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Tm3+ centers in the D2 sites of gadolinium gallium garnet (GGG) exhibit stark levels in the absorption and emission spectra of Tm3+. The stark levels are used for the computation of GGG's crystal field complex with nine parameters for D2 site symmetry.

The direct pumping into the emitting level of Nd(super 3+) in Nd:YVO4 crystal has a much larger global effect on the intracavity frequency doubling of the 1064-nm emission than for Nd:YAG. These results indicate that the modality of pumping could be instrumental in the enhancement of performances of second-harmonic devices based on Nd vanadates or of other strongly absorbing Nd laser materials and for their scaling to higher power.

The optical spectroscopic properties of RE3+ (Nd, 1 at. % or Yb, 1 to 10 at. %)-doped calcium-lithium-niobium-gallium garnet (CLNGG) single crystals and ceramics in the 10 K-300 K range are analyzed. In these compositionally disordered materials, RE3+ substitute Ca2+ in dodecahedral sites and the charge compensation is accomplished by adjusting the proportion of Li+, Nb5+, and Ga3+ to the doping concentration. The crystals and ceramics show similar optical spectra, with broad and structured (especially at low temperatures) bands whose shape depends on temperature and doping concentration. At 10 K, the Nd3+ 4I9/2 → 4F3/2, 5/2 and Yb3+ 2F7/2 → 2F5/2 absorption bands, which show prospect for diode laser pumping, can be decomposed in several lines that can be attributed to centers with large differences in the crystal field. The positions of these components are the same, but the relative intensity depends on the doping concentration and two main centers dominate the spectra. Non-selective excitation evidences broad emission bands, of prospect for short-pulse laser emission, whereas the selective excitation reveals the particular emission spectra of the various centers. The modeling reveals that the nonequivalent centers correspond to RE3+ ions with different cationic combinations in the nearest octahedral and tetrahedral coordination spheres, and the most abundant two centers have 4Nb and, respectively, 3Nb1Li in the nearest octahedral sphere. At 300 K, the spectral resolution is lost. It is then inferred that the observed optical bands are envelopes of the spectra of various structural centers, whose resolution is determined by the relative contribution of the temperature-dependent homogeneous broadening and the effects of crystal field disordering (multicenter structure, inhomogeneous broadening). The relevance of spectroscopic properties for selection of pumping conditions and of laser design that would enable utilization of the broad optical bands for efficient laser emission and reduced heat generation is discussed. [ABSTRACT FROM AUTHOR]

The spectroscopic characteristics of Dy3+ in YAG (Y3Al5O12) transparent ceramics prepared by solid state synthesis were investigated, with special attention to the visible (yellow, blue) emissions that could be pumped directly by the new developed blue-violet or near UV laser diodes. The absorption and emission spectra, recorded at different temperatures from 10 to 300 K, were analyzed and relevant new parameters, improved energy level scheme, temperature effects, intensity parameters based on Judd-Ofelt theory and radiative transition rates, branching ratios, etc., were estimated and the data are compared with previous reports on garnet single crystals. The potential of the Dy3+: YAG transparent ceramics for yellow or blue laser emission is discussed. [ABSTRACT FROM AUTHOR]

The characteristics of Nd→Yb energy transfer in (Nd, Yb):Y3Al5O12 (YAG) transparent ceramics, obtained from steady state and dynamic spectral studies on different single doped and codoped samples, prepared by solid state synthesis, are presented. The Yb3+ emission in codoped (Nd, Yb):YAG samples under cw excitation of the donors (Nd3+) revealed efficient energy transfer to Yb3+ (at low temperatures too), due to the overlap of the Nd3+ 4F3/2→4I9/2 emission and Yb3+ 2F7/2→2F5/2 absorption. From the global decays of the Nd3+ 4F3/2 level in single and codoped samples, the transfer efficiencies were estimated; they increase with Yb3+ content reaching ∼93% for 1 at. % Nd, 5 at. % Yb:YAG sample. The mechanisms and parameters of the Nd→Yb energy transfer were inferred from the Nd3+ decays in the codoped samples, after the separation of the self-quenching inside the donors (Nd3+) from the transfer to acceptors (Yb3+). It was proved that the Nd→Yb energy is resonant and dominated by dipole-dipole interactions. Due to the large transfer efficiencies, (Nd, Yb):YAG ceramic could be a promising material for Yb3+ emission under pumping in strong Nd3+ absorption lines. [ABSTRACT FROM AUTHOR]

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 5I7→5I8 and 5I6→5I8 transitions of special interest for laser application were determined. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Spectroscopic investigation of Er3+ doped Sc2O3 transparent ceramics was performed in order to assess its potential as a laser material for different emission wavelengths. The Judd–Ofelt intensity parameters for the f-f transitions of the C2-symmetry center of Er3+ in Sc2O3 transparent ceramics, inferred from the room temperature absolute intensities of the absorption bands in the 370–1600 nm range, are Ω2=3.57×10-20 cm2, Ω4=1.61×10-20 cm2, and Ω6=0.79×10-20 cm2. These parameters are comparable to those reported for Er3+ in other sesquioxide single crystals. The Judd–Ofelt intensity parameters are used to determine the emission probabilities, radiative lifetimes, and branching ratios of the different Er3+ transitions. The emission cross sections of the potential laser transitions at ∼1.5 μm were determined using the reciprocity method, and the potential laser gain versus wavelength for the 4I13/2→4I15/2 was analyzed. [ABSTRACT FROM AUTHOR]