Photoluminescence Decay Curves Research Articles

Brightening dark excitons in inorganic halide perovskites by local symmetry breaking

Thermally activated delayed fluorescence (TADF) phenomenon, defined as thermal activation of triplet dark-state excitons into singlet state excitons through reverse intersystem crossing (RISC), has become a prevalent principle for designing organic-based electro-/photo-luminescent molecules. However, activating dark excitons in inorganic metal halide perovskites (MHPs) still remains challenging. Herein, we report an efficient strategy of doping-induced local symmetry breaking to brighten dark excitons in inorganic halide perovskite Cs2ZrCl6, which result in a 500 % enhancement of low-temperature luminescence emission. Lattice symmetry breaking confirmed by the X-ray absorption spectroscopy measurements could disturb the local coordination environment at the Zr site. The singlet-triplet energy gap (ΔEST) fitted from temperature-dependent photoluminescence decay curves decreases from 0.087 to 0.071 eV, thus reducing up-conversion barrier of dark excitons. Theoretical calculation indicates large spatial separation of charge density favorable for enhanced TADF emission. Furthermore, a flexible X-ray scintillator screen with poly (dimethylsiloxane) as the matrix could obtain high-quality X-ray imaging with a 14 lp mm−1 resolution. This work gives insights into improving photoemission of inorganic MHPs via brightening dark excitons.

Synthesis and optical properties of highly efficient Na7Mg13La(PO4)12:Eu3+ powders with excellent thermal stability

In the pursuit of efficient red-emitting phosphors, a series of red-emitting Na7Mg13La(PO4)12:Eu3+ phosphors was prepared using a high-temperature solid-state synthesis method. The phase purity was monitored using powder X-ray diffraction (XRD). The morphological features of the synthesized samples were evaluated by taking scanning electron microscopy (SEM) images. The optical properties of the synthesized polycrystalline samples were investigated by recording room-temperature and temperature-dependent (77–500 K interval) excitation and emission spectra, and photoluminescence (PL) decay curves. The calculated TQ1/2 values were above 420 K, regardless of the Eu3+ concentration, indicating the high thermal stability of the phosphors. The optimal Eu3+ concentration was 100 %, which indicated the absence of concentration quenching in the given host. Furthermore, the quantum efficiency of fully Eu3+-substituted compound reached 100 %, which is an excellent feature for practical phosphor applications.

Luminescence properties of cerium-doped Li2O–Gd2O3 –ZrO2–P2O5 glasses for scintillator application

In this study, we developed the phosphate glass doped with CeF3 for scintillator applications. The phosphate glasses, 20Li2O−5Gd2O3–2ZrO2−(73-x) P2O5−xCeF3 were synthesized at different CeF3 concentrations by using the conventional melt-quenching technique. The density, molar volume, transmittance, photoluminescence (PL) and radioluminescence (RL) properties were investigated and quantified. The study found a positive correlation between the concentration of CeF3 with the density values and refractive index of the glass samples. The transmission spectra exhibited a red shift as the level of CeF3 increased. The emission spectra revealed a wide range of wavelengths resulting from the transition between the 5d and 4f transitions of the Ce3+ ion. The maximum intensity of emission for both PL and RL were observed at a concentration of 0.50 mol% CeF3. Moreover, the results of the emission spectra measured under Gd3+ excitation and the PL decay curves of Gd3+ in glass samples showed clearly evidence energy transfer (ET) from Gd3+ to Ce3+. The XPS spectra revealed the existence of phosphorus oxidation states. The XANES analysis revealed the existence of Ce3+ and Ce4+ in all glass samples, as evidenced by the appearance of peaks at approximately 5.728 keV for Ce3+, 5.732 keV and 5.739 keV for Ce4+. The scintillation efficiency of CeF3-doped phosphate glass with a concentration of 0.50 mol% was found to be 60.63% when compared to BGO crystal. Additionally, the decay time is extremely fast, varying from 17.52 to 25.93 ns, which is a critical attribute in the development of radiation detectors. In addition, X-ray imaging was conducted to investigate its potential efficacy in scintillator applications for X-ray imaging. The X-ray imaging investigation had a spatial resolution of 10 lp/mm with an MTF of 0.25. The results suggest that CeF3-doped phosphate glass has the potential to serve as a scintillator in X-ray imaging systems.

