Conversion of infrared radiation into visible emission in NaY(WO4)2:Yb, Ho crystal

The spectroscopic characteristics and fluorescence dynamics for Yb³⁺/Ho³⁺:NaY(WO₄)₂ crystal were investigated. The parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the stimulated emission cross sections have been calculated based on Judd-Ofelt theory and Füchtbauer-Ladenburg method. The energy transfer efficiency from Yb³⁺ to Ho³⁺ was 65.85%. The green emission (530-570 nm) corresponding to (⁵F₄, ⁵S₂)→⁵I₈ transition, red emission (640-670 nm) due to ⁵F₅→⁵I₈ transition and NIR emission (740-770 nm) attributed to (⁵F₄, ⁵S₂)→⁵I₇ transition were observed on 974 nm excitation at room temperature. Under low pump power, the intensity of green light emission is weaker than that of the red light, while under high pump power, the case is on the contrary. The upconversion is based on the two-photon process either the energy transfer from Yb³⁺ ions or by the excited state absorption. The proposed mechanisms of upconversion emissions were provided.     

Characterization of single-crystalline In2O3 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

Epitaxial In₂O₃ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). The films were deposited at different substrate temperatures (450-750 °C). The film deposited at 650 °C has the best crystalline quality, and observation of the interface area shows a clear cube-on-cube epitaxial relationship of In₂O₃(1 0 0)||YSZ(1 0 0) with In₂O₃[0 0 1]||YSZ[0 0 1]. The Hall mobility of the single-crystalline In₂O₃ film deposited at 650 °C is as high as 66.5 cm² V⁻¹ s⁻¹ with carrier concentration of 1.5 × 10¹⁹ cm⁻³ and resistivity of 6.3 × 10⁻³ Ω cm. The absolute average transmittance of the obtained films in the visible range exceeds 95%.     

Study of TL properties of LaAlO3:Ce,Dy crystals for UV dosimetry

Thermoluminescence properties of lanthanum aluminum oxide (LaAlO₃) crystals doped with optically active rare earth ions have been investigated for ultraviolet dosimetry purposes. Single crystals co-doped with 5.0 at.% of Ce³⁺ and 1.0 at.% of Dy³⁺ ions have two thermoluminescent (TL) peaks at 151 °C and 213 °C which can be sensitized after 1 h of UV exposure. The material shows very high TL output and linear response for UV spectral irradiance ranging from 0.04 to 1.20 mJ cm⁻², that corresponds to 10 times the TL response of the Al₂O₃:C oxides. From 0.62 to 148.0 mJ cm⁻² the dependence is linear with the logarithm of the spectral irradiance. The investigation demonstrates that LaAlO₃:Ce,Dy crystals are very attractive to be investigated as UV dosimeters.     

Intense blue-emitting Ca5Al8O14: Eu phosphor for mercury free lamp

The calcium aluminates doped with Eu ions, Ca₅Al₈O₁₄: Eu, phosphors are prepared by the combustion method. The formation of crystalline aluminates was confirmed by X-ray diffraction pattern. The prepared phosphors were characterized by SEM, TGA, DTA, particle size analyzer and Photoluminescence (PL) techniques. From the UV-excited luminescence spectra it was found that the Eu ions acts as a luminescent centre with luminescence at the blue (λ _max = 470 nm) region due to 4f ⁶5d ¹ → 4f ⁷ transition. The excitation spectra show the broad band at 355 nm wavelength (λ _em = 470 nm). The excitation 355 nm is a mercury free excitation and therefore Ca₅Al₈O₁₄: Eu may be useful for the solid state lighting phosphor in lamp industry.      

