Photoluminescence Excitation Spectra Research Articles

Multiwavelength Excitation in Ho3+-Doped All-Inorganic Double Perovskites Achieved by Codoping Mn2+ for Warm-White LEDs and Plant Growth.

Doping lanthanide ions is an efficient method to modify the optical properties of lead-free double-perovskite halides. However, most lanthanide-doped double perovskites show a low luminescence efficiency and require a high excitation energy. Here, we have successfully prepared a series of Ho3+-doped Cs2NaBiCl6 microcrystals through a simple hydrothermal method and obtained strong characteristic emissions of Ho3+ at 492 and 657 nm under low-energy excitation (449 nm). After codoping Mn2+, apart from the characteristic emissions from Ho3+ under 450 nm wavelength excitation, the orangish-red luminescence consisting of the emission band centered at 591 nm from Mn2+ and a sharp emission peak at 657 nm from Ho3+ is obtained under 355 nm UV light excitation. Photoluminescence (PL) emission and excitation spectra, along with the PL decay curves, confirm the existence of an energy-transfer channel from Cs2NaBiCl6 to Mn2+ and then from Mn2+ to Ho3+. The enhanced absorption efficiency (10.5 → 70.7%) suggests that the codoping of Mn2+ overcomes the low absorption efficiency caused by f-f forbidden transitions of Ho3+. Finally, the diverse luminescent performance within the Cs2NaBiCl6:Ho3+, Mn2+ phosphor is realized by altering the excitation wavelength, thereby enabling its application in warm-white-light-emitting diodes and plant growth in this work.

Robust Free Excitons in CH3NH3PbI3 Halide Perovskite Revealed by Four‐Wave Mixing

AbstractDirect bandgap semiconductors possess a unique attribute: the presence of a free exciton state with a high total oscillator strength. This property makes them highly promising for applications in ultrafast optical signal processing and optical computing. One such protocol for optical computing is based on four‐wave mixing (FWM). In this study, the nonlinear optical effect in polycrystalline thin films of halide perovskite MAPbI3 (MA+ = CH3NH) at low temperatures is demonstrated. Through analyzing the spectroscopy of the FWM signal, studying the photoluminescence excitation spectra, and comparing the findings with results from MAPbI3 single crystals, it has been discovered that the strongest nonlinear response is observed at the free exciton resonance and in the region of shallow defect states. Surprisingly, the presence of FWM in cross‐linear excitation geometry has been observed, indicating potential involvement of other nonlinear or many‐body effects. The observations of FWM with free excitons even in highly defective MAPbI3 thin films demonstrate the robustness of the exciton resonance and highlight the practical prospects for utilizing this material in optical computing.

Luminescence of silver, thulium and ytterbium doped oxyfluoride glasses

Abstract Silver and lanthanide (Tm3+, Yb3+) doped oxyfluoride glasses have been prepared by melt-quenching method. The absorption of the glasses was measured in the range from 350 to 550 nm revealing the absorption edges of Ag nanoclusters and Tm3+ transition. The photoluminescence spectra of the glasses were detected in the range from 400 to 1100 nm under excitation in the range from 300 to 500 nm. The photoluminescence excitation spectra showed that Ag nanoclusters and Tm3+ ions can effectively harvest energy in UV-range and convert to visible and infrared (through emission by Yb3+ ions) ranges making the glasses perspective as white light emitters and solar spectrum downconverters.

A Bifunctional Luminescent Whitening and Sensing Material Based on Photoluminescence and Mechanoluminescence.

A bifunctional luminescent whitening and luminescent sensing composite material, BaMgAl12O17:Eu2+/polydimethylsiloxane (BAM/PDMS), that utilizes natural sunlight and mechanical energy is presented. By increasing the Eu2+ content, the photoluminescence (PL) excitation spectrum of the material shows a maximum redshift of 23 nm due to 5d level splitting of Eu2+, resulting in more spectral overlap with sunlight and an excellent PL whitening effect. Meanwhile, the self-recoverable mechanoluminescence (ML) of the material can be easily excited under mechanical stimuli due to contact electrification, exhibiting a unique stress sensing effect. Based on the unique features of PL whitening and ML sensing, the material is applied to model cars through a spray process, and the results demonstrate that the bifunctional BAM/PDMS material shows promising applications in automobile decoration.

