Self-induced three-level echo

A new type of three-level photon echo has been predicted and analytically described. In contrast to the conventional three-level echo, whose formation involves three resonant ultrashort excitation pulses spaced in time, two of which are resonant to different optically allowed and adjacent transitions with different frequencies, the echo predicted arises under the conditions of formation of the conventional two-pulse echo and requires only two pump pulses of the same frequency. A theory is developed for the conditions of experiments on generation of a superradiance pulse at the ³ P ₀-³ H ₆ transition in impurity praseodymium ions in the LaF₃ matrix upon ultrashort coherent excitation of the adjacent optically allowed ³ H ₄-³ P ₀ transition in praseodymium. It is shown that the superradiance pulse after its deexcitation does not polarize the medium at the ³ P ₀-³ H ₆ generation transition and completely eliminates polarization at the ³ H ₄-³ P ₀ excitation transition. However, simultaneously, the superradiance pulse transfers the optical coherence from the excitation transition to the optically forbidden ³ H ₆-³ H ₄ transition. Thus, the phase memory about the effect of the excitation superradiance pulse is retained in the medium within a time interval that is shorter than the irreversible relaxation time of the optically forbidden transition.     

Isotopic shift measurement of the 3P1-3P0 fine structure transition of 24Mg and 26Mg

The isotopic frequency shift for the ³P₁-³P₀Δm_j=0 fine structure transition in the first metastable triplet of ²⁴Mg and ²⁶Mg is reported. The transitions corresponding to the two even isotopes of Mg have been observed via the fluorescence emission at 4571 Å of the intercombination line ³P₁-¹P₀ in a metastable atomic beam. The center frequencies have been measured with an uncertainty of 7×10^-9; the isotopic shift turned out to be 1706 ± 2 kHz.     

Luminescent properties of trivalent praseodymium-doped lanthanum aluminum germanate LaAlGe2O7

The luminescent characteristics of Pr³⁺-activated LaAlGe₂O₇ were investigated. In response to excitement using 448 nm blue light, the emission spectra involved most of the ³P₀→³H_J transitions. The dominant emission came from the ³P₀→³H₄ transition at 487 nm. ¹D₂ fluorescence quenching was observed in highly doped samples and is related to the cross-relaxation processes among neighboring Pr³⁺ ions. In contrast with conventional Pr³⁺-activated phosphors, the extraordinary excitation spectra showed only intense f-f transition of Pr³⁺ ions, while the 4f-5d transition was eliminated. This is ascribed to photoionization. By analyzing absorption and excitation spectra, it is recognized that no efficient energy transfer occurs between Pr³⁺ and the host lattice in LaAlGe₂O₇.     

Photoluminescence characteristics of ZnTiO3: Bi nanocrystals

The photoluminescence properties of the Bi³⁺ in sol-gel derived ZnTiO₃ nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the ³P₁-¹S₀ transition of Bi³⁺ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant.     

Spectral analysis of Pr-, Sm- and Dy-doped transparent GeO2-BaO-TiO2 glass ceramics

In this paper, we present the photoluminescence properties of Pr³⁺-, Sm³⁺- and Dy³⁺-doped germanate glasses and glass ceramics. From the X-ray diffraction measurement, the host glass structure was determined. These glasses have shown strong absorption bands in the near-infrared (NIR) region. Compared to Pr³⁺-, Sm³⁺- and Dy³⁺-doped glasses, their respective glass ceramics have shown stronger emissions due to the Ba₂TiGe₂O₈ crystalline phase. For Pr³⁺-doped glass and glass ceramic, emission bands centered at 530 nm (³P₀→³H₅), 614 nm (³P₀→³H₆), 647 nm (³P₀→³F₂) and 686 nm (³P₀→³F₃) have been observed with 485 nm (³H₄→³P₀) excitation wavelength. Of them, 647 nm (³P₀→³F₂) has shown bright red emission. Emission bands of ⁴G_5/2→⁶H_5/2 (565 nm), ⁴G_5/2→⁶H_7/2 (602 nm) and ⁴G_5/2→⁶H_9/2 (648 nm) for the Sm³⁺:glass and glass ceramic, with excitation at ⁶H_5/2→⁴F_7/2 (405 nm) have been recorded. Of them, ⁴G_5/2→⁶H_7/2 (602 nm) has shown a bright orange emission. With regard to the Dy³⁺:glass and glass ceramic, a bright fluorescent yellow emission at 577 nm (⁴F_9/2→⁶H_13/2) has been observed, apart from ⁴F_9/2→⁶H_11/2 (667 nm) emission transition with an excitation at 454 nm (⁶H_15/2→⁴I_15/2) wavelength. The stimulated emission cross-sections of all the emission bands of Pr³⁺, Sm³⁺ and Dy³⁺:glasses and glass ceramics have been computed based on their measured full-width at half-maxima (FWHM, Δλ) and lifetimes (τ_m).     

