Luminescence and nonlinear optical properties of borates LnGa$_{3}$(BO$_{3}$)$_{4}$ (Ln = Nd, Sm, Tb, Er, Dy, Ho)

Luminescence spectra of single crystals of rare-earth gallium borates LnGa$_{3}$(BO$_{3}$)$_{4}$ (Ln = Nd, Sm, Tb, Er, Dy, Ho) at room (300 K) and cryogenic (10 K) temperatures are presented for the first time. Photoluminescence has been recorded in the wavelength range of 470–5000 nm (2000–21 300 cm$^{-1}$) with a high spectral resolution (down to 0.1 cm$^{-1}$) upon excitation by different diode lasers. The spectra obtained cannot be unambiguously interpreted within one luminescent center, which can be due to the presence of defects and/or inclusions of other crystalline phases. The optical nonlinearity of rare-earth–gallium borates has been estimated using the Kurtz–Perry powder technique. The typical intensities of the second-harmonic generation in gallium borate powders are 30–40 (with respect to quartz), and the optical nonlinearity is as good as the nonlinearity of the efficient rare-earth aluminum borate YAl$_{3}$(BO$_{3}$)$_{4}$.