High pressure spectroscopy of Pr in LiNbO3

Absorption, emission, and luminescence excitation spectra of the LiNbO₃ crystal doped with 0.5% Pr³⁺ and 0.8% Yb³⁺ are presented. Additionally the photoluminescence spectra at high pressure have been measured. Hydrostatic pressures up to 135 kbar were applied with a diamond anvil cell. Absorption of the Pr³⁺:LiNbO₃ crystal is characterized by the strong threshold at about 400 nm, related to the band-to band-transitions and the sharp structure in the visible region attributed to the transitions to ³P_J and ¹D₂ levels of Pr³⁺ ion. After the 488 nm excitation the yellow emission related to the ¹D₂→³H_J transition of Pr³⁺ have been observed when the ³P₀ emission has not been detected. The excitation spectra of the ¹D₂ luminescence consist of the sharp lines related to the ³H₄→³P_J (J=0, 1, 2) transitions and two broad bands peaked at 340 and 400 nm related probably to the bound exciton. The ¹D₂→³H_J emission shifts with pressure toward the lower energies with the rate of −2.4 cm⁻¹ kbar⁻¹. Additionally, for higher pressures the ¹D₂ emission is considerably quenched. This is explained as being due to the decrease of the energy of the bound exciton with pressure which results in the higher nonradiative depopulation rate of the ¹D₂ state.     

Spectroscopic properties of praseodymium-doped YVO4 crystal grown by the Czochralski technique

Optical absorption and emission spectra of YVO₄ crystal containing 1 at.% of praseodymium have been measured at 4.2 and 300 K. Absorption spectra recorded with polarised light at 4.2 K are found to be strongly inhomogeneously broadened but generally consistent with selection rules for D_2d local symmetry except for the ³H₄(1)−³F₂ transition.

Extensive vibronic side-bands of electronic lines corresponding to transitions from the ground ³H₄(1) state to the ³P₀ and ³P₁ states have been observed. Luminescence decay curves have been recorded at several temperatures between 4.2 and 300 K. Strong dependence of the ¹D₂ lifetime on sample temperature and lack of the ³P₀ emission at any temperature between 4.2 and 300 K has been discussed.     

Synthesis, characterization and microwave dielectric properties of nanocrystalline CaZrO3 ceramics

The energy-transfer mechanisms and frequency upconversion emissions in 0.5Er³⁺/xHo³⁺ co-doped tellurite glasses by exciting at 980 nm have been investigated. Three intense upconversion luminescence emissions are observed at around 525, 548, and 660 nm, which correspond to Er³⁺:²H_11/2 → ⁴I_15/2, Er³⁺:⁴S_3/2 → ⁴I_15/2 + Ho³⁺:⁵S₂(⁵F₄) → ⁵I₈, and Er³⁺:⁴F_9/2 → ⁴I_15/2 + Ho³⁺:⁵F₅ → ⁵I₈ transitions, respectively. The upconversion emissions reach the maximum values when Ho₂O₃ is 0.5 mol%, and the intensities of the green and red light emissions were about 4.5 and 6 times stronger than those un-doped Ho₂O₃, respectively. The possible upconversion mechanisms and energy transfer between Er³⁺ and Ho³⁺ were also estimated and evaluated. All the three emissions are based on two photon absorption processes.     

Upconversion dynamics in Er doped nanocrystalline YAlO3

We report the luminescence and upconversion spectra of nanocrystalline YAlO₃ doped with trivalent erbium at concentrations of 5.0, 1.0 and 0.1 mol.%. The powder samples were prepared using a solution combustion reaction method, and the resulting YAlO₃ nanocrystals show, under wide-angle X-ray diffraction, a size in the range 20–40 nm. Efficient green and red emissions are observed at room temperature under continuous-wave pumping at 980 nm. A weak emission can also be detected in the blue at 410 nm. The upconversion dynamics were studied measuring the decay times and the pump-power dependence of the transitions to the ⁴I_15/2 ground state starting from the ²H_11/2, ⁴S_3/2 and ⁴F_9/2 excited states. Excited-state absorption (ESA) is found to be responsible for the higher energy (²H_11/2, ⁴S_3/2→⁴I_15/2) green transitions. On the other hand, for the ⁴F_9/2→⁴I_15/2 red transition a competing energy-transfer upconversion (ETU) mechanism is found, which accounts for the more than 100-fold increase in intensity of the red emission on passing from the lowest (0.1 mol.%) to the highest (5 mol.%) erbium concentration.     