Luminescence of Ca(NbO3)2:Pr at ambient and high hydrostatic pressure

In this contribution, photoluminescence and time-resolved photoluminescence spectra of Ca(NbO₃)₂ doped with Pr³⁺ obtained at high hydrostatic pressure up to 72 kbar applied in a diamond anvil cell are presented. At ambient conditions, the emission spectrum obtained in the time interval 0-1 μs is dominated by spin-allowed transitions from the ³P₀ state. On the other hand, transitions from ¹D₂, characterized by a decay time equal to 30 μs dominate the steady-state luminescence.At pressures lower than 60 kbar, the continuous wave emission spectrum consists of sharp lines peaking between 600 and 625 nm, related to the ¹D₂→³H₄ transition and three lines at 500, 550 and 650 nm related to emission transitions originating from the ³P₀ level of Pr³⁺. The emission from the ¹D₂ excited state depends weakly on the pressure. Its decay time decreases from 33 μs at ambient pressure to less than 22 μs at 68 kbar. On the other hand, the ³P₀ emission is strongly pressure dependent. At pressures of 60 kbar and higher, the Pr³⁺ emission intensity from the ³P₀ state decreases. This is accompanied by a strong shortening of the luminescence decay time.The observed pressure quenching of the f-f emission transitions and the concomitant lifetime shortening have been attributed to increasing crossover from the ³P₀ state of Pr³⁺ to a Pr³⁺-trapped exciton state.     

Luminescence properties of red-emitting praseodymium-activated BaTi4O9 phosphor

The photoluminescence and low-voltage cathodoluminescence characteristics of BaTi₄O₉:Pr³⁺ were investigated. The excitation band of intervalence charge transfer (IVCT) of BaTi₄O₉:Pr³⁺ emerged distinctly at 330 nm. The resultant emissions appeared at 606-643 nm corresponding to the ¹D₂→³H₄ transition. In BaTi₄O₉:Pr³⁺, the emission of ³P₀→³H₄ transition at 490 nm was not observed. The results were in a pure red color emission.     

Photoluminescence properties of Sm in LBTAF glasses

Room temperature visible and near infrared optical absorption and emission spectra of Sm³⁺-doped lead borate titanate aluminum fluoride (LBTAF) glasses with molar composition (50−x) PbO−30H₃BO₃−10TiO₂−10AlF₃−xSm₂O₃ (x=0.1, 0.5, 1.0 and 2.0) have been analyzed. Energy parameters for the 4f⁵ electronic configuration of Sm³⁺: LBTAF glasses have been evaluated using free-ion Hamiltonian model. The experimental oscillator strengths of absorption bands have been used to determine the J-O parameters. Fluorescence spectra were recorded by exciting the samples with 402 nm. Using the J-O parameters and luminescence data, the radiative transition probabilities (A_R), branching ratios (β_R) and stimulated emission cross-sections (σ_e) were obtained. The decay curves of ⁴G_5/2→⁶H_7/2 transition exhibit single exponential for lower concentration (0.1 mol%) and non-exponential for higher concentrations. This concentration quenching has been attributed to the energy transfer through cross-relaxation between Sm³⁺ ions. From the values of the radiative parameters, it is concluded that 1.0 mol% Sm³⁺-doped LBTAF glass may be used for laser active medium with emission wavelength at 600 nm.     

