Scientists from HSE University and the Institute of Petrochemical Synthesis of the Russian Academy of Sciences have found a method to regulate both the hue and intensity of the light produced by rare earth elements. These materials usually exhibit consistent luminescent properties; for instance, cerium is known to emit UV light.
Nevertheless, researchers have shown that this condition can be modified. They developed a chemical setting where a cerium ion started emitting a yellow luminescence. These discoveries might aid in the creation of novel lighting solutions, display technologies, and laser systems.
study
has been published in
Optical Materials
.
Rare earth elements find applications in microelectronics, LEDs, and fluorescent substances due to their capability to produce light at specific wavelengths. This phenomenon hinges on the behavior of their electrons as they absorb and release energy.
If an atom gains energy, for instance from illumination or an electrical discharge, one of its electrons may get promoted to a more energetic orbit. Yet, this elevated state is transient, and soon afterward, the electron drops back down to its initial position, emitting the surplus energy in the form of light. This phenomenon is referred to as luminescence.
In rare earth elements, the luminescence occurs due to electron movements between 4f orbitors—which are zones near the atomic core where electrons can be found. Generally, the energy of these shifts is consistent, causing the emitted light’s hue to remain steady; for instance, cerium produces non-visible UV radiation, whereas terbium generates a green emission.
The 4f orbitals reside deeply inside the atom and have minimal interaction with the outside world. Conversely, the 5d orbitals are more responsive to external factors yet typically do not play a role in the luminescent properties of lanthanide elements because they possess very high energies.
However, scientists from HSE University and the Institute of Petrochemical Synthesis of the Russian Academy of Sciences have demonstrated that the color of the radiation can be altered by adjusting the chemical environment of the metals. They synthesized cerium, praseodymium, and terbium complexes using organic ligands—molecules that surround metal ions. These ligands shape the geometry of the complex and influence its properties.
In all cases, three cyclopentadienyl anions were symmetrically arranged around the metal. These anions consist of regular pentagons of carbon atoms, to which large organic fragments are attached, providing the required structure for the complex. This environment generates a specific electrostatic field around the ion, which alters the energy of the 5d orbitals and, consequently, affects the luminescence spectrum.
Earlier, a shift in the glow’s hue was noticed, though the reason remained unclear. However, working alongside our physics peers, we’ve managed to grasp the process responsible for this phenomenon. We intentionally crafted molecules possessing an electron configuration uncommon among lanthanide elements.
Daniil Bardonov, a master’s student at the HSE Faculty of Chemistry, remarks, ‘Instead of concentrating on just one instance, we combined various compounds ranging from cerium to terbium to examine shifts in their characteristics and uncover recurring trends.’
In traditional compounds, cerium releases ultraviolet light with wavelengths ranging from 300 to 400 nanometers. However, within the newly developed complexes, this emission moved towards the red spectrum, extending as far as 655 nanometers. This suggests that the energy difference between the 4f and 5d orbitals has narrowed down. An analogous adjustment in electron configurations was noted across the other examined lanthanide elements, leading to alterations in their respective luminescent properties.
“To comprehend this process, one must initially understand the mechanism of energy transfer. Usually, a ligand molecule captures ultraviolet light, transitions into an excited state, and subsequently passes this energy onto the metal atom, resulting in the emission of light,” clarifies Dmitrii Roitershtein, who serves as the Academic Supervisor for the Chemistry of Molecular Systems and Materials Program and is also a co-author of the study.
In contrast, within the newly synthesized materials, the transfer of energy happened through a different mechanism: rather than being directed imparted onto the 4f electrons, it went through an intermediary step involving the 5d state.
Researchers think that forecasting the luminescence spectrum would enable them to develop materials with specific traits more effectively by reducing reliance on lengthy experimental iterations. This advancement might accelerate the development of novel and sophisticated lighting solutions.
We have shown precisely how the atomic environment affects electronic transitions and lanthanide luminescence,” states Fyodor Chernenkiy, a bachelor’s degree candidate at the HSE Faculty of Chemistry. “This allows us to deliberately choose compound structures to manage luminescence and develop materials with desired optical characteristics.
More information:
Lada N. Puntus and colleagues explored the efficiency of energy transfer via the 5d state of the Ln ions.
3+
In complexes featuring diarylcyclopentadienyl ligands,
Optical Materials
(2025).
DOI: 10.1016/j.optmat.2025.116734
Furnished by the National Research University Higher School of Economics
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