Upconversion-induced ultraviolet emission in Ho doped SrLaGa3O7 and SrLaGaO4 crystals

An analysis of the red to ultraviolet wavelength upconversion in Ho³⁺ in SrLaGa₃O₇ and SrLaGaO₄ crystals is given. Upconverted, ultraviolet emission from the ³D₃ level under cw 647 nm excitation at room temperature was observed. Excitation of the ⁵F₅ level, corresponding to the ⁵I₈→⁵F₅ transition, leads to intense emission from the ⁵I₇, ⁵I₆, ⁵F₅, ⁵S₂, ⁵F₃, ³G₅ and ³D₃ levels. Based on the energy level diagram of Ho³⁺, the pump intensity dependencies and experimental time dependencies of the observed emissions, an excitation scheme is proposed.     

Luminescence properties of La1−χTmχTa7O19

The luminescence properties of Tm³⁺ in La_1−χTm_χTa₇O₁₉ solid solutions were examined systematically. The substitution of Tm³⁺ for La³⁺ was carried out by a decomposition reaction of nitrates involving the corresponding constituents at 1200 °C in air. X-Ray diffraction patterns of the solid solutions indicated that the crystal structure consisted of a network of (La_1−χ³⁺Tm_χ^staggered|3+, Ta⁵⁺)—O²⁻ polyhedra interstratified with a double layer of Ta⁵⁺—O²⁻ polyhedra. According to the excitation and emission spectra, the most intense emission was found near 460 nm and quenched above χ=0.14 in La_1−χTm_χTa₇O₁₉. Also, lifetime results verified that the emission could be assigned not to the transition ¹G₄ å ³H₆, but to the transition ¹D₂ å³H₄. Upon cathode ray excitation some emissions of Tm³⁺ were superimposed by a broad emission due to the clusters of Ta⁵⁺—O²⁻ polyhedra. As a result, a low dimensional arrangement of Tm³⁺ was much more preferable for getting intense emission because it reduced the energy migration between Tm³⁺ ions.     

Properties of ytterbium and neodymium doped alkali metal yttrium double phosphates of the M3Y1−xLnx(PO4)2 type

The spectroscopic behaviour of the Nd³⁺ and Yb³⁺ doped alkaline metal yttrium double phosphates, M₃Y_1−xLn_x(PO₄)₂ (M=Na, Rb; x=0.01–0.3) were studied for both powder and single crystal samples. The high resolution absorption and emission spectra were measured in the visible and IR regions. Spectral changes with the Nd³⁺ and Yb³⁺ concentration were interpreted. The absorption strengths of the 4f–4f transitions were analysed and used to assess the structural modifications of the two double phosphates. Based on the 4 K absorption spectra the number of metal sites occupied by the dopants was investigated.

Strong emission from Na₃Y_1−xNd_x(PO₄)₂ involving the ⁴F_3/2→⁴I_9/2,⁴I_11/2,⁴I_13/2,⁴I_15/2 transitions were observed whereas the corresponding emission from the rubidium phosphate was presumably quenched by multiphonon processes due to the water molecules absorbed in the channel-like structure.

The IR spectra were used to assign the vibronic components of the electronic transitions. The Yb³⁺ emission bands were broadened depending on the Yb³⁺ concentration (1–10 mol%). The tentative energy level scheme of the ground and excited ²F_J (J=7/2, 5/2) levels was described.     

Raman active phonons of RFe3(BO3)4, R=La or Nd, single crystals

Oriented single crystals of RFe₃(BO₃)₄, with R=La or Nd, have been studied by Raman spectroscopy. Spectra with the relevant polarization configurations have been recorded in order to obtain the symmetry of the observed phonons. The factor group analysis and the correlation with the free (BO₃)³⁻ ion are done in order to identify most of the phonons associated with the two different types of (BO₃)³⁻ ion present in the crystal. The number and symmetries of the optical Raman active modes are 7A₁+19E, among which 4A₁+8E can be assigned as mostly due to (BO₃)³⁻ vibrations. 7A₁+18E modes were observed.

