Y2O3:Yb3+ 5 at% ceramics have been synthesized by the reactive sintering method using different commercial yttria powders (Alfa-Micro, Alfa-Nano, and ITO-V) as raw materials. It has been shown that all Y2O3 starting powders consist from agglomerates up to 5–7 µm in size which are formed from 25–60 nm primary particles. High-energy ball milling allows to significantly decreasing the median particle size D50 below 500 nm regardless of the commercial powders used. Sintering experiments indicate that powder mixtures fabricated from Alfa-Nano yttria powders have the highest sintering activity, while (Y0.86La0.09Yb0.05)2O3 ceramics sintered at 1750 °C for 10 h are characterized by the highest transmittance of about 45%. Y2O3:Yb3+ ceramics have been obtained by the reactive sintering at 1750–1825°C using Alfa-Nano Y2O3 powders and La2O3+ZrO2 as a complex sintering aid. The effects of the sintering temperature on densification processes, microstructure, and optical properties of Y2O3:Yb3+ 5 at% ceramics have been studied. It has been shown that Zr4+ ions decrease the grain growth of Y2O3:Yb3+ ceramics for sintering temperatures 1750–1775 °C. Further increasing the sintering temperature was accompanied by a sharp increase of the average grain size of ceramics referred to changes of structure and chemical composition of grain boundaries, as well as their mobility. It has been determined that the optimal sintering temperature to produce high-dense yttria ceramics with transmittance of 79%–83% and average grain size of 8 µm is 1800 °C. Finally, laser emission at ∼1030.7 nm with a slope efficiency of 10% was obtained with the most transparent Y2O3:Yb3+ 5 at% ceramics sintered.

No abstract

No abstract

Systematic high resolution spectral investigations of trivalent holmium doped in Sc2O3 polycrystalline transparent ceramic were performed. The spectral characteristics (Stark energy levels, absorption, and emission cross sections) as well as the Judd–Ofelt (JO) intensity parameters Ωt(t=2,4,6) for the f-f transitions of the C2-symmetry center of Ho3+ in Sc2O3 transparent ceramics were determined. The JO intensity parameters are used to estimate the emission probabilities, radiative lifetimes, and branching ratios of the different Ho3+ transitions. The emission gain cross section for the I57→I58 and I56→I58 transitions of special interest for laser application were determined.

No abstract

No abstract

Incongruent melting nonlinear optical (NLO) crystals of La x Gd y Sc z (BO 3 ) 4 (x + y + z = 4) -LGSB have been grown by the Czochralski method, for the first time to our knowledge. The crystal growth conditions are discussed, and the melt composition and growth parameters were optimized. The chemical composition of the best quality grown crystal was determined to be La 0.64 Gd 0.41 Sc 2.95 (BO 3 ) 4 . It crystallizes in the noncentrosymmetric space group R32 (Z = 3) with cell dimensions a = 9.794(4) Å and c = 7.961(6) Å. The transmission window and refractive indices were measured, and the phase-matching curves for type-I and type-II second harmonic generation and (ω + 2ω) sum frequency generation have been determined based on Sellmeier equations.

An analysis of the high resolution optical spectra (10 and 300 K) of the self-stimulated Raman scattering active Nd:SrWO4 crystal was performed. Crystals doped only with low concentrations of Nd or codoped with Na+ or Nb5+ grown in N2 or air atmosphere were investigated. The single Nd-doped crystals show five main centers, whereas codoping with Na+ in the ratio Na/Nd=3/1 (in melt) simplifies considerably the spectra. Codoping with Nb5+ does not lead to a dominant center and introduces a new one. Growth in air revealed the role of the oxygen in the charge compensation and multicenter structure of the spectra. The spectral characteristics of the nonequivalent centers (levels, intensities, and polarization) function on concentration of Nd3+ and of codoping ions and growth conditions were analyzed. The polarization data show that only one center has ideal local symmetry S4. Based on the crystal structure, previous results, and the new spectral data, an attempt to connect various spectral nonequivalent centers to the charge compensators (Sr2+ vacancies, interstitial oxygen, Na+, and Nb5+) is made and structural models for various centers are proposed. The implications of these findings on the laser emission characteristics and on the selection of the pumping transitions are also discussed.