Red Line Emission Research Articles

Investigating high-frequency quasi-periodic oscillations in the 6374 Å red coronal line observed during the total solar eclipse on August 21, 2017

Context. We present the results of the search for high-frequency quasi-periodic oscillations (HFQPOs) in the 6374-Å red line emission from the solar corona during the 2017 total solar eclipse (TSE). Aims. The existence of HFQPOs of coronal intensity remains unclear. Motivated by previous observations, this paper focuses on searching for the HFQPOs (> 0.1 Hz) during the 2017 TSE. Methods. Wavelet analysis tools were used to analyze the radiation intensity oscillations in different height layers, local regions of interest (such as the east coronal loop, west cavity, etc.), and coronal feature points as well as changes in oscillations along coronal feature structures and the kinematic wobble of the coronal magnetic features. Results. We have observed oscillatory signals at multiple spatial locations, which reveal the existence of quasi-periodic slow magnetoacoustic waves. These signals display periods ranging from approximately 3 to 9 seconds, with a notable focus on periods around 4 seconds. Conclusions. High-frequency quasi-periodic slow magnetoacoustic oscillations (with periods less than 9.63 seconds) have been identified in the inner corona (at heights less than 1.4 R⊙) in the 6374 Å red coronal line radiation.

Impact of assembly bias on clustering plus weak lensing cosmological analysis

Context. Empirical models of galaxy-halo connection such as the halo occupation distribution (HOD) model have been widely used over the past decades to intensively test perturbative models on quasi-linear scales. However, these models fail to reproduce the galaxygalaxy lensing signal on non-linear scales, over-predicting the observed signal by up to 40%. Aims. With ongoing Stage-IV galaxy surveys such as DESI and Euclid that will measure cosmological parameters at sub-percent precision, it is now crucial to precisely model the galaxy-halo connection in order to accurately estimate the theoretical uncertainties of perturbative models. Methods. This paper compares a standard HOD (based on halo mass only) to an extended HOD that incorporates as additional features galaxy assembly bias and local environmental dependencies on halo occupation. These models were calibrated against the observed clustering and galaxy-galaxy lensing signal of eBOSS luminous red galaxies and emission line galaxies in the range 0.6 < z < 1.1. We performed a combined clustering-lensing cosmological analysis on the simulated galaxy samples of both HODs to quantify the systematic budget of perturbative models. Results. By considering not only the mass of the dark matter halos but also these secondary properties, the extended HOD offers a more comprehensive understanding of the connection between galaxies and their surroundings. In particular, we found that the luminous red galaxies preferentially occupy denser and more anisotropic environments. Our results highlight the importance of considering environmental factors in empirical models with an extended HOD that reproduces the observed signal within 20% on scales below 10 h−1 Mpc. Our cosmological analysis reveals that our perturbative model yields similar constraints regardless of the galaxy population, with a better goodness of fit for the extended HOD. These results suggest that the extended HOD should be used to quantify modelling systematics. This extended framework should also prove useful for forward modelling techniques.

Galaxy clustering in modified gravity from full-physics simulations – I. Two-point correlation functions

ABSTRACT We present an in-depth investigation of galaxy clustering based on a new suite of realistic large-box galaxy formation simulations in $f(R)$ gravity, with a subgrid physics model that has been recalibrated to reproduce various observed stellar and gas properties. We focus on the two-point correlation functions of the luminous red galaxies (LRGs) and emission line galaxies (ELGs), which are primary targets of ongoing and future galaxy surveys such as Dark Energy Spectroscopic Instrument (DESI). One surprising result is that, due to several non-trivial effects of modified gravity on matter clustering and the galaxy–halo connection, the clustering signal does not depend monotonically on the fifth-force strength. For LRGs, this complicated behaviour poses a challenge to meaningfully constraining this model. For ELGs, in contrast, this can be straightforwardly explained by the time evolution of the fifth force, which means that weaker $f(R)$ models can display nearly the same – up to 25 per cent – deviations from Lambda cold dark matter model as the strongest ones, albeit at lower redshifts. This implies that even very weak $f(R)$ models can be strongly constrained, unlike with most other observations. Our results show that galaxy formation acquires a significant environment dependence in $f(R)$ gravity, which, if not properly accounted for, may lead to biased constraints on the model. This highlights the essential role of hydrodynamical simulations in future tests of gravity exploring precision galaxy-clustering data from the likes of DESI and Euclid.