Realize short-wave infrared luminescence in NaScP2O7:Cr3+,Yb3+ phosphor: Spectral and energy transfer

Short-wave infrared emitting phosphors have extensive applications for spectroscopy technology. The near-infrared phosphor NaScP2O7:Cr3+ that we present in this work has a full width at half maximum (FWHM) of approximately 196 nm, which ranges from 700 to 1200 nm. To achieve efficient short-wave infrared, Yb3+ ions were co-doped. The NaScP2O7:Cr3+,Yb3+ material emitted infrared bands with peaks at 970 and 1003 nm upon excitation at450 nm. Benefitting from energy transfer (ET), the light in the 900–1200 nm from Yb3+ is effectively enhanced. Photoluminescence spectra, thermal quenching, and decay curves of Cr3+/Yb3+ single and codoped NaScP2O7 were investigated. An internal quantum yield of 29.6 % wasdemonstrated by the optimized phosphor NaScP2O7:Cr3+,Yb3+. Furthermore, The final fabrication of the short-wave infrared pc-LED was done through the combination of a blue-emitting chip and NaScP2O7:Cr3+,Yb3+ phosphor, thereby showing great promise for real implementations.

Luminescence of Yb3+ incorporated into SrTi1-xZrxO3 solid-solutions: Inquiring into the charge transfer state nature in lanthanide-doped titanates

For more than forty years, quenching of the 3P0 → 3H4 emission in favor of the 1D2 → 3H4 one in Pr3+-doped titanates has been explained by a mechanism involving a metal-to-metal charge transfer (MMCT) state, profusely designated in the literature as IVCT Pr3+/Ti4+ → Pr4+/Ti3+ state. Here, we present experimental evidence making unnecessary this mechanism and supporting theoretical results that points towards an alternative process based on a ligand-to-metal charge transfer (LMCT) O2−/Ti4+ → O−/Ti3+ state as being responsible for that quenching (Z. Barandiarán et al. J. Phys. Chem. Lett. 2017, 8, 3095). Photoluminescent spectra of Yb3+ incorporated into SrTi1-xZrxO3 solid-solutions interpreted in the framework of phenomenological models leading to vacuum referred binding energy diagrams and compared with equivalent solid solutions but doped with Pr3+, indicate that the emission of both lanthanide ions is excited through the same host state: the LMCT O2−/Ti4+ → O−/Ti3+ state. Photoluminescence spectra and decay curves performed in Pr-doped SrTiO3 as a function of the temperature suggest a thermally activated mechanism as being responsible for the quenching of the emission associated with the 3P0 → 3H4 transition.

Comparative study of luminescence in alkali‐metal‐based yttrium fluoride nanophosphor for biophotonic applications

AbstractAlkali‐metal‐based yttrium fluoride host (AY1‒xF4:xEu3+; A: Li/Na/K) nanophosphors were developed using co‐precipitation method. Phase analysis and emission spectral behavior were established for the said nanophosphors. The highest emission observed for NaYF4 doped with Eu3+ was then optimized to achieve maximum photoluminescence (PL) emission for varied dopant amount. The downconversion and upconversion PL studies revealed pure red emission under n‐ultraviolet and infrared excitations. The CIE coordinates are observed to be lie in the red hue of the CIE diagram. The PL decay curves reported to study lifetime of the emitting state and to identify quantum efficiency using Auzel's model for the said nanophosphor. Thermal stability was also evaluated from temperature‐sensitive luminescent spectra. The studies conducted on AYF4:.05Eu3+ (A: Li/Na/K) nanophosphors contemplates that NaYF4 nanophosphors doped with Eu3+ ions are best suited for biophotonic applications as the later one show relatively high emission.

Luminescent properties and dosimetric behavior of Eu-ion-doped ASO4 (A = Ca, Sr, and Ba)

We investigated the luminescence properties and dosimetric behavior of Eu-ion-doped ASO4 (A = Ca, Sr, or Ba) phosphors synthesized using the coprecipitation method. Structural analysis of the phosphors was performed using X-ray diffraction patterns, which revealed that the prepared samples exhibited a pure phase with diffraction peaks matching those of undoped orthorhombic structures. The luminescence properties of the phosphors were examined by measuring photoluminescence and photoluminescence excitation spectra. We found that both Eu2+ and Eu3+ emissions were detected for A = Ba and Ca, whereas only Eu2+ emission was observed for A = Sr. Further, time-resolved photoluminescence decay curves indicate the presence of Eu2+ and Eu3+ luminescence with different lifetimes. The optically stimulated luminescence (OSL) and thermoluminescence (TL) responses of the samples were investigated. The OSL and TL responses were found to vary linearly with the irradiation dose. This study sheds light on the potential applications of Eu-ion-doped ASO4 phosphors in radiation dosimetry and optoelectronic devices.

