Luminescence of yttrium aluminum borate single crystals doped with manganese

The optical absorption and luminescence spectra of single crystals of yttrium aluminum borate YAl₃(BO₃)₄ doped with manganese ions are measured. It is established that the optical absorption spectra of yttrium aluminum borate single crystals doped with manganese ions are determined primarily by the contribution from the Mn⁴⁺ ions. The luminescence spectra of the YAl₃(BO₃)₄ single crystals doped with manganese exhibit narrow lines attributed to the Mn⁴⁺ ions and an extended multiband structure which is associated primarily with the contribution from the Mn²⁺ ions.     

Local structure distortion and spin Hamiltonian parameters of oxide-diluted magnetic semiconductor Mn-doped ZnO

The local structure distortion, the spin Hamiltonian (SH) parameters, and the electric fine structure of the ground state for Mn²⁺(3d⁵) ion in ZnO crystals are systematically investigated, where spin--spin (SS), spin--other--orbit (SOO) and orbit--orbit (OO) magnetic interactions, besides the well-known spin--orbit (SO) coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zero-field splitting (ZFS) parameter D, the fourth-order ZFS parameter (a-F), the Zeeman g-factors: g_// and g_⊥, and the energy differences of the ground state: \delta₁ and \delta₂ for Mn²⁺ in Mn²⁺: ZnO are in good agreement with experimental measurements when the three O^2- ions below the Mn²⁺ ion rotate by 1.085^o away from the [111]-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn²⁺ ions in Mn²⁺: ZnO crystals. It is found for Mn²⁺ ions in Mn²⁺: ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO～SS～SOO～OO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.     

Study of optical absorption and EPR spectra of Mn<Superscript>2+</Superscript> ion in cadmium maleate dihydrate

The optical absorption and EPR spectra of Mn²⁺ ion doped in cadmium maleate dihydrate have been theoretically investigated by diagonalizing the complete energy matrices for a d⁵ configuration ion in a trigonal ligand-field. According to the suggestion of the optical absorption studies, we assume that the Mn²⁺ ion enters the host lattice interstitially and the distorted octahedral symmetry for the impurity ion is trigonal. Moreover, the local lattice structure parameters of the system are determined. The results show that the six oxygen ions around the Mn²⁺ ion are at the same distance R=2.115 ?, and there are three Mn-O bonds forming an angle θ₁ of 66.26° with the C₃-axis and three others forming an angle θ₂ of 43.40°.     

Optical investigations of Mn2+ ion in Cs2CdCl4 and CsCaCl3 single crystals

Summary Polarized absorption, emission and excitation spectra of Cs₂CdCl₄∶Mn²⁺ and emission as well as excitation spectra of CsCaCl₃∶Mn²⁺ single crystals at temperatures down to 77 K are reported. The general features of the spectra are fruitfully analysed within the framework of the strong field scheme of Tanabe and Sugano including Trees' correction. Some finer structure of the crystal field independent levels are observed which are rationalized in terms of vibrational mechanism. A detailed analysis of the spectra indicates octahedral site symmetry around the central metal ion. The authors of this paper have agreed to not receive the proofs for correction.     

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

Good quality single crystals of pure and metal ion (Ni²⁺) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni²⁺doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni²⁺doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.     

Epr studies of divalent manganese ions in magnesium maleate dihydrate single crystals

Abstract

An EPR study of Mn²⁺ ions doped in single crystals of Dihydrate Magnesium Maleate has been carried out at room temperature at X-band. From the observed spectra, spin-Hamiltonian parameters have been evaluated. Mn²⁺ ions have been found to enter the lattice interstitially.     

First-principles study of color centers in PbMoO4 crystals

Electronic structures of PbMoO₄ crystals containing Mn ion impurities located at Pb²⁺ sites are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that Mn²⁺ ions have donor energy levers in the forbidden band, which may correspond to the yellowish color absorption band of PbMoO₄ as-grown in air. The new-formed Mn³⁺ ions have acceptor energy levers in the forbidden band, which may relate to the photochromic effect in PbMoO₄ crystal.     

