Co-doped Single Crystals Research Articles

Original Na5(Lu1–x–yGdxYy)9F32: Pr3+/Ho3+ Hybrid Single Crystals for Efficient ∼2.9 μm Mid-Infrared Emission

A novel Ho3+/Pr3+/Y3+/Gd3+ multiply doped Na5Lu9F32 mixed single crystal was successfully grown via a modified Bridgman technique. The structure of the mixed crystal was characterized by means of X-ray diffraction and Raman spectra. The impacts of Y3+ and Gd3+ ions on the 2.9 μm emission of Na5Lu9F32 single crystals, which incorporated fixed Ho3+/Pr3+, were investigated systematically with the aid of the optical spectra and decay curves of fluorescence. The 2.9 μm emission intensity (Ho3+: 5I6 → 5I7) was further heightened upon gradually introducing both Y3+ and Gd3+ ions into Ho3+/Pr3+-incorporated single crystals pumped at 640 nm. The brokenness of ionic quenching clusters of [Ho3+–Ho3+] and the release of more luminescent ions are in charge of the augment of emission at 2.9 μm by introducing Gd3+ or Y3+ ions into the Ho3+/Pr3+ codoped single crystals. A value of ∼8.2 × 10–21 cm2 was estimated for the maximum emission cross section at 2.9 μm of the mixed crystal. The processing of energy transfer among Ho3+, Pr3+, Y3+, and Gd3+ ions was investigated, and the energy transfer efficiency for Ho3+: 5I7 → Pr3+: 3F2 was approximately 57.32%. The Na5Lu9F32-doped Ho3+/Pr3+/Y3+/Gd3+ mixed crystals may be a new laser gain medium for 2.9 μm generation because of their special spectral and physicochemical properties.

Negative effect of Hf and Zr co-doping on alumina film growth of nickel-aluminium single-crystals during thermal cyclic oxidation

ABSTRACT The microstructure and cyclic oxidation behaviour of Hf and Zr co-doped B2 NiAl single-crystal alloys at 1473 K were investigated. Hf and Zr co-precipitated into one phase during alloy manufacturing. The RE-free single-crystal alloy obtained a double-layered alumina film comprised of outer equiaxed grains and inner columnar grains and exhibited lower oxidation rate than the corresponding poly-crystal alloy, while the co-doped single-crystal alloy displayed higher oxidation rate than the RE-free single-crystal alloy and no synergistic effect was discovered. The effect of Hf and Zr co-doping on the growth behaviour of the alumina film was discussed. It is proposed that the existence of grain boundaries is an important precondition for activating the reactive element effect. The absence of grain boundaries significantly weakened the positive effect of Hf and Zr co-doping and distinctly magnified its negative effect on the cyclic oxidation resistance of the alloy in the meantime. Highlights Cyclic oxidation behaviour of Hf and Zr co-doped NiAl single-crystals is compared. The undoped alloy obtains a double-layered alumina film during oxidation. The co-doped alloy shows higher alumina film growth rate than the undoped alloy. The absence of alloy grain boundaries suppresses the reactive element effect.

Effect of Li+ co-doping on the luminescence and defects creation processes in Gd3(Ga,Al)5O12:Ce scintillation crystals

Photo- and thermally stimulated luminescence characteristics, as well as photostimulated defects creation processes are investigated in the 85–510 K temperature range for the Li+ co-doped single crystal of Gd3(Ga,Al)5O12:Ce (GAGG:Ce). The results for GAGG:Ce,Li are compared with the corresponding characteristics of the GAGG:Ce and GAGG:Ce, Mg single crystals of similar host composition. The influence of Li+ and Mg2+ ions on the Ce3+ - related emission band position, temperature dependence of the photoluminescence intensity, efficiency of the Gd3+ → Ce3+ energy transfer, intensity and decay kinetics of the afterglow, and thermally stimulated luminescence characteristics is revealed. The presence of the Ce3+ → Ce4+ conversion in GAGG:Ce,Li is confirmed. The conclusion is made that, unlike GAGG:Ce,Mg, the compensation of the Li+ excess negative charge in GAGG:Ce,Li occurs due to both the Ce3+ → Ce4+ conversion and the effective formation of intrinsic crystal lattice defects. The origin of these defects as well as the origin of the electron and hole trapping centers in the GAGG:Ce,Li crystal are discussed.

Improved electrical conductivity and power factor in Sn and Se co-doped melt-grown Bi2Te3 single crystal

In the current work, growth and thermoelectric characterization of tin and selenium co-doped single crystal bismuth telluride have been carried out in the range of temperature 10–400 K. The crystals show hexagonal crystal structure with Roverline{3 }m space group. The direction of growth, quality of the single crystals, the density of dislocation, and dopants effect on the inner plane structure of the crystals have been analyzed through high-resolution X-ray diffraction study. Energy dispersive analysis of X-rays approves the elemental composition, and field emission scanning electron microscopy shows uniform growth with micro precipitates on the surface of the crystals. Quasi degenerate and non-degenerate electrical resistivity is observed in the pristine and doped samples, respectively. Temperature-dependent Seebeck coefficient measurements confirm the n-type semiconducting nature of the pristine as well as doped samples. Temperature-dependent power factor of (Bi0.96Sn0.04)2Te2.7Se0.3 is found to increase by 1.1 times, and electrical resistivity reduced by 3.3 times as compared to pristine Bi2Te3.

