Large single crystals of optical quality of BiB3O6:RE3+ (RE3+ = Pr3+, Nd3+, Gd3+, Er3+, Tm3+) were grown from nearly stoichiometric melts using the top‐seeding growth technique to dimensions up to 12 x 12 x 18 mm3. Absorption spectra were measured in the wavelength range from 10000 cm‐1 to 30000 cm‐1 with an absorption spectrometer to estimate the doping concentration of RE3+. For the determination of the phonon energies and the quenching behaviour of the host lattice IR and Raman spectra were recorded.