Hidden local symmetry of Eu³⁺ in xenotime-like crystals revealed by high magnetic fields

The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu³⁺ sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO₄:Eu³⁺ crystal, which resulted from the alignment of Gd³⁺ magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO₄ nanocrystals at the Eu³⁺ sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu³⁺ centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics