5D0

5D0 is a term symbol used in atomic spectroscopy to designate a specific excited energy level, most commonly associated with europium in the Eu3+ ion. In Russell–Saunders coupling, the symbol ^5D0 indicates a multiplicity of 5 (S = 2), an orbital angular momentum L = 2 (D), and a total angular momentum J = 0. For Eu3+ (configurationally 4f^6), ^5D0 is one of the lowest excited states above the ground term ^7F0 and is a key level in luminescent materials.

In practice, the ^5D0 level serves as the emitting state in many Eu3+-doped phosphors. Radiative transitions from ^5D0 to the ^7FJ manifold (where J = 0–6) produce sharp, narrow lines in the visible spectrum. The strongest and most widely cited transition is ^5D0 → ^7F2, which appears around 612 nm and is responsible for characteristic red emission in many Eu3+-doped materials. The ^5D0 → ^7F1 transition near 590 nm is also commonly observed, while ^5D0 → ^7F0 can appear in sites lacking inversion symmetry.

The transitions are 4f–4f (inner-shell) transitions, which are shielded from the crystal field. Consequently, they are relatively insensitive to host material, though crystal-field effects can cause small shifts and splitting. The lifetime of the ^5D0 level is typically on the order of hundreds of microseconds to several milliseconds, depending on the host lattice and quenching processes.

Beyond Eu3+, the ^5D0 designation is a useful example of how term symbols describe specific, spectroscopically important energy levels in ions, particularly in the study of luminescent materials and optical spectroscopy.