Phonon Sidebands Research Articles

Phonon sidebands of Eu3+ in BaGd2ZnO5

Three phonon sidebands (energies 229 cm-1, 343 cm-1, and 470 cm-1) of Eu3+ in BaGd2ZnO5, associated with the 7F0 → 5D2 transition, are evidenced using excitation spectra monitored on transition 7F0 → 5D2. The corresponding electron-phonon coupling factor is calculated for each sideband. The multiphonon transition probabilities from the 5D2 and 5D1 Eu3+ levels are estimated using the Miyakawa-Dexter model. A redshift of the charge transfer band Eu3+ - O2- with the increase of the europium concentration is observed and discussed correlating the spectroscopic results with the X-ray diffraction data. An increase of the asymetry factor with the increase of the europium concentration is also observed.

Spectroscopic investigation on Europium (Eu3+) doped strontium zinc lead phosphate glasses with varied ZnO and PbO compositions

A series of europium (Eu3+) doped SrO + ZnO + PbO + P2O5 glasses with varied ZnO and PbO compositions have been prepared by melt quenching method. The structural and optical properties of the samples are analysed by XRD, FTIR, absorption, optical band gap energy, excitation, phonon sideband (PSB) spectrum, luminescence emission, decay profile and CIE chromaticity coordinates. The most intense emission is found at 611 nm (red) corresponding to 5D0 → 7F2 transition. Using the luminescence emission spectra, the branching ratio (βm), effective bandwidth (Δλeff) and emission intensity ratio (R) have been calculated. The decay profile of the 5D0 excited state is fitted with a single exponential function and thereby lifetime is evaluated. The high colour purity of 97.4% in the red region is estimated for the EuSr30ZnPbP glass. The luminescence properties indicate that the present glasses could be used for red laser materials and optical display devices.

Microring resonator-coupled photoluminescence from silicon W centers

Silicon defect centers are promising candidates for waveguide-integrated silicon light sources. We demonstrate microresonator- and waveguide-coupled photoluminescence from silicon W centers. Microphotoluminescence measurements indicate wavelengths on-resonance with resonator modes are preferentially coupled to an adjacent waveguide. Quality factors of at least 5,300 are measured, and free spectral ranges closely match expectation. The W center phonon sideband can be used as a spectral diagnostic for a broader range of waveguide-based devices on cryogenic silicon photonic platforms.

Phonon sideband and Judd–Ofelt analyses of trivalent europium doped fluoroborosilicate glasses for red emitting device applications

Present study reports the characterization of Eu3+ ions doped fluoroborosilicate glasses (FBSEU) with chemical composition 10BaO + 10ZnF2 + 10K2O + 20SiO2 + (50 − x) B2O3 + xEu2O3 (x = 0.1,0.5,1,1.5 and 2 mol%) synthesized using melt quenching technique. XRD and FTIR analyses were carried out to obtain the structural characteristics. Through Differential Scanning Calorimetry (DSC) analysis, the glass transition temperature (Tg) of the sample was determined. To study the luminescence properties and local structural evolution, absorption, photoluminescence emission and excitation spectra were recorded and analysed. For evaluating the Eu3+-ligand bond within the host, bonding parameter was calculated and is found to be covalent. The phonon energy of the prepared sample was calculated from PSB (phonon side band) spectrum and is obtained as 990 cm−1. The glasses show strong red emission via 5D0 → 7F2 transition with 392 nm excitation. Judd–Ofelt (JO) analysis was implemented using the emission spectra to assess the radiative properties such as radiative transition probabilities (A), radiative lifetime (τR), branching ratios (βR), etc. A higher branching ratio (64%) recommends the present glassy system for laser applications. The luminescent lifetime was calculated from the decay curve analysis (2.87 ms) and compared with theoretically predicted values (4.2 ms) using JO theory. Quantum efficiency of the sample was also determined experimentally and theoretically. The emission intensities were characterized using CIE chromaticity diagram and the FBSEU glasses gives red emission with excellent colour purity.

