For the first time to our knowledge, a single-phase solid solution Sr(MoO_4) 0.8 (WO_4) 0.2 was used as an active medium of a Raman laser. Using the high-intensity synchronous picosecond pumping satisfying the condition of phase capture of the parametric Raman interaction on the second vibrational mode made it possible to oscillate six components of Raman radiation with a combined frequency shift on the first (888 cm -1 ) and second (327 cm -1 ) vibrational modes in the wavelength range of 1194-1396 nm. Oscillation efficiency of the multiwavelength Raman laser radiation was as high as 10%. By detuning the Raman laser cavity length, the pulse shortening down to 6 ps for the Raman laser radiation components with the combined frequency shift was obtained, which is an order of magnitude shorter than the pumping pulse duration (64 ps). Keywords: stimulated Raman scattering, single-phase solid solution, vibrational mode, synchronous pumping.

Highly transient stimulated Raman scattering in a SrMoO 4 crystal on both stretching (888cm - 1 ) and bending (327cm - 1 ) Raman modes under ultrafast double-pulse pumping by orthogonally polarized pump pulses at 1030 nm with a controllable chirp and a different delay between them was investigated.

Whitlockite-type polycrystalline and single-crystal (Ca 3_ x Sr x )(VO 4 ) 2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca 3_ x Sr x )(VO 4 ) 2 solid solutions with & khcy; = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca 1.8 Sr 1.2 )(VO 4 ) 2 (CSVO) revealed its actual composition (Ca 2.982(11) Sr 0.031 )(V & Ocy; 4 ) 2 . Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr 2 + ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca 2 + ions are in the Ca5 and Ca5 A sites, forming two independent strongly distorted tetrahedral Ca5O 4 and octahedral Ca5 A O 6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with Xray absorption spectroscopic study of ( & Scy; a 2.4 Sr 0.6 )(VO 4 ) 2 doped with 0.5 and 1.0 wt% Tm 2 O 3 ( & Scy; SVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5 A site, the localization of Sr 2 + ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm 3 + ions, forming an individual eightcoordinated environment, in the refined compositions (Ca 2.776(7) Sr 0.210(4) Tm 3 + 0.008(1) )(VO 4 ) 2 and (Ca 2.855 (7) Sr 0.140(7) Tm 3 + 0.009(1) square 0.022(7) )(VO 4 ) 2 , respectively, with vacancies (marked by a square, square ) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm 3 + environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm 3 + ions were analyzed and the most correct one was proposed.

The effect of magnesium co-doping on growth conditions, crystal composition, optical and spectral properties of manganese or chromium-doped Ca3(VO4)2 (CVO) crystal was studied. The single crystals were grown by the Czochralski method. Effective segregation coefficients of manganese and chromium in the CVO matrix with magnesium co-doping were calculated. A redistribution of the absorption lines intensities was observed in the absorption spectra of CVO:Mn:Mg and CVO:Cr:Mg. Low (15 K) temperature fluorescence measurements confirmed that co-doping CVO crystal with Mg ions leads to the redistribution of Mn ions concentration in different valence states, but does not cause changes in their spectral properties. In the presence of magnesium, additional annealing of the materials resulted in a slower reduction of the valence state of doping ions and a noticeable change in crystal coloration. All investigated impurities have practically no effect on the specific ferroelectric domain structure of CVO.

For the first time to our knowledge, multiwavelength, highly transient, single-pass stimulated Raman scattering with a low wavelength spacing on dual (stretching and bending) Raman modes in Sr(MoO4)0.8(WO4)0.2 and Sr(MoO4)0.4(WO4)0.6 solid solutions in a range of 1000-1300 nm (transparence window of biological tissue) under ultrafast chirped pulse laser pumping is comparatively investigated in the interests of multicolor two-photon imaging of a living tissue. For both the solid solutions, the optimum range (1-5 ps) of chirped pump pulse durations for multiwavelength Raman conversion on dual Raman modes was wider than for SrMoO4 (2-3 ps) due to the higher integral cross section of the bending Raman mode. Higher efficient SRS conversion took place at negative chirping of the pump pulse with its stretching from 0.25 ps up to 5 ps due to the compensation of a positive chirp caused by nonlinear phase modulation with total Raman conversion efficiency of up to 36 degrees lc for Sr(MoO4)0.8(WO4)0.2 and 49 degrees lc for Sr(MoO4)0.4(WO4)0.6. The highest number (five) of Stokes components in the desired range (1000-1300 nm) was observed in the optimum Sr(MoO4)0.4(WO4)0.6 solid solution, which has the Raman modes with comparable intensities. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

For the first time, to the best of our knowledge, we demonstrate highly transient, multiwavelength, single-pass Raman generation with combined frequency shifts on two Raman modes of an SrMoO4 crystal with high total Raman conversion efficiency of up to 48% in conditions of competition with self-phase modulation (SPM). A 58-mm-long SrMoO4 crystal was used as the active medium under pumping by the 1030-nm, 40-µJ laser pulses with controllable dispersive stretching in a range of 0.25-6 ps at negative and positive chirping. The pump pulse chirping was optimized for both high- and low-frequency Raman shifts on the primary (888 cm-1) and secondary (327 cm-1) Raman modes of the crystal. At the optimal conditions, four Stokes components of stimulated Raman scattering (SRS) radiation with high- and low-frequency Raman shifts at the wavelengths of 1066, 1134, 1177, and 1261 nm were efficiently generated.

