Zero-phonon Line Position Research Articles

Analysis of EVI parameters in the 3d states of Cu+ ions in MgS phosphor

This paper reports a study of the electron-phonon interaction (EVI) for the 3d states of the Cu + doped in MgS phosphor. Its spectroscopic results were utilized for determining the strength of the electron-phonon coupling in this sulphide-based phosphor. In Cu + metal ion, 3d 10 →3d 9 4 s 1 transition is responsible for obtaining the photoluminescence (PL) spectra. Using the values of the stokes shift and the full-width at half maxima (FWHM) of the PL emission and the excitation spectra from the experimental results, the Huang-Rhys factor (S), Phonon energy (ħω) and Zero-phonon line (ZPL) position were determined. The obtained values of the Huang-Rhys factor (S) and the Phonon energy (ħω) were validated by modeling the emission spectra.

Two types of isolated (quantum) emitters related to dislocations in crystalline CdZnTe

Based on the measurements of spectra and polarization of low-temperature (5 K) microphotoluminescence, two types of isolated quantum emitters formed due to the dislocations in crystalline CdZnTe have been identified. For an emitter of the first type, the spectral position of zero-phonon emission line (ZPL) corresponds to the well-known dislocation luminescence of CdZnTe. In this case, position and intensity of ZPL demonstrate high stability over time. For an emitter of the second type, ZPL is located 30–50 meV above the usual dislocation luminescence and is subjected to giant fluctuations of spectral position (~ 10 meV) and intensity. For each of the two types of emitters, coupling with lattice is confirmed by the presence of phonon replicas associated with longitudinal optical phonons in CdZnTe. A noticeable degree of linear polarization in the plane containing 〈110〉 directions indicates the strongly anisotropic nature of the corresponding electronic states and confirms their connection with dislocations.

Influence of the growth temperature on the Si-V photoluminescence in diamond thin films

The influence of growth temperature (350 ÷ 1100 °C) on the intensity of Si-V colour centres photoluminescence was studied in diamond thin films. The films were grown by a microwave plasma enhanced chemical vapour deposition system. The film quality and surface morphology were characterised by Raman spectroscopy and scanning electron microscopy, respectively. For selected samples, the temperature behaviour of steady-state photoluminescence emission spectra was studied within the range 11 ÷ 300 K as well. The photoluminescence properties are related to the film growth temperature. We found that 800 °C is the optimal growth temperature, at which the highest intensity of the Si-V centre photoluminescence was observed. For all the samples, the blue shift in the position of the Si-V centre photoluminescence zero-phonon line is observed with decreasing temperature, which is attributed to the effects of lattice contraction and quadratic electron–phonon coupling. The zero-phonon line narrowing is discussed regarding vibrations of the perturbed lattice.

Spectroscopic study of NE8 defect in synthetic diamond for optical thermometry

We carried out a laser spectroscopic investigation of high-pressure, high-temperature (HTHP) synthetic diamond containing NE8 defects. In the photoluminescence (PL) emission spectra the defects have a zero-phonon line (ZPL) at 794nm. Under 730nm excitation the width and position of the ZPL as well as the Debye-Waller factor showed systematic temperature dependences which were modelled in accordance of a modified model of impurity defects in solids. A strong dependence of the position of the 794nm ZPL on temperature suggests that NE8-containing diamond could be suitable for sensitive optical thermometry above 200K. Further, the PL in the NIR spectral range makes the diamond crystalline particles promising temperature sensors for biomedical applications.

Investigation of thermoluminescence and electron-vibrational interaction parameters in SrAl2O4:Eu2+, Dy3+ phosphors

Combustion synthesis method was employed for the synthesis of green-emitting monoclinic SrAl2O4:Eu2+, Dy3+ phosphors. The phase-purity of the prepared phosphors were examined using X-ray diffraction (XRD). The prepared phosphors exhibited green light emission with the peak centred at 510 nm, under 350 nm UV excitation. The excitation and emission spectra were analysed and the parameters of electron-vibrational interaction (EVI), such as the Huang–Rhys factor, effective phonon energy and zero-phonon line position were estimated using the spectrum fitting method. Thermoluminescence (TL) behaviour of the as-prepared phosphors were analysed for UV and 137Cs γ-ray source irradiation. TL glow curves for UV-irradiated SrAl2O4:Eu2+, Dy3+ phosphors were analysed.