SubAuroral Red Arcs Generated by Inner Magnetospheric Heat Flux and by SubAuroral Polarization Streams

AbstractSubauroral red (SAR) arcs are commonly observed ionospheric red line emissions. They are usually attributed to subauroral electron heating by inner magnetospheric heat flux (IMHF). However, the role of IMHF in changing the ionosphere‐thermosphere (IT) still remains elusive. We conduct controlled numerical experiments with the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM). Coulomb collisional heat flux derived with the Comprehensive Inner Magnetosphere Ionosphere (CIMI) model and empirical subauroral polarization streams (SAPS) are implemented in TIEGCM. The heat flux causes electron temperature enhancement, electron density depletion, and consequently SAR arcs formed in the dusk‐to‐midnight subauroral ionosphere region. SAPS cause more substantial plasma and neutral heating and plasma density variations in a broader region. The maximum enhancement of subauroral red line emission rate is comparable to that caused by the heat flux. However, the visibility of SAR arcs also depends on the relative enhancement to the background brightness.

A multitracer analysis for the eBOSS galaxy sample based on the effective field theory of large-scale structure

ABSTRACT We perform a multitracer full-shape analysis in Fourier space based on the effective field theory of large-scale structure (EFTofLSS) using the complete Sloan Digital Sky Survey IV (SDSS-IV) extended Baryon Oscillation Spectroscopic Survey (eBOSS) DR16 luminous red galaxy (LRG) and emission line galaxy (ELG) samples. We study in detail the impact of the volume projection effect and different prior choices when doing the full-shape analysis based on the EFTofLSS model. We show that adopting a combination of Jeffreys prior and Gaussian prior can mitigate the volume effect and avoid exploring unphysical regions in the parameter space at the same time, which is crucial when jointly analysing the eBOSS LRG and ELG samples. We validate our pipeline using 1000 eBOSS EZmocks. By performing a multitracer analysis on mocks with comparable footprints, we find that cosmological constraints can be improved by $\sim 10-35~{{\ \rm per\ cent}}$ depending on whether we assume zero stochastic terms in the cross power spectrum, which breaks the degeneracy and boosts the constraints on the standard deviation of matter density fluctuation σ8. Combining with the Big Bang Nucleosynthesis (BBN) prior and fixing the spectral tilt ns to Planck value, our multitracer full-shape analysis measures H0 = 70.0 ± 2.3 km s−1Mpc−1, $\Omega _m=0.317^{+0.017}_{-0.021}$, $\sigma _8=0.787_{-0.062}^{+0.055}$, and $S_8=0.809_{-0.078}^{+0.064}$, consistent with the Planck 2018 results. In particular, the constraint on σ8 is improved beyond that obtained from the single tracer analysis by 18 per cent, or by 27 per cent when assuming zero stochastic terms in the cross power spectrum.

Cosmological constraints on early dark energy from the full shape analysis of eBOSS DR16

ABSTRACT We evaluate the effectiveness of early dark energy (EDE) in addressing the Hubble tension using the luminous red galaxy (LRG), quasar (QSO), and emission line galaxy (ELG) samples from the completed eBOSS survey. We perform cosmological parameter measurements based on full shape analysis of the power spectrum employing the effective field theory of large-scale structure (EFTofLSS). EDE is known to strongly suffer from volume projection effects, complicating cosmological constraints’ interpretation. To quantify the volume projection effects within an EDE full shape analysis, we explore the impact of different prior choices on the nuisance parameters of EFTofLSS through an extensive mock study. We compare classical Gaussian priors to the non-informative Jeffreys prior, known to mitigate volume projection effects in ΛCDM. Our full shape analysis combines eBOSS and BOSS data with Planck, external Baryon Acoustic Oscillation (BAO), PantheonPlus, and SH0ES supernova data. EDE reduces the tension from 5.2σ to 3σ compared to ΛCDM, yielding $H_0=71.73_{-0.86}^{+0.82}$ km s−1 Mpc−1 with $f_\mathrm{EDE} = 0.1179_{-0.022}^{+0.025}$ (Gaussian priors) and $H_0=72.03_{-0.87}^{+0.82}$ km s−1 Mpc−1 with $f_\mathrm{EDE} = 0.1399_{-0.022}^{+0.023}$ (Jeffreys prior). Although the Hubble tension is mitigated compared to ΛCDM, the inclusion of eBOSS data amplifies the tension within EDE from 2σ to 3σ, in contrast to the full shape analysis of BOSS data with Planck, external BAO, PantheonPlus, and SH0ES. This highlights the significance of incorporating additional large-scale structure data in discussions concerning models aiming to resolve the Hubble tension.