The spectroscopic properties of cobalt ions in Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during synthesis are investigated. The diffusion doped crystal shows the potential for higher cobalt doping while maintaining its high initial optical quality. The redistribution of several absorption and fluorescence lines intensities with cobalt concentration is attributed to the formation of Co 2+ optical centers with sufficiently different local environments. The fluorescence decay times of Co 2+ optical centers are measured to differ by an order of magnitude (95 and 13 μs) and are attributed to centrosymmetric M1 and low symmetry M2 types of Co 2+ optical centers, possibly corresponding to Ca(4) and Ca(1) positions of Ca 3 (VO 4 ) 2 crystal, respectively. Nonlinear transmission of Co 2+ M2 centers is measured, and efficient absorption cross‐sections of 1.4 × 10 −19 and 2.4 × 10 −19 cm 2 are evaluated at 1300 and 1500 nm, respectively. The narrow fluorescence line of cobalt ions peaking at about 1170 nm, detected in both Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during synthesis, is attributed to Co ions in a trivalent state.

Whitlockite-type polycrystalline and single-crystal (Ca3−xSrx)(VO4)2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca3−xSrx)(VO4)2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca1.8Sr1.2)(VO4)2 (CSVO) revealed its actual composition (Ca2.982(11)Sr0.031)(VО4)2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5A sites, forming two independent strongly distorted tetrahedral Ca5O4 and octahedral Ca5AO6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa2.4Sr0.6)(VO4)2 doped with 0.5 and 1.0 wt% Tm2O3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca2.776(7)Sr0.210(4)Tm3+0.008(1))(VO4)2 and (Ca2.855(7)Sr0.140(7)Tm3+0.009(1)□0.022(7))(VO4)2, respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed.

High-temperature diffusion doping has been used for the introduction of active cobalt ions in calcium orthovanadate Ca3(VO4)2 single crystals (CVO). The test samples have been produced from nominally pure Cz CVO single crystals. High-temperature diffusion conditions have been optimized for the obtaining of doped optical quality single crystals in open or closed zone annealing. The diffusion coefficients of cobalt ions have been calculated for different conditions. Temperature regime, process time, diffusant type were defined. The samples have been annealed at 1150–1300 °C for 24–48 h with Co3O4, Ca10Co0.5(VO4)7 and Ca3(VO4)2 : 2 wt.% Co3O4 as diffusants. The diffusion direction has been parallel or perpendicular to the optical axis of the CVO crystal. The diffusion coefficients have been calculated to be in the range of 2.09 · 10-8 – 1.58 · 10-7 cm2/s. The diffusion activation energies have been determined to be 2.58 ± 0.5 and 2.63 ± 0.5 eV for the [001] and [100] directions, respectively. The maximum cobalt concentration in the doped CVO crystals has been found to be 2 · 1020 cm-3. The absorption spectrum of the diffusion doped Ca3(VO4)2 : Co samples has exhibited absorption bands typical of the Co2+ and Co3+ ions. It has been shown that the intensity ratio between the characteristic absorption bands varies depending on crystal obtaining technique. The optical anisotropy of the crystal increases with dopant concentration.

The spectroscopic properties of cobalt ions in Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during Czochralski growth process are studied. The spectroscopic properties of M1 and M2 Co 2+ optical centers are presented. A narrow fluorescence line at 1170 nm is attributed to trivalent Coions.

New high optical quality calcium orthovanadate Ca-3(VO4) (2) crystal doped by chromium ions was synthesized. Polyvalent character of doping chromium ions in as-grown crystal was revealed. Crystal annealing at 1000 degrees C seems to result in increase of chromium ions in four plus state. Spectroscopic properties of chromium ions in Ca-3(VO4)(2) crystal were investigated.

For the first time to our knowledge, a single-phase solid solution Sr(MoO4)0.8(WO4)0.2 was used as an active medium of a Raman laser. Using the high-intensity synchronous picosecond pumping satisfying the condition of phase capture of the parametric Raman interaction on the second vibrational mode made it possible to oscillate six components of Raman radiation with a combined frequency shift on the first (888 cm–1) and second (327 cm–1) vibrational modes in the wavelength range of 1194-1396 nm. Oscillation efficiency of the multiwavelength Raman laser radiation was as high as 10%. By detuning the Raman laser cavity length, the pulse shortening down to 6 ps for the Raman laser radiation components with the combined frequency shift was obtained, which is an order of magnitude shorter than the pumping pulse duration (64 ps).