The highest energy peaks have been assigned to the regular planar (BO₃)³⁻ and to the three irregular (BO₃)³⁻ groups. The two lowest energy peaks of A₁ symmetry (around 180 and 300 cm⁻¹) are very probably related to the BO₃ rotatory mode and to Fe displacements. R ions do not participate in A₁ symmetry modes. The E mode around 90 cm⁻¹ (the lowest frequency mode) is probably due to the R ions which have the longest bonds and are the heaviest ions.     

Spectral properties of Yb ions in LiNbO3 single crystals: influences of other rare-earth ions, OH ions, and γ-irradiation

Absorption spectra have been studied in 190–3100 nm region at various temperatures from 16 to 292 K for Yb³⁺-doped and Yb³⁺/Nd³⁺-, Yb³⁺/Er³⁺- and Yb³⁺/Pr³⁺-co-doped LiNbO₃ single crystals before and after γ-irradiation with a dose of 10⁵–10⁷ Gy. Intense 400 and 500 nm absorption bands were observed after γ-irradiation, which are due to the creation of oxygen vacancy (F-type color center) and Nb⁴⁺ polaron, respectively. Different change was observed in the 2870 nm OH⁻ absorption band intensity among the various rare-earth doped crystals. These are interpreted by discrepancy of ionic radii between substituting rare earth dopant ion and Li⁺ or Nb⁵⁺ host ion. The observed temperature dependence of the hot bands is understood by electronic transition from the thermally populated ²F_7/2 Stark levels to the excited ²F_5/2 level. The position of the Yb^{3+ 2}F_7/2→²F_5/2 first resonant line was observed to be slightly different among the co-doped crystals. This is due to the perturbation of Yb³⁺ by co-doped rare earth ion which is located at the neighborhood of theYb³⁺.     

Crystal structure of the new ternary aluminide CeRu3−xAl10+x (x = 0.17)

A large and transparent Yb³⁺:GdYCOB crystal with dimensions up to 30 mm× 58 mm have been grown by the Czochralski method. The spectral properties of Yb³⁺:GdYCOB crystal has been investigated. The absorption cross-section (σ_a) is 1.65 × 10⁻²⁰ cm² at 977 nm. The emission cross-section (σ_e) is 0.25 × 10⁻²⁰ cm² with an FWHM of 37.2 nm at 1020 nm. The fluorescence lifetime is 3.00 ms.     

Spectroscopy, magnetism and non-radiative processes in heteronuclear Cu:Pr squarate; [Pr2Cu(C4O4)4(H2O)16]·2H2O

In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystal, where squarate anions participate as bridging ligands between metal ions.

The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A_1g→E_u) and π–π*(A_1g→E_g) ligand transitions. In visible and IR regions, t_2g–e_g of copper Cu(II) as well as ³H₄→³P_J, ¹D₂, ¹G₄, ³F_J, ³H₆ Pr(III) transitions at 293 and 4 K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of ³H₄→¹G₄ transition is probably due to the intensity borrowing from the Cu (II) d–d transition.

The ³P₀ and ¹D₂ emission of Pr(III) in the [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystals is quenched even at 77 K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by e_g levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7 K temperature range and are discussed in relation to the structure.

Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown.     

High-pressure synthesis and crystal structures of two new polyphosphides, NaP5 and CeP5

Two novel polyphosphides, NaP₅ and CeP₅, were prepared in a BN crucible by the reaction of elemental components under a high pressure of 3 GPa at 800–950 °C. The X-ray structural analysis showed that NaP₅ crystallizes in an orthorhombic space group Pnma with a=10.993(2) Å, b=6.524(1) Å, c=6.903(1) Å, Z=4 and CeP₅ in the monoclinic group P2₁/m with a=4.9143(5) Å, b=9.6226(8) Å, c=5.5152(4) Å, β=104.303(6)°, Z=2. The crystal structure of NaP₅ consists of a three-dimensional framework _∞³[P₅]¹⁻ constructed by P---P bonds among four crystallographically inequivalent phosphorus sites, with large channels hosting the sodium cations, while CeP₅ is a layered compound containing _∞²[P₅]³⁻ polyanionic layers that are separated by Ce³⁺ ions. NaP₅ exhibits the diamagnetic behavior, while the temperature-dependent magnetic susceptibility of CeP₅ essentially follows the Curie–Weiss law.     

