Growth and Faraday rotation characteristics of TbVO4 crystals

TbVO₄ (TV) single crystals with dimensions of 18 × 18 × 16 mm³ were grown by Czochralski method under different atmosphere. XPS studies revealed the presence of V⁴⁺ and Tb⁴⁺ in TV crystal grown at 99.9% N₂ atmosphere, which caused a wide absorption peak centered at 950 nm in the transmission spectrum. TV crystal grown at 80% N₂ + 20% CO₂ mixed atmosphere has high transmittance at 600–1500 nm waveband. Faraday rotation spectra of TV crystal were measured. TV crystal has a larger Faraday rotation than terbium gallium garnet (TGG) crystal at 500–1500 nm waveband.     

Microstructure,luminescence and thermal stability properties of NaSrPO4:Tb3+ phosphors with various doping concentrations prepared using conventional solid-state sintering

This paper reports the microstructure, luminescence and thermal stability properties of the NaSr_1−xPO₄:xTb³⁺ powders (x = 0.008, 0.01, 0.02, 0.04 and 0.06) via the conventional solid-state sintering at 1200 °C for 5 h. The X-ray diffraction result verifies all diffraction peaks are pure phase of NaSrPO₄. The luminescence results show that the NaSrPO₄:xTb³⁺ powders mainly excited at 370 nm have a series of the emission-states, related to the typical 4f → 4f intra-configuration forbidden transitions of Tb³⁺, and a major emission peak of around 546 nm. The concentration quenching of the NaSr_1−xPO₄:xTb³⁺ phosphors is appeared at x = 0.02. The decay time values of the NaSr_1−xPO₄:xTb³⁺ phosphors for the ⁵D₄ state of the Tb³⁺ are around 3.30 ms to 3.60 ms. It is also found the chromaticity coordinate of NaSrPO₄:Tb³⁺ phosphor varies with the increase of the concentration of Tb³⁺ ions from blue to green. Moreover, the thermal stability of the NaSrPO₄:xTb³⁺ phosphors is slightly better than that of conventional YAG phosphors.     

Luminescence properties of ZnMoO4:Tb3+ green phosphor prepared via co-precipitation

Tb³⁺-doped ZnMoO₄ green phosphor was synthesized by a co-precipitation method. The morphology and structure of the phosphor were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photoluminescence (PL) spectra were also used to characterize the ZnMoO₄:Tb³⁺ samples. The results show that ZnMoO₄:Tb³⁺ phosphor has triclinic structure with diameters ranging from 1.0 to 2.0 μm. The obtained ZnMoO₄:Tb³⁺ phosphor emits green light emission centered at 541 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ when excited by 378 nm or 488 nm. The optimized concentration of Tb³⁺ is 15 mol.% for the highest emission intensity at 541 nm, and the concentration quenching occurs when the Tb³⁺ concentration is beyond 15 mol.%. The concentration quenching mechanism can be interpreted by the quadrupole–quadrupole interaction of Tb³⁺ ions. The present work suggests a convenient, cost-effective method for green phosphor, which may lead to potential applications in white light-emitting diodes (WLED).     

Growth and Faraday rotation characteristics of Tb3−xNdxGa5O12 single crystal

Tb_3−xNd_xGa₅O₁₂ single crystal with dimension of Φ22 mm × 28 mm and a good optical quality was grown by the Czochralski method. X-ray powder diffraction was carried out and lattice parameters were calculated, which showed that the single crystal belongs to cubic crystal system. The transmission spectrum in the wavelength range of 450–1500 nm, which indicated the crystal has low absorption coefficient at 900–1450 nm. The Verdet constants of Tb_3−xNd_xGa₅O₁₂ at 532, 633 and 1064 nm wavelengths calculated by the extinction method are 225, 145 and 41 radm⁻¹ T⁻¹, respectively, which are larger than that of commercial TGG (Tb₃Ga₅O₁₂) reported. The magneto-optical figures of merit of the crystal calculated is 3162°/dB at 1064 nm, and the extinction ratio is larger than that of commercial TGG.     

A comparative study of ferroelectric triglycine sulfate (TGS) crystals grown by conventional slow evaporation and unidirectional method

Unidirectional 〈0 1 0〉 TGS single crystal of diameter 35 mm and length 80 mm was grown by Sankaranarayanan–Ramasamy (SR) method. Nearly two times higher d₃₃ value has been obtained for the SR grown TGS crystal compared to conventional grown TGS. The etch pit density of SEST and SR method grown TGS crystal is 2.1 × 10² cm^?2 and 1.5 × 10² cm^?2 respectively. The values of hardness were found to be 152 kg/mm² for SR grown TGS and 108 kg/mm² for SEST grown TGS crystal. The average laser damage threshold obtained on the SEST grown TGS crystal was 29 mJ/cm² whereas a high damage threshold of 39 mJ/cm² was obtained for the SR grown crystal. The SR method grown TGS has 5% higher transmittance as against conventional method grown crystal. Dielectric study showed higher dielectric permittivity and lower dielectric loss in SR grown TGS crystal.     

Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

Spinel (MgAl₂O₄) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al₂O₃, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn²⁺ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.     

The growth of benzophenone crystals by Sankaranarayanan–Ramasamy (SR) method and slow evaporation solution technique (SEST): A comparative investigation

Longest unidirectional〈1 0 0〉 benzophenone (BP) crystal having dimension of 1060 mm length and 55 mm diameter was grown by Sankaranarayanan–Ramasamy method. The growth rate was measured by monitoring the elevation of the crystal–solution interface at different temperatures. The high resolution X-ray diffraction and etching measurements indicate that the unidirectional grown benzophenone crystal has good crystalline perfection and less density of defects. The optical damage threshold of SEST and SR grown BP crystals has been investigated and found that the SR grown benzophenone crystal has higher laser damage threshold value than the conventional method grown crystal. Microhardness measurement shows that crystals grown by SR method have a higher mechanical stability than the crystals grown by SEST method. Dielectric permittivity and birefringence are high in SR grown crystal compared to SEST grown BP crystal. The UV–vis-NIR results show that SR method grown crystal exhibits 7% higher transmittance as against crystals grown by conventional method.     

Growth of CuInTe2 single crystals by iodine transport and their characterization

The single crystals with stoichiometry close to 1:1:2 of CuInTe₂ (CIT) have been grown by chemical vapor transport (CVT) technique using iodine as the transporting agent at different growth temperatures. Single crystal X-ray diffraction studies have confirmed the chalcopyrite structure for the grown crystals and the volume of unit cell is found to be the same for the crystals grown at different conditions. Energy dispersive X-ray (EDAX) analysis of CIT single crystals grown shows almost the same stoichiometric compositions. Scanning electron microscope (SEM) analysis reveals kink, step and layer patterns on the surface of CIT single crystals depending on the growth temperatures. The optical absorption spectra of as-grown CIT single crystals grown at different conditions show that they have same band gap energies (1.0405 eV). Raman spectra exhibit a high intensity peak of A₁ mode at 123 cm^?1. Annealed at 473 K in nitrogen atmosphere for 40 h CIT single crystals have higher hole mobility (105.6 cm²V^?1s^?1₎ and hole concentration (23.28 × 10¹⁷ cm^?3) compared with values of hole mobility (63.69 cm² V^?1 s^?1) and hole concentration (6.99 × 10¹⁵ cm^?3) of the as-grown CIT single crystals.     

Czochralski growth of Sr2Tb8(SiO4)6O2 crystals for visible–near IR magneto-optical applications

Sr₂Tb₈(SiO₄)₆O₂ crystals have been grown and investigated for the first time for magneto-optical applications. The X-ray powder diffraction confirms that the compound crystallizes in the hexagonal system, with a common oxyapatite structure. The as-grown crystal exhibits low thermal expansion anisotropy (α_a/α_c ≈ 1.1), and the hardness is about 5.0 Moh. The temperature dependence of the magnetic susceptibility indicated that the Sr₂Tb₈(SiO₄)₆O₂ crystal exhibits paramagnetic behavior over the experimental temperature-range 2–300 K. The present investigations demonstrate that Sr₂Tb₈(SiO₄)₆O₂ crystals show a higher visible transparency and a larger Faraday rotation than terbium gallium garnet (TGG) crystals. Sr₂Tb₈(SiO₄)₆O₂ is therefore a very promising material in particular for new magneto-optical applications in the visible–near IR wavelength region.     

Growth,optical and electro-optical characterisations of potassium hydrogen phthalate crystals doped with Fe3+ and Cr3+ ions

Potassium hydrogen crystals have good electro-optic properties that are in order of urea crystal. Trivalent ions doped KAP crystals KAP:M⁺³ (M = Fe³⁺, Cr³⁺) ions were grown using solution growth technique. Optical and electro-optical characterisations on the coefficient r₅₁ were carried out. The refractive matching offered by the KAP:M⁺³ crystals was investigated. One of the factors causing the observed enhancement in the electro-optics properties is the ligand interactions due the presence of trivalent ions in KAP lattice.     