Sensitized fluorescence of Ce3+/Mn2+ system in phosphate glass

The preparation of sodium phosphate glasses singly and doubly doped with rare earth ion Ce³⁺ and transition metal ion Mn²⁺ by a melt quench method is described. The spectroscopic characterizations of the samples are conducted by absorption, excitation, and emission spectra. The orange red emission of divalent manganese sensitized by trivalent cerium ions in a phosphate glassy matrix has been investigated. Energy transfer (ET) from optically excited Ce³⁺ to Mn²⁺ in sodium phosphate glass, by nonradiative process is confirmed by fluorescence studies with various activator concentrations. The mechanism of ET is mainly electric dipole–dipole in nature.     

The transition from dynamics to statics in the electron-spin-resonance spectra of impurity Mn2+ ions in strontium titanate

The electron-spin-resonance (ESR) spectra of SrTiO₃:Mn single crystals have been investigated. Results unambiguously indicate that the impurity center formed by an Mn²⁺ ion has a dynamic nature. In the high temperature range (T > 100 K), ESR spectra of Mn²⁺ ions reveal cubic symmetry; the spectrum is found to broaden significantly with a decrease in temperature. Upon cooling to T < 10 K, low-symmetry centers of Mn²⁺ ions with a strong orientational dependence emerge in the spectra. Temperature evolution of the ESR spectrum can be described within the model of a dynamic off-center Mn²⁺ ion substituting for the Sr²⁺ ion, with a transition to the static regime at low temperatures with an average localization energy of ～2.4 ± 0.4 meV for Mn²⁺ centers due to random deformations.     

EPR and optical absorption studies of Cu and VO impurities in diammonium d-tartarate single crystal grown in ammonium dihydrogen phosphate buffer

The study is extended by growing the Cu²⁺ and VO²⁺ doped diammmonium d-tartarate single crystal in buffered solution with different pH values and the results are discussed referring to the color center forming property by means of transition metal impurities which are stable point defects. XRD study shows that the crystals grown in ammonium dihydrogen phosphate buffer with pH value of 5.9 which is smaller than that of water, the monoclinic symmetry of the crystal changes to orthorhombic and the number of paramagnetic centers is doubled. The spin-Hamiltonian parameters are determined and the ground state wave functions of Cu²⁺ ions are constructed. The optical absorption spectrum of both Cu²⁺ and VO²⁺ doped single crystals show three absorption bands corresponding to the splitting of d orbitals of metal ions in octahedral environment with tetragonal distorsion. Two of the bands lie in visible range and third one lies in infrared region.     

Effect of Co2+ on the growth,optical properties and laser damage threshold of potential nonlinear optical l-alanine single crystal

Good transparent bulk single crystals of pure l-alanine (LA) and cobalt doped LA crystals have been synthesized and successfully grown by slow-cooling method from their aqueous solutions. The concentration of metal dopants in the mother solution with 0.5 mol% for cobalt was carried out individually and crystals were obtained with well defined morphology. The as grown metal doped and pure single crystals were characterized by single crystal XRD studies which confirm that the incorporation of metallic dopants has not changed the basic structure of the parent crystal. The absorption of these crystals was analyzed and the result confirms that they possess low absorption in the range 230–1100 nm. Fourier transform infrared (FTIR) spectroscopy was carried out to investigate the molecular vibrations of these crystals and to confirm the incorporation of the dopants. The thermal properties have been studied by TGA/DTA curves. The EDAX measurement and surface morphology were studied for pure and metal doped LA crystals. The second harmonic generation (SHG) signals were observed using Nd: YAG laser with fundamental wavelength of 1064 nm in pure and metal doped crystals. The laser damage threshold was measured for pure and metal doped LA crystals and also tested by using a Q-switched Nd: YAG laser showed enhanced LDT value for metal (Co²⁺) doped LA crystal compared to pure LA crystal due to the metallic substitutions thus proving their useful candidature for nonlinear optical applications.     