Effect of composition on the spontaneous emission probabilities, stimulated emission cross-sections and local environment of Tm in TeO2-WO3 glass

Effect of composition on the structure, spontaneous and stimulated emission probabilities of various 1.0 mol% Tm₂O₃ doped (1−x)TeO₂+(x)WO₃ glasses were investigated using Raman spectroscopy, ultraviolet-visible-near-infrared (UV/VIS/NIR) absorption and luminescence measurements.Absorption measurements in the UV/VIS/NIR region were used to determine spontaneous emission probabilities for the 4f-4f transitions of Tm³⁺ ions. Six absorption bands corresponding to the absorption of the ¹G₄, ³F₂, ³F₃ and ³F₄, ³H₅ and ³H₄ levels from the ³H₆ ground level were observed. Integrated absorption cross-section of each band except that of ³H₅ level was found to vary with the glass composition. Luminescence spectra of the samples were measured upon 457.9 nm excitation. Three emission bands centered at 476 nm (¹G₄→³H₆ transition), 651 nm (¹G₄→³H₄ transition) and 800 nm (¹G₄→³H₅ transition) were observed. Spontaneous emission cross-sections together with the luminescence spectra measured upon 457.9 nm excitation were used to determine the stimulated emission cross-sections of these emissions.The effect of glass composition on the Judd-Ofelt parameters and therefore on the spontaneous and the stimulated emission cross-sections for the metastable levels of Tm³⁺ ions were discussed in detail. The effect of temperature on the stimulated emission cross-sections for the emissions observed upon 457.9 nm excitation was also discussed.     

Time-dependent self-consistent perturbation theory and applications to molecules

The two most intense bands of the 370 nm electronic band system of tropolone have been rotationally analysed. They are separated by 18·93 cm^-1 and it has been shown that the high wavenumber band is the 0^--0^- (H₁ ¹) transition in what is almost certainly the internal hydrogen-bonding vibration v _H : the low wavenumber band is the 0⁺-0⁺ (0₀ ⁰) transition. A rotational contour analysis of both bands shows that there is an intensity alternation in K _a″ such that the ratio K _a″ even : odd is 10 : 6 in the 0⁺-0⁺ band and 6 : 10 in the 0^--0^- band. The intensity alternation, the nearly equal intensities of the 0⁺-0⁺ and 0^--0^- bands, the separation of these two bands and the anharmonic behaviour of v _H show that the separation of the 0⁺ and 0^- levels is small in the ground electronic state (probably less than 50 cm^-1) and is 18·93 cm^-1 larger in the excited electronic state.

The 0⁺-0⁺ and 0^--0^- bands are both type B showing that the electronic transition is à ¹ B ₂-X ¹ A ₁ and therefore π*-π rather than π*-n. The π*-n transition is probably shifted to high wavenumber by the internal hydrogen-bonding.     

Enhanced blue-green-red up-conversion and 1.3-μm emission of Pr/Yb-codoped oxyhalide tellurite glasses with PbCl2 doping

We report on the blue-green-red up-conversion spectroscopic properties of Pr³⁺/Yb³⁺-codoped oxyhalide tellurite glasses upon excitation of a conventional 980 nm laser diode (LD). Significant enhancement of the blue-green-red up-conversion emission intensity has been observed with increasing PbCl₂ doping. The up-conversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. The population of the Pr³⁺ upper ³P₀ emitting level was accomplished through a combination of a ground state absorption, energy transfer and excitated state absorption. 1.3-μm emission in the second telecom window originated from Pr³⁺:¹G₄→³H₅ transition has also been investigated upon excitation at 980 nm LD. The measured peak wavelength and full width at half-maximum of the fluorescent are 1335 nm and ∼100 nm, respectively. An enhanced 1.3μm emission with increasing PbCl₂ doping has also been observed. Codoping of Yb³⁺ significantly enhance both the blue-green-red up-conversion emission and 1.3-μm emission intensity by way of a nonradiative Yb³⁺:²F₅→Pr³⁺:¹G₄ energy transfer.     

The Fourier Transform Emission Spectrum of BΠ1-XΣ Band-System of InCl

The emission spectrum of the B³Π₁-X¹Σ⁺ band-system of the InCl molecule has been recorded on a Fourier transform spectrometer at an apodized resolution of 0.025 cm⁻¹. The rotational structure of 1-0, 2-1, 0-0, 0-1, 1-2, 0-2, and 1-3 bands belonging to the B³Π₁-X¹Σ⁺ transition of In³⁵Cl has been analyzed and accurate equilibrium rotational constants of the B³Π₁ state, have been obtained. Precise Λ-doubling constants of the B³Π₁ state (v=0, 1, and 2) are also reported for the first time.     