Judd-Ofelt analysis and spectroscopic study of Tb:CaF2 and Tb/Pr:CaF2 co-doped single crystals

Abstract High quality of Tb3+-single doped and Tb3+/Pr3+ co-doped CaF2 crystals were grown by the temperature gradient technique (TGT). Pr3+ ions were used as sensitizing ions of Tb3+. Optical properties including absorption spectrum, emission spectrum, and fluorescence decay curve were recorded. Through co-doping sensitizing ions of Pr3+, the absorption cross section around 480 nm increased from 0.007 × 10−20 cm2 to 0.3 × 10−20 cm2, the large value is beneficial for the absorption of LD pump source. Judd-Ofelt theory was used to analyze the spectroscopic parameters. Fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency were determined as well. The emission cross section of Tb,Pr:CaF2 for the green emission at 544 nm and yellow emission at 587 nm corresponding to the transition of 5D4→7F5 and 5D4→7F4 were calculated to be 5.56 × 10−22 cm2 and 8.78 × 10−23 cm2, respectively, which is comparable to the Tb3+ doped CaF2 crystal.

Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals.

In this study, we grew Cu co-doped single crystals of a topological superconductor candidate SrBiSe, and studied their structural and transport properties. We reveal that the addition of even as small an amount of Cu co-dopant as 0.6 atomic %, completely suppresses superconductivity in SrBiSe. Critical temperature (∼2.7 K) is rather robust with respect to co-doping. We show that Cu systematically increases the electron density and lattice parameters a and c. Our results demonstrate that superconductivity in SrBiSe-based materials is induced by significantly lower Sr doping level than commonly accepted , and it strongly depends on the specific arrangement of Sr atoms in the host matrix. The critical temperature in superconductive Sr-doped BiSe is shown to be insensitive to carrier density.

Enhanced red and green up-conversion in Er3+-Yb3+ doped Na5Lu9F32 single crystals through Tb3+ incorporation

Er3+/Yb3+/Tb3+ tri-doped Na5Lu9F32 single crystals were prepared by a Bridgman method. The spectroscopic characteristics of the synthesized single crystals were systematically investigated. Intense green and red emissions originated from transitions for Er3+ and Tb3+ ions were observed. It was found that the introduction of Tb3+ ions to the Er3+/Yb3+ co-doped single crystals can effectively adjust the emission from near-infrared (NIR) to visible region for Er3+ ions. The emissions at 660, 522 and 542 nm from Er3+/Yb3+ co-doped single crystals were enhanced as the Tb3+ concentration increases. The energy transfer mechanisms among Er3+, Yb3+ and Tb3+ ions were also discussed. Analysis on the decay curves suggests that electric dipole-dipole is dominant for the energy transfer from Tb3+ to Er3+ ions. According to the measured lifetimes of Er3+/Yb3+ and Er3+/Yb3+/Tb3+ doped samples, the maximum energy transfer efficiency from Tb3+ to Er3+ approaches up to 11.7%. The intense green and red up-conversion observed in the Er3+/Yb3+/Tb3+ tri-doped Na5Lu9F32 single crystals make them promising candidates for solid-state multicolor displays, temperature sensors, and biomedical imaging applications.

Growth and characterization of neodymium and ytterbium doped barium chloride dihydrate single crystals

Pure, Nd doped and Nd:Yb co-doped barium chloride dihydrate (BaCl2·2H2O) single crystals were grown and analyzed with various characterization techniques. The measured unit cell parameters show that the grown crystals belong to monoclinic system. Powder X-ray diffraction spectra indicates that the dopants enhance (2 1 0) orientation of BaCl2·2H2O crystal. X-ray rocking curves have been recorded to analyze the crystallinity of the grown single crystals. Optical absorption spectra of the grown crystals contain strong absorption bands in infrared region. Spectral overlap of absorption bands of Yb3+ and Nd3+ ion around 850 nm–1060 nm in Nd:Yb co-doped single crystal indicates the prospect of energy transfer between them. A significant enhancement has been observed in the photoluminescence spectrum of Nd:Yb co-doped single crystal recorded with 244 nm laser excitation. Photon upconversion ability of the crystals was tested using Nd:YAG laser of wavelength 1064 nm. An unusual upconverted green emission from pure centrosymmetric BaCl2·2H2O single crystal has been observed. The energy of upconverted green light of Nd:Yb co-doped barium chloride dihydrate single crystal is higher which may be due to energy transfer occurred between Yb3+ and Nd3+ ions. FTIR and FT-Raman spectral analyses were carried out to study the vibrational modes of pure, Nd doped and Nd:Yb co-doped BaCl2·2H2O single crystals.

