Lanthanum-Based Blue-Emitting Phosphor Shows Promise for Solid-State Lighting Applications

Recently, a group of researchers from Mexico examined a new way to improve solid-state lighting. The study, published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, presented a new blue-emitting phosphor based on a lanthanum (III) complex (1). Led by Dr. Scanda of Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada del Instituto Politécnico Nacional, the research project highlighted the synthesis, structural characterization, and photophysical properties of the [La(Phen)₂(NO₃)₃] complex (1).

What is solid-state lighting?

Solid-state lighting is lighting emitted by solid-state electroluminescence (2). Instead of using electrical filaments, solid-state lighting uses light-emitting diodes (LEDs) (2). Some examples of LEDs include semiconductor LEDs, polymer LEDs, and organic LEDs. Common applications of solid-state lighting include traffic lights and modern vehicle lights (2).

What was the research team’s approach?

In the study, the team synthesized the phosphor material by combining lanthanum (III) with two 1,10-Phenanthroline ligands and three nitrate ions using a straightforward, energy-efficient precipitation method. This approach yielded a coordination compound with a monoclinic crystal system, verified by powder X-ray diffraction (PXRD) and refined using the Le Bail method (1). The crystal structure confirmed the decacoordination of the lanthanum center, facilitated by the two nitrogen-containing organic ligands and three nitrate groups (1).

Then, the research team tested the compound’s coordination environment. This process involved using Fourier transform infrared (FT-IR) spectroscopy to study the vibrational bands associated with carbon-carbon and carbon-nitrogen bonds. The FT-IR results confirmed the binding of the phenanthroline ligands to the La³⁺ ion (1). Furthermore, alterations in the symmetric and asymmetric stretching modes of the nitrate ions suggested a more symmetric, isobidentate coordination mode (1).

What was the role of photoluminescence spectroscopy in the study?

In the study, the researchers also used photoluminescence spectroscopy to understand more about lanthanum coordination and how it influences luminescent behavior. By using this technique, the researchers found that the [La(Phen)₂(NO₃)₃] complex emits strongly in the blue region under UV excitation (1). When excited at 350 nm, the compound exhibited three distinct emission peaks at 370, 388, and 410 nm (1). These bands correspond to π* → π transitions of the organic ligand and were absent in uncoordinated 1,10-Phenanthroline (1).

The complex also demonstrated an absolute quantum yield of 3% and a luminescence lifetime of 5616 nanoseconds (ns), measured through a monoexponential fit (1). While the quantum yield remains modest, the emission lifetime is relatively long, which could be advantageous for specific photonic applications.

What was unique about this study?

This study was unique in that the researchers conducted photometric analysis to learn more about the blue emission’s color purity. The researchers discovered through this process that the chromaticity coordinates of (0.15, 0.05) on the CIE 1931 color diagram had a calculated color purity of 96% (1). These metrics signify that the compound delivers a saturated blue light suitable for use in high-quality displays and lighting systems (1).

The research team also investigated the phosphor's thermal performance across a temperature range of 20–150 °C. Despite a 47% decrease in emission intensity at the upper temperature limit, the material retained a substantial portion of its luminescent signal, indicating solid thermal resilience (1). The activation energy for thermal quenching was calculated to be 0.13 electronvolts (eV), marking the first time such a value has been reported for a lanthanum (III) complex with 1,10-Phenanthroline ligands (1).

What are the next steps in this work?

Based on the findings of this study, the authors suggest that future research efforts could improve luminescent efficiency through structural modifications or doping strategies (1). As the demand for energy-efficient, stable, and color-accurate lighting materials grows, the development of novel phosphors like [La(Phen)₂(NO₃)₃] is essential. The research presented here adds to the growing body of knowledge surrounding rare-earth-based phosphors (1).

References

1. Scanda, K.; Salas-Juarez, Ch. J.; Guzman-Silva, R. E.; et al. Synthesis and Photoluminescent Spectroscopic Analysis of Lanthanum (III) Coordinated with 1,10-Phenanthroline: A Study of its Thermally Stable Behavior. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2025, 325, 125046. DOI: 10.1016/j.saa.2024.125046
2. Industrial Light & Power, Solid State/LED. Industrial Light & Power. Available at: https://www.industriallightandpower.com/lighting-maintenance/solid-state-led/#:~:text=Solid%2Dstate%20lighting%20(SSL)%20refers%20to%20a%20type,lamps%20such%20as%20fluorescent%20lamps)%2C%20or%20gas. (accessed 2025-06-27).