Lower Atmospheric Sources of Observed Thermosphere Medium Scale Traveling Atmospheric Disturbances Over Alaska During the 2012–2013 Winter Months

AbstractThis paper investigates the lower‐to‐upper atmosphere coupling at high latitudes (>60°N) during the northern winter months of 2012–2013 years, which includes a period of major Sudden “Stratospheric” Warming (SSW). We perform statistical analysis of thermosphere wind disturbances with periods of 30–70 min, known as the medium scale traveling atmospheric disturbances (MSTADs) in atomic oxygen green line (557.7 nm) near ∼120 km and red line (630.0 nm) emissions near ∼250 km observed from Scanning Doppler Imagers (SDIs) over Alaska. The SDI MSTADs observations (60°–75°N) are interpreted in conjunction with the previous daytime medium‐scale traveling ionospheric disturbance (MSTID) observations by SuperDARN midlatitudes (35°–65°N) radars in the F‐region ionosphere and western hemisphere, which confirm findings from the SDI instruments. Increases in MSTAD activity from SDIs show correlations with the increasing meridional planetary wave (PW) amplitudes in the stratosphere derived from MERRA2 winds. Furthermore, a detailed study of the lower atmospheric conditions from MERRA2 winds indicates that the lower atmospheric sources of MSTADs are likely due to the stratospheric generated Gravity Waves (GWs) and not orographic GWs. Favorable stratospheric propagation conditions and polar vortex disturbances resulting from the increased PW activity in the stratospheric region both appear to contribute to increased MSTAD activity in the thermosphere. Additionally, the results show that the MSTID activity from SuperDARN HF radars at mid latitudes during the January 2013 SSW is lower than the MSTAD activity in SDI winds at high latitudes.

Substrate temperature dependence of structure and optical properties of ZnTiO3:Er3+/Yb3+ thin films synthesized by pulsed laser deposition

ZnTiO3:Er3+,Yb3+ thin film phosphors were successfully deposited by pulsed laser deposition (PLD) at different substrate temperatures. The distribution of the ions in the films was investigated and the chemical analysis showed that the doping ions were homogeneously distributed in the thin films. The optical response of the phosphors revealed that the reflectance percentages of the ZnTiO3:Er3+,Yb3+ vary with the silicon substrate temperature due to the differences in the thickness and morphological roughness of the thin films. Under 980 nm diode laser excitation, the ZnTiO3:Er3+,Yb3+ film phosphors displayed up-conversion emission from the Er3+ electronic transitions, with violet, blue, green, and red emission lines at 410, 480, 525, 545 and 660 nm from 2H9/2 → 4I15/2, 4F7/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. The up-conversion emission was enhanced by increasing the silico (Si) substrate temperature during the deposition. Based on the photoluminescence properties and decay lifetime analysis, the energy level diagram was established and the up-conversion energy-transfer mechanism was discussed in detail.

Do the Throat Auroras Create Polar Cap Patches?

AbstractThroat auroras and polar cap patches are common phenomena in the polar ionosphere resulting from magnetosphere‐ionosphere coupling. A campaign was organized, with all‐sky imagers at Yellow River Station, the European Incoherent Scatter Svalbard Radar, and coordinated low‐altitude spacecraft observations. During periods of radial interplanetary magnetic field (IMF), observations showed that, as poleward moving throat auroras faded around the polar cap boundary, they linked to poleward moving ionization patches. The throat auroras were produced by soft‐electron precipitation associated with dayside magnetic reconnection. The red line emission intensity of throat auroras was correlated with dayside reconnection events. Dense plasma from lower latitudes was transported poleward via enhanced convection in the throat auroras to form patches. This is a potentially new formation mechanism for patches associated with throat auroras and magnetic reconnection for radial IMF. Moreover, the patches move anti‐sunward due to the E × B drift.