Influence of substrate temperature in BiFeO3-CoFe2O4 nanocomposites deposited on SrTiO3 (0 0 1)

BiFeO₃-CoFe₂O₄ epitaxial nanocomposites have been deposited on SrTiO₃ (0 0 1) substrates by pulsed laser deposition. We present here a study of the influence of the deposition temperature (T_S), in the 550-800 °C range, on the film composition, morphology and microstructure. Electron-probe microanalysis shows strong reduction of the Bi content in the films when increasing T_S. Films prepared at T_S=750 °C and above are virtually Bi-free. X-ray diffraction (XRD) data show that, due to the volatility of Bi, there is a progressive reduction in the amount of BiFeO₃. The deposition temperature and the concomitant presence of Fe_xO_y spurious phases in the nanocomposites grown at high temperature promote radical changes in film morphology and magnetization. It thus follows that a temperature range suitable for controlled modification of nanocomposites morphology would be extremely narrow.     

The ν1 + 3ν2 + 3ν3 and 4ν1 + ν2 + ν3 bands of ozone by CW-cavity ring down spectroscopy between 5900 and 5960 cm

The absorption spectrum of ozone, ¹⁶O₃, has been recorded in the 5903-5960 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 5 × 10⁻¹⁰ cm⁻¹). The ν₁ + 3ν₂ + 3ν₃ and 4ν₁ + ν₂ + ν₃ A-type bands centred at 5919.15 and 5947.07 cm⁻¹ were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few K_a = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.     

The influence of Pr co-doping on the luminescent properties of Lu2O3:5 mol% Eu films

Uniform and crack free polycrystalline lutetium oxide (Lu₂O₃:(Eu,Pr)) films were fabricated by Pechini sol-gel method combined with the spin-coating technique. X-ray diffraction (XRD) and atomic force microscope (AFM) characterizations indicated that the obtained film was composed of polycrystalline cubic Lu₂O₃ phase with an average grain size around 30 nm. The photoluminescence(PL) spectra and decay performances of the Lu₂O₃:5 mol% Eu films co-doped by 0-0.5 mol% Pr³⁺ with different concentrations were characterized. It was found that the afterglow was reduced obviously due to the introduction of 0-0.5 mol% Pr³⁺ in the Lu₂O₃:5 mol% Eu films coupled by decrease in the emission intensity at 612 nm. The mechanism of afterglow diminishing was discussed based on the thermoluminescence measurements.     

CO2 adsorption on Cr(1 1 0) and Cr2O3(0 0 0 1)/Cr(1 1 0)

We attempt to correlate qualitatively the surface structure with the chemical activity for a metal surface, Cr(1 1 0), and one of its surface oxides, Cr₂O₃(0 0 0 1)/Cr(1 1 0). The kinetics and dynamics of CO₂ adsorption have been studied by low energy electron diffraction (LEED), Aug er electron spectroscopy (AES), and thermal desorption spectroscopy (TDS), as well as adsorption probability measurements conducted for impact energies of E_i = 0.1-1.1 eV and adsorption temperatures of T_s = 92-135 K. The Cr(1 1 0) surface is characterized by a square shaped LEED pattern, contamination free Cr AES, and a single dominant TDS peak (binding energy E_d = 33.3 kJ/mol, first order pre-exponential 1 × 10¹³ s⁻¹). The oxide exhibits a hexagonal shaped LEED pattern, Cr AES with an additional O-line, and two TDS peaks (E_d = 39.5 and 30.5 kJ/mol). The initial adsorption probability, S₀, is independent of T_s for both systems and decreases exponentially from 0.69 to 0.22 for Cr(1 1 0) with increasing E_i, with S₀ smaller by ∼0.15 for the surface oxide. The coverage dependence of the adsorption probability, S(Θ), at low E_i is approx. independent of coverage (Kisliuk-shape) and increases initially at large E_i with coverage (adsorbate-assisted adsorption). CO₂ physisorbs on both systems and the adsorption is non-activated and precursor mediated. Monte Carlo simulations (MCS) have been used to parameterize the beam scattering data. The coverage dependence of E_d has been obtained by means of a Redhead analysis of the TDS curves.     