Upconversion luminescence from terbium and ytterbium codoped LiYF4 single crystals

Upconversion (UC) luminescence and its pump power dependent on UC emissions were investigated under excitation of near infrared light at 960nm for the Tb3+/Yb3+ codoped LiYF4 single crystals. UC emissions at 488, 541, 654, and 669nm and 382, 413, 436, 465, 477, and 484nm arise transitions 5D4→7FJ (J=6, 5, 3, and 1) and 5D3→7FJ (J=6, 5, 4, 3, 2, and 1) of Tb3+, respectively. UC mechanisms are proposed by analyzing the pump power dependent UC emission. The yellowish green light can be achieved from 0.32mol%Tb3+ and 7.98mol% Yb3+ codoped LiYF4 crystal with chromaticity coordinates of (0.2874, 0.6733) and color temperature Tc=6280K. A cooperative energy transfer process from excited Yb3+ to Tb3+ in main form of two-photons has been presented in LiYF4 at room temperature. The green and red emissions originating from upper 5D4 state of these Tb3+/Yb3+ codoped single crystals may be considered as a promising potential application in the field of photonics, solid state lasers, and light emitting devices.

Dosimetric studies of YAlO3: Mn co-doped with transition (Co, Cu, Fe) and rare earth (Yb, Ce) metal ions

Dosimetric studies on single crystals of YAlO3:Mn co-doped with transition (Co, Cu, Fe) and rare earth (Yb, Ce) metal ions using UV radiation exposure for the duration 5–30 min have been studied. A single well resolved thermoluminescence glow peak was observed at 183 °C in Co and Cu co-doped single crystals. In Fe co-doped single crystals, two well resolved glow peaks at 196 °C and 238 °C were observed. A well resolved glow peak at 215 °C in Yb and 176 °C in Ce co-doped single crystals was observed. Variations of thermoluminescent (TL) glow peaks intensity in all the co-doped crystals with different UV-exposures were studied. TL glow peak intensity increases sublinearly in Co, Cu co-doped crystals, whereas in Fe co-doped crystals glow peaks at 196 °C and 238 °C increase linearly. Fading effect was studied at different intervals up to 30 d for all co-doped crystals exposed to UV source for 10 min. Strong fading was observed initially and stabilized after 15 d. Fe co-doped YAlO3:Mn2+ records 40% fading, whereas other samples of YAlO3:Mn2+ co-doped with Cu, Co, Yb and Ce show 60% fading. The kinetic parameters (E, b, s) were estimated using glow peak shape method for UV irradiated samples and results are discussed in detail.

Enhanced emission of 2.7μm from Er3+/Nd3+-codoped LiYF4 single crystals

An Er3+/Nd3+ co-doped LiYF4 single crystal of ∼Φ 12 mm × 95 mm size with high quality was grown by a Bridgman method. The luminescent properties of the crystals with different Er3+ and Nd3+ concentrations were studied. Compared with the Er3+ single-doped LiYF4 crystal extremely enhanced emission at 2.7 μm from the Er3+/Nd3+ co-doped LiYF4 was observed upon excitation of an 800 nm laser diode. Meanwhile, the green up-conversion emission and near infrared emission at 1.5 μm from Er3+ in the co-doped crystals were effectively restricted. The luminescent mechanisms for the Er3+/Nd3+ co-doped crystals were analyzed and the possible energy transfer processes were proposed. The energy transfer efficiencies for (Er3+:4I13/2, Nd3+:4I9/2) → (Er3+:4I15/2, Nd3+:4I15/2) and (Nd3+:4F3/2, Er3+:4I15/2) → (Nd3+:4I9/2, Er3+:4I9/2) were calculated. It was found that Er3+/Nd3+ co-doped single crystal may be a potential host for 2.7 μm lasers.

Electronic structure of cobalt-doped manganites

The electronic structure of the single crystals La 0.74Ba 0.26Mn 1− y Co y O 3 ( y=0.12,0.16,0.22) has been investigated with X-ray photoelectron spectroscopy (XPS). The transition-metal core level spectra, as well as the valence band (VB) spectra, were studied. By analyzing the valence band spectra we have determined that the Co 3d contribution to the VB of Co-doped single crystals La 0.74Ba 0.26Mn 1− y Co y O 3 ranges from approximately 1.0 to 4.5 eV binding energy. Co 2p core level spectra indicate a divalent character of the Co ions.

Precipitate identification in co-doped InP

The nature of precipitates found in Co-doped single crystals of InP grown by the LEC method has been investigated using scanning electron microscopy (both secondary and back scattered electrons and energy dispersive X-ray analysis (EDAX)) and Debye–Scherrer X-ray diffraction. Two phases have been detected. One has been positively identified as the cubic CoP 3 phase and was found to exist in two distinct morphologies, as cuboids at and near to the surface of the crystal and as fine rods in a eutectic CoP 3-InP mixture within the bulk of the crystal. in some crystals another phase has been observed which is also a cobalt phosphide but significantly more Co-rich than CoP 3. Thus far, the crystal structure of this phase has not been identified.