New Insight Into the Transition From a SAR Arc to STEVE

AbstractIn this study, we present an analysis of the spectral transition of a Stable Auroral Red (SAR) arc to Strong Thermal Emission Velocity Enhancement (STEVE) emission observed by the Transition Region Explorer (TREx) Spectrograph on the night of 10 April 2022, recorded overhead in Lucky Lake, Saskatchewan. On this night, we see an unusually bright (∼2 kR) SAR arc with enhanced ionospheric flow channels in the conjugate southern hemisphere. Over a short time, on the order of minutes, we observe the spectra change from the typical SAR arc pure redline (630 and 636 nm) emission to the air glow continuum, a broadband enhancement across all wavelengths, characteristic of STEVE. We propose the presence of threshold conditions required for the SAR arc to evolve into STEVE. In addition, we present parameters such as transition times, luminosities, and arc motion to be applied to ionospheric models.

Photoluminescence spectroscopy of Cr3+ in β-Ga2O3 and (Al0.1Ga0.9)2O3

Alloying β-Ga2O3 with Al2O3 to create (AlxGa1−x)2O3 enables ultra-wide bandgap materials suitable for applications deep into ultraviolet. In this work, photoluminescence (PL) spectra of Cr3+ were investigated in monoclinic single crystal β-Ga2O3, and 10 mol. % Al2O3 alloyed with β-Ga2O3, denoted β-(Al0.1Ga0.9)2O3 or AGO. Temperature-dependent PL properties were studied for Cr3+ in AGO and β-Ga2O3 from 295 to 16 K. For both materials at room temperature, the red-line emission doublet R1 and R2 occurs at 696 nm (1.78 eV) and 690 nm (1.80 eV), respectively, along with a broad emission band at 709 nm (1.75 eV). The linewidths for AGO are larger for all temperatures due to alloy broadening. For both materials, the R-lines blue-shift with decreasing temperature. The (lowest energy) R1 line is dominant at low temperatures due to the thermal population of the levels. For temperatures above ∼50 K, however, the ratio of R2 to R1 peak areas is dominated by nonradiative combination.

Photoluminescence study of rare earth ions doped Sr2CeO4 phosphor prepared via conventional solid-state reaction method

The lanthanide ions either in their divalent or trivalent charge state form a very important class of luminescence activators in phosphors and single crystals. Doping these lanthanide ions in different host lattices are widely utilized in many areas for example the 5d-4f emission of Ce3+ used in scintillators for γ-ray detection, cathode ray tubes and electroluminescence phosphors. The photon cascade emission from 4f2 levels of Pr3+ used for developing high quantum efficiency phosphors excited by means of a Xe discharge in the vacuum-UV. The narrow line 4f3 transition in Nd3+ is used in laser crystals. The Sm3+ emission used as an electron trap and in information storage properties like optical memory applications, X-ray imaging phosphor applications. The famous 5D0-7Fj 4f6 redline emission of Eu3+ and the blue to red 5d-4f emission of Eu2+ are used in display and lighting phosphors. The 4f8 line emission of Tb3+ is used in tricolor tube lighting. The Dy3+ emission plays an important role in the persistent luminescence phosphors. Er3+, Tm3+ used to investigate for possible photon cascade emission phosphor applications. This is brief and still incomplete summary illustrates the diversity of applications involving the luminescence of lanthanide ions.

Exploring Altitudinal Resolution of Twilight Airglow Red Lines Using Twilight Photometer