Assessment of electron-vibrational interaction (EVI) parameters of YAG:Ce3 +, TAG:Ce3 + and LuAG:Ce3 + garnet phosphors by spectrum fitting method

The electron–vibrational interaction (EVI) in 4f↔5d optical transitions of Ce3+ ions in YAG, TAG and LuAG garnet phosphors have been analysed in this work. The main EVI parameters that have been estimated and reported here are Huang-Rhys factor, effective phonon energy, Stokes shift, red shift and Zero-phonon line position. The EVI parameters were estimated from the room temperature photoluminescence results that were recently reported. The spectrum fitting method was employed to determine the EVI parameters. An emission band was modelled with the aid of the calculated EVI parameters. The agreement between the modelled emission bands with the experimentally obtained ones validated the estimated values of EVI parameters.

Study of electron-vibrational interaction in 5d states of Ce3+ ions in the chloroapatite system

Electron-vibrational interaction (EVI) in interconfigurational 5d-4f transition of Ce3+-doped alkaline-earth chlorophosphates, also known as apatites, is studied for the first time in this work. Using the configurational coordinate model, the main EVI parameters such as Huang-Rhys factor, effective phonon energy and the zero-phonon line (ZPL) position are determined for all samples studied. Photoluminescence characteristics of these compounds are utilized to estimate EVI parameters. As a reliable test validating the obtained results, the emission band shape of was modeled to yield good agreement with experimental emission spectra. The values of EVI parameters were systematically compared for all studied materials as well as with similar systems with halide ions.

Study of electron-vibrational interaction and concentration quenching effect of Cu+ ions in lithium based sulphate phosphors

The objective of this work is to study electron-vibrational interaction (EVI) and concentration quenching and their manifestation in experimental photoluminescence spectra of Cu+ ion in various lithium based phosphors namely, Li2SO4, LiNaSO4 and LiKSO4. The main parameters of EVI, such as the Stokes shift, Huang-Rhys factor and zero-phonon line positions, were estimated. The studied systems shows strong electron lattice coupling. The validity of results was established by modeling the shape of the emission spectra, which was found to be in good agreement with experimental photoluminescence spectra. The concentration quenching study is also carried out for these compounds. The studied systems correspond to the nearest neighbor energy transfer mechanism.

Exploration of electron-vibrational interaction in the 5d states of Eu2+ ions in ABaPO4 (A=Li, Na, K and Rb) phosphors.

This work reports the theoretical analysis of the electron-vibrational interaction (EVI) in 4f-5d optical transitions of Eu2+ ions in ABaPO4 (A=Li, Na, K and Rb) systems. The EVI parameters were estimated from the recently reported room temperature photoluminescence results, by employing the spectrum-fitting method. Parameters such as the Huang-Rhys factor, effective phonon energy, Stokes shift and zero-phonon line position were estimated and are reported here. The estimated EVI parameters were validated by modeling the emission band and establishing the agreement between the experimental and modeled emission bands. Copyright © 2016 John Wiley & Sons, Ltd.

Novel blue-emitting phosphors - BaBeSiO_4:Eu^2+: luminescence properties and its application for UV-light emitting diodes

A new Eu2+-doped barium beryllium silicate, BaBeSiO4:xEu2+ (1% ≤ x ≤ 10%) phosphor was successfully synthesized by the high temperature solid-state reaction. The phosphor system was investigated as a novel candidate for phosphor-converted white light-emitting diode (LED) applications. The evolution of luminescence and structure of the phosphors induced by variation of sintering temperature are investigated using photoluminescence spectra and X-ray diffraction techniques. The concentration quenching and thermal quenching process of the phosphor were also investigated in detail. The BaBeSiO4:Eu2+ phosphor exhibits broad excitation spectra ranging from 250 to 400 nm, and a blue emission band centered at 460 nm under λex = 337 nm. The main parameters of the electron-vibrational interaction, such as Huang-Rhys factor, effective phonon energy, and zero-phonon line position, were all estimated. The optimal concentration of Eu2+ ions in BaBeSiO4 was determined to be 3 mol.%. The corresponding concentration quenching mechanism was verified to be the electric dipole−dipole interaction. The activation energy of BaBeSiO4:Eu2+ for thermal quenching was calculated to be 0.19 eV with the Arrhenius equation. The LED device exhibited an excellent color-rendering index Ra of 90.13 at a correlated color temperature of 4077 K with CIE color coordinates of (0.38, 0.39) under a 350 mA forward-bias current. Based on these results, we are currently evaluating the potential application of BaBeSiO4:Eu2+ as a white-emitting UV-convertible phosphor for high power LED applications.