Microstructure and photoluminescent properties of BaY2ZnO5:Tb3+ phosphors with addition of lithium carbonate

In this paper, Tb³⁺ activated BaY₂ZnO₅ phosphors with addition of lithium carbonates (0, 0.0125, 0.025, 0.05, 0.1, and 0.2 molar ratio) were synthesized using the solid-state reaction, and the morphology and photoluminescent properties are investigated. When BaY₂ZnO₅:Tb³⁺ phosphors to which lithium carbonates were added were sintered at 1250 °C for 12 h, X-ray powder diffraction analysis showed that the un-reacted Y₂O₃ raw material decreased and scanning electron microscopy showed that the grain growth is improved. From PL studies, the photoluminescent properties were decreased when Li⁺ ion was added, which might be resulted from the increase of the oxygen vacancy in BaY₂ZnO₅:Tb³⁺ phosphors. The green emission of the BaY₂ZnO₅:Tb³⁺, Li⁺ phosphors showed the CIE chromaticity coordinates in the range of x = 0.3361–0.3510 and y = 0.5202–0.5492.     

Effect of symmetry reduction on the electronic transitions in polytypic GdAl3(BO3)4:Eu:Tb crystals

The existence of a recently described monoclinic phase (C2/c, Z = 8) (Beregi et al., 2012) in addition to the well-known Huntite type rhombohedral (R32) polytypic modification of the GdAl₃(BO₃)₄ (GAB) crystal at room temperature provides a unique possibility to investigate the incorporation of rare earth dopants into slightly modified crystal lattice by spectroscopic methods. In these characteristic GAB structures the dopant ions, e.g. Tb³⁺ or Eu³⁺, possess slightly different neighbor geometries and local symmetries. The Tb³⁺: ⁷F₆ → ⁵D₄ and Eu³⁺: ⁷F_0,1,2 → ⁵D_0,1,2 electronic transitions were successfully identified in the absorption spectra using polarization, concentration and temperature dependent measurements in both polytypic modifications. The positions of the investigated Tb lines are shifted by up to 10 cm⁻¹ due to symmetry changes. In addition, some of the Eu lines show splittings of about 4–30 cm⁻¹ as a consequence of the change of the local environment. From the room temperature absorption measurements some of the low energy crystal field levels of ⁷F and ⁵D states of the Eu³⁺ ions were successfully determined for both modifications.     

Structure,crystalline perfection,mechanical, second harmonic generation efficiency,laser damage threshold and piezoelectric properties of bis nicotinamidium bis D-tartrate 1.25-hydrate single crystals

Bis nicotinamidium bis D-tartrate 1.25-hydrate single crystals have been grown by slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallizes in monoclinic system with space group P2₁. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal is free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. The second harmonic generation efficiency of the grown crystal has been checked and its value is 1.24 times that of potassium dihydrogen phosphate. The surface laser damage threshold for the crystal has been analyzed and its value is 0.644 GW/cm². Piezoelectric d₃₃ co-efficient for the crystal has been examined and its value is 29.8 pC/N.     

Crystal growth and characterization of Tm doped mixed rare-earth aluminum perovskite

In this work, we present results of structural characterization and optical properties including radio luminescence of (Lu_xGd_yY_0.99?x?yTm_0.01)AP single crystal scintillators for (x, y) = (0.30, 0.19), (0, 0.19) and (0, 0) grown by the micro-pulling-down (μ-PD) method. The grown crystals were single phase materials with perovskite structure (Pbnm) as confirmed by XRD and had a good crystallinity. The distribution of the crystal constituents in growth direction was evaluated, and significant segregation of Lu and Gd was detected in (Lu_0.30Gd_0.19Y_0.50Tm_0.01)AP sample. The crystals demonstrated 70% transmittance in visible wavelength range and some absorption bands due to Tm³⁺, Gd³⁺ and color centers were exhibited in 190–900 nm. The radioluminescence measurement under X-ray irradiation demonstrated several emission peaks ascribed to 4f–4f transitions of Tm³⁺ and Gd³⁺. The ratio of emission intensity in longer wavelength range was increased when Y was replaced by Lu or Gd.     

Enhanced emission of 2.7 μm 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⁺:⁴I_13/2, Nd³⁺:⁴I_9/2) → (Er³⁺:⁴I_15/2, Nd³⁺:⁴I_15/2) and (Nd³⁺:⁴F_3/2, Er³⁺:⁴I_15/2) → (Nd³⁺:⁴I_9/2, Er³⁺:⁴I_9/2) were calculated. It was found that Er³⁺/Nd³⁺ co-doped single crystal may be a potential host for 2.7 μm lasers.     