Effect of interface states associated with transitional nanophase precipitates in the enhancement of red emission from SrAl12O19:Pr by Ti incorporation

SrAl₁₂O₁₉:Pr³⁺, Ti⁴⁺ phosphor suitable for field emission displays is prepared by the wet chemical gel-carbonate method and the mechanism of enhancement in red photoluminescence (PL) intensity with Ti⁴⁺ therein has been investigated. The PL spectra of Pr³⁺ show both ¹D₂-³H₄ and ³P₀-³H₆ emission in the red region with very weak intensity when excited at 355 nm. The emission intensity has increased by about 100 times at room temperature in the compositional range SrAl_12−xTi_xO_19+x/2:Pr³⁺, with 0.1≤x≤0.3 in comparison to Ti-free SrAl₁₂O₁₉:Pr³⁺. TEM investigations show the presence of exsolved nanophase of SrAl₈Ti₃O₁₉, the precipitation of which is preceded by the presence of defect centers at the interfacial regions between the semicoherent transient phase and the parent SrAl₁₂O₁₉ matrix. The presence of transitional nanophase and the associated defects modify the excitation-emission process by way of formation of electronic sub-levels at lower energy (3.5 eV) than the band gap of SrAl₁₂O₁₉ (∼7 eV) followed by non-resonance energy transfer to Pr³⁺ level, leading to magnetic-dipole related red emission with enhanced intensity. The PL intensity of Pr³⁺ decreases at high Ti⁴⁺ concentrations (x>0.3) due to higher extent of segregation of non-emissive SrAl₈Ti₃O₁₉:Pr³⁺ phase.     

Luminescence centers in thin films of yttrium oxide and yttrium-aluminum garnet activated with bismuth

Luminescence spectra and photoluminescence excitation spectra of Y₂O₃:Bi and Y₃Al₅O₁₂:Bi thin films were investigated. Luminescence was stimulated by the emission from two types of centers that were associated with the substitution of Bi³⁺ for Y³⁺ in sites of the crystal lattice of Y₂O₃ (Y₃Al₅O₁₂) with point symmetries C₂ and C_3i (D₂ and C_3i). The emission of Bi³⁺ in the site with point symmetry C_3i causes blue luminescence in both Y₂O₃:Bi and Y₃Al₅O₁₂:Bi films with maxima at 3.03 eV and 3.15 eV, respectively, that is related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry C₂ gives green luminescence in Y₂O₃:Bi with the maximum at 2.40 eV that is also related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry D₂ leads to ultraviolet luminescence in Y₃Al₅O₁₂:Bi with the maximum at 3.75 eV that corresponds to the ³P₁-¹S₀ transition. The red luminescence band with the maximum at 1.85 eV in Y₂O₃:Bi is due to the presence of structural defects. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 202–207, March–April, 2008.     

Diagnosis of OH radical by optical emission spectroscopy in a wire-plate bi-directional pulsed corona discharge

The emission spectrum of the molecule OH (A²Σ→X²Π, 0–0) during a high-voltage, bi-directional pulsed corona discharge consisting of a gas mixture of N₂ and H₂O in a wire-plate reactor has been successfully recorded under severe electromagnetic interference at atmospheric pressure. The relative vibrational populations and the vibrational temperature of N₂ (C, v′) have also been determined. Due to the difficulty of determining the exact overlapping spectral line shape function of the OH (A²Σ→X²Π, 0–0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g), a practicable Gaussian form is used for calculating the emission intensity of OH (A²Σ→X²Π, 0-0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g). The emission intensity of OH (A²Σ→X²Π, 0–0) has been evaluated with a satisfactory accuracy by subtracting the emission intensity of the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g) from the overlapping spectra. The relative population of OH (A²Σ) has been obtained by the emission intensity of OH (A²Σ→X²Π, 0–0) and Einstein's transition probability. The influences of peak voltage, pulse repetition rate and O₂ flow rate on the relative population of OH (A²Σ) radicals have also been investigated. We found that the relative population of OH (A²Σ) rises with an increase in both the peak applied voltage and the pulse repetition rate. When oxygen is added to an N₂ and H₂O gas mixture, the relative population of OH (A²Σ) radicals decreases exponentially with an increase in added oxygen. The main physicochemical processes involved are also discussed in this paper.     