Phonon sideband analysis, structural and spectroscopic properties of Eu3+ ions embedded SiO2–B2O3– CaF2– NaF– Na2O glasses

The trivalent Europium (Eu3+) ions with varied concentrations doped in sodium-based fluoroborosilicate glasses were prepared via the melt quenching method. The prepared glasses were subjected to study their structural, optical, and fluorescence properties. The bonding and J-O intensity parameters (Ω2, Ω4) were calculated from the obtained absorption spectrum and emission spectra, respectively. Two phonon sidebands were observed in the vibronic excitation spectrum. Among all prepared glasses, the prepared glass doped by 1.5 mol% Eu3+ ions exhibits the maximum emission intensity. For the all prepared glasses, intensity of electric dipole transition (5D0 → 7F2) has been varied with proportionate to concentration of trivalent Eu ions. Radiative parameters like bandwidth (Δλeff), radiative transition probability, experimental and calculated branching ratios and stimulated emission cross-section were calculated. Eu3+ ions excited state (5D0 level) lifetime was calculated using fluorescence decay analysis for varying concentrations of Eu3+ ions in prepared fluoroborosilicate glasses. The results obtained reveal that the investigated fluoroborosilicate glasses could be used for the design and development of red laser (612 nm) and display device applications.

High tantalum oxide content in Eu3+-doped phosphate glass and glass-ceramics for photonic applications

Abstract Transparent Eu3+-doped tantalum phosphate glass-ceramics containing Na2Ta8O21 nanocrystals were successfully obtained by a two-step heat treatment. Structural analyses were performed using X-ray diffraction, Transmission Electron Microscopy, Nuclear Magnetic Resonance and Raman spectroscopy. Due to the high Ta/P ratio (= 2) the glass network is built from a mixed 3D PO4–TaO6 chain in which TaO6-rich regions are inserted and responsible for crystallization of an alkali tantalum oxide phase Na2Ta8O21. Eu3+ and their optical properties was used as a sensitive probe to study it site structure in the host matrix. The radiative properties of Eu3+ emission levels were predicted using the Judd-Ofelt theory. The chemical environment and local phonon energy around the rare-earth ions have been proposed based on phonon side band associated with the 7F0 → 5D2 transition, 5D0 → 7F2/7F1 relative intensity and narrowing of the emission bands. High tantalum content precursor glass exhibits high photoluminescence quantum efficiency due to low phonon energy and high refractive index (1.9461 at 633 nm). A perovskite-like bronze crystalline structure is formed in the glass-ceramic (nucleated at 925 °C for 0.5 h and grown at 940 °C for different times) and is considered promising for nonlinear optical applications and studies.

(Invited) Origin of Lineshape Asymmetry in the Photoluminescence Spectra of Cryogenic Carbon Nanotubes

Photoluminescence spectra of cryogenic carbon nanotubes exhibit a peculiar lineshape asymmetry that has been interpreted as arising from the interplay of temperature-driven exciton localization and the one-dimensional reservoir of acoustic phonons [1] with pronounced phonon sidebands in the limit of a gapped phonon reservoir [2,3]. Based on our recent experimental studies of PFO-wrapped nanotubes at cryogenic temperatures, we present an alternative model to explain the origin of the lineshape asymmetry.[1] C. Galland et al., Non-Markovian decoherence of localized nanotube excitons by acoustic phonons, Phys. Rev. Lett. 101, 067402 (2008).[2] F. Vialla et al., Unifying the low-temperature photoluminescence spectra of carbon nanotubes: The role of acoustic phonon confinement, Phys. Rev. Lett. 113, 057402 (2014).[3] I. Sarpkaya et al., Strong acoustic phonon localization in copolymer-wrapped carbon nanotubes, ACS Nano 9, 6383 (2015).

Charge-state conversion in nitrogen-vacancy centers mediated by an engineered photonic environment

The nitrogen-vacancy (NV) center in nanodiamonds has emerged as an excellent platform in quantum technologies due to its applications in spin manipulation and nanoscale sensing. However, their use is limited by the unavoidable charge-state conversion under optical pumping. In this study, we investigate the control of charge-state conversion in NV centers using an engineered photonic environment and thus change the available local density of optical states (LDOS). The spectral- and pump-dependent decay rate measurements are performed to study the redistribution of emission rates due to the change in LDOS and their effect on charge-state conversion. We have achieved an 8% enhancement of emission rate at the zero phonon line which is accompanied with a 10% suppression in the phonon sideband emission rate in the low-pump-power regime. In the high-pump-power regime, the charge-state conversion becomes inevitable and leads to the deterioration of LDOS-induced modification in the NV center emission lifetimes. The results are useful for efficient NV center spin readout and charge-state depletion microscopy utilizing reversible charge-state conversion.