5d–4f emission of Eu2+ and electron-vibrational interaction in several alkaline earth sulfides doped with Eu2+ and Er3+

Several alkaline earth sulfides doped with Eu2+ and Er3+ ions have been synthesized and shown to be potential phosphors for applications in the visible spectral range. The excitation and emission spectra corresponding to the 4f–5d interconfigurational transitions of Eu2+ were analyzed with an aim of extraction of the main parameters of the electron-vibrational interaction. The values of the Huang–Rhys factor, effective phonon energies, and zero-phonon line positions were systematically compared for all studied materials; physical trends were discussed. As a test for the validity of the obtained parameters, the Eu2+ 5d–4f emission bands were modeled to yield good agreement with the experimental spectra.

Isotopically varying spectral features of silicon-vacancy in diamond

The silicon-vacancy centre () in diamond has exceptional spectral properties for single-emitter quantum information applications. Most of the fluorescence is concentrated in a strong zero phonon line (ZPL), with a weak phonon sideband extending for 100 nm that contains several clear features. We demonstrate that the ZPL position can be used to reliably identify the silicon isotope present in a single centre. This is of interest for quantum information applications since only the 29Si isotope has nuclear spin. In addition, we show that the sharp 64 meV phonon peak is due to a local vibrational mode of the silicon atom. The presence of a local mode suggests a plausible origin of the measured isotopic shift of the ZPL.

Zero-phonon line characteristics of SiV center emission in microcrystalline diamond probed with intensive optical excitation

Zero-phonon line (ZPL) position, broadening and intensity of the SiV center emission was monitored in microcrystalline diamond film by using intensive laser excitation of 2.54eV photon energy. Excitation intensity was varied from 150kW/cm2 to 700kW/cm2 to explore changes in the emission region of the zero-phonon line. Two types of characteristic behavior were found in diamond microcrystals. Both the ZPL position and half width of the SiV center emission remain nearly the same in the one type of microcrystalline samples, whilst considerable broadening and red shift of the ZPL of SiV center with the increasing intensity was observed in the other type of microcrystalline samples. GR1 defect center emission under intensive laser excitation is discussed as a possible origin of the observed changes.

Electron-Vibrational Interaction in the 5d States of Eu2+ Ions in Sr6-xEuxBP5O20 (x = 0.01-0.15)

We report on the combined experimental and theoretical study of the Sr6-xEuxBP5O20 (x = 0.01; 0.03; 0.05; 0.07; 0.09; 0.11; 0.13; 0.15) phosphors. Spectroscopic measurements were followed by the analysis of the room-temperature absorption and emission spectra, which yielded the main parameters of the electron-phonon coupling, such as Huang-Rhys factor, Stokes shift, effective phonon energy, and zero-phonon line position. All these parameters were determined for the studied system for the first time to the best of the authors’ knowledge. Reliability of the obtained parameters was checked by modeling the emission band shapes, which perfectly reproduced the experimental emission spectra of all samples.

Phonon-assisted optical bands of nanosized powdery SrAl2O4:Eu2+ crystals: Evidence of a multimode Pekarian

A stoichiometric powder composed of nanosized grains of SrAl2O4:Eu2+ was synthesized by combustion method at 500 °C with the subsequent calcination at 1000 °C. The zero-phonon line position, parameter of the Stokes shift, heat release factor and effective phonon energy were studied experimentally and analyzed in the framework of the multimode Pekar–Huang–Rhys model. Experimental data show that the optical 4f–5d transitions in Eu2+ ion exhibit a broad asymmetric electron–vibrational bands with a pronounced structure near the maxima. The form-function of the absorption and luminescence bands are theoretically analyzed in the framework of the model of the linear electron–vibrational interaction assuming strong coupling with the local vibration (estimated Pekar–Huang–Rhys parameter a=2S=10 and frequency ℏω=509 cm−1) and relatively weak interaction with the crystal phonons. The last results in an effective temperature dependent broadening of the discrete lines corresponding to the local vibrations and to a specific shape of the whole phonon assisted band (multimode Pekarian). Providing specific interrelation between the key parameters the calculated absorption and luminescence bands exhibit peculiar temperature dependent structured peaks in a qualitative agreement with the experimental data.

