The visible luminescence of Pr³⁺ and Tm³⁺ ions in lead borate glasses has been investigated as a function of activator concentration. The Judd–Ofelt analysis and the Inokuti–Hirayama model for energy transfer between activator ions have been applied for investigations of the radiative and non-radiative relaxation of the Pr and Tm excited states. Based on the luminescence decay curve analysis, the concentration quenching of the ¹D₂ emission of Pr³⁺ and ¹G₄ emission of Tm³⁺ ions has been attributed to cross-relaxation processes. The infrared spectroscopic measurements provide information on structural changes in the borate network initiated by optically active (Pr or Tm) ions. Contrary to the praseodymium ions, the thulium ions play an additional role as a glass-modifier in the PbO–B₂O–Al₂O₃–WO₃ composition.