Growth and characterization of pure and doped NLO L-arginine acetate single crystals

Single crystals of pure, Cu²⁺ and Mg²⁺ doped L-arginine acetate (LAA) were grown successfully by slow evaporation technique. In order to improve the device characteristics of LAA crystals, metal dopants of Cu²⁺ and Mg²⁺ were incorporated into the parent crystals. The grown pure and doped crystals were confirmed by X-ray powder diffraction studies. The pure and doped crystals were characterized by Fourier transform Raman (FT-Raman) and thermal studies. Absorptions of these grown crystals were analysed using UV-Vis-NIR studies, and it was found that these crystals possess minimum absorption in the entire visible region. Nonlinear optical studies of pure and doped crystals were carried out and it reveals that the dopants have increased the efficiency of LAA crystals.     

Crystal growth and spectral properties of pure and Co2+-doped Mg3B2O6 crystal

Novel pure and cobalt-doped magnesium borate crystals (Mg₃B₂O₆) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co²⁺:Mg₃B₂O₆ (MBO) were described. From the absorption peaks for the octahedral Co²⁺ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm⁻¹ and 821.6 cm⁻¹, respectively. The fluorescence lifetime of the transition ⁴T₁(⁴P) → ⁴T₂ centered at 717 nm was measured to be 9.68 ms.     

On luminescence properties of CsI crystals scavenged by Mg2+

Features of radioluminescence spectra and scintillation light decay curves of CsI crystals grown from the melt preliminarily scavenged by different amounts of Mg²⁺ (MgCl₂) are reported. The scintillation light of CsI usually contains 3 components with the decay time constants equal to 7 ns (I), 30 ns (II) and 2 μs (III). The addition of Mg²⁺ amount equivalent to the total concentration of oxide ions in molten CsI results in complete destruction of carbonate and sulfate ions. This is confirmed by the disappearance of 370–550 nm band in the radioluminescence spectrum of CsI crystal; thereat the fraction of component III in CsI scintillation light decreases. The excessive in relation to O^2? concentration amounts of Mg²⁺ lead to the decrease of O^2? equilibrium molality in CsI melt from 10^? 3 to 10^?10 mol kg^? 1. That causes a considerable increase of fraction of component I as compared with component II from 0.63:0.35 to 0.88:0.07. The fraction of the slow component III approaches the minimum at the equivalent ratio of initial molalities of Mg²⁺ and O^2?.     

Microhardness,FTIR and transmission spectral studies of Mg2+ and Zn2+ doped nonlinear optical BTCC single crystals

Pure, Mg²⁺ and Zn²⁺ doped BTCC single crystals are grown from their aqueous solutions at 301 K. The grown crystals are characterized by single crystal XRD, FTIR and UV–Vis-NIR spectral studies. The preliminary investigations of the UV–Vis-NIR spectra on the doped samples suggest an increased percentage of transmission in comparison to pure BTCC crystals. The SHG efficiency of the metal doped BTCC crystals is found better than the pure ones. It is estimated from the microhardness studies that the mechanical strength of the BTCC crystals are improved due to the metallic (Mg²⁺ and Zn²⁺) substitutions.     

Optical investigations on Tb3+ doped l-Histidine hydrochloride mono hydrate single crystals grown by low temperature solution techniques

The potential nonlinear optical material of Terbium (Tb³⁺) ion doped l-Histidine hydrochloride monohydrate (LHHC) single crystals were successfully grown. Tb³⁺:LHHC crystals of 7 mm × 5 mm × 3 mm and 59 mm length and 15 mm diameter have been grown by the slow solvent evaporation and Sankaranarayanan-Ramasamy (SR) techniques respectively. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystalline structure and morphology. High resolution X-ray diffraction (HRXRD) studies revealed that the SR grown sample shows relatively good crystalline nature with 9″ full-width at half-maximum (FWHM) for the diffraction curve. Functional groups were identified by Fourier transform infra-red spectroscopy (FTIR). The optical transparency and band gaps of grown crystals were measured by UV–Vis spectroscopy. Thermogravimetric and differential thermal analysis (TG/DTA) studies reveal that the crystal was thermally stable up to 155 °C in SR grown crystal. Surface morphology of the growth plane was observed using scanning electron microscopy (SEM). The incorporation of Tb ion was estimated by EDAX. The frequency-dependent dielectric properties of the crystals were carried out for different temperatures. Vickers hardness study carried out on (1 0 0) face at room temperature shows increased hardness of the SR method grown crystal. Second harmonic generation efficiency of SEST and SR grown crystals are 3.2 and 3.5 times greater than that of pure KDP. The Photoluminescence (PL) studies of Tb³⁺ ions result from the radiative intra-configurational f-f transitions that occur from the ⁵D₄ excited state to the ⁷F_j (j = 6, 5, 4, 3) ground states. The decay curve of the ⁵D₄ level of emission was observed with a long life time of 319.2041 μs for the SR grown Tb³⁺:LHHC crystal.     