Optical spectroscopy of yttrium double phosphates doped by cerium and praseodymium ions

This paper reports the spectroscopic properties of cerium- and praseodymium-doped alkali metal yttrium double phosphates, M₃Y(PO₄)₂:Pr³⁺, Ce³⁺; M = Na, Rb. These phosphates were obtained by a solid state reaction between lanthanide phosphate hydrates and M₃PO₄. The absorption, reflection, emission and excitation spectra were measured at room temperature, 77 and 4 K in the IR-vis-ultraviolet (UV) range. For both the Ce³⁺- and Pr³⁺-doped double phosphates, the 4f^N↔4f^N−15d transitions were detected. For the Pr³⁺-doped double phosphates, the 4f–4f transitions from the ³H₄ ground manifold were analyzed. The low temperature ³H₄→³P₀ absorption spectra were used to characterize the structural modifications between the sodium and rubidium salts. For the Ce³⁺-doped double phosphate, the strong blue 5d¹→4f¹ emission band splits into two components due to the ²F_5/2−²F_7/2 splitting of the 4f¹ configuration. Intense emission occurs mainly from the ³P₀ level at high dopant concentrations, since the ¹D₂ emission is strongly quenched but was detected at the 2 mol% doping level. In spite of the forbidden 4f–4f character, the ³P₀ transitions have very short decay times, of the order of one μs. Dynamics of the excited states will be discussed based on the decay times and selective excited emission.     

Red photoluminescence and morphology of Eu doped Ca3La3(BO3)5 phosphors

Europium doped phosphors Ca₃La₃(BO₃)₅ were first synthesized by a sol–gel process technique. The reaction temperature of the sol–gel process was 300 °C lower than that of the solid-state reaction and the reaction time of the sol–gel process was shorter. The photoluminescence properties of Eu³⁺ doped Ca₃La₃(BO₃)₅ indicated that the phosphors exhibited a strong luminescence of ⁵D₀–⁷F₂ transition at 612 nm under the excitation at 237 nm. The emission intensity of the phosphors prepared by the sol–gel process was higher than those prepared by the solid-state reaction. The relationship between optical properties and morphologies were studied. In particular, Li⁺ ion doping effectively enhanced the luminescent properties of the Eu³⁺ doped Ca₃La₃(BO₃)₅ phosphors. The highest brightness was observed in the phosphor Ca₃La_2.82Eu_0.1Li_0.08B₅O_15−δ prepared by the sol–gel process.     

Structural and luminescent properties of nanostructured KGdF4:Eu synthesised by coprecipitation method

The single-phase low-temperature cubic form of KGdF₄, with the average crystallites size of 19 nm precipitates from a solution. The cubic phase is stable up to approximately 460 °C. At higher temperatures the cubic KGdF₄ transforms, first to the orthorhombic and then to the trigonal phase, however, the transformation is not complete and the cubic form is still present. The highest concentrations of orthorhombic and trigonal phases were observed at temperatures of 540 and 720 °C, respectively. The single-phase high-temperature cubic form of KGdF₄ was obtained when the as-received sample was heated at 790 °C. In contrast to a coprecipitation (CP) method, the single-phase orthorhombic modification of KGdF₄ was obtained by a solid state (SS) reaction conducted at 650 °C. In excitation spectra recorded for CP samples the characteristic Eu³⁺–O²⁻ CT bands expected at 260 nm are not present, which indicates that oxygen impurities are practically absent. However, both IR spectra and the ⁵D_1,2,3/⁵D₀ emission branching ratio points to the presence of OH⁻ groups incorporated into a fluoride lattice and a heat treatment at temperature of at least 650 °C is indispensable to get rid of them. Emission spectra for samples with different processing conditions were recorded and are discussed.     

Red photoluminescence properties and crystal structure of sodium rare earth oxyborate

The subsolidus phase relations of the system Y₂O₃–Na₂O–B₂O₃ are reported. There are seven binary compounds and two ternary compounds in this system. A new ternary compound Na₂Y₂B₂O₇ is identified. The structure has been determined for the compound Na₂Y₂B₂O₇ from powder X-ray diffraction. The lattice constants of P2₁/c for the compound Na₂Y₂B₂O₇ are a=10.5993(1) Å, b=6.2311(1) Å, c=10.2247(1) Å, β=117.756(1)° and z=4. The structure can be described as being made up of isolated BO₃ triangles and YO₈ polyhedra. The photoluminescence properties of Eu ion-doped Na₂Y₂B₂O₇ and Na₃Y(BO₃)₂ show strong red-emission of the ⁵D₀–⁷F₂ transitions at 611 and 615 nm, respectively. The results of emission spectra are in good agreement with the crystallographic study. The relationship between Eu ion content and emission intensity is analyzed too.     