AbstractTwilight Photometer observations were carried out at low latitude station Kolhapur (16039’42.2”N, 74014’20.8”E) India, during the period 1 January 2009 to 31 December 2011 to yield a reasonable qualitative picture of the day‐to‐day variability of the vertical distribution of the atmospheric aerosols from about 6 km to a maximum of 350 km. In this study, one attempt was made to observe twilight airglow red lines having wavelengths in between 6100 Å and 7100 Å using the vertical profiles of aerosols. The rate of change of red light due to the twilight airglow shows narrow peaks with ∼600%–1000% rise in intensity than due to aerosol twilight glow. Our observations provides information about ionized Nitrogen (N2) emissions at 6482.05 Å, 6610.56 Å and 6482.70 Å, oxygen red emission lines of 6300 Å and 6364 Å, emission caused by formation of a molecule of nitric oxide (NO), metallic emissions of sodium four red lines between 6500 and 6700 Angstroms and lithium near 6708 Å, hydroxyl (OH) emission at 6329 Å and red sprites emissions (at altitudes 50–90 km). The principal aspiration of this study is to highlight the conspicuous capability of Semiautomatic twilight photometer to study the twilight airglow emission lines. This is the first attempt in India to obtain the twilight airglow data using Twilight photometer. Twilight Photometer, although currently seldom used, is still a very effective and the most appropriate ground based passive remote sensing tool for long‐term monitoring of different atmospheric components in a wide range of altitude for day‐to‐day basis. It is an efficient system having a simple and inexpensive underlying principle of operations, yet exhibits extremely accurate and precise usage and can be operated by even a person of average skill. However, it can be seen that the resultant data was consistent with nearest peer technologies, such as LIDARs, Balloon‐Borne instruments, rocket measurements, satellite observations etc.

Temperature dependence of red luminescence in pure β-Ga2O3: An estimation of electron-phonon interaction

Electron-Phonon (e-ph) interactions have been studied from temperature dependent photoluminescence (PL) of red emission line originating from Cr3+ ions unintentionally present in pure β-Ga2O3 powder. Excitonic recombination is determined to be the nature of observed PL at low temperatures for both R1 and R2 lines. On the basis of mean phonon temperature, obtained from the temperature dependence of PL peak energy and line width of R1 and R2 lines, it is found that the low frequency phonon modes belonging to translation and liberation of GaO4 tetrahedrons chain and medium frequency phonon modes belonging to deformation of GaO6 octahedrons and GaO4 tetrahedrons mainly interact with the carriers for R1 and R2 lines respectively. A carrier transfer from R1 line to R2 line with an increase in the temperature has been noted at low temperature region (40 K–150 K). Our results are helpful in understanding the physical processes behind the e-ph interactions occurring in β-Ga2O3.

Polar Cap Boundary Identification Using Redline Optical Data and DMSP Satellite Particle Data

AbstractThe location of the polar cap boundary is typically determined by using low‐orbit satellite measurements in which the boundary is identified by its unique signature of a sharp decrease in energy and particle flux poleward of the auroral oval. In principle, this decrease in precipitating particles should appear as a concomitant sharp change in auroral luminosity. Based on a few events, Blanchard et al. (1995, https://doi.org/10.1029/94JA02631) suggested that a dramatic gradient in redline aurora may also be an indicator of the polar cap boundary. In recent years, advances in capabilities and the deployment of ground‐based all‐sky imagers have ushered in a new era of auroral measurements. Auroral imaging has moved well beyond the capabilities of the instrumentation in the previous study in terms of both spatial and temporal resolution. We now have access to decades of optical data from arrays spanning a huge spatial range, enabling a fresh examination of the relationship between redline aurora, particle precipitation, and the polar cap open closed boundary. In this study, we use data from the Defense Meteorological Satellite Program satellites in conjunction with the University of Calgary's Redline Emission Geospace Observatory (630.0 nm) data to assess the viability of automated detection of the 2‐dimensional polar cap boundary. Our results exhibit good agreement between the optical and particle polar cap boundary and suggest that a luminosity in redline emission could serve as a reasonable proxy for the location of the electron poleward boundary, while providing both high temporal and spatial resolution maps of the open‐closed boundary.

Illustrating galaxy–halo connection in the DESI era with illustrisTNG

ABSTRACT We employ the hydrodynamical simulation illustrisTNG to inform the galaxy–halo connection of the Luminous Red Galaxy (LRG) and Emission Line Galaxy (ELG) samples of the Dark Energy Spectroscopic Instrument (DESI) survey at redshift z ∼ 0.8. Specifically, we model the galaxy colours of illustrisTNG and apply sliding DESI colour–magnitude cuts, matching the DESI target densities. We study the halo occupation distribution (HOD) model of the selected samples by matching them to their corresponding dark matter haloes in the illustrisTNG dark matter run. We find the HOD of both the LRG and ELG samples to be consistent with their respective baseline models, but also we find important deviations from common assumptions about the satellite distribution, velocity bias, and galaxy secondary biases. We identify strong evidence for concentration-based and environment-based occupational variance in both samples, an effect known as ‘galaxy assembly bias’. The central and satellite galaxies have distinct dependencies on secondary halo properties, showing that centrals and satellites have distinct evolutionary trajectories and should be modelled separately. These results serve to inform the necessary complexities in modelling galaxy–halo connection for DESI analyses and also prepare for building high-fidelity mock galaxies. Finally, we present a shuffling-based clustering analysis that reveals a 10–15 ${{\ \rm per\ cent}}$ excess in the LRG clustering of modest statistical significance due to secondary galaxy biases. We also find a similar excess signature for the ELGs, but with much lower statistical significance. When a larger hydrodynamical simulation volume becomes available, we expect our analysis pipeline to pinpoint the exact sources of such excess clustering signatures.

