Optical Floating Zone Method Research Articles

Mn doping-induced twofold spin reorientation and multi-step spin switching in NdFeO3 single crystal

Magnetization reversal and magnetic state regulation are the basis of application for magnetic materials in information processing. Here, twofold spin reorientation transitions (SRT) and field-induced multi-step spin switching phenomena were observed in NdMn0.2Fe0.8O3 (NMFO) single crystals grown via the optical floating zone method. Magnetic anisotropy was systematically investigated in both Zero-Field-Cooled (ZFC) and Field-Cooled (FC) modes. The NMFO single crystal exhibited twofold SRTs: from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) and from Γ1 (Ax, Gy, Cz) to Γ2 (Fx, Cy, Gz). Furthermore, a magnetic field-induced spin reorientation transition was identified along the c-axis. Additionally, closer proximity to the SRT temperature corresponded to a reduced magnetic field requirement for inducing the spin reorientation transition. These findings contribute to our comprehension of spin dynamics in NMFO, presenting possibilities for future device applications.

Highly efficiency up and down -conversion photoluminescence in Er/Tm/Yb co-doped lutecia-stabilized zirconia single crystals

High-quality transparent cubic lutecia-stabilized zirconia and LSZ:Yb1Er0.05Tm0.5 single crystals were grown by the optical floating zone method for the first time. For comparison, YSZ and YSZ:Yb1Er0.05Tm0.5 single crystals were also grown. No absorption peaks were observed in the 200 ∼1100 nm range in the transmission and absorption spectra of LSZ and YSZ, indicating that both crystals are excellent matrix crystals. The absorption spectra of LSZ:Yb1Er0.05Tm0.5 and YSZ:Yb1Er0.05Tm0.5 crystals exhibit several absorption peaks at 377, 408, 462, 488, 516, 679, 785 nm and a strong broad absorption band in the 836 ∼ 1050 nm range. The up-conversion photoluminescence of the LSZ:Yb1Er0.05Tm0.5 crystal excited by a 980 nm laser exhibited several distinct emission peaks at 300, 372, 476, 531, 548, 642 and 798 nm; similar emission peaks were observed in the up-conversion photoluminescence spectrum of the YSZ:Yb1Er0.05Tm0.5 crystal, except for the absence of the 300 nm peak. The intensity of the emission peaks of the former was higher than that of the corresponding peaks of the latter. Power curves indicated that the 300 nm emission is a four-photon up-conversion process, the 372 nm and 476 nm emissions are three-photon processes, and the 548 nm and 642 nm emissions are two-photon processes. Under excitation at 379 nm, the down-conversion photoluminescence spectra of the LSZ:Yb1Er0.05Tm0.5 and YSZ:Yb1Er0.05Tm0.5 crystals showed emission peaks at 450, 457, 511, 531 and 637 nm, the peak intensities of the former are higher than those of the latter, which is due to the former with higher density and lower phonon energy as compare to the latter. These results indicate that LSZ:Yb1Er0.05Tm0.5 single crystal has advantages over YSZ:Yb1Er0.05Tm0.5 single crystal for luminescence in photonic devices.

Growth, structure and spectroscopic properties investigation on a novel Tm3+-doped disordered Ca(GdxY1-x)Al3O7 hybrid melilite crystal

A disordered Tm3+-doped Ca(GdxY1-x)Al3O7 hybrid melilite crystal (Tm:CGYAM) was successfully grown by using the optical floating zone method, and its structure and spectroscopic properties were studied thoroughly. Structure analysis shows that the Tm:CGYAM crystallizes in tetragonal system. The maximum phonon energy of Tm:CGYAM crystal is estimated to be 765.8 cm−1. Absorption spectrum shows that the absorption cross-section of the Tm:CGYAM crystal is 0.44 ×10−20 cm2 at 788.5 nm, with a FWHM of 34.5 nm. The radiative lifetime of Tm3+:3F4→3H6 transition in Tm:CGYAM crystal is calculated to be 5.35 ms by J-O analysis. The emission cross-sections are 0.321×10−20 cm2 at 1785 nm and 0.324×10−20 cm2 at 1945 nm. The FWHM of Tm3+:3F4→3H6 transition emission band reaches 280 nm. By fitting the fluorescence decay curve, the fluorescence lifetime of Tm3+:3F4 level is estimated as 4.55 ms. The gain cross-section of Tm:CGYAM crystal achieves positive in the range of 1771–2200 nm once the population inversion level reaches 10 %. All the experimental results support the Tm:CGYAM crystal can be a promising candidate material for solid state tunable or ultrashort pulse laser application.