Progress towards blue emitting MgO-ZnO-Ga2O3 nanocomposites synthesized by bio mediated route

MgO-ZnO-Ga2O3 nanocomposites are synthesized by solution combustion method using Aloe Vera gel as a reducing agent to increase the efficiency of blue emission. The appearance of Bragg reflections corresponding to MgO, ZnO and Ga2O3 clearly indicates the formation of nanocomposites. The surface morphology consists irregular shape and sized NPs. The Energy dispersive X-ray analysis confirms the purity of the sample. The band energy gap was tuned to 3.1 eV. The Photoluminescence excitation and emission spectra was discussed and compared it with emission spectra of individual oxides as well as with other reported blue emitted nanophosphors. Further, the chromaticity coordinates and Color correlated temperature coordinates clearly confirms their warm blue emission. Further, the powder dusting method was employed to collect the latent fingerprints on the pores and non-pores surfaces. The synthesized MgO-ZnO-Ga2O3 nanocomposites exhibits well-resolved ridge patterns that can be used to identify latent finger prints with clarity. From all these results, the present synthesized MgO-ZnO-Ga2O3 nanocomposite might find an application in display technology as a blue nanophosphor material and for latent finger print detection in crime investigation.

Phase composition and luminescent properties of cesium lead bromide perovskite nanopowders

Halide perovskite nanopowders were synthesized by ligand-assisted re-precipitation technique with different volume ratios of mixture solution to antisolvent (toluene). It was found that with an increase in the proportion of toluene, the phase formed as a result of recrystallization changes predominantly from Cs4PbBr6 to the CsPbBr3, while less stable CsPb2Br5 phase was also discovered. The change in the phase composition of powders obtained with different volume ratios of mixture solution to toluene is explained by the salting out effect of slightly soluble compounds. The phase composition had a correlation with the crystal size distribution, as well as with the photoluminescence quantum yield. Optical properties, including absorption spectra, photoluminescence excitation and luminescence spectra were investigated. Nanopowders obtained with a ratio of the mixture of solution to toluene of about 1:0.9 had the maximum quantum efficiency. The following was associated with the formation of low-dimensional CsPbBr3 “slabbed” crystals sticked on rhombohedral Cs4PbBr6 crystals. The composite film based on nanocrystals and thermoplastic polyurethane was made by hot pressing, the potential of its use as a phosphor coating for an ultraviolet LED was shown.

Response of InGaN/GaN multiple quantum well structure to UV-C and vacuum UV optical excitation

We report on the behavior of InGaN/GaN multiple quantum well structure during excitation in UV-C and vacuum UV spectral region. Photoluminescence excitation spectra show peaks with positions different to the peaks in absorption spectra. The very high absorption coefficient in order of 107 cm−1 at energies above 6.9 eV causes the excitation in the surface region which enhances the non-radiative surface recombination. The mechanism explains the differences between absorption and excitation spectra measured in a studied range of energies between 5.8 and 40 eV.

Structural and optical properties of Zn2.95Ga2−xSnO8:xCr3+: An excellent X-ray charging-based persistent phosphor

This study investigates structural and luminescence properties of Cr3+ doped Zn2.95Ga2SnO8 phosphor. XRD analysis determines the phase purity and lattice parameters, while SEM and TEM analysis were utilized to study the particle size and surface morphology of the sample. UV–visible absorption and PL excitation spectra provided information on the excitation bands and the band-gap of both the undoped and Cr3+ doped Zn2.95Ga2SnO8. The optical band-gap of the material decreases upon doping with Cr3+ ions. Analysis of the Racah parameter and Tanabe Sugano diagram highlights a robust crystal field within Cr3+: Zn2.95Ga2SnO8, causing 2Eg level to become the lowest excited state with sharp emission at 699 nm. Concentration quenching at higher Cr3+ concentrations (> 0.6 mol%) is primarily attributed to the quadrupole-quadrupole interactions. Two distinct traps with trap depths at 0.51 eV and 0.73 eV were identified by using thermoluminescence measurement. The material gives persistent luminescence with a decay time of more than 30 min when charged with blue light (420 nm) and an excellent decay time of more than 16 h when charged with X-rays. Notably, this is the first report on X-ray charging-based persistent luminescence in Zn2.95Ga2SnO8. The outstanding persistent luminescence makes this material highly promising for various applications.

