Photoluminescence properties of Eu3+ doped ZrO2 with different morphologies and crystal structures

Highlights: • Eu³⁺-doped ZrO₂ nanotube arrays were prepared in inorganic and organic electrolytes. • Eu³⁺-doped ZrO₂ nanoparticles were prepared by chemical co-precipitation method. • Anodizing and annealing conditions affect the crystal structure of ZrO₂ nanotube arrays. • Photoluminescence properties of Eu³⁺ vary with morphology and crystal structure of ZrO₂. • Monoclinic phase is more favorable to energy absorption and transfer than tetragonal phase. -- Abstract: Eu³⁺-doped ZrO₂ nanotube arrays and Eu³⁺-doped ZrO₂ nanoparticles were prepared by anodisation of the Zr–Eu alloy and by chemical co-precipitation method, respectively. The effects of anodisation conditions and annealing temperature on the morphology, crystalline phase and properties of Eu³⁺-doped ZrO₂ nanotube arrays were studied. The photoluminescence (PL) excitation and emission spectra of different samples were compared and the related reasons were discussed. Results show that the crystal structures of ZrO₂ nanotube arrays prepared in organic (Eu-ZNTA-o) or water (Eu-ZNTA-w) solution and the Eu³⁺-doped ZrO₂ nanoparticles (Eu-ZP) are much different. When annealed at 600 °C, the ZrO₂ nanotube arrays contain both tetragonal and monoclinic phases (with only 5.9% of tetragonal phase for Eu-ZNTA-o and 64.1% tetragonal ZrO₂ for Eu-ZNTA-w), while the Eu³⁺-doped ZrO₂ nanoparticles are pure tetragonal phase. The PL emission spectra of Eu-ZNTA-o and Eu-ZP are significantly different. The PL emission spectra of Eu-ZNTA-w approximate the superposition of the former two. Compared with the tetragonal phase, the monoclinic phase matrix is more favorable to the absorption and transfer of energy. In addition, the morphology of the sample can lead to lattice distortion, which can also have an effect on the photoluminescence properties.