Spectroscopic and electrical properties of europium doped bismuth antimony fluoroborate glasses

Strong luminescence in the red spectral region is a well-known characteristic of the trivalent europium ion (Eu3+). We investigate a novel europium doped glassy substance for their use in optical devices, optoelectronics and radiation shielding. By using the traditional melt quenching technique, Bismuth antimony fluoroborate glasses are synthesized. XRD investigations support the amorphous nature of the material. Spectral measurements of absorption, photoluminescence (PL) excitation, PL emission, and PL decay curve are made in order to study the lasing properties. Judd-Ofelt (J-O) intensity parameters, from emission spectra, exhibit the trend Ω2> Ω4 furthermore used to find the radiative parameters-transition probability (AR), branching ratio (βR), radiative lifetime (τR), and stimulated emission cross-section (σse) for all the glasses. Decay curves show single exponential behavior and is used to find the quantum efficiency of the prepared glasses. The dielectric properties (dielectric constant (ɛ′), dielectric loss (ɛ″)), impedance and electrical conductivity (σac) of these glasses with variation in frequency have also been studied at the ambient temperature. The radiation shielding properties are evaluated for the photon energy range (1 keV–15 MeV). Based on the trends noticed in the radiative parameters, electrical conductivities and radiation shielding parameters, the present glasses could be found useful as optoelectronic devices, non-linear optical materials, battery anode materials and radiation shielding purposes.

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.

Seed-mediated growth synthesis and tunable narrow-band luminescence of quaternary Ag-In-Ga-S alloyed nanocrystals.

Silver-based I-III-VI-type semiconductor nanocrystals have received extensive attention due to their narrow-band luminescence properties. Herein, we demonstrated a seed-mediated growth of quaternary Ag-In-Ga-S (AIGS) nanocrystals (NCs) with narrow-band luminescence. By conducting partial cation exchange with In3+ and Ga3+ based on Ag2S NCs and controlling the Ag/In feeding ratios (0.25 to 2) of Ag-In-S seeds as well as the inventory of 1-dodecanethiol, we achieved optimized luminescence performance in the synthesized AIGS NCs, characterized by a narrow full width at half maximum of less than 40 nm. Meanwhile, narrow-band luminescent AIGS NCs exhibit a tetragonal AgGaS2 crystal structure and a gradient alloy structure, rather than a core-shell structure. Most importantly, the kinetics decay curves of time-resolved photoluminescence and the ground state bleaching in transient absorption generally agree with each other regarding the lifetime of the second decay component, which indicates that the narrow-band luminescence is due to the slow radiative recombination between trapped electrons and trapped holes located at the edge of the conduction band and the deep silver-related trap states (e.g., silver vacancy), respectively. This study provides new insights into the correlation between the narrow-band luminescence properties and the structural characteristics of AIGS NCs.

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.

Sites engineering induced adjustable emission in orange-red Ca4-xLu2xHf1-xGe3O12:Eu3+ phosphor with excellent photoluminescent property

The advancement of white light-emitting diode(WLED) performance is still limited by the scarcity of highly efficient narrow band red emitting phosphors. A series of Ca4-xLu2xHf1-xGe3O12:yEu3+(0 ≤ y ≤ 0.15) (CLHGO:Eu3+) phosphors with typical garnet structure were successfully synthesized through solid-state reaction. Based on the XRD pattern analysis and density functional theory calculation, Eu3+ ions in Ca4HfGeO12:xEu3+ can exist in the form of both EuO6 and EuO8 structures. As the concentration of Lu3+ increases, the amount of EuO6 decreases and ultimately leading to the predominant presence of Eu3+ ions in an EuO8 structure in Ca3Lu2Ge3O12:Eu3+. The special site occupation situation results in a significant spectra variation of Eu3+ that Ired/Iorange ratio changes from 2 to 0.85. Based on the measurements of photoluminescence spectra and decay curves, the energy migration between the Eu3+ ions is limited and no obvious concentration quenching appears in CLHGO:Eu3+ phosphors. The CLHGO:0.15Eu3+ samples with different Lu3+ concentration all exhibit remarkable quantum efficiency within 81.1 %–91.2 %. Moreover, their thermal quenching property is remarkably excellent, the remaining intensity at 150 °C all exceeds 85 % of that at room temperature. The comprehensive performance is better than that of commercial materials Y2O3:Eu3+. Using Ca4HfGe3O12:Eu3+ and Ca3Lu2Ge3O12:Eu3+ samples to provide red compositions, two white LEDs are obtained with a correlated color temperature of 6252K and 5468K. All the results proves the potential application value of our phosphors in WLED lighting fields.