Optical properties and Judd-Ofelt analysis of Dy3+ doped CoAl2O4 nanocrystals.

CoAl2O4:xDy3+ nanocrystals (x = 0, 0.1, 0.5, 1.0, and 3.0 mol%) with spinel structures were prepared using the co-precipitation method. The crystal structure, optical properties, and presence of elements were respectively analyzed using X-ray diffraction, photoluminescence excitation, photoluminescence spectra, luminescence lifetime, and X-ray photoelectron spectroscopy. The influence of temperature on material fabrication was studied using differential scanning calorimetry and thermogravimetric techniques. The color characteristics of Dy3+ luminescence in the CoAl2O4 host were evaluated using CIE chromaticity coordinates and correlated color temperature. For the first time, the electronic dipole transitions in the photoluminescence excitation spectra were used to calculate the optical parameters of Dy3+ ions in the CoAl2O4 host using Judd-Ofelt theory. The Inokuti-Hirayama model was used to explain the energy transfer process between Dy3+ ions, the main interaction mechanism, and energy transfer parameters for the luminescence of Dy3+ ions.

NaGdF4:Dy3+ nanocrystals: new insights into optical properties and energy transfer processes.

NaGdF4:Dy3+ nanocrystals (NCs) have been synthesized using a precipitation technique. The structural characteristics and morphology of the materials were analyzed using X-ray diffraction patterns and scanning electron microscopy images, respectively. The photoluminescence excitation spectra, emission spectra and decay curves of all samples were recorded at room temperature. The color feature of Dy3+ luminescence was estimated using CIE chromaticity coordinates and the correlated color temperature. The radiative properties of the Dy3+:4F9/2 level in the material were analyzed within the framework of JO theory. In NaGdF4:Dy3+ NCs, the energy transfer from Gd3+ to Dy3+ causes an enhancement in the luminescence of the Dy3+ ions. The rate of the processes taking part in the depopulation of Gd3+ ions was estimated. The energy transfer between Dy3+ ions leads to the luminescence quenching of NaGdF4:Dy3+. In this process, the dipole-dipole interaction, which is found by using the Inokuti-Hirayama model, is the dominant mechanism. The characteristic parameters of the energy transfer processes between Dy3+ ions have also been calculated in detail.

Structural and spectroscopic studies of lithium tetraborate glass co-doped with Sm and Cu.

The local structure and spectroscopic properties of Cu-Sm co-doped Li2B4O7 glass have been studied using XRD, EPR, UV-Vis-NIR absorption and luminescence methods and compared with the corresponding results for Sm-doped and Cu-doped Li2B4O7 glasses. The EPR spectrum reveals an axially-symmetric signal with a characteristic hyperfine structure belonging to Cu2+ ions. The Cu2+/Cutotal ratio was determined. The optical absorption spectrum shows a broad, intense band attributed to Cu2+ ions and several weaker narrow bands attributed to Sm3+ ions. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra as well as PL decay kinetics of Sm3+ and Cu+ ions were registered, analyzed, and discussed. The PL spectra show a broad band assigned to the 3d94s1 → 3d10 transition of Cu+ ions and four narrow bands assigned to the 4G5/2 → 6HJ (J = 5/2-11/2) transitions of Sm3+ ions. The observed changes in PL intensity, shortening of the Sm3+ lifetime and prolongation of the Cu+ lifetime were explained by energy transfer from Sm3+ → Cu+ and re-absorption of the Sm3+ emission by Cu2+ ions.

Synthesis and Structural Features of Tunable Emitting Single- Phased Eu3+/ Tb3+ Co- Doped LaAlO3 Nanophosphors

