Luminescence Lifetime Research Articles

Construction and fine tuning of host-guest doping systems and the underlying mechanism of room temperature phosphorescence

To obtain ultralong and efficient pure organic room temperature phosphorescent materials, as well as explore the intrinsic mechanisms affecting the phosphorescence performance of host-guest doping systems, two carbazole derivatives with the same molecular structure, named as L-CzIPCN and CzIPCN, were prepared by using carbazole synthesized in the laboratory and commercial carbazole. By choosing L-CzIPCN/CzIPCN and polymethyl methacrylate (PMMA)/polyvinyl alcohol (PVA)/benzophenone derivatives (BP, F-BP, Br-BP, and DF-BP) as the guest and host respectively, a series of new doping systems were constructed, and optimized by tuning doping ratios between host and guest materials. Among of them, F-BP/L-CzIPCN shows the longest room temperature phosphorescence (RTP) lifetime (501.23 ms), with RTP quantum yield of 31.19 %, followed by 0.2 % L-CzIPCN@PVA film (221.66 ms, 5.86 %) and 0.2 % L-CzIPCN@PMMA film (102.73 ms, 4.28 %) respectively. Moreover, L-CzIPCN displays different RTP spectra in diverse hosts, with dual-band RTP emission at 550 nm and 600 nm in benzophenone derivatives, but single RTP emission maxima in PMMA films, as well as a main emission peak at 470–510 nm and a shoulder peak at 550–590 nm in PVA films. The UV–Vis absorption spectra, fluorescence and phosphorescence spectra, and theoretical calculations indicate that RTP comes from the guest monomers in benzophenone derivatives/L-CzIPCN doping systems, with local triple characteristics, and host materials with large dipole moment, appropriate T1 energy level, and small energy gap between S1 and T1 contribute to improving RTP performance of the doping systems. Based on the excellent luminescence and different RTP lifetimes of the doping systems, some high-level anti-counterfeiting, and information encryption patterns were successfully constructed.

Competition between built-in polarization and p–n junction field in III-nitride heterostructures

The high