Concentration quenching of praseodymium ions Pr³⁺ in BaGd ₂(MoO₄)₄ crystals

The concentration effect on the photoluminescence (PL) of the praseodymium Pr³⁺ ion is studied at 298-12 K for barium gadolinium molybdate (BaGd₂(MoO₄)₄, called BGM) crystals with a wide Pr³⁺ concentration range of 0.05-25.0 mol%. Three types of concentration dependences are observed for the emissions although all types show PL quenching at high concentrations. The first type (Type A) has the maximum PL intensity at about 10 mol% with a non-zero intensity at high concentrations, which is observed for the ³P₀ emissions except for emission at 621 nm. The second and third types (Type B-1 and B-2) have the maximum at about 1 mol% with a finite residual intensity and nearly zero intensity at high concentrations, respectively, which are observed for the 621 nm emission and all the ¹D₂ emissions. It is suggested that the energy migration mechanism is responsible for Type A, while the non-resonant cross-relaxation is responsible for Type B-1 and the resonant cross-relaxation for Type B-2.