Spin switching and magnetocaloric effect of high-entropy orthoferrite single crystal

The concept of high-entropy oxides/alloys was introduced into the rare-earth orthoferrite (RFeO3, R represents a rare-earth ion) system. Doping five different rare-earth ions with equal molar ratios at the R-site, a single crystal of high-entropy orthoferrite (Y0.2Sm0.2Eu0.2Gd0.2Er0.2)FeO3 (HERFO) was synthesized using optical floating zone method. At high temperatures, the weak ferromagnetic (wFM) moments induced by the distortion of the Fe sublattices align along the c axis, with a spin configuration of Γ4. As the temperature decreases, a spin reorientation transition (SRT) occurs from Γ4 to Γ2 due to the Fe3+-R3+ super-exchange interactions, with an immediate state Γ24. The wFM moments gradually rotate from the c axis to the a axis within the ac plane. In the zero-field-cooling (ZFC) mode, both the type-I and type-II spin switching (SSW) are observable along the a axis. Under low magnetic fields, the type-II SSW is magnetically controlled. The trigger temperature and variation in net moment of the type-II SSW exhibit systematic changes concerning the applied magnetic field. The rich magnetic phase transitions in HERFO make it a promising candidate for spintronic applications aimed at spin manipulation. Additionally, HERFO single crystal exhibits a large magnetocaloric effect (MCE) and magnetic entropy anisotropy, with the negative magnetic entropy change (‐ΔSm) along the c axis (14.45 J/(kg·K)) being greater than that along the a and b axes (9.57 J/(kg·K) and 10.32 J/(kg·K)). Consequently, HERFO holds great promise as a novel material for magnetic refrigeration applications aimed at achieving rotational magnetic cooling.

Optical properties and passive self Q-switching of floating zone grown Cr–Nd co-doped YVO4 crystal

Single crystals of Cr (0.7, 1.0, 1.4 and 2.0 at%) and Nd (0.7 at%) co-doped yttrium vanadate (YVO4) were grown by optical floating zone method. [100]-oriented elements were fabricated from the grown crystals for optical and lasing studies. The refractive index analysis revealed that the values of ordinary refractive indices (no) for 0.7, 1.0, 1.4 and 2.0 at% Cr doped samples were found to be almost constant except for a slight increase corresponding to 532 nm. But the extraordinary refractive indices (ne) was found to increase with Cr doping concentration and it is maximum at 1.4 at% for all the wavelengths. The thermal coefficient of ne and no increases slightly and becomes constant beynd 1.4 at% of Cr. The band gap of the crystal is polarization sensitive with the values in the range of 3.51–3.55 eV and 3.59–3.62 eV for electric field parallel and perpendicular to c axis, respectively. The band gap does not exhibit any significant change on Cr doping. The emission spectrum with excitation at 808 nm is characterized by three broad asymmetric bands centered at 896, 1064 and 1341 nm. The emission intensity for the peak around 1064 nm decreases with an increase in Cr due to a broad absorption around 1100 nm of Cr5+ ion and, therefore, this band is exploited for passive Q-switching in the crystal. Further, excitation at 400 nm of Cr band revealed that there is strong emission at 1064 nm, which may be explored for pumping the gain medium with solar radiation. Finally, a stable passive Q-switching at 1064 nm was demonstrated in [100] element fabricated from the gown crystal having 1.4 at% Cr. An output power of ∼108 mW having pulse-width ∼220 ns and repetition rate ∼239 kHz was achieved for a pumping of ∼14.6 W at 808 nm.