Photocatalytic activity of TiO2 doped with Zn2+ and V5+ transition metal ions: Influence of crystallite size and dopant electronic configuration on photocatalytic activity

Anatase TiO₂ was prepared by sol–gel method through the hydrolysis of titanium tetrachloride and doped with transition metal ions like V⁵⁺ and Zn²⁺. The photocatalysts were characterized by various analytical techniques. Powder X-ray diffraction studies revealed only anatase phase for the doped samples. The band gap absorption for the doped samples showed red shift to the visible region (～456 nm) as confirmed by UV–vis absorption spectroscopy and diffuse reflectance spectral studies. The surface area of the Zn²⁺ doped samples were higher than the V⁵⁺ doped samples as observed by BET surface area measurements due to their smaller crystallite size. Scanning electron microscopy showed almost similar morphology, while energy dispersive X-ray analysis confirmed the presence of dopant in the TiO₂ matrix. The photocatalytic activities of these catalysts were tested for the degradation of Congo Red under solar light. Although both the doped samples showed similar red shift in the band gap, Zn²⁺ (0.06 at.%) doped TiO₂ showed enhanced activity and its efficiency was five fold higher compared to Degussa P-25 TiO₂. This enhanced activity was attributed to smaller crystallite size and larger surface area. Further completely filled stable electronic configuration (d¹⁰) of Zn²⁺ shallowly traps the charge carriers and detraps the same to the surface adsorbed species thereby accelerating the interfacial charge transfer process.     

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.     

Optical studies on X and γ irradiated vacuum grown CsBrI:Eu2+ crystals

CsBr_0.9I_0.1:Eu²⁺ crystals were grown by Bridgman technique. Optical absorption spectrum of the unirradiated CsBr_0.9I_0.1:Eu²⁺ crystals show absorption bands at 270 nm and 340 nm. Irradiated CsBr_0.9I_0.1:Eu²⁺ shows single F band for F(Br⁻) and F(I⁻) centers at 730 nm. Conversion of Eu²⁺ to Eu³⁺ after irradiation is confirmed by optical absorption technique. Sharp and single Photoluminescence (PL) emission band is observed at 440 nm for CsBr_0.9I_0.1:Eu²⁺ crystals. Photostimulated Luminescence (PSL) emission band observed for CsBr_0.9I_0.1:Eu²⁺ crystals at 442 nm due to excitation at 730 nm shows that the F centers are photostimulable. PSL emission intensity increases linearly with irradiation dose up to 2.5 Krad.     

Growth and spectroscopy of Ni2+ in ZnWO4 crystal

Single-crystal ZnWO₄ doped with nickel ion has been grown by the Czochralski technique. The XRD is investigated and the absorption spectrum as well as the emission spectrum is measured. Along crystallographic axes, refractive indices are presented. In octahedral approximation, using the Tanaba–Sugano theory, crystal field split is discussed, and so the Racah parameter B and crystal field parameters 10Dq are calculated. Compared with pure ZnWO₄ (∼ 4 eV), the band edge obtained was 3.7 eV for ZnWO₄:Ni²⁺.     

Effect of cobalt (Co<Superscript>2+</Superscript>) concentration on structural,optical, thermal and mechanical properties of potassium acid phthalate (KAP) crystals

Single crystals of pure and Co²⁺ (0.2, 0.4 and 0.6 mol%) doped KAP crystals were grown by low temperature slow evaporation method. The grown crystals were subjected to various characterization techniques such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV–visible spectroscopy and Second Harmonic Generation studies. The XRD profile confirms that Co²⁺ ions incorporated into the KAP crystal lattice. The existence of functional groups in the grown crystals have been studied by FTIR analysis. Optical transmission is decreased when doping Co²⁺ concentration increase. After melting point, no decomposition is found in the pure crystal. Vickers micro hardness studies revealed that the doped crystals possess very high hardness values. The dielectric constant, dielectric loss and thermal stability values have been measured as a function of frequency and temperature respectively for the doped crystals.     

