Stark manifold ultraviolet emission in Gd-implanted β-Ga2O3 thin films

Gadolinium (Gd) is a promising optically active lanthanide for UV emission. In this work, the optical emission properties of Gd-implanted monoclinic gallium oxide ($\beta$-Ga${}_2$O${}_3$) thin films are investigated. Second phase formation ($\gamma$-Ga${}_2$O${}_3$) is observed due to implantation-induced damage of the $\beta$-Ga${}_2$O${}_3$ lattice. Annealing the implanted films results in various $\beta$-Ga${}_2$O${}_3$ grain orientations. The relationship between the crystalline nature and the optical properties of the $\beta$-Ga${}_2$O${}_3$:Gd${}^{3+}$ films is studied. Optical activation occurs after annealing at 700 °C, revealing a photoluminescence (PL) band at 3.92 eV. This emission is attributed to the ${}^6$P${}_{7/2}\to {}^8$S${}_{7/2}$ transition of Gd${}^{3+}$ in $\beta$-Ga${}_2$O${}_3$. Its four constituent emission components at 3.9118 eV, 3.9153 eV, 3.9221 eV and 3.9348 eV, due to the ion’s ${}^6$P${}_{7/2}$ Stark splitting in the $\beta$-Ga${}_2$O${}_3$ crystal field, are investigated. The transition energies are independent of annealing temperature and film growth method, highlighting the insensitivity of the 4f${}^7$ orbital to minor changes in the monoclinic crystal environment.