Photoluminescence and electron-vibrational interaction in 4fn−15d states of Ce3+ or Pr3+ ions doped LnBO3 (Ln=Lu, Y, La) orthoborates materials

Calcite, vaterite and aragonite type rare earth LnBO3 (Ln=Lu, Y, La) orthoborate powders, doped with 1% cerium or praseodymium, were prepared by the classical solid state reaction method. The structure and the morphology of these powder materials were checked by X-ray Diffraction, Fourier Transform Infra Red Spectroscopy (FTIR) and Scanning Electron Microscopy. Room temperature excitation and emission spectra of four compounds: LuBO3 with calcite and vaterite structure, YBO3 (vaterite type structure) and LaBO3 with aragonite, doped with 1% cerium or praseodymium ions, have been measured and investigated. The effect of Ce3+ and Pr3+ crystalline environment in these compounds on the position of their 5d (4f5d) levels has been discussed. This work is also devoted to the problem of the electron-vibrational interaction (EVI) in 4f–5d optical transitions in orthoborate materials. The emission and excitation 4f–5d transitions resulted in broad vibronic bands whose shape functions were described and found. The main EVI parameters, such as the Huang-Rhys factor, effective phonon energy, and zero-phonon line position, were estimated. These values are checked by modeling the Ce3+ 5d–4f and Pr3+ 4f5d–4f2 emission lines shapes, in which good agreement with experimental spectra confirms validity of the performed analysis.

Electron–vibrational interaction in the 5d states of Ce 3+ ions in halosulphate phosphors

Using the literature data on excitation and luminescence spectra of Ce 3+ ions in NaMgSO 4F, Na 3SO 4F, and KZnSO 4Cl halosulphate phosphors [S.C. Gedam, S.J. Dhobe, S.V. Moharil, J. Lumin. 126 (2007) 121], we performed comparative studies of electron–vibrational interaction (EVI) of the cerium 5d states with host lattices. The main EVI parameters, such as the Huang-Rhys factor, effective phonon energy, and zero-phonon line position, were estimated and reported for these systems for the first time. The obtained results were checked by modeling the Ce 3+ 5d–4f emission line shapes; good agreement with experimental spectra confirms validity of the performed analysis.

Preparation and spectroscopic studies of the Mg xSr 1−xAl 2O 4:Eu, Dy ( x = 0.05–0.25) persistent phosphors

Mg x Sr 1− x Al 2O 4:Eu, Dy ( x = 0.05–0.25) phosphors were prepared by the solid-state reaction method; their excitation and emission spectra corresponding to the transitions between the ground 4f 7 and excited 4f 65d 1 configurations of Eu 2+ ion were studied. Broad band UV excited luminescence attributed to Eu 2+ ions was observed around 19,500 cm −1 (513 nm). From the comparison between the excitation and emission spectra, the crystal field splitting of the Eu 2+ 5d states and the parameters of electron–vibrational interaction, such as the Huang–Rhys factor, effective phonon energy, and zero-phonon line position for the studied compound were estimated for the first time.

Studies of electron-vibrational interaction and crystal field splitting in 5d states of Eu2+ in CaAl2O4 co-doped with Eu2+ and Er3+

CaAl2O4 co-doped with Eu2+ and Er3+ were prepared by the solid-state reaction method and investigated for their photoluminescence properties. Broad band UV excited luminescence was observed for CaAl2O4 : Eu2+, Er3+ in the blue region due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. From the analysis of excitation and emission spectra, the crystal field splitting of the 5d states of Eu2+and the parameters of electron-vibrational interaction, such as the Huang–Rhys factor, effective phonon energy and zero-phonon line position of this system, were estimated for the first time.

Photoluminescence in MgxSr1−xAl2O4:Eu2+, Nd3+and electron–vibrational interaction in the Eu2+ 5d states

Green phosphor compositions MgxSr1−xAl2O4:Eu, Nd (with x=0.05–0.25) were prepared by solid state reaction method. The effect of Mg substitution on photoluminescence characteristics was investigated. The photoluminescence show intense green emission for MgSrAl2O4:Eu2+, Nd3+ with long persistence. This green emission corresponds to transitions from 4f65d1 to 4f7 of Eu2+ ion. Comparative analysis of the excitation and emission spectra were used to evaluate the crystal field splitting of the 5d states of Eu2+ and the parameters of electron–vibrational interaction, such as Huang–Rhys factor, effective phonon energy, and zero-phonon line position.