Influence of W5+ ions on the optical properties of doped Bi12TiO20

There have been studied single crystals of undoped and doped Bi₁₂TiO₂₀ with two concentrations of W⁵⁺ (2.62 × 10¹⁷ cm⁻³ and 2.62 × 10¹⁸ cm⁻³). There have been obtained absorption spectra in the energy range of 10,482–15,408 cm⁻¹ by classical measurements. There have been determined the cross-section (σ_a) of the impurity absorption and the oscillator strength of d–d transitions. There have been calculated the refractive index of doped crystals and the concentration of Ti³⁺ ions in an undoped sample through an experiment.     

Electron paramagnetic resonance and optical absorption studies of Cu2+ ion doped polyvinyl alcohol films

Electron paramagnetic resonance (EPR) and optical absorption studies have been carried out on Cu²⁺ ions doped in polyvinyl alcohol films (PVA). EPR spectrum at room temperature exhibits hyperfine structure characteristic of Cu²⁺ ions in tetragonal symmetry. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy is calculated. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures and the Curie constant is evaluated from 1/χ versus T graph. The optical absorption spectrum exhibits a broad band which has been assigned to the transition ²B_1g → ²B_2g.     

Infrared-to-green up-conversion in Er3+, Yb3+-doped monoclinic KGd(WO4)2 single crystals

Optical spectroscopy of the green emission of erbium in KGd(WO₄)₂ (KGW) single crystals codoped with ytterbium ions is investigated. To do this, we firstly grew good-optical-quality KGW single crystals doped with Er³⁺ and Yb³⁺ at several dopant concentrations by the Top-seeded-solution-growth slow-cooling method (TSSG). Green photoluminescence of Er³⁺ in KGW host was studied at room temperature (RT) and low temperature (10 K) by means of Yb³⁺ sensitization after infrared excitation at 981 nm (10194 cm⁻¹). We calculated the emission and gain cross-sections and compared these with those of other known Er³⁺-doped laser materials like LiYF₄ :Er (YLF:Er) and Y₃Al₅O₁₂:Er (YAG:Er) at RT. Our study also focused on determining the optimal concentration of ions for generating the most intense green emission. We measured the lifetime of the green emission after infrared pump at several Yb³⁺ concentrations. From the low-temperature emission experiments, we determined the energy position of the sublevels of the ground state of erbium.     

Highly dispersible and uniform size Cu2ZnSnS4 nanoparticles for photocatalytic application

Highly dispersible, uniform size (～7 nm) single-phase Cu₂ZnSnS₄ nanoparticles have been synthesized by hydrothermal method using non-toxic surfactant (oleic acid). High resolution transmission electron microscopy image indicates good crystallinity of the Cu₂ZnSnS₄ nanoparticles with the growth along (1 1 2) plane. X-ray photoelectron spectroscopy analyses suggested that the formation of with Cu, Zn, and Sn in +1, +2 and +4 oxidation states. The optical absorption spectrum of Cu₂ZnSnS₄ nanoparticles exhibits an absorption in the visible region and its optical band gap was found to be ～1.72 eV, which could be much more appropriate for photocatalytic application under visible light irradiation. These Cu₂ZnSnS₄ nanoparticles have been shown high photocatalytic degradation activity of methylene blue (MB) dye in the presence of visible light irradiation. The rate constant (k) value of Cu₂ZnSnS₄ nanoparticles is found to be 0.0144 min^?1. We have discussed the mechanism of dye degradation process that drives the photocatalytic degradation process. The reusability of the Cu₂ZnSnS₄ nanoparticles for the dye degradation is also demonstrated.     

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.     

Vapor growth of CdSe:Cr and CdS:Cr single crystals for mid-infrared lasers

Single crystals of CdSe:Cr and CdS:Cr with the doping level up to 10¹⁹ cm⁻³ were grown by a vapor phase contact-free technique. An efficient room-temperature pulsed and continuous wave (CW) lasing with the CdSe:Cr crystal was achieved. First a pulsed lasing with the CdS:Cr crystal was also demonstrated. The slope efficiency on the absorbed energy was as high as 46.5% for Cr²⁺:CdSe and 39% for Cr²⁺:CdS lasers. Using an intra-cavity prism, the Cr²⁺:CdSe laser wavelength was continuously tuned from 2.26 to 3.61 μm while the Cr²⁺:CdS laser from 2.2 to 3.3 μm. For the laser wavelength, the crystal passive loss coefficient was estimated to be smaller than 0.045 cm⁻¹ for CdSe:Cr crystals and 0.039 cm⁻¹ for CdS:Cr crystals. For the Cr²⁺:CdSe laser, the CW output power up to 1.07 W was achieved.     