Theoretical and experimental studies were conducted on providing conditions for the generation of multiple radiation components with a small wavelength spacing in a crystalline synchronously pumped SRS laser with combined frequency shift on high-frequency and low-frequency vibrational modes of an SRS-active crystal. A theoretical analysis has shown an important role of four-wave parametric Raman interactions on the low-frequency vibrational mode of the crystal provided the conditions of coherence and of nonlinear phase capture of such interactions are satisfied. For the first time, SRS generation was carried out at five closely spaced wavelengths of 1194, 1242, 1294, 1336, and 1396 nm in a SrMoO 4 crystal under synchronous pumping by a high intensity picosecond YAlO 3 :Nd 3+ laser at a wavelength of 1079 nm satisfying the condition of nonlinear phase capture.

In this work, the high-temperature diffusion doping method was used for introduction of active cobalt ions into calcium orthovanadate Ca3(VO4)2crystals. Experimental samples were made from a nominally pure CVO single crystal obtained by the Czochralski method. The high-temperature diffusion conditions have been optimized to obtain doped crystals of optical quality during annealing in open and closed zones. Diffusion coefficients of cobalt ions (D) were calculated for various conditions: annealing time 24 - 48 hours; temperature range 1150-1300°C; diffusants - oxide compounds of calcium, cobalt and vanadium: Co3O4, Ca10Co0.5(VO4)7 and Ca3(VO4)2:2wt.%Co3O4; diffusion direction is parallel or perpendicular to the CVO crystal optical axis. The calculated values of the diffusion coefficient varied between 2.09·10-8—1.58·10-7 cm2/s. The activation energy of the diffusion process was determined to be 2.58±0.5 and 2.63±0.5 eV for the [001] and [100] directions, respectively. The maximum cobalt concentration in doped CVO crystals was 2·1020 cm–3. The absorption spectrum of diffusion-doped Ca3(VO4)2:Co samples demonstrates the presence of absorption bands characteristic for Co2+ and Co3+ ions. It was shown that the intensity ratio of the characteristic absorption bands varies depending on the crystal doping method. The optical anisotropy of the crystal increases with dopant concentration increase.

Luminescence properties of nominally pure and doped with Eu3+ and Pr3+ ions SrMoO4 single crystals grown by the Czochralski method have been studied. Thermal quenching of intrinsic emission of pure and doped SrMoO4 single crystals has been observed, as well as a correlation of thermal quenching activation energies with rare-earth ion concentration has been observed. Tunable laser was used to study time-resolved luminescence in a range from 10 K to room temperature. The effect of dopant nature and concentration on intrinsic emission and decay kinetics has been elucidated.

In this work, on the base of piezoelectric and pyroelectric measurements, it was shown that the calcium orthovanadate crystals pure and doped exhibit a natural unipolar state. Doping these crystals with manganese and thulium ions did not affect the magnitude and behavior of dielectric permittivity. However, the presence of doping ions led to reducing the local piezoelectric response and stabilizing the unipolar state.

Multi-Stokes ultrashort pulse shapes and their relative positions of synchronously pumped stimulated Raman scattering (SRS) on combined primary and secondary vibrational modes in a BaWO4 crystal are investigated. An original method of its simultaneous measurement with the help of a streak camera has been developed. The structure of SRS pulses at the pulse shortening effect down to the pulse duration, close to the dephasing time of the secondary Raman mode of the BaWO4 crystal, is registered and analyzed for the detuning of the Raman laser cavity length.

We studied the luminescence properties of calcium and strontium molybdates, pure and activated with neodymium ions. The temperature dependences of the luminescence spectra and decay kinetics demonstrated the effect of temperature on the processes of energy transfer from the intrinsic luminescence centers to the activator. The significant potential of the studied compounds in contactless luminescence thermometry in a wide temperature range is concluded.

We studied the luminescence properties of calcium and strontium molybdates, pure and activated with neodymium ions. The temperature dependences of the luminescence spectra and decay kinetics demonstrated the effect of temperature on the processes of energy transfer from the intrinsic luminescence centers to the activator. The significant potential of the studied compounds in contactless luminescence thermometry in a wide temperature range is concluded.

Luminescence properties of calcium and strontium molybdates, undoped as well as doped with Nd3+ ions were studied. The influence of temperature on the energy transfer processes from the intrinsic emission centers to activator is shown on the basis of the analysis of the temperature dependencies of luminescence spectra and decay kinetics. It is concluded that the studied compounds are promising for non-contact luminescent thermometry in a wide temperature range.