Phonon-Induced Optical Dephasing in Single Organic Molecules.

We present a joint experiment-theory analysis of the temperature-dependent emission spectra, zero-phonon linewidth, and second-order correlation function of light emitted from a single organic molecule. We observe spectra with a zero-phonon line together with several additional sharp peaks, broad phonon sidebands, and a strongly temperature dependent homogeneous broadening. Our model includes both localized vibrational modes of the molecule and a thermal phonon bath, which we include nonperturbatively, and is able to capture all observed features. For resonant driving we measure Rabi oscillations that become increasingly damped with temperature, which our model naturally reproduces. Our results constitute an essential characterization of the photon coherence of molecules, paving the way to their use in future quantum information applications.

Double sites occupancy of Mn4+ in Cs2NaAlF6 with enhanced photoluminescence for white light-emitting diodes

In this work, we present a novel single-phase red phosphor of Cs2NaAlF6:Mn4+ with two Al3+ lattice sites, which shows two groups of vibrational phonon sidebands and ultra-intense zero phonon line (ZPL) under blue light illumination. The evidences have shown that the interesting spectral features originate from the non-equivalent occupation of Mn4+ for both Al3+ sites, which induces the neighboring cation vacancies surrounding Mn4+ and highly distorted [MnF6] octahedral in the Cs2NaAlF6 host. The luminescent behavior of double sites occupied by Mn4+ can absorb researchers’ interest on novel red-emitting phosphors. Profiting from the photoluminescence (PL) features, superior color rendering index of Ra = 90.3, R9 = 81, and low correlated color temperature of Tc = 3967 K are achieved from white light-emitting diode (LED) by using yellow Y3Al5O12:Ce3+ (YAG) and red Cs2NaAlF6:Mn4+ phosphors as blue light converters. These results suggest that Cs2NaAlF6:Mn4+ for phosphor has a stupendous potential for LED lighting.

Enhanced red luminescent PBTNAEu glasses for solid state lasers

The luminescence characteristics of Eu3+ activated 30 PbO+(50–x) B2O3+5 TeO2+10 NaF+5 AlF3+x EuF3 (PBTNAEu) glasses prepared by melt-quenching process were studied for red laser applications. The phonon-side band mechanism of Eu3+: 5D2 emission state was discussed with the help of photoluminescence excitation and the Raman spectral features. The Judd-Ofelt intensity parameters that will be used to evaluate various laser characteristic parameters were determined from both the absorption and the emission spectra. The absorption from 7F0 ground and 7F1 first excited states was considered by applying the thermal correction. The emission spectra were used to study the luminescence enhancement and the asymmetric environment around the Eu3+ ions. The quantum efficiency of emitted luminescence was determined from the experimental and radiative decay times of 5D0 emission state. From the experimental results, it was suggested that the PBTNAEu glass containing 2.0 mol% of EuF3 has more potentiality for red laser applications.

Eu3+ ions doped SrO-CaO-Li2O-B2O3glasses foroptical display material application

The glass systems with composition 20SrO-5CaO-40Li2O-(35-x) B2O3-x Eu2O3 (x = 0.3, 0.5 and 1 mol%) glasses were prepared by melt quenching technique to study absorption and luminescence properties and understand their lasing properties. Thepresent work reports the studies on Physical, Optical and luminescence properties of the prepared glass systems. The photoluminescence (PL) intensity of the glass increases with increase in Eu2O3 content up to 1mol%. The increase in the density and decrease in molar volume reveals the close packing of glass network. For Eu3+ emission the most intense red emission has been observed at the wavelength of 614nm for the transitions5D0 →7F2. The phonon energy was measured from phonon side band spectra which showed 1280cm−1, typical value for the borate glasses. Luminescence intensity ratio and lifetime analysis has been measured and discussed in the present work. The present glasses are very near to reddish orangeregion and thus can be key entrant for optical display device applications.