Investigation of thermoluminescence and photoluminescence properties of Tb3+, Eu3+, and Dy3+ doped NaYF4 phosphors for dosimetric applications.

Hexagonal phase sodium yttrium fluoride activated with lanthanide ions; Tb3+, Eu3+ and Dy3+ doped NaYF4 phosphors were synthesized using a simplistic hydrothermal method. The photoluminescence studies demonstrated green, red and blue emission lines corresponding to 5D4 → 7FJ (J = 6, 5, 4, 3), 5D0 → 7FJ (J = 1, 2 and 4) and 4F9/2 to 6HJ (J = 15/2 and 13/2) transitions, which are characteristic of Tb3+, Eu3+ and Dy3+ ions, respectively. The as-synthesized samples were subjected to annealing at varying temperatures from 500 °C to 800 °C primarily for the optimization of the thermoluminescence glow curve. Meanwhile, we studied the influence of thermal annealing treatment on the crystal phase, morphological features, and photoluminescence properties of the phosphors. The spherical-like morphology of NaYF4:Tb3+ phosphor changed to micro block-like structures and the hexagonal phase of NaYF4 transforms into a cubic phase at a higher annealing temperature of ∼800 °C. The photoluminescence emission intensity also varied at different annealing temperatures. The systematic study using different dopants and annealing temperatures was carried out to accomplish efficient thermoluminescence (TL) properties. The most suitable TL dosimetric glow peak was attained for NaYF4:0.5%Tb3+ phosphor, which was annealed at a temperature of 800 °C, located at 194 °C. The NaYF4:Tb3+ phosphor exhibited TL response fairly linear in the dose range from 1 kGy to 25 kGy of gamma radiation. The phosphor showed TL response at higher doses, which stipulates that the NaYF4:Tb3+ is reasonably well suitable for high dose measurements and respective applications. The phosphor exhibited negligible fading and good reproducibility features. Trap-level analysis and experimental determination of activation energy were performed using the Tm-Tstop technique and initial rise method (IRM). The trapping parameters of the TL glow curve, such as activation energy (E), order of kinetics (b), and frequency factor (s) were estimated by Chen's glow peak shape (PS) method and glow curve deconvolution (GCD) method. The trapping parameters obtained using the IRM, PS and GCD methods are in good accordance with each other. Henceforth, along with efficient photoluminescence properties, the NaYF4:Tb3+ phosphor exhibited favorable thermoluminescence dosimetric properties. Consequently, this study provides new opportunities for utilizing these phosphors in the area of radiation dosimetry applications such as environmental and food monitoring, space dosimetry etc.

A novel Eu-dependent G-La2Si2O7 single matrix phosphor for white light-emitting diodes

