SYNTHESIS AND PROPERTIES OF Ag3SbS3, CRYSTALS DOPED WITH PRASEODYMIUM

Abstract

The article presents the results of a study on the synthesis, structural, and optical properties of praseodymium (Pr)- doped pyrargyrite Ag3SbS3 crystals. This work belongs to the field of chalcogenide semiconductor materials, which, due to their unique electrophysical and optical characteristics, have found wide application in optoelectronics, sensor technology, thermoelectrics, and nonlinear optics. Ternary compounds, particularly Ag3SbS3, are known for combining chemical stability with high sensitivity to doping, making them suitable for targeted modification of electronic properties. Ag3SbS3 crystals were synthesized from high-purity elements-silver, antimony, and sulfur-using the Bridgman– Stockbarger method under a controlled temperature regime. Additionally, a series of samples doped with praseodymium at concentrations of 0.3, 0.6, and 0.9 at.% were obtained. The synthesis was carried out using precision vacuum equipment and prolonged homogenizing annealing to ensure material uniformity. X-ray phase analysis (DRON-4-13, CuKα radiation) confirmed the single-phase nature of all doped samples, the absence of secondary phases, and the structural stability of pyrargyrite, indicating the successful incorporation of Pr ions into the Ag3SbS3 crystal lattice. Doping with the rare-earth element led to significant changes in the optical properties of the compound. Absorption spectra measurements showed a consistent decrease in the optical band gap with increasing Pr concentration: from 1.84 eV for 0.3 at.% to 1.81 eV for 0.9 at.%. This trend indicates the formation of additional energy levels near the valence and conduction band edges, caused by the partially filled 4f orbitals of praseodymium. These states act as intermediate energy levels that reduce the interband transition energy and shift the fundamental absorption edge toward lower photon energies. Simultaneously, doping is accompanied by the formation of point defects, vacancies, and local lattice distortions, which further affect the material’s electronic structure. Thus, the combined effect of electronic and structural factors results in the narrowing of the band gap. The reduction of the band gap directly influences the nonlinear optical properties of the material. The study of second harmonic generation (SHG), conducted using the Kurtz–Perry powder technique, demonstrated an increase in SHG intensity with rising praseodymium concentration, i.e., with a decreasing Eg value. This observation agrees with theoretical predictions that link enhanced electronic polarizability to materials with smaller interband transition energies. In such cases, valence band electrons are more easily perturbed by the electromagnetic field of laser radiation, leading to an increase in the second-order nonlinear susceptibility (χ2) and enhancement of second harmonic generation. The obtained results prove that doping Ag3SbS3 with praseodymium is an effective way to control its optical parameters. The reduction of the band gap and the enhancement of SHG efficiency make these crystals promising candidates for use in nonlinear optical components, radiation modulators, infrared laser frequency conversion systems, and next-generation sensor devices. Given their structural stability, reproducible synthesis, and predictable electronic modifications under doping, the Ag3SbS3–Pr system can be considered a promising basis for developing new functional materials with tunable optoelectronic properties.