Construction of Z-scheme NiO/BiOBr heterojunction for facilitating photocatalytic degradation of oxytetracycline and 2-mercaptobenzothiazole

Z-scheme NiO/BiOBr heterojunction was prepared by mechanical ball milling method and applied for the photodegradation removal of oxytetracycline (OTC) and 2-mercaptobenzothiazole (MBT). The Z-scheme electron transport pathway optimizes the separation of photogenerated carriers, thereby significantly increasing the generation capacity of reactive oxygen species (ROS). The photocatalytic degradation experiments demonstrate that the optimized OTC and MBT removal efficiency of NiO/BiOBr (NBOB) composites could reach 72.6% (120 min) and 97.7% (9 min), respectively. Photoluminescence (PL) spectra and PL decay curves indicate that NBOB-2 composites exhibit low photoinduced electron-hole recombination rate and accelerated electron separation efficiency. In addition, ESR spectra confirm that the Z-scheme NiO/BiOBr heterojunction can generate a larger quantity of ROS species. The possible photodegradation pathways and toxicity analysis for the OTC and MTB photodegradation intermediates are elucidated by HPLC-MS measurement and T.E.S.T. application. The manuscript provides a reference for the macro-preparation of bismuth-based photocatalysts with superior performance and high stability.

Near‐Infrared Emission of Sm2+ in Oxynitrides

AbstractNear‐infrared (NIR) luminescent materials hold promising applications in NIR spectroscopy technologies, but the NIR emitters are largely limited to some transition metals with spin‐forbidden transitions that lead to low absorption efficiency of the pumping light. Exploring novel efficient NIR emitters is thus an urgent and challenging task for developing high‐efficiency NIR luminescent materials. Here, an interesting NIR emission of Sm2+ is reported in BaAlSi5O2N7, which exhibits both a line spectrum at 682 nm and a broadband centered at 778 nm with a full‐width at half maximum (FWHM) of 141 nm. Temperature‐dependent photoluminescence spectra and decay curves evidence that the thermally assisted electrons crossover (TAEC) process contributes to the enhancement of the broadband NIR emission. The fabricated NIR phosphor‐converted light‐emitting diode (pc‐LED) shows promising potential as a NIR lighting source and proves robust thermal stability under high‐temperature aging test. The present surprising NIR emission from Sm2+ in highly stable oxynitrides opens a way to explore efficient and reliable NIR phosphors that are suitable for commercial LED chips.

Nd3+ doped oxide thermal probes based on luminescence intensity ratio within BW-II and excitation in BW-I

The Nd3+ have taken a central place in the field of nanothermometry thanks to the presence of several narrow Stark emission and is easily excited through the lasers commercially available. With the goal to boost the development of Nd3+-based nanothermometers, especially working with emissions into BW-II, the thermal response of different oxide matrices Y2O3, Y2Ge2O7, Y3Al5O12, YBO3, and Y3BO6 were evaluated considering emissions from the Nd3+ 4F3/2 → 4I11/2 transition, which falls into the BW-II. Interestingly, we observed these lines are more intense than those located in BW-I, which can enhance the signal-to-noise ratio. Therefore, the design of thermal probes emitting in BW-II showed to be an excellent strategy to provide more accurate thermal sensing as the scattering of the light by the tissues is reduced in BW-II. In light of this, we also maximized the luminescence intensity of the matrices by Nd3+ doping from 0.1 to 10 mol%. Furthermore, their structure and luminescence properties were investigated using X-ray diffraction, transmission electron microscope, diffuse reflectance spectroscopy, photoluminescence, and radiative decay curve measurements. Additionally, exploring thermal response and luminescence emission optimization in several compounds offers enriched information support to design new high-level Nd3+-based thermal probes. Among Y2O3, Y2Ge2O7, Y3Al5O12 (YAG), YBO3, and Y3BO6 matrices studied, Y2O3 is the promising matrix to conduct thermal sensing due to exhibiting the highest Sr value around 0.4 %.K−1 in which 0.5 mol% Nd3+ is the deal doping to maximize its luminescence intensity.