Watt-level mid-infrared continuous-wave Tm:YAG laser operating on the 3H4 → 3H5 transition

We report on the first continuous-wave mid-infrared Tm:Y3Al5O12 laser operating on the 3H4 → 3H5 transition. The 3.2 at.% Tm:Y3Al5O12 laser generated a maximum output power of 1.07 W at ~2.19 & 2.32 μm with a high slope efficiency of 46.3% (vs. the absorbed pump power) exceeding the Stokes limit. Depending on the output coupling and the pump power, a set of discrete laser lines in the range of 2.164–2.346 μm was observed. The spectroscopic properties of Tm:Y3Al5O12 relevant for the mid-infrared laser operation are revised. The maximum stimulated-emission cross-section for the 3H4 → 3H5 transition is 0.35 × 10−20 cm2 at 2324 nm and the emission bandwidth is ~37 nm. The overlap of the 3F4 → 3H6 and the 3H4 → 3H5 transitions is quantified revealing the formulas for Stokes and anti-Stokes phonon sidebands of emission bands. Tm:Y3Al5O12 is promising for broadly tunable (2.1–2.5 μm) and mode-locked mid-infrared oscillators.

Acoustic phonon sideband dynamics during polaron formation in a single quantum dot.

When an electron-hole pair is optically excited in a semiconductor quantum dot, the host crystal lattice adapts to the presence of the generated charge distribution. Therefore, the coupled exciton-phonon system has to establish a new equilibrium, which is reached in the form of a quasiparticle called a polaron. Especially, when the exciton is abruptly generated on a timescale faster than the typical lattice dynamics, the lattice cannot follow adiabatically. Consequently, rich dynamics on the picosecond timescale of the coupled system is expected. In this study, we combine simulations and measurements of the ultrafast, coherent, nonlinear optical response, obtained by four-wave mixing (FWM) spectroscopy, to resolve the formation of this polaron. By detecting and investigating the phonon sidebands in the FWM spectra for varying pulse delays and different temperatures, we have access to the influence of phonon emission and absorption processes, which finally result in the emission of an acoustic wave packet.

Role of modifier ion radius in luminescence enhancement from 5D4 level of Tb3+ ion doped alkali-alumino-telluroborate glasses

Alkali-alumino-telluroborate glasses with the different network modifier elements were prepared by melt–quenching method. Absorption, excitation, luminescence spectra as well as decay curves of 5D4 level were measured at room temperature. A phonon side band of 7F6 → 5D4 transition has been obtained from the excitation spectra of Tb3+ ion. The role of modifier ion radius in luminescence enhancement from 5D4 level of Tb3+ ion was discussed in detail. In prepared glasses, multiphonon relaxation rate from 5D3 level to 5D4 is enhanced in the host glasses containing modifier ions with large radius. This is main reason leading to the enhancement of luminescence from 5D4 level of Tb3+ ion in alkali-alumino-telluroborate glasses under excitation at 350 nm. Additionally, the Judd-Ofelt theory was used to estimate the features of ligand field and radiative properties of Tb3+ ion. The calculated results have shown that the 5D4→7F5 transition has potential applications for laser action and optical amplifier.

Spectroscopic investigations of negatively charged tin-vacancy centres in diamond

The recently discovered negatively charged tin-vacancy centre in diamond is a promising candidate for applications in quantum information processing (QIP). We here present a detailed spectroscopic study encompassing single photon emission and polarisation properties, the temperature dependence of emission spectra as well as a detailed analysis of the phonon sideband and Debye–Waller factor. Using photoluminescence excitation spectroscopy we probe an energetically higher lying excited state and prove fully lifetime limited linewidths of single emitters at cryogenic temperatures. For these emitters we also investigate the stability of the charge state under resonant excitation. These results provide a detailed insight into the spectroscopic properties of the SnV− centre and lay the foundation for further studies regarding its suitability in QIP.

Structural and spectroscopic investigations on Eu3+ ions doped boro-phosphate glasses for optical display applications

Eu3+ ions incorporated Boro-phosphate glasses 51H3BO3+10ZnO+20Li2Co3+9SrCo3+ (10−x)H6NO4P + xEu2O3 (where x = 0.1,0.25,0.5,1,2 and 3 in mol%) containing alkali, alkaline and heavy metals were prepared by melt quenching technique. The structural and optical behavior has been studied employing X ray diffraction, FTIR, UV–Vis-IR absorption, emission and decay spectral data. FT infrared investigations probe the availability of fundamental stretching vibrational groups in the present glasses. The phonon side band observed pertaining to the larger energy part of the 7F0→5D2 transition is ascribed to the link between coordination ions and Eu3+ions. The Judd-Ofelt (JO) parameters obtained from the emission spectra are utilized to determine the radiative parameters for the 5D0→7FJ=1,2,3 and 4 bands pertaining to the Eu3+ ions. The increasing Ω2 and the larger R values certify the higher asymmetry of the Eu3+ ions site and Eu–O covalency. The experimental lifetime pertaining to the 5D0 excited level of the Eu3+ ions in the titled glasses have been investigated through decay curve analysis. Emission intensities characterized through the CIE diagram and (x = 0.617, y = 0.323) color coordinates suggests that acute red emission exhibited by the titled glasses are appropriate for lighting applications and display devices.

