Optical spectra and emission characteristics of terbium-doped potassium-lead double chloride crystals (KPb2Cl5:Tb3+)

摘要

Optical transitions in KPb2Cl5:Tb3+ crystals are studied experimentally and theoretically. The absorption cross-section spectra are plotted and the oscillator strengths of transitions from the ground terbium state to excited multiplets are determined. Intensity parameters Omega(t) for KPC:Tb3+ are determined by the Judd-Ofelt method to be Omega(2) = 2.70 x 10(-20) cm(2), Omega(4) = 7.0 x 10(-20) cm(2), and Omega(6) = 0.72 x 10(-20) cm(2). These values were used to calculate such characteristics of spontaneous radiative transitions as oscillator strengths, probabilities of radiative transitions, and radiative lifetimes. The emission spectra of KPb2Cl5:Tb3+ crystals upon UV excitation and the decay kinetics of luminescence from the excited (5) D (3) and (5) D (4) levels are studied experimentally, the lifetimes of these levels are determined, and the dependences of the rates of nonradiative relaxation from the excited (7) F (j) (j = 0-5), (5) D (4), and (5) D (3) levels to lower-lying terbium levels are calculated. It is shown that the population of the (5) D (4) level in KPC:Tb3+ crystals occurs according to a cascade scheme, which leads to quenching of the (5) D (3) level. The calculated data agree well with the known experimental rates of multiphonon nonradiative transitions for Dy:KPC, Nd:KPC, Er:KPC, Tb:KPB, and Nd:KPB crystals. It is shown that transitions in the near-IR (3-6 mu m) region in double halide crystals (MPb(2)Hal(5)) are almost unquenched and the rates of nonradiative relaxation of excited levels spaced by energy gaps Delta E (ji) > 1000 cm(-1) are W (ji) (NR) < 10(3)s(-1). This circumstance suggests that it is possible to obtain stimulated emission in KPb2Cl5:RE3+ crystals in the IR spectral region up to 6 mu m.