Light Emission from Rare Earth-Doped GaN

The rare earth (RE) or lanthanide elements denote the metallic elements having atomic numbers 57 to 71. These elements, which are listed in Table 9.1 , have very similar chemical properties [ 1 ]. They are known as rare earths due to the difficulty in extracting them from materials known as earths , e.g., lime and alumina. Actually, rare earth elements constitute about one-fourth of the known metals, and several are more abundant than gold or silver. The electronic structure of each tri valent rare earth (RE 3+ ) element consists of a partially filled inner 4f subshell and completely filled outer 5s 2 and 5p 6 subshells. With increasing nuclear charge, electrons enter into the underlying 4f subshell rather than the external 5d subshell, as shown in Table 9.1 . The ground state of each RE 3+ is represented as m L j , where L is the total orbital angular momentum, J is the total angular momentum, and m is the multiplicity of terms in the atomic configuration. Since the filled 5s 2 and 5p 6 subshells screen the 4f electrons, the rare earth elements have very similar chemical properties. They are highly reactive with many other elements and readily form a variety of organic complexes.