Up- and down-conversion photoluminescence properties of Ho2O3 doped YbAG single crystals prepared by optical floating zone method

Single crystals of garnets with composition Yb2.96-xYxHo0.04Al5O12 (x = 0, 2.92, 2.96) were grown by optical floating zone method, and shown by XRD measurements to be in the cubic phase. EDS spectra show that Ho3+ and Yb3+ were homogenously distributed in the structure. As shown by the transmission and absorption spectra, the Yb2.96-xYxHo0.04Al5O12 crystals are highly transparent and can function as excellent optical crystals. Compared to the Y2.96Ho0.04Al5O12 crystal, the Yb2.96Ho0.04Al5O12 crystal has an additional strong broad absorption in the 836–1070 nm range, which increases its absorption of 980 nm photons. The optical band gaps of the Yb2.96-xYxHo0.04Al5O12 crystals decrease with increasing Yb2O3 concentration. Furthermore, differences with Yb2O3 concentrations in the Yb2.96-xYxHo0.04Al5O12 crystals were observed for the first time in the up- and down-conversion photoluminescence. Under excitation with a 980 nm laser, the up-conversion PL spectra of the Yb2.96-xYxHo0.04Al5O12 crystals show several emission peaks at 548 nm, 665 nm and 775 nm, and their intensities increase with Yb2O3 concentrations. In the Yb2.96Ho0.04Al5O12 crystal, Yb3+ not only is a component of the garnet structure, but it also acts as a sensitizer. In regards of down-conversion, under excitation at 454 nm, the down-conversion PL spectra of the Yb2.96-xYxHo0.04Al5O12 crystals show strong emission peaks at 550 nm, and their intensities decrease with increasing Yb2O3 concentrations, which is considered to be the consequence of increasing matrix density.

Spin reorientation, spin switching, and magnetic compensation in Er1−xSmxFeO3 single crystals

We investigated spin reorientation, magnetic compensation and spin switching transitions in a series of high-quality single crystals of Er1−xSmxFeO3 (x = 0, 0.2, 0.4, 0.6, 0.8) prepared using the optical floating zone method. Structural and other preliminary characterizations confirmed the quality and phase purity of the crystals. Rietveld refinement of powder XRD data indicates that lattice parameters a and c increase linearly with increasing Sm concentration, whereas b remained constant. Field-cooled cooling (FCC) measurements revealed a temperature-induced spin reorientation transition (SRT) from Γ4 (Gx, Ay, Fz) to Γ2 (Fx, Cy, Gz) for all the samples. SRT temperature increased with Sm concentration and spread widely above and below room temperature. Moreover, magnetic compensation is common to all the compositions but decreases as Sm doping increases. We also observe type-I spin switching in samples with x = 0, 0.2, and 0.4 at an applied field of 60 Oe under FCC protocol, with a reduction in spin switching temperature as Sm content increased. For Sm-rich samples (x = 0.6, 0.8), spin switching was absent at 60 Oe.

Magnetic Characterization of Zone-Refined Rare-Earth Orthoferrite Crystals Grown by the Optical Floating Zone Method

Magnetic Characterization of Zone-Refined Rare-Earth Orthoferrite Crystals Grown by the Optical Floating Zone Method

Metamagnetic phase transition induced large magnetocaloric effect in a Dy0.5Ho0.5MnO3 single crystal.