Adsorption of CO, CO2 and NO molecules on a BaTiO3 (0 0 1) surface

Since the development of Scanning Tunnelling Microscopy (STM) technique, considerable attention has been devoted to various molecules adsorbed on various surfaces. Also, a new concept emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale are thus particularly invaluable. The present work describes the first Density Functional Theory (DFT) study of adsorption of CO, CO₂ and NO molecules on a BaTiO₃ surface following a first preliminary calculation of O and O₂ adsorption on the same surface. In the previously considered work, we found that a (0 0 1) surface with BaO termination is more stable than the one with TiO₂-termination. Consequently, we extended our study to CO, CO₂ and NO molecules adsorbed on a (0 0 1) surface with BaO termination. The present calculation was performed on a (1 × 1) cell with one monolayer of adsorbed molecules. Especially, a series of cases implying CO molecules adsorbed in various geometrical configurations has been examined. The corresponding adsorption energy varies in the range of −0.17 to −0.10 eV. The adsorption energy of a CO₂ molecule directly located above an O surface atom (called O_s) is of the order of −0.18 eV. The O-C distance length is then 1.24 Å and the O-C-O and O-C-O_s angles are 134.0° and 113.0°, respectively. For NO adsorption, the most important induced structural changes are the followings: (i) the N-O bond is broken when a NO molecule is absorbed on a Ba-O_s bridge site. In that case, N and O atoms are located above an O and a Ba surface atom, respectively, whereas the O-Ba-O_s and N-O_s-Ba angles are 106.5° and 63.0°, respectively. The N-O distance is as large as 2.58 Å and the adsorption energy is as much as −2.28 eV. (ii) In the second stable position, the NO molecule has its N atom adsorbed above an O_s atom, the N-O axis being tilted toward the Ba atom. The N-O_s-Ba angle is then 41.1° while the adsorption energy is only −0.10 eV. At last, the local densities of states around C, O as well as N atoms of the considered adsorbed molecules have also been discussed.     

VUV sensitisation of Eu emission by Tb in Ba3Tb(PO4)3-Eu

The luminescence properties of Ba₃Tb_0.9Eu_0.1(PO₄)₃ and Ba₃Gd_0.9Eu_0.1(PO₄)₃ phosphors were studied for excitation over the 120-300 nm wavelength range. It is found that Tb³⁺, which exhibits a strong vacuum-ultraviolet (VUV) absorption band, provides sensitisation of Eu³⁺ emission in this host. This effect can be used to develop phosphors with enhanced conversion efficiency of the VUV radiation into visible light.     

Improved color purity in nano-size Eu-doped YBO3 red phosphor

Nano-size YBO₃:Eu³⁺ phosphor has been synthesized by the co-precipitation method. X-ray diffraction (XRD) pattern confirmed the formation of hexagonal vaterite-type structures of YBO₃:Eu³⁺ nanoparticles. The transmission electron microscopy (TEM) study revealed the formation of spherical YBO₃:Eu³⁺ nanoparticles with size 20-40 nm. The photoluminescence spectra revealed that the ratio of the red emission (⁵D₀-⁷F₂) to the orange emission (⁵D₀-⁷F₁) was much higher in the synthesized nano-size YBO₃:Eu³⁺ phosphor. The improved relative intensity, i.e., higher R/O value of emission peaks, is due to a lower symmetry of crystal field around Eu³⁺ ions.     