High-speed holographic recording of 500 images in a rare earth doped solid

We present experimental results demonstrating high-speed storage and retrieval of 500 single-page time-domain holograms in an Eu³⁺:Y₂SiO₅ crystal. The holograms were stored in the inhomogeneously broadened ⁷F₀–⁵D₀ transition of the crystal by wavelength multiplexing at a temperature of 2.5 K. Each hologram occupied a narrow spectral channel of around 500 kHz and was separated from its adjacent channels by only around 700 kHz. Both the recording and playback of the holograms were performed at a speed of 30 frames s⁻¹ with the use of a 100 mW cw laser. The experimental results project an achievable frame transfer speed in excess of 13×10³ frames s⁻¹. Implications of the results for high-speed digital data storage are discussed.     

Synthesis, crystal structure and X-ray excited luminescent properties of LuBa3B9O18

A new compound LuBa₃B₉O₁₈ has been prepared by a high-temperature solid-state reaction and its crystal structure was determined by powder X-ray diffraction methods. The results of Rietveld refinement show that it is isotypic to YBa₃B₉O₁₈. The X-ray excited luminescent properties of LuBa₃B₉O₁₈ were investigated. It shows a broad emission band in the wavelength range of 300–550 nm with peak center at 385 nm. Its room temperature fluorescent decay profile exhibits a single-exponent shape with decay time of 15 ns. It is believed that the lattice defects have played an important role on the luminescent performances of LuBa₃B₉O₁₈ powders and its thermal luminescence measurement confirmed the existence of lattice defects in it. Considering the emission wavelength, luminescence intensity, decay time, melting point, density and non-hygroscopic property of LuBa₃B₉O₁₈, one has reason to assume that it might find an application as a new scintillation material.     

Preparation of nanocrystalline Lu2O3:Eu phosphor via a molten salts route

The paper reports on the course of decomposition of hydrated lutetium nitrate and lutetium chloride to Lu₂O₃ in the eutectic mixture of NaNO₂ and KNO₂. It was shown that a crystallographically pure phase of the cubic Lu₂O₃ is formed at temperature as low as 250 °C. IR spectra revealed that the recovered powder contains some OH-contamination, however. The powders are characterized by crystallites sizes in the range of 18–30 nm in average. Emission and excitation spectra of Eu-doped powders show characteristic features for Eu³⁺ ion in an oxide host, which indicates that the procedure is appropriate for making activated nanoparticulate oxide phosphors. Most profound emission appears around 611 nm and the luminescence from the powder made starting with Lu(NO₃)₃ was noticeably higher compared to the product obtained from LuCl₃. The excitation spectrum of Eu³⁺ emission at 611 nm contains a band related to the fundamental absorption of the lutetia host lattice, which indicates an existence of the host-to-activator energy transfer.     

Ba4In2−x(CO3)1+xO6−2.5x and Ba4In0.8Cu1.6(CO3)0.6O6.2—new indium oxycarbonates closely related to n=3 Ruddlesden–Popper phases

Investigations of phase relations in the Ba-rich part of the In₂O₃–BaO(CO₂)–CuO pseudo-ternary system at 900 °C have revealed the existence of new indium–copper oxycarbonate – Ba₄In_0.8Cu_1.6(CO₃)_0.6O_6.2. Rietveld refinement of the X-ray powder diffraction data combined with infrared studies gives evidence that this phase is a oxycarbonate crystallising in the tetragonal structure (space group I4/mmm) with unit cell parameters: a=4.0349(1) Å and c=29.8408(15) Å. In the binary part of the In₂O₃–BaO(CO₂) system we have identified the occurrence of Ba₄In_2−x(CO₃)_1+xO_6−2.5x oxycarbonate solid solution showing a crystal structure also described by I4/mmm space group, but with the unit cell parameters: a=4.1669(1) Å and c=29.3841(11) Å for x=1. The existence range of this phase, −0.153<x<0.4, includes chemical compositions of earlier found phases: Ba₅In_2+xO_8+0.5x with 0≤x≤0.45 (known as the -solid solution), as well as the binary Ba₄In₂O₇ phase. The crystal structures of both new oxycarbonates are isomorphic and related to n=3 member of the Ruddlesden–Popper family.