A novel G-La2Si2O7: Eu phosphor has been synthesized through SiC-reduction assisted with sol-gel method. Divalent Eu2+ and trivalent Eu3+ luminescent centers coexist in G-La2Si2O7: Eu lattice. Furthermore, two types of Eu2+ luminescent centers exist in G-La2Si2O7: Eu lattice, labeled as Eu1 and Eu2, arising from two La3+ crystallographic sites in G-La2Si2O7 host. Eu1 represents blue band emission while Eu2 shows green-yellow emission. Eu2+ selective occupation introduces Eu2+ large-scale blue-yellow regulation. Eu3+ shows typical red sharp line emission mainly located at 593 nm and 611 nm assigned to 5D0→7FJ (J = 1, 2) transitions. The luminescence process in G-La2Si2O7: Eu is discussed in details. Energy transfer processes from Eu3+ to Eu1 and Eu2, Eu1 to Eu2 occurs in G-La2Si2O7: Eu lattice. The influence of Eu dopant concentration is explored. As Eu increases, the dominant emission changes from Eu2+ to Eu3+. The coexistence of Eu1, Eu2 and Eu3+ brings G-La2Si2O7: Eu blue to red regulation. Fixing Eu doping at 0.5%, G-La1.99Si2O7: 0.01Eu sample shows a single-phased white light-emitting phosphor. At ultraviolet light 254 nm excitation, the emission spectrum approximate to full spectrum with a high rendering index of Ra = 91 is obtained using La1.99Si2O7: 0.01Eu sample at 254 nm excitation. Besides, G-La2Si2O7: Eu represents a good fluorescent thermal stability with luminous intensity keeping 80% (160 °C) of that at room temperature (30 °C), indicating G-La2Si2O7: Eu is a great potential single-matrix candidate in nUV-chip WLEDs.

X-ray, Hirshfeld surfaces analyses, DSC-TGA thermal stability, infrared, and optical properties studies of phenylammonium tetrachlorozincate hydrate (C6H5NH3)2ZnCl4.H2O

This paper reports the synthesis, crystal structure reinvestigation at 296 ​K, Hirshfeld surfaces, DSC, TG-dTG, Infrared, and UV studies of (C6H5NH3)2ZnCl4.H2O, which crystalized in the triclinic space group P-1 [Z ​= ​2, a ​= ​7.575(3) Å, b ​= ​9.894(3) Å, c ​= ​13.101(4) Å, α ​= ​95.903(13)°, β ​= ​102.408(14)° and γ ​= ​111.659(13)°]. The crystal structure consists of two cations C6H5NH3+ linked to a distorted ZnCl42− tetrahedron anion, together linked to the water molecule via hydrogen bonds of N-H⋯Cl, N-H⋯O and O-HW···Cl types. The ZnCl42− tetrahedra and H2O molecules form an infinite two-dimensional layer parallel to (0 0 2) plan between the organic sheets. The powder and single-crystal X-ray analyses confirm the pure phase of the synthetized compound. The Hirshfeld surfaces and fingerprint plots, used to analyse quantitatively the interactions in the crystal structure, showed that Cl⋯H/H⋯Cl contacts due to O-H⋯Cl and N-H⋯Cl hydrogen bonding are the major contributor in the total crystal packing surface of (C6H5NH3)2ZnCl4.H2O. The DSC-TGA analyses showed that the compound dehydration made at around 80 ​°C, gives an anhydrous compound thermally stable between 80 ​°C and 120 ​°C. The anhydrous compound decomposition process is predicted, and confirmed by Infrared spectra at various temperatures. The observed bands are assigned and discussed based on the theoretical analyses; the non-fundamental bands resulted in the formation of hydrogen bonding are assigned. The photoluminescence spectra investigated at room temperature showed a red emission line at 2.60 ​eV, which may be associated with radiative recombination of exciton confined within the ZnCl42−. This suggests potential applications for this compound as UV detection and optical materials.

Effect of different type of dopants on the enhancement of KCl single crystal optical properties

As the most attractive phosphors, the enhancement of the optical properties of single crystalline alkali halides such as KCl using different types of dopants was approached. Pure and doped KCl single crystals were grown using Czochralski method. Different activators such as Ag, In, Mn, and Sn ions were employed to enhance the optical properties of grown KCl single crystals. The structure of the single crystalline samples was investigated through X-ray diffraction (XRD). The optical properties of the samples were studied by employing UV–vis spectroscopy, photoluminescence (PL) analysis and ion beam-induced luminescence (IBIL), to confirm the incorporation of dopants into the host lattice. In the PL spectra of the samples, two UV and near UV emission lines and one red emission line were detected in the PL spectrum of the pure sample at 357 nm, 420 nm and 697 nm respectively that have not been reported before. Dopants led to the change in the intensity and position of the peaks. The peaks at 420 nm and 697 nm in the doped samples were shifted towards shorter wavelengths and a 500 nm emission was emerged due to impurities. The IBIL analysis proposed the violet color center for the Sn and Mn doped samples. These peaks turn the KCl single crystals into attractive phosphors.