Mn:BiFeO3/Zn:BiFeO3 bilayered thin films of (1 1 1) orientation

Ferroelectric and fatigue behavior of bilayered thin films consisting of Mn⁴⁺-modified BiFeO₃ and Zn²⁺-modified BiFeO₃, which were deposited on SrRuO₃-buffered Pt coated silicon substrates, were systematically investigated. The (1 1 1) orientation is induced for the BiFe_0.95Mn_0.05O₃/BiFe_0.95Zn_0.05O₃ bilayer, due to the introduction of the bottom BiFe_0.95Zn_0.05O₃ layer. With increasing the thickness ratio of the BiFe_0.95Mn_0.05O₃ layer, their leakage current decreases, and the fatigue endurance is greatly improved owing to the introduction of the BiFe_0.95Mn_0.05O₃ layer with a lower fatigue rate. The BiFe_0.95Mn_0.05O₃/BiFe_0.95Zn_0.05O₃ bilayer with the thickness ratio of 3:1 exhibits a larger remanent polarization of 2P_r ∼ 161.0 μC/cm² than those of bilayers with different thickness ratios, while their coercive field slightly increases with increasing the thickness ratio of the BiFe_0.95Mn_0.05O₃ layer.     

Effect of crystallinity of Co layer on perpendicular exchange bias in Au-capped ultrathin Co film on Cr2O3(0 0 0 1) thin film

The effect of the crystalline quality of ultrathin Co films on perpendicular exchange bias (PEB) has been investigated using a Au/Co/Au/α-Cr₂O₃ thin film grown on a Ag-buffered Si(1 1 1) substrate. Our investigation is based on the effect of the Au spacer layer on the crystalline quality of the Co layer and the resultant changes in PEB. An α-Cr₂O₃(0 0 0 1)layer is fabricated by the thermal oxidization of a Cr(1 1 0) thin film. The structural properties of the α-Cr₂O₃(0 0 0 1) layer including the cross-sectional structure, lattice parameters, and valence state have been investigated. The fabricated α-Cr₂O₃(0 0 0 1) layer contains twin domains and has slightly smaller lattice parametersthan those of bulk-Cr₂O₃. The valence state of the Cr₂O₃(0 0 0 1) layer is similar to that of bulk Cr₂O₃. The ultrathin Co film directly grown on the α-Cr₂O₃(0 0 0 1) deposited by an e-beam evaporator is polycrystalline. The insertion of a Au spacer layer with a thickness below 0.5 nm improves the crystalline quality of Co, probably resulting in hcp-Co(0 0 0 1). Perpendicular magnetic anisotropy (PMA) appears below the Néel temperature of Cr₂O₃ for all the investigated films. Although the PMA appears independently of the crystallinequality of Co, PEB is affected by the crystalline quality of Co. For the polycrystalline Co film, PEB is low, however, a high PEB is observed for the Co films whose in-plane atom arrangement is identical to that of Cr³⁺ in Cr₂O₃(0 0 0 1). The results are qualitatively discussed on the basis of the direct exchange coupling between Cr and Co at the interface as the dominant coupling mechanism.     

Ground state rotational spectrum of nitrogen trifluoride: The K = 3 splittings of NF3 and NF3

The ground state rotational spectrum of the ¹⁴NF₃ and ¹⁵NF₃ isotopic species of nitrogen fluoride has been observed in the ∼450-810 GHz frequency range. This investigation allowed us to improve the rotational parameters for both isotopologues. In particular, for the first time the K = 3 line splitting parameter and the sextic centrifugal distortion constants have been determined for ¹⁵NF₃.     

High-efficiency Nd:YVO4 laser emission under direct pumping at 880 nm

We report a high-efficiency Nd:YVO₄ laser pumped by an all-solid-state Q-switched Ti:Sapphire laser at 880 nm in this paper. Output power at 1064 nm with different-doped Nd:YVO₄ crystals of 0.4-, 1.0- and 3.0-at.% under the 880 nm pumping was measured, respectively. Comparative results obtained by the traditional pumping at 808 nm into the highly absorbing ⁴F_5/2 level were presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power of the 1.0-at.% Nd:YVO₄ laser under the 880 nm pumping was 17.5% higher and 11.5% lower than those of 808 nm pumping. In a 4-mm-thick, 1.0-at.% Nd:YVO₄ crystal, a high slope efficiency of 75% was achieved under the 880 nm pumping, with an optical-to-optical conversion efficiency of 52.4%.     