Intense orange emission in Pr3+ doped lead phosphate glass

Spectroscopic properties of one mol% Pr₂O₃ embedded in 40%PbO–60%P₂O₅ glass have been investigated at room temperature. From the absorption spectra energy levels of the observed bands are assigned. Using free ion Hamiltonian theoretical values of energy of 13 multiplets of Pr³⁺ are calculated. Judd–Ofelt intensity parameters have been estimated by including and excluding the hypersensitive transition (³H₄→³P₂). The best set of Judd–Ofelt parameters are obtained by omitting ³H₄→³P₂ transition from the calculation. These parameters are used to evaluate the important laser parameters for various emission lines. Our investigation reveals that the present glass may be utilized as a laser active medium corresponding to ³P₀→³H₄ and ¹D₂→³H₄ transitions respectively, for 484.6 nm (blue) and 599.5 nm (strong orange) emissions. Indirect and direct optical band gap energies of Pr³⁺ doped lead phosphate glass matrix have also been reported.     

Laser spectroscopy of Nd and Dy ions in lead borate glasses

The spectroscopic and laser properties of Nd³⁺ and Dy³⁺ ions in lead borate glass were studied. Luminescence spectra recorded in the near-infrared and visible ranges correspond to ⁴F_3/2-⁴I_J/2 (J=9, 11, 13) transitions of Nd³⁺ and ⁴F_9/2-⁶H_J/2 (J=11, 13, 15) transitions of Dy³⁺, respectively. Luminescence decay curves were analyzed as a function of activator concentration. Luminescence quenching is observed, which is due to Ln-Ln interaction increasing. Several spectroscopic parameters relevant to laser potential of Ln³⁺ ions (Ln=Nd, Dy) in lead borate glass were determined. The relatively large values of the quantum efficiency and the room-temperature emission cross-section for the ⁴F_3/2-⁴I_11/2 transition of Nd³⁺ at 1061 nm and the ⁴F_9/2-⁶H_13/2 transition of Dy³⁺ at 573 nm imply that Ln-doped lead borate glasses can be considered as promising solid-state materials for laser applications.     

Contribution of hexadecapole alignment to the polarization of quadrupole emission under laser excitation conditions

The linear polarization of quadrupole emission by the J=2-J ₀=0 transition under conditions of laser excitation in a gas medium is studied. Cases of excitation through dipole and quadrupole absorption of monochromatic laser radiation are considered. Taking into account the anisotropy of collisional relaxation, the contributions of polarization moments of the second and fourth ranks, i.e., those with usual and hexadecapole alignments, to the signal of linear polarization of quadrupole emission are calculated. The dependence of this signal on the laser frequency, the density of the gas medium, and the angles determining the orientation of the system of axes of observation of light polarization relative to a laser ray is studied. The numerical calculations of contributions of usual and hexadecapole alignment to the signal of linear polarization are made for the magnetic quadrupole transition J=2-J ₀=0 between the states 2p ⁵(² P ₁ ^2/0 )3p′[3/2]₂ and 2p ⁵(² P ₁ ^2/0 )3s 3s′[1/2]⁰ of neon atoms in the xenon atmosphere.     

Electrostatic cnoidal waves and soliton structures in multi‐ions plasmas

Using a reductive perturbation technique (RPT), the Korteweg‐de Vries (KdV) equation for nonlinear electrostatic waves in multi‐ion plasmas is derived with appropriate boundary conditions. Furthermore, compressive and rarefactive cnoidal wave and soliton solutions are discussed. In our model, the multi‐ion plasma consists of light dynamic warm ions, heavy cold ions, and inertialess electrons, which follows the Maxwell‐Boltzmann distribution. It is observed that in such an unmagnetized multi‐ion plasma, two characteristic electrostatic waves i.e., slow ion‐acoustic (SIA) waves and fast ion‐acoustic (FIA) waves, can propagate. The results are discussed by considering two types of multi‐ion plasmas i.e., H⁺–O⁺–e plasma and H^?–O⁺–e plasma that exist in space plasmas. It is found that for H⁺–O⁺–e plasma, the SIA cnoidal wave and soliton form both positive (compressive) and negative (rarefactive) potential pulses, which depend on the temperature and density of the light and warm ions. However, only electrostatic positive potential structures are obtained for FIA cnoidal wave and soliton in H⁺–O⁺–e plasma. In the case of H^?–O⁺–e plasma, the SIA cnoidal wave and soliton form only compressive structures, while the FIA cnoidal wave and soliton compose rarefactive structures. The effects of light ions' density and temperature on nonlinear potential structures are investigated in detail. The parametric results are also demonstrated, which are applicable to space and laboratory multi‐ion plasma situations.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.