Magnetic refrigeration based on the magnetocaloric effect is gaining interest in orthogonal or hexagonal rare-earth manganite. However, a more comprehensive understanding of the underlying mechanism is still required. We grew a high-quality single crystal of Dy0.5Ho0.5MnO3 using the optical floating zone method, since the parent crystals DyMnO3 and HoMnO3 have orthogonal and hexagonal structures, respectively. The magnetic and magnetocaloric properties and refrigeration mechanisms are thoroughly investigated. Doping modifies the magnetism according to the results obtained from the investigation of magnetic and dielectric properties and heat capacity. The spin reorientation transition shifts towards low temperature in comparison to HoMnO3. Near the Néel temperature of rare-earth sublattices (5 K), the highest changes in negative magnetic entropy under 0-70 kOe are 18 J kg-1 K-1 and 13 J kg-1 K-1 along the a- and c-axes, respectively. The low-temperature metamagnetic phase transition caused by the alterations in the magnetic symmetry of Ho3+ contributes to an increased magnetocaloric effect in comparison to the parent crystals, rendering it a promising choice for magnetic refrigeration applications. Dy0.5Ho0.5MnO3 exhibits a clear magnetocrystalline anisotropy with enhanced refrigeration capacity and negative magnetic entropy change along the a-axis. The adiabatic temperature change of Dy0.5Ho0.5MnO3 is 8.5 K, larger than that of HoMnO3, rendering it a promising choice for low-temperature magnetic refrigeration applications.

Growth and characterization of Dy1−xSmxMnO3 single crystals by optical floating zone technique

Dy1−xSmxMnO3 powders were synthesized by solid-state reaction and single crystals were grown using optical floating zone method for the full composition range 0 ≤ x ≤ 1.0. Energy dispersive x-ray spectroscopy (EDS) confirms the nominal composition for all the grown crystals of Dy1−xSmxMnO3. Rietveld refinement analysis using synchrotron X-ray powder diffraction data on powders obtained after crushing the crystals confirms the orthorhombic phase with Pnma space group for all the compositions studied. The lattice parameters and unit cell volume are shown to increase with increasing Sm3+ content at the Dy3+ site in DyMnO3. Magnetization measurements on Dy1−xSmxMnO3 single crystals reveal that the Sm3+ substitution systematically decreases the rare-earth ordering temperature (TDy3+).

Preparation and optical properties of high-quality green cobalt sapphires

A series of (Al2O3)100-x(Co3O4)x (x = 0, 0.04, 0.1, 0.2, 0.3, 0.4) single crystals were successfully prepared by the optical floating zone method for the first time, even though natural cobalt-containing sapphires have not been observed. It has been found that the (Al2O3)99.70(Co3O4)0.30 single crystal is a high-quality, beautiful, and stable green cobalt sapphire like an emerald, and its density is 3.984 g/cm3. XRD and Raman spectra of the (Al2O3)100-x(Co3O4)x crystals show that cobalt is successfully incorporated in the Al2O3 which retains its hexagonal structure. Two strong broad absorption peaks at 436 nm and 652 nm were observed in the UV–Vis absorption spectra, which are assigned to the 1A1→1T1 and 1A1→1T2 transitions of Co3+, respectively. Whilst the optical band gaps were in the range 4.43–3.95 eV. Under excitation at 436 nm, one strong emission peak at 864 nm and a weak emission peak at 692 nm were found in the photoluminescence (PL) spectra of the cobalt sapphires. At Co3O4 concentrations lower than 0.30 mol%, the intensities of both emission peaks increase with Co3O4 concentration, and reach their maxima at 0.30 mol%, then decrease with the further increases in Co3O4. Also, X-ray excited luminescence (XEL) spectra show that the cobalt sapphires have a high sensitivity for X-ray detection. Overall, cobalt sapphires can have various potential uses, such as in jewelry, as ultraviolet detectors, in X-ray detection, and in near-infrared emission devices.

Evaluation of photoluminescence and scintillation properties of Eu-doped YVO4 single crystals synthesized by optical floating zone method

0.1, 0.5, 1.0, and 5.0 % Eu-doped YVO4 single crystals were fabricated to assess photoluminescence (PL) and scintillation properties. The powder X-ray diffraction patterns of all the fabricated samples were the same as that of reference, and a single-phase structure of YVO4 was observed. The emission peaks owing to the 4f-4f transitions of Eu3+ ions were observed at 590, 605, 615, 620, and 695 nm in PL and scintillation spectra. Based on the pulse height spectra, Eu-doped samples had the light yield of 28,000 (0.1 % Eu), 33,000 (0.5 % Eu), 42,000 (1.0 % Eu), and 37,000 (5.0 % Eu) photons/MeV. In afterglow profiles, the afterglow level of 0.1, 0.5, 1.0, and 5.0 % Eu-doped samples was 58.1, 61.1, 49.1, and 35.6 ppm.

