Optical properties of single crystalNd3+-dopedBi4Ge3O12: Laser transitions at room and low temperature

Abstract

A ${\mathrm{Nd}}^{3+}$-doped ${\mathrm{Bi}}_{4}{\mathrm{Ge}}_{3}{\mathrm{O}}_{12}$ (BGO) single crystal was grown by the modified Czochralski method. Using the $4f$-energy matrix diagonalization procedure various interaction parameters viz. Slater-Condon (${F}^{2}$, ${F}^{4}$, and ${F}^{6}$), spin-orbit $(\ensuremath{\xi})$, two body interaction ($\ensuremath{\alpha}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$), Judd parameter (${T}^{2}$, ${T}^{3}$, ${T}^{4}$, ${T}^{6}$, ${T}^{7}$, and ${T}^{8}$), spin-other-orbit parameters (${M}^{0}$, ${M}^{2}$, and ${M}^{4}$) and electrostatically correlated spin-orbit interaction parameters (${P}^{2}$, ${P}^{4}$, and ${P}^{6}$), and the crystal-field parameters $({B}_{q}^{K})$ were evaluated. The crystal-field analysis has also been carried out for ${\mathrm{Nd}}^{3+}:{\mathrm{Bi}}_{4}{\mathrm{Si}}_{3}{\mathrm{O}}_{12}$, ${\mathrm{Eu}}^{3+}:\mathrm{BGO}$, and ${\mathrm{Er}}^{3+}:\mathrm{BGO}$ systems. The potential of a BGO crystal as a laser crystal for 1064.4 and $1341.8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ was established by quantitative analysis of the absorption, emission spectrum, and fluorescence decay characteristics. Judd-Ofelt parametrization was employed to compute the radiative spectral parameters such as radiative transition probabilities, fluorescence branching ratios, stimulated emission cross sections, and quantum efficiencies of the observed bands in the fluorescence spectrum. Using the measured radiative properties, 100% quantum efficiency was obtained for the principal emission band at $1064.4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ with an effective stimulated emission cross section of $1.34\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$. The high stimulated emission cross section, fluorescence branching ratio, and quantum efficiency indicate that the ${\mathrm{Nd}}^{3+}$-doped BGO crystal can be a suitable host for 1064.4 and $1341.8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ emission wavelengths in $Q$-switched laser applications.