Luminescence features of Ho3+ , Er3+ and Tm3+ ions in red lead added non-conventional antimony oxide glass system.

In this study, a glass system based on heavy metal oxides, namely Pb3 O4 -Sb2 O3 -SiO2 , was prepared with Ho2 O3 , Er2 O3 , and Tm2 O3 as dopants. The prepared glass were characterized using X-ray diffraction (XRD) and infrared (IR) studies. The luminescence efficiencies of the three rare earth ions viz., Ho3+ , Er3+ , and Tm3+ in the glass system were investigated, specifically focusing on green (Ho3+ , Er3+ ), blue (Tm3+ ), and near-infrared (NIR) emissions. The optical absorption (OA) and photoluminescence (PL) spectra of RE mixed glass displayed strong bands in the visible and NIR regions, which were analyzed using the Judd-Ofelt (J-O) theory. The J-O coefficients (Ωλ ) were found to be in the order of Ω2 > Ω4 > Ω6 for all the three glass. Notably, the Tm3+ -doped glass exhibited the lowest Ω2 value, which was attributed to a larger degree of disorder in the glass network due to lower fractions of Sb5+ and Pb4+ ions that take part in the glass network forming. This conclusion was arrived based on the IR studies. Furthermore, the quantitative analysis of PL spectra and decay curves indicated that SbHo and SbEr glass were suitable for efficient green emission, while SbTm glass is a promising choice for blue laser emission.

Study of time-resolved photoluminescence decay curves in Al-doped ZnO and Eu-doped Cd1−xZnxS nanophosphors

Study of time-resolved photoluminescence decay curves in Al-doped ZnO and Eu-doped Cd1−xZnxS nanophosphors

Mercaptosuccinic acid capped cadmium telluride quantum dots as luminescent thermometer over a wide temperature range of −100 to 60℃

Thermal-sensitive photoluminescence (PL) properties of cadmium telluride quantum dots capped with mercaptosuccinic acid (MSA-CdTe QDs) were investigated by collecting QDs’ PL steady-state spectra and decay curves from a cryogenic temperature of −100℃ to 60℃. These QDs display peak wavelength redshift and shorten fluorescence lifetime with the increase of temperature. In situ XRD patterns showed that the QDs’ grain size increases due to thermal expansion induced by the increasement of temperature, which further leads to the redshift of luminescence peak wavelength position. The results prove MSA-CdTe QDs are excellent candidates for luminescence thermometry over a broad temperature range of −100 to 60℃.

Satellite Red Emission from a Single Green-Emissive MnBr42- Tetrahedron in Soft Hybrid Single Crystals.

Photoinduced self-trapped exciton emission is common in soft matter metal halide semiconductors, whereas analogous phenomena in metal halide insulators with localized emitting centers and delayed satellite emission have rarely been identified. In this study, a new zero-dimensional Mn(II) hybrid of [3DPTPP]MnBr4 (3DPTPP = (3-(dimethylamino)propyl)(triphenyl)phosphonium) with only one crystallographic Mn2+ site but dual emission is reported. The delayed red emission (∼630 nm) is successfully assigned to a satellite of the green-emissive (∼530 nm) MnBr42- tetrahedron shifted by N-H vibration (∼2500 cm-1), directly evidenced by the Raman spectra and further supported by density functional theory calculation. The photoluminescence decay curves demonstrate their same origin, but the red emission exhibits a delayed process. The temperature- and pressure-dependent PL spectra, temperature-dependent distortion of the MnBr42- tetrahedron, and light polarization spectra confirmed the consistency and distinctness of the dual emission. This study will inspire further research on self-trapped optoelectronic processes in soft metal halides.

Photoluminescence of high energy xenon ion irradiated magnesium aluminate spinel single crystals

Laser confocal microscopy technique (60 ps laser pulse excitation at 445 nm) and a time-correlated single photon counting (TCSPC) technique have been used to study the photoluminescence (PL) in 152 MeV Xe ion irradiated MgAl2O4 single crystals. It was shown that radiation defects produced by swift xenon ions give rise to broad luminescence band positioned in the 470–800 nm wavelength range. The measurements of the PL decay curves have evidenced that lifetime of defect-related PL signal gradually increases from 6 to 10 ns in 500–620 nm spectral range and decreases with ion fluence increasing. The decrease of the luminescence intensity observed after fluences ∼1013 cm−2 is attributed to overlapping of individual ion track core regions.