Shedding light on exciton's nature in monolayer quantum material by optical dispersion measurements.

Strong light-matter interactions based on two-dimensional excitons formed in quantum materials such as monolayer transition-metal dichalcogenides have become a major subject of research in recent years. Particularly attractive is the extraordinarily large oscillator strength as well as binding energy of the excitonic quasiparticles in these atomically-thin crystal lattices. Numerous theoretical studies and experiments have been devoted to the exploration of the excitonic systems that could be exploited in future nano-scaled optoelectronic devices. To obtain unique insight into the exciton's characteristics in an archetype monolayer quantum material, we directly measure the quasiparticle energy-momentum dispersion for the first time optically. Our results for h-BN encapsulated single-layer WSe2 clearly indicate an emission regime with a dispersion in the meV range in within the light cone at cryogenic temperatures. The amount of dispersion agrees well with calculations for an exciton-polariton based on the material's monolayer exciton, or energetic modifications caused by exciton exchange interactions predicted for this material family. The measurable dispersion slightly weakens for elevated excitation densities, whereas at elevated temperatures, it even becomes immeasurable. The obtained reduction in dispersion is attributed to an enhanced role of uncorrelated charge carriers as well as the formation of phonon sidebands above 100 K.

Effect of sodium oxide and sodium fluoride in gadolinium phosphate glasses doped with Eu2O3 content

Sodium gadolinium phosphate oxide and sodium gadolinium oxyfluoride glasses doped with europium oxide were synthesized by melt-quenching method. The density, molar volume and refractive index of the glass samples were carried out. Density and molar volume of oxide glass is more than oxyfluoride glass. The average phosphate to phosphate distance for oxide glass seems to be more than oxyfluoride glass. Polaron radius, inter-ionic radius shows 1.181 nm, 2.88 nm and 1.174 nm, 2.86 nm for oxide glass and oxyfluoride glasses respectively. Oxide electronic Polarizability and optical basicity of the oxide glass are lower than oxy-fluoride glass. Theoretical optical basicity shows higher for oxide glass than oxyfluoride suggesting increase in covalency of the cation to oxygen bonds in oxide glass. Optical band gap was estimated and found to be 3.061eV and 3.204 eV for oxide and oxyfluoride glass. Theoretical two photon absorption coefficient β were evaluated and found to be 11.96 and 10.80 for oxide and oxyfluoride glasses respectively. Electron-phonon coupling strength were evaluated from the phonon side band spectra for the oxide and oxy-fluoride glasses. The asymmetry ratio (R) show higher for NaF doped glass than Na2O confirming their role in elevated ionicity for oxyfluoride glass than oxide glass. Furthermore, the glasses were subjected to study for their luminescence properties of the oxide and oxyfluoride glass samples.

Structure, optical properties and energy transfer in potassium-alumino-borotellurite glasses doped with Eu3+ ions

KABxTyE (xB2O3+yTeO2 +10K2O+10Al2O3 +0.5Eu2O3) glasses with the variation of B2O3/TeO2 ratios (x/y = 30/50, 40/40 and 50/30) and KABTzEu glasses ((50-z)B2O3+30TeO2+10Al2O3+10K2O + zEu2O3, with z = 0.1, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mol%) were prepared by melt–quenching technique. The structure of glasses was analyzed through X-ray diffraction (XRD) patterns, Fourier-transform infrared spectroscopy (FTIR) and phonon-sideband (PSB) spectra. The Judd-Ofelt (JO) theory was used to estimate the properties of ligand and the radiative parameters of prepared glasses such as lifetime (τcal), effective line width (Δλeff), stimulated emission cross-section (σP), gain bandwidth (σP × Δλeff), optical gain (σP × τcal) and quantum efficiency (η). The influence of B2O3/TeO2 ratio and Eu3+ concentration on structure and optical properties of materials was discussed in detail. Energy transfer process between Eu3+ ions was studied by using Inokuti-Hirayama and Yokota-Tamimoto models. The energy transfer channels between Eu3+ ions were also proposed.