were obtained using a mixture of water and glycerol as solvents. Luminescence properties of 5% Eu 3+ doped GdPO 4 NPs and NWs were investigated. As-obtained luminescent NWs:Eu and NPs:Eu powders were post-annealed at 750 °C since this temperature did not change neither their initial morphology nor their crystalline structure and led to luminescence efficiency intense enough to suit optical applications. A post-heating treatment of the samples at higher temperature (1000 °C) resulted in a change in both the crystalline structure from hexagonal to monoclinic form and the morphology. Excitation and emission spectra as well as luminescence decays were recorded on both post-annealed luminescent NW:Eu and NP:Eu powders. A comparative study of the optical results obtained for the different morphologies and structures was carried out by calculating the asymmetry ratio ( A 21 ) of Eu 3+ from emission spectra. The symmetry of the local environment of Eu 3+ activators has been described in the frame of Judd–Ofelt theory, using Ω 2 and Ω 4 intensity parameters derived from emission spectra data analysis, adopting a standard procedure. It was observed that Ω 2 value for the NPs is different from that of the NWs indicating that the environment surrounding the active ion changes depending on the sample morphologies. The radiative lifetimes of the 5 D 0 excited state and the corresponding branching ratios for different emission transitions were also estimated and compared to the recorded luminescence decay rates at room temperature.