Spectroscopic characteristics of praseodymium-doped cubic double sodium-yttrium fluoride crystals Na0.4Y0.6F2.2:Pr3+. Intensities of optical transitions and luminescence kinetics

Using the Bridgman-Stockbarger technique, we have grown a series of cubic crystals Na0.4Y0.6F2.2:Pr3+ (NYF:Pr3+) with a content of praseodymium in the range of 0.04–9 at %. We have determined the composition of crystals, evaluated their optical quality, and found the incorporation coefficient of Pr3+ ions into the Na0.4Y0.6F2.2 matrix (K Pr ∼ 0.9). We have examined optical spectra of NaYF:Pr3+ crystals at room and low (7 K) temperatures in the range of 200–2500 nm. The low-temperature absorption spectra of NYF:Pr3+ crystals have been shown to consist of broad weakly structured bands. Based on the analysis of low-temperature absorption spectra, the structure of the Stark splitting of praseodymium levels has been represented in terms of a model of “quasi-centers,” which are characterized by an inhomogeneous broadening of Stark components. From experimental absorption cross-section spectra at T = 300 K, we have calculated oscillator strengths for transitions from the ground state 3 H 4 to excited multiplets 3 H 5, 3 H 6, 3 F j (j = 2, 3, 4), 1 G 4, 1 D 2, and (3 P j ,1 I 6) (j = 0, 1, 2). Using the Judd-Ofelt method, we have determined intensity parameters Ω t and found that Ω2 = 0, Ω4 = 4.4 × 10−20, and Ω6 = 2.28 × 10−20 cm2. With these values, we have calculated the probabilities of radiative transitions, the branching coefficients, and the lifetimes of the radiative levels 1 D 2 and 3 P 0. The probabilities of multiphonon nonradiative transitions in NYF:Pr3+ crystals have been estimated. Using the method of kinetic spectroscopy with selective excitation, we have investigated the luminescence decay kinetics of praseodymium from the 3 P 0 and 1 D 2 levels upon their selective resonant excitation by nanosecond laser pulses. The inference has been made that Na0.4Y0.6F2.2:Pr3+ crystals are processable; admit doping by praseodymium in high concentrations; and, with respect to all their radiative characteristics, can be potentially considered as active media for converters of optical radiation and solid-state continuously tunable lasers in the visible range.