Interaction of Sb ions with Eu ions during the room temperature synthesis of luminescent Sb2O3 nanorods: Probed through Eu luminescence

The interaction of Eu³⁺ with Sb³⁺ ions during the room temperature synthesis of luminescent Sb₂O₃ nanorods is investigated using luminescence and vibrational spectroscopic techniques. Our results demonstrate that well crystalline, oriented Sb₂O₃ nanorods having length of around 3-4 μm, a width of around 100-200 nm and luminescence at around 390 nm can be synthesized at room temperature. Incorporation of Eu³⁺ in these nanorods has been attempted and it is found that Eu³⁺ ions do not have any interaction with nanorods and their orientation. Detailed Eu³⁺ luminescence and XRD studies confirmed that a part of Sb³⁺ ions reacts with Eu³⁺ ions in the presence of hydroxyl ions (present in the medium) to form an amorphous antimony europium hydroxide compound. The amorphous compound on heating at high temperatures leads to its decomposition, giving hydrated Sb(V) oxides and Eu₂O₃ as major phases.     

Solid state reaction synthesis and luminescence properties of Dy-doped Gd2Mo3O9 phosphor

Gd₂Mo₃O₉ phosphors with various Dy³⁺ concentrations were synthesized by a traditional solid-state reaction using Na₂CO₃ as a flux. The influence of reaction temperature and Dy³⁺-doping concentration on the crystal structure of the phosphors was examined by XRD (X-ray diffraction). The effect of Dy³⁺-doping concentration on the emissions of Mo-O bond and Dy³⁺ was experimentally investigated. The energy transfers between host and Dy³⁺ ions, and between Dy³⁺ ions were analyzed based on both the Van Uitert and I-H models. The chromatic properties of the phosphors were also discussed.     

Ab initio simulation of the BaZrO3 (0 0 1) surface structure

Electronic and atomic structures of different terminations of the (0 0 1) non-polar orientation of BaZrO₃ surfaces have been studied using first-principles calculations. We found that surface energies at both possible surface terminations, BaO and ZrO₂, were very close. The (0 0 1)-BaO and (0 0 1)-ZrO₂ terminated surfaces have bandgap values smaller than that of a bulk BaZrO₃ crystal. In addition, the relative surface stability has been analyzed as a function of chemical environment.     

Energy transfer between activators at different crystallographic sites in Sr3SiO5:Eu

A yellow phosphor, Sr₃SiO₅:Eu²⁺, was synthesized by a high temperature solid-state method. Sr₃SiO₅:Eu²⁺ exhibits a single yellow emission under the blue radiation excitation. However, Sr₃SiO₅:Eu²⁺ shows a two-peak emission under the ultraviolet radiation excitation when Eu²⁺ doping content is less than 0.01 mol. Moreover, the blue emission disappears and the yellow emission reaches the peak value when Eu²⁺ doping content is 0.01 mol. Namely, the energy transfer takes place between the Eu²⁺ activators, which is located at two different crystallographic sites in the Sr₃SiO₅. And the energy transfer mechanism is the dipole-dipole interaction.     

Intense green/yellow emission in Ca8Zn(SiO4)4Cl2:Eu, Mn through energy transfer for blue-LED lighting

Eu²⁺ and Mn²⁺ co-doped Ca₈Zn(SiO₄)₄Cl₂ phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu²⁺ to Mn²⁺ is observed. The emission spectra of the phosphors show a green band at 505 nm of Eu²⁺ and a yellow band at 550 nm of Mn²⁺. The excitation spectra corresponding to 4f⁷-4f⁶5d transition of Eu²⁺ cover the spectral range of 370-470 nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu²⁺ followed by simultaneous increase of fluorescent intensity of Mn²⁺ with increasing Mn²⁺ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu²⁺ and Mn²⁺ co-doped Ca₈Mg(SiO₄)₄Cl₂ and Ca₃SiO₄Cl₂, demonstrating a potential application in phosphor converted white LEDs.