Absorption and emission spectra of yttria-stabilized zirconia and magnesium oxide

We have investigated the luminescence and absorption spectra of doped and undoped ZrO₂-Y₂O₃ and MgO crystals at room- and low temperatures. The crystals used are partly doped with the transition metals Ni, Co, Cr and the rare earth Pr. The emission spectra were obtained under laser excitation at different wavelengths. The observed optical emission and absorption bands of the MgO crystals doped with Ni, Co and Cr correspond to transitions between spin-orbit split crystal field levels of the transition metals. Luminescence and absorption bands of undoped yttria-stabilized zirconia (YSZ) crystals are due to color centers, absorption bands of the doped YSZ correspond to the well known transitions of the Ni²⁺, Co²⁺ and Pr³⁺ ions, respectively. The emission spectra of the doped YSZ obtained under various laser excitations can be explained by an energy transfer process between the color center and the doping materials. The influence of annealing on the absorption and emission of Pr³⁺/Pr⁴⁺ is investigated.     

Growth and luminescent properties of the Ce,Pr doped NaCl single crystals grown by the modified micro-pulling-down method

We have investigated luminescent properties of nondope, Ce and Pr doped NaCl [nondope NaCl, Ce:NaCl, Pr:NaCl] single crystals grown by a modified micro-pulling-down method with a removable chamber system. Nondope, Ce 1% and Pr 1% doped NaCl crystals with a single phase of NaCl structure were obtained and the crystals indicated general crystal quality by the X-ray rocking curve measurement. For the nondope NaCl and Pr:NaCl crystals, the transmittance spectra indicated almost more than 60% in the wavelength from 200 to 800 nm and an absorption of Ce³⁺ ion was observed in the transmittance spectrum of Ce:NaCl crystal. The emission spectrum originated from Ce³⁺ 5d–4f transition appeared around 300 nm in the photoluminescence spectrum and the decay time was 19.7 ns.     

Optical properties of Cu+ centers in NaCl

Different aggregation-precipitation states of Cu⁺ have been characterized by absorption bands peaked at 305, 350 and 372–383 nm.The absorption bands at 372–383 nm, observed exclusively in the most doped crystal, have been associated with the Z₁₂, Z₃ excitons of CuCl microcrystals incorporated into the NaCl matrix Their positions shift to low energies with increasing concentration, as expected for a decrease in the stress over the precipitate.The Z1₁₂, Z₃ exciton bands of CuCl microcrystals precipitated in NaCl can be observed by the optical absorption spectrum without reaching saturation Therefore, this technique could be an alternative method to studies of CuCl thin-film depositions or reflectivity of CuCl single crystals.The red emission band observed at 600 nm is a long-lived emission (τ? 29 ms) at variance with the behavior reported for the Cu⁺ emission It is related to energy transfer processes from Cu⁺ to Mn²⁺.     

Growth and characterization of pure and doped L-Lysine monohydrochloride dihydrate (L-LMHCl) nonlinear optical single crystals

Semi-organic nonlinear optical single crystals of pure, Ni²⁺ and Cd²⁺ doped L-Lysine monohydrochloride dihydrate (L-LMHCl) were grown from aqueous solution by slow evaporation technique. Single crystal X-ray diffraction analysis reveal that the pure and doped L-LMHCl crystals belong to monoclinic system with the space group P2₁. The presence of functional groups present in the pure and doped crystals was determined qualitatively by using Fourier Transform Infrared (FTIR) spectroscopy. Optical absorption studies reveal very low absorption for the doped crystal than that of the pure crystal. Dielectric studies have been carried out for the grown crystals and the results were discussed in detail.     

Optical properties of 3d-ions doped RbCdF3. Radiation effects

Abstract

The optical properties of RbCdF₃ crystals doped with Cr³⁺, Mn²⁺ and Ni²⁺ have been studied. Absorption and photoluminescence spectra correspond to these ions in an octahedral environment. The lifetimes of the emitting levels have been measured at different temperatures. Single exponential decays are obtained for Mn²⁺ and Ni²⁺ while a non-exponential decay is found in the case of Cr³⁺. Radiation effects have also been studied. A new absorption band is produced in the 305 nm region by RT X-irradiation. Exciting with light in this band the 3d-ions emissions are observed.     