The effect of Pr3+ concentration on the microstructure, luminescence and scintillation properties of Pr:LuAG single crystals

High-quality lutetium aluminum garnet doped with various Pr3+ concentrations ((Lu1-xPrx)3Al5O12, abbreviated to Pr:LuAG) single crystals were grown by the optical floating zone method. The concentration of Pr3+ dependence on microstructure, luminescence and scintillation properties were systematically studied. Based on the results of Rietveld refinement, the doping of Pr3+ leads to lattice distortion and lowers its symmetry. The symmetry of the LuO8 dodecahedron center is lowest at 0.010, as confirmed by the Raman spectra. When excited at 450 nm and X-rays, the primary emission peak at 614 and 300 nm, respectively, induced by Pr3+ 4f2-4f2 and 4f5d-4f2 transitions. The optimal doping concentration is 0.010. The electric dipole-electric dipole interaction between adjacent Pr3+ was responsible for the concentration quenching in the Pr:LuAG single crystals. (Lu0.990Pr0.010)3Al5O12 shows the shortest average scintillation decay time (22.55 ns) and highest light yield (23,842 ± 2300 ph./MeV) under 662 KeV 137Cs gamma-ray irradiation. In terms of overall luminescence and scintillation performance, 0.010 doping was the best for Pr3+ doped LuAG single crystals.

Optical floating zone growth and thermionic emission properties of La0.9Sr0.1B6 single crystal

This paper has studied the crystal structure, growth orientation, crystal quality and thermionic emission properties of the La0.9Sr0.1B6 single crystal prepared by the optical floating zone method. By the means of XRD, single crystal X-ray diffraction, X-ray Laue diffraction, X-ray rocking curve and TEM, the La0.9Sr0.1B6 single crystal grown along [100] orientation is determined to be a single-phase solid solution of Sr-doped LaB6 with the typical cubic structure and have a good crystal quality and integrity. The higher J1kV (42.55 A/cm2), Jo (31.19 A/cm2) and lower Φeff (2.492 eV) than LaB6 under the cathode operating temperature of 1500 °C as well as the good thermionic emission stability strongly suggest that the grown La0.9Sr0.1B6 single crystal has a good potential to be a promising hot cathode material.

Bulk crystal growth and characterization of intrinsic scintillator CaNb2O6

Single crystal CaNb2O6 was grown by the optical floating-zone method and characterized for a new intrinsic scintillator. Under Ar and O2 growth atmospheres, the as-grown crystal rods (Ф 4–5 mm) exhibit a greyish and a colorless appearance, respectively, which are related with the oxygen vacancy. They both show a broad emission band with the maximum at 480 nm under UV excitation, while the one grown in O2 is brighter with a photoluminescence quantum efficiency of 44%. Consequently, a 25% higher scintillation light yield was obtained in the crystals grown in O2 compared to those in Ar. The other scintillation properties including radioluminescence spectrum, pulsed X-ray decay and afterglow were also characterized and compared.

Highly Efficient Orange-Red Emission in Sm3+-Doped Yttrium Gallium Garnet Single Crystal