Spectroscopic properties of Er3+ ions in La2(WO4)3 crystal

Er³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. The absorption spectra, fluorescence spectra and fluorescence decay curves of the crystals were measured at room temperature. The spectroscopic parameters, including intensity parameters Ω_t (t = 2, 4, 6), spontaneous emission probability, fluorescence branching ratio, radiative lifetime, and stimulated emission cross-section were estimated. The fluorescence decay curves of fluorescence manifolds ⁴I_13/2, ⁴I_11/2, and ⁴S_3/2 were measured for crystal and powder samples, respectively. The effect of radiation trapping on the spectroscopic parameters was discussed. Green up-conversion fluorescence bands centered at wavelengths of 530 nm and 550 nm were observed when the crystal was excited at 977 nm. The possible up-conversion mechanisms were proposed.     

Cation distribution in the Bi4 − xRExTi3O12 (RE = La,Nd) solid solution and Curie temperature dependence

Bi_4 ? xRE_xTi₃O₁₂ (RE = La, Nd) ferroelectric powders were prepared by a co-precipitation route. Raman spectroscopy and X-ray diffraction were employed to determine the crystal site of La³⁺ and Nd³⁺ as well as the effect of their addition on the crystal structure. It was found that La atoms were not only placed preferentially in pseudo-perovskite A sites for concentrations x ≤ 1.2 but also substituted for Bi³⁺ in (Bi₂O₂)^2 + layers for greater concentrations. A similar behavior was observed with the limit value x = 0.8 in case of Nd³⁺. In solid solution La or Nd³⁺ ions diminish the distortions in the octahedron formed by oxygen atoms, so there is a tendency to undergo a transition in crystal symmetry from orthorhombic to tetragonal. Finally differential scanning calorimetry (DSC) shows a linear dependence of the Curie temperature (T_c) when the amount of La³⁺ or Nd³⁺ was increased.     

Polyvinylpyrrolidone (PVP)-assisted solvothermal synthesis of flower-like SrCO3:Tb3+ phosphors

Well-crystallized flower-like SrCO₃:Tb³⁺ phosphors have been synthesized by an inexpensive and friendly solvothermal process using polyvinylpyrrolidone (PVP, K30) as an additive without further annealing treatment. X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM) as well as photoluminescence spectroscopy (PL) were used to characterize the resulting samples. The amount of PVP and the reaction time have strong effect on the morphology of the SrCO₃:Tb³⁺ particles. The results of XRD confirm the formation of a well-crystallized SrCO₃ phase with an orthorhombic structure. The possible formation mechanism for flower-like SrCO₃:Tb³⁺ phosphor is proposed. The SrCO₃:Tb³⁺ phosphors show the characteristic ⁵D₄–⁷F_J (J = 6, 5, 4, 3) emission lines with green emission ⁵D₄–⁷F₅ (544 nm) as the most prominent group under ultraviolet excitation.     

Synthesis of green-emitting (Gd,La, Tb)2O(WO4)2 phosphors

Green-emitting (Gd_1−x−yLa_xTb_y)₂O(WO₄)₂ (0 ⩽ x ⩽ 0.05, 0.05 ⩽ y ⩽ 0.15) phosphors were synthesized in a single phase form by the conventional solid-state reaction method, and their photoluminescent properties were characterized. The (Gd_1−x−yLa_xTb_y)₂O(WO₄)₂ phosphors showed strong and broad excitation bands from 230 to 350 nm, corresponding to the energy transition from the 4f⁸ to 4f⁷5d configuration of Tb³⁺ and the charge-transfer (CT) transition of O²⁻−W⁶⁺. The oxytungstate phosphors exhibited typical emission peaks assigned to the transition from ⁵D₄ to ⁷F_J (J = 6, 5, 4, and 3) of Tb³⁺, and the luminescence emission intensity was effectively enhanced by the La³⁺ doping into the host Gd₂O(WO₄)₂ lattice. The highest green emission intensity was obtained for (Gd_0.87La_0.03Tb_0.10)₂O(WO₄)₂, where the relative emission intensity was 63% that of a commercial green-emitting (La_0.52Ce_0.31Tb_0.17)PO₄ phosphor.     

Structural and photophysical properties of lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide

Lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide (HPMSP) as new sensitizers of visible luminescence were obtained. The series of stable lanthanide complexes Na[Ln(PMSP)₄], where Ln = Eu³⁺, Gd³⁺, Tb³⁺ were characterized by X-ray diffraction, IR, absorption, emission, and excitation spectra at 295 and 77 K as well as luminescence decay times and intrinsic emission quantum yields. The Tb complex, exhibiting relatively efficient ligand-to-metal energy transfer and strong metal-centred emission, is a promising candidate for effective UV-to-visible energy converters. Temperature dependent quenching of sensitized ⁵D₀ europium emission and presence of ⁵D₁ emission are discussed.