Luminescent materials derived from the surface-modification of Ln3+-doped zeolite L with a silylated terpyridine

Herein we report luminescent materials of Ln³⁺ (Ln = Eu or Tb) doped disc shaped zeolite L crystals (Eu³⁺/ZLD, Tb³⁺/ZLD) modified with a silylated terpyridine (Terpy-Si). The modified crystals show bright red emission and green emission under UV-light irradiation due to the energy transfer from the Terpy-Si to the Eu³⁺ and Tb³⁺ ions. The obtained materials were characterized with FT-IR, SEM, XRD and elemental analysis. Luminescence spectroscopy was used to study the luminescence properties of the modified Eu³⁺(Tb³⁺)/ZLD crystals. The formation of europium(III) and terbium(III) Terpy-Si silicon complexes and energy transfer from Terpy-Si to Eu³⁺ ions and Tb³⁺ have been confirmed by luminescence spectroscopy.     

Nature of intrinsic and impure luminescence of MAlP2O7 crystals

The results of the photoluminescence (PL) investigation of pure and chromium-doped MAlP₂O₇ (M = Na, K, Cs) compounds are presented. The spectra of the intrinsic luminescence of MAlP₂O₇ crystals consist of a separated UV band at a peak position near 330 nm and a complex wide band which covers the region of visible light up to 750 nm at excitation by VUV synchrotron radiation. The “red” band in 600–1000 nm diapason appears in the PL spectra of crystals doped with chromium ions. The effect of the temperature on the structure, the peak positions and intensities of the luminescence bands was studied. An assumption about the nature of the intrinsic PL was made. The “red” luminescence was considered as a result of the ⁴Т₂ → ⁴А₂ radiation transitions in the impurity Cr³⁺ ions located in the intermediate crystal field.     

Synthesis and luminescence properties of red long-lasting phosphor Y2O2S:Eu3+, Mg2+, Ti4+ nanoparticles

We report an effective method to synthesize Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ nanoparticles. Tube-like Y(OH)₃ were firstly synthesized by hydrothermal method to serve as the precursor. Nanocrystalline long-lasting phosphor Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ was obtained by calcinating the precursor with co-activators and S powder. XRD investigation shows a pure phase of Y₂O₂S, indicating no other impurity phase appeared. SEM and TEM observation reveals that the precursor synthesized via a hydrothermal routine has tube-like structure and the final phosphor reveals a hexagonal shape. The fine nanoparticles which have the particle size ranging from 30 to 50 nm show uniform size and well-dispersed distribution. From the spectrum, the main emission peaks are ascribed to Eu³⁺ ions transition from ⁵D_J (J = 0, 1, 2) to ⁷F_J (J = 0, 1, 2, 3, 4). After irradiation by 325 nm for 10 min, the Y₂O₂S:Eu³⁺, Mg²⁺, Ti⁴⁺ long-lasting phosphor shows very bright red afterglow and the longest could last for more than 1 h even after the irradiation source had been removed. It is considered that the long-lasting phosphorescence is due to the contribution from the electron traps with suitable trap depth.     

Concentration quenching,surface and spectral analyses of SrF2:Pr3+ prepared by different synthesis techniques

Pr³⁺ doped strontium fluoride (SrF₂) was prepared by hydrothermal and combustion methods. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Photoluminescence (PL) spectroscopy. XRD patterns indicated that the samples were completely crystallized with a pure face-centred cubic (space group: Fm3m) structure. SEM images showed different morphologies which is an indication that the morphology of the SrF₂:Pr³⁺ phosphor strongly depends on the synthesis procedure. Both the SrF₂:Pr³⁺ samples exhibit blue–red emission centred at 488 nm under a 439 nm excitation wavelength (λ_exc) at room temperature. The emission intensity of Pr³⁺ was also found to be dependent on the synthesis procedure. The blue–red emission has decreased with an increase in the Pr³⁺ concentration. The optimum Pr³⁺ doping level for maximum emission intensity was 0.4 and 0.2 mol% for the hydrothermal and combustion samples, respectively. The reduction in the intensity for higher concentrations was found to be due to dipole–dipole interaction induced concentration quenching effects.