High-quality single crystals with empirical composition Y2.96Sm0.04Ga5O12 (YGG: Sm3+) were successfully prepared by the optical floating zone method for the first time and compared with related single crystals of Y2.96Sm0.04Al5O12 (YAG: Sm3+). With both crystals, XRD showed that Sm3+ entered the cubic-phase structure. Optical absorption spectra produced a series of peaks from Sm3+ in the 250 nm to 550 nm range, and photoluminescence excitation (PLE) spectra detected at 613 nm showed strong excitation peaks at 407 nm and 468 nm. A strong emission peak at 611 nm (orange-red light) was observed in the photoluminescence (PL) spectra under excitations at both 407 and 468 nm, respectively, but it was much brighter under excitation at 407 nm. Furthermore, with both emission spectra, the peaks from the YGG: Sm3+ crystal were significantly more intense than those from the YAG: Sm3+ crystal, and both experienced a blue shift. In addition, under excitation at 407 nm, the color purity of the emitted orange-red light of YGG: Sm3+ was higher than that of the YAG: Sm3+ crystal, and the fluorescence lifetime for the 4G5/2 → 6H7/2 transition of YGG: Sm3+ was longer than that of the YAG: Sm3+ crystal. The optical properties of the YGG: Sm3+ crystal are better than those of the YAG: Sm3+ crystal.

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er3+, Tm3+ and Yb3+ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm3+1G4→3H6 transition, 531 and 547 nm (green) from the Er3+2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, and 640 and 662 nm (red) from the Er3+4F9/2 → 4I15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er2O3, 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3, and this crystal is suitable for use in highly efficient white light emission devices.

The Spatial Correlation and Anisotropy of β-(AlxGa1-x)2O3 Single Crystal.

The long-range crystallographic order and anisotropy in β-(AlxGa1-x)2O3 (x = 0.0, 0.06, 0.11, 0.17, 0.26) crystals, prepared by optical floating zone method with different Al composition, is systematically studied by spatial correlation model and using an angle-resolved polarized Raman spectroscopy. Alloying with aluminum is seen as causing Raman peaks to blue shift while their full widths at half maxima broadened. As x increased, the correlation length (CL) of the Raman modes decreased. By changing x, the CL is more strongly affected for low-frequency phonons than the modes in the high-frequency region. For each Raman mode, the CL is decreased by increasing temperature. The results of angle-resolved polarized Raman spectroscopy have revealed that the intensities of β-(AlxGa1-x)2O3 peaks are highly polarization dependent, with significant effects on the anisotropy with alloying. As the Al composition increased, the anisotropy of Raman tensor elements was enhanced for the two strongest phonon modes in the low-frequency range, while the anisotropy of the sharpest Raman phonon modes in the high-frequency region decreased. Our comprehensive study has provided meaningful results for comprehending the long-range orderliness and anisotropy in technologically important β-(AlxGa1-x)2O3 crystals.

Effects of Preparation Atmosphere and Doping Concentration on Scintillation and Photoluminescence Properties of Lu2O3:Eu Scintillation Single Crystals

Lu2O3:1%Eu and Lu2O3:8%Eu series single crystals were grown by optical floating zone method under air, N2, and H2-Ar mixed atmosphere (5 vol%H2 and 95 vol%Ar). The effects of preparation atmosphere and doping concentration on the scintillation and photoluminescence properties have been investigated and discussed. Correlated measurements of afterglow curves, X-ray excited luminescence spectra, photoluminescence excitation and photoluminescence, photoluminescence decay, and thermal stimulated luminescence curves were performed. Although Eu(S6) luminescence can be significantly depressed under oxidizing atmosphere, Lu2O3:8%Eu grown under weak reducing atmosphere presents the lowest afterglow intensity. This phenomenon was explained by different interstitial oxygen atom concentrations in the samples.

Structure and spectroscopic properties of a disordered Nd:CaGdAl3O7 crystal

A disordered Nd3+-doped CaGdAl3O7 crystal was grown by the optical floating zone method. The absorption and fluorescence spectra of Nd:CaGdAl3O7 crystal were measured, and the spectroscopic properties were studied intensively with the Judd–Ofelt theory. The calculated absorption cross-section was 3.78 × 10-20 cm−2 at 808.5 nm with a full width at half maximum (FWHM) of 19.3 nm. The emission cross-section centered at 1061.6 nm was estimated to be 4.94 × 10-20 cm2 with a FWHM of 12.6 nm, and the fluorescence lifetime of 4F3/2 energy level was measured as 260.7 μs. The experimental results revealed the potential of Nd:CaGdAl3O7 crystal applied in 1.06 μm laser system.