In the prevailing study, single- phased color- tunable La1-x-yEuxTbyAlO3 co- doped nanocrystalline phosphors have been synthesized via the most simplistic and low cost urea- aided solution combustion synthetic route. This was done by adjusting the doping concentration of Eu3+ (x = 0.01, 0.03, 0.05, 0.07 mol) and Tb3+ (y = 0.03 mol) ions in the LaAlO3 host lattice. The X- ray powder diffraction (XRD) and Rietveld refinement analysis confirmed the formation of single- phased La0.97-xAlO3: xEu3+/ 0.03Tb3+ (x = 0.07), co- doped nanophosphor at 800°C. The synthesized nanophosphors were crystallized in cubic crystal system having Pm3̄m space group with 221 space group number. The morphological studies i.e., field emission scanning electron microscopy (FE- SEM), and transmission electron microscope (TEM) images depicted the agglomerated clusters of distinct spherical shaped particles of La0.97-xAlO3: xEu3+/ 0.03Tb3+ in nano- regime. Energy dispersive X- ray analysis (EDAX) was employed to ascertain the real elemental mapping of the fabricated phosphors. Through diffuse reflectance (DR) spectroscopy measurements, the optical band gap value for La0.92Eu0.05Tb0.03AlO3 nanocrystalline phosphor was determined to be 5.26 eV. The photoluminescent excitation (PLE) and photoluminescent emission (PL) spectra were studied in detail as a function of Eu3+ ion contents and La1-x-0.03AlO3: xEu3+/ 0.03Tb3+ (x = 0.05 mol) co- doped sample exhibits strongest emission and over the 0.05 Eu3+ ions doping concentration, the emission intensity falls as a consequence of the quenching phenomenon. The concentration quenching in directed co- doped nanophosphors was attributed to the dipole - dipole interactions. With the exploitation of photoluminescent data, Commission International de I'Eclairage 1931 (CIE) color coordinates (x, y) of co- doped samples have been calculated from the emission spectra, which revealed the color could be tuned i.e., from orange to red region in La0.97-xAlO3: xEu3+/ 0.03Tb3+ samples with divergences in the Eu3+ and other significant photometric assets viz. correlated color temperature (CCT), color purity (CP) of the synthesized La1-x-yAlO3: xEu3+, yTb3+ co- doped nanocrystalline photoluminescent materials were also determined. The studies outcomes suggested that Eu3+/ Tb3+ co- doped LaAlO3 phosphors have great potential as color- tunable luminescent material in solid- state lighting and display technologies.

Synthesis and tunable photoluminescence properties of Er3+/Eu3+ co-doped Na5La(MoO4)4 phosphors

The tunable emission characteristics of Er3+ doped and Er3+/Eu3+ co-doped Na5La(MoO4)4 phosphors prepared via high-temperature solid phase method were investigated. The microstructure of the modified phosphor was studied by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy, and its luminescence properties were analyzed by photoluminescence excitation and photoluminescence spectra. The energy transfer mechanism of Er3+ ions to Eu3+ ions was investigated by changing the concentration of Eu3+ ions to induce the spectral changes, and the photoluminescence decay lifetime was measured to validate the findings. Notably, under excitation at 380 nm, the co-doped phosphors exhibited tunable emission ranging from green to orange-red. Furthermore, Na5La(MoO4)4:0.04Er3+/0.04Eu3+ phosphor, when combined with a 380 nm chip, achieved desired warm white light emission. These promising results underscore the potential application of Na5La(MoO4)4:0.04Er3+/0.04Eu3+ phosphor in solid-state lighting.

Effect of synthesis temperature on crystal structure, optical and magnetic properties of SmCuO3-δ ceramic phosphor

Effect of synthesis temperature on crystal structure, optical and magnetic properties of SmCuO3-δ ceramic phosphor is investigated in this work. The SmCuO3-δ ceramic has been synthesized using a sol-gel method. Rietveld analysis reveals that SmCuO3-δ ceramic crystallizes into coexisting tetragonal (I4/mmm) and monoclinic (C2/c) crystal structures. The phase fraction of the tetragonal and monoclinic phases strongly depends on the synthesis temperature. The crystallite size and particle size increase with increasing calcination temperature. The X-ray photoelectron spectroscopic spectra reveal the presence of (Cu2+, Cu3+) and (Sm2+, Sm3+) ions alongwith the oxygen vacancy centres in the phosphor. The SmCuO3-δ ceramic shows multiple magnetic phase transitions. The FTIR spectra show the presence of vibrational bands due to Cu-O and Sm-O groups. The optical band gap of the SmCuO3-δ phosphor decreases with an increase in calcination temperature and crystallite size. The photoluminescence excitation spectra show the peaks at 363, 402, 505 and 542 nm at the fixed emission wavelength of 609 nm, whereas the photoluminescence emission spectra contain peaks at 465, 515 and 609 nm at the fixed excitation wavelength of 402 nm. The photoluminescence emission intensity of the sample increases with the rising calcination temperature upto 900 °C and finally, it quenches at 1000 °C. Therefore, the SmCuO3-δ ceramic phosphor may be useful for solid state lighting, LEDs and magnetic devices.

