A rare earth metal oxide: lanthanum oxide

Introduction

Generally, a good host for luminescent ions must exhibit properties such as transparency for visible and infrared light and good chemical and structural stability. Rare earth oxides have attracted much research because of their prospective use as catalytic materials and their excellent thermal, chemical, electrical, magnetic, ceramic, and optical properties. Among all rare earth metal oxides, lanthanum oxide (La2O3) is recognized as having a relatively lower cost compared to other rare earth oxides (e.g., Lu2O3, Gd2O3) and as being an excellent host lattice for luminescent ions.

Chemical property

The chemistry of La primarily concerns the formation of the predominant +3 oxidation state. Lanthanum oxide, La2O3, can be prepared directly from the element[1]. When water is added to La2O3, it “slakes” like lime, with the evolution of much heat and a hissing sound. La2O3 belongs to the hexagonal (trigonal crystal system) family with space group P3m1 (No. 164). Each La3+ ion has equivalent surroundings, with C3v site symmetry and coordination number seven (three O2- ions being slightly further than the other four)[2].

La2O3 has various optical applications, such as in infrared transmitting glass ceramics and as an additive to various transparent ceramic laser materials to improve their optical properties. It has also been assessed as a phosphor host doped with Eu, Bi, Er, and Yb ions. Rare-earth ions are usually used as activators for luminescent materials due to their intra-configurational 4f transitions.

References

[1] Wedeen, R. B. Berlinger and J. Aaseth. “Chapter 42 – Lanthanum.”Handbook on the Toxicology of Metals (Fourth Edition) (2015): 903-909.

[2] B.M. Jaffar . “Luminescence properties of Bi doped La2O3 powder phosphor.” Journal of Luminescence 209 (2019): Pages 217-224.

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