EPR spectra of Mn2+ ions in precipitated divalent impurity phases in monocrystalline NaCl

The EPR spectra of Mn²⁺ ions embedded into precipitated phases of Mg²⁺, Cd²⁺, Fe²⁺ and Ca²⁺ in NaCl single crystals have been investigated. The spectrum from samples whose major impurity is Mg, Cd or Fe corresponds to Mn²⁺ substituting some divalent cation inside the Suzuki phase (6NaCl.MCl₂). The existence of such a phase has been ascertained by means of Raman spectroscopy. On the other hand, the EPR spectrum of Ca²⁺ doped samples has been attributed to Mn²⁺ inside various CaCl₂ precipitates.     

EPR and IR spectral studies on Mn ions in nickel maleate tetrahydrate single crystals

Electron paramagnetic resonance (EPR) studies have been carried out on Mn²⁺ ions doped in nickel maleate tetrahydrate single crystals in the temperature range 103-413 K on X-band frequency. The EPR spectrum at room temperature exhibits a group of five fine structure transitions each splits into six hyperfine components. Angular variation studies reveal the presence of a single site and it is found that Mn²⁺ ions enter the lattice substitutionally. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The variation of zero-field splitting parameter (D) with temperature is measured. The observed EPR spectra exhibit a large anisotropy in the widths of Mn²⁺ resonance lines. The widths of Mn²⁺ resonance lines increase with the Zeeman field intensity and these observations have been discussed in detail. The infrared spectrum exhibits bands characteristic of the carboxylic acid salts.     

Pseudo-Zeeman splitting of excited states in MnI2: Cu+

MnI₂ doped with CuI shows extra absorption lines in the spectral region between 24000 and 30000 cm^-1. At low temperature these lines have an anomalously large Zeeman splitting in an applied magnetic field, with apparent g values as large as 150. This effect is attributed to exchange coupling of an electron (or hole) in the excited state with the spins of the surrounding Mn²⁺ ions. The applied magnetic field partly aligns the Mn²⁺ ion spins and this causes the observed very large pseudo-Zeeman splitting of the absorption lines.     

Growth and characterization of pure and doped bis thiourea zinc acetate: Semiorganic nonlinear optical single crystals

Metal–organic coordination complex single crystals bis thiourea zinc acetate (BTZA) and Cd²⁺ doped BTZA have been synthesized and grown successfully by slow-cooling technique from their aqueous solutions. Single crystals of pure and Cd²⁺ doped BTZA with dimensions of 35 × 4 × 2 mm³ and 10 × 5 × 6 mm³, respectively were obtained with well defined morphology. The as grown single crystals are characterized by single crystal XRD studies and melting point measurements which reveal the incorporation of metallic dopants has not changed the structure of the parent crystal. The powder X-ray diffractogram of the grown crystals has been recorded and the various planes of reflection identified shows shift in the peak positions. The metal coordination with thiourea through sulphur in pure and Cd²⁺ doped BTZA were ascertained by FTIR studies and optical absorption study to identify the UV cut-off range. The presence of metals in pure and Cd²⁺ doped BTZA crystal lattice were confirmed by atomic absorption spectroscopy (AAS). The thermal decomposition of pure and Cd²⁺ doped BTZA crystals were investigated by thermo gravimetric analyses (TGA) and differential thermal analysis (DTA) indicate that doped crystals are more stable than pure crystals. The dielectric response of the crystals were studied in the frequency range 100 Hz–5 MHz at different temperatures and the results are discussed. Second harmonic generation (SHG) measurement confirms that the pure and Cd²⁺ doped BTZA have nonlinear optical (NLO) property. Laser damage threshold value of 12.44 MW/cm² has been determined using Q-switched Nd:YAG laser operating at 1064 nm and with 8 ns pulses in single shot mode for pure BTZA single crystal is reported for the first time.