Luminescence properties of Eu3+ doped Li2SrSiO4 phosphor

The modified solid-state reaction method has been used in this work to prepare Eu3+ doped Li2SrSiO4. PL spectroscopy was used to investigate photoluminescence (PL) properties of the sample. X-ray powder diffraction study was used to confirm the crystalline nature and phase purity of the sample. The particle size of prepared material ranges from 37 to 56 nm was observed from XRD. From PLE and PL spectrum the excitation and emission spectra of photoluminescence for Eu3+ doped Li2SrSiO4 were recorded. The prepared Eu3+ doped Li2SrSiO4 phosphor might have application in solid state lighting.

Yellow Emissive CsCu2I3 Nanocrystals Induced by Mn2+ for High-Resolution X-ray Imaging.

Recently, low-dimensional copper(I)-based perovskite or derivatives have gained extensive attention in scintillator applications because of their environmental friendliness and good stabilities. However, the unsatisfactory scintillation performance and complex fabrication processes hindered their practical applications. Herein, efficient yellow emissive CsCu2I3 nanocrystals (NCs) were successfully prepared via a simple Mn2+-assisted hot-injection method. The added Mn2+ effectively induced the phase transformation from Cs3Cu2I5 to CsCu2I3, leading to the preparation of single-phase CsCu2I3 NCs with few defects and a high fluorescence performance. The as-prepared "optimal CsCu2I3 NCs" exhibited superior photoluminescence (PL) performance with a record-high PL quantum yield (PLQY) of 61.9%. The excellent fluorescence originated from the radiative recombination of strongly localized one-dimension (1D) self-trapped excitons (STEs), which was systematically investigated via the wavelength-dependent PL excitation, PL emission, and temperature-dependent PL spectra. These CsCu2I3 NCs also exhibited outstanding X-ray scintillation properties with a high light yield (32000 photons MeV-1) and an ultralow detection limit (80.2 nGyair s-1). Eventually, the CsCu2I3 NCs scintillator film achieved an ultrahigh (16.6 lp mm-1) spatial resolution in X-ray imaging. The CsCu2I3 NCs also exhibited good stabilities against X-ray irradiation, heat, and environmental storage, indicating their great application potential in flexible X-ray detection and imaging.

Luminescence and photoconversion properties of Ce-doped Ca3Sc2Si3O12 crystal

This work is dedicated to investigation of the luminescent properties of the prospective photoconversion material based on the crystal of Ce3+ doped Ca3Sc2Si3O12 (CSSG) garnet. The GSSG:Ce crystal was grown using the micro-pulling-down (μPD) method. The CSSG:Ce crystal exhibited an intensive photoluminescence (PL) emission band with two sub-bands peaked at 504 and 545 nm, corresponding to 5d-4f (2F5/2;7/2) transitions. Furthermore, we have investigated also the formation of cerium multicenters in the GSSG:Ce crystal using analyses of the structure of Ce3+ photoluminescence emission and excitation spectra under excitation of the luminescence of this crystal by synchrotron radiation. The formation of Ce3+-multicenters in CSSG:Ce garnet is caused by the local inhomogeneity of the dodecahedral sites of garnet lattice due to localization of the hetero-valent Sc3+ and Si4+ cations in the octahedral and tetrahedral positions of the garnet host. The existence of Ce3+ multicenters resulted in a significant enhancement of the Ce3+ emission band in the red range and improving the performance of conventional YAG:Ce phosphor. The next task of our work was to evaluate the possibility of application of the GSSG:Ce crystal as a light phosphor-converter (pc) for white light-emitting diodes (WLEDs). In the frame of this task, we have successfully developed a prototype of WLED by employing the CSSG:Ce crystal as a phosphor-converter (pc) with blue 450 emitting LED as well as investigated the color characteristics of this pc-WLED.

Host-sensitized colour-tunable emission and Judd-ofelt analysis for Dy3+-doped ZnGa2O4 phosphor through exciton-mediated energy transfer

Single-phase Dy3+-doped zinc gallate (ZnGa2O4) phosphors were synthesized using a conventional solid-state fabrication technique. The structural properties of the host phosphor were determined through X-ray powder diffraction (XRPD) and Rietveld refinement, revealing a cubic spinal structure with a space group of Fd3m. The reflectance properties of the host and doped samples were measured using UV–Vis spectroscopy. The obtained data were used to estimate the bandgap of all the synthesized samples, ranging from 4.18 to 3.69 eV, confirming the formation of a wide bandgap semiconductor. Morphological, compositional, and surface mapping analyses were conducted using a field emission scanning electron microscope, energy dispersive electron spectroscopy, and time-of-flight secondary ion mass spectroscopy. X-ray photoelectron spectroscopy was employed to confirm the oxidation state of the constituent elements and for an in-depth study of the crystal structure. Photoluminescence excitation and emission spectra were recorded to analyze the luminescent properties of the synthesized phosphors. It was confirmed that when using an excitation wavelength of 247 nm, all samples exhibited broad host emission with decreasing intensity. In contrast, Dy3+ emission displayed an increasing trend, confirming host sensitization in this phosphor. To analyze the radiative properties of the activator ion, theoretical analysis using the Judd-Ofelt theory was carried out. The results revealed an overlapping of orbitals between the O2− ion and Dy3+, indicating its higher-order covalent nature and the increased symmetric nature of the activator ion in the present host. This characteristic allowed for the generation of near-white light emissions. A concentration of 7 mol% of Dy3+ was observed to match well with achromatic white (0.32, 0.33) on the color chromaticity diagram. The luminous properties of this material suggest that it is a desirable candidate for use in LEDs and AC electroluminescent systems.

Effects of Na/Al ratio on phonon sideband spectra and luminescent characteristics of Eu3+ doped sodium aluminosilicate glasses

In this work, sodium aluminosilicate (NAS) glass systems were fabricated via traditional melting technique with various Na/Al ratios. Structure and surface morphology of the fabricated glasses were investigated by X-ray diffractometer, Raman spectroscopy and SEM images. Optical characteristics of the fabricated glasses were inspected by photoluminescence (PL) and photoluminescence excitation (PLE) spectra, and the observations showed that intensity of the excitation peak of Eu3+ ions in the NAS glasses at 392 nm increases while one at 463 nm decreases with the increasing of Na/Al ratio. Analysis of the phonon sideband spectra shown a change of multiphonon relative rate (Wmp/W0) of the synthesized glasses relates to Na/Al ratio. By applying the Judd-Ofelt theory, Ωλ = 2,4,6 parameters were evaluated from the PL spectra and used these parameters to estimate the radiative parameters like calculated lifetime (τcal), effective line width (Δλeff), transition probability rate (A), emission cross-section (σp) and branching ratio (βR). Decay curves were measured to investigate luminescence quantum efficiency (η) of Eu3+ emission and η gets value in the 53%–65% region. The color coordinates (x, y) and correlated color temperature (CCT) were also estimated for the synthesized NAS glasses.

Dopant-assisted stabilization of negatively charged single nitrogen-vacancy centers in phosphorus-doped diamond at low temperatures

Charge state instabilities have been a bottleneck for the implementation of solid-state spin systems and pose a major challenge to the development of spin-based quantum technologies. Here we investigate the stabilization of negatively charged nitrogen-vacancy (NV−) centers in phosphorus-doped diamond at liquid helium temperatures. Photoionization of phosphorous donors in conjunction with charge diffusion at the nanoscale enhances NV0 to NV− conversion and stabilizes the NV− charge state without the need for an additional repump laser. The phosphorus-assisted stabilization is explored and confirmed both with experiments and our theoretical model. Stable photoluminescence-excitation spectra are obtained for NV− centers created during the growth. The fluorescence is continuously recorded under resonant excitation to real-time monitor the charge state and the ionization and recombination rates are extracted from time traces. We find a linear laser power dependence of the recombination rate as opposed to the conventional quadratic dependence, which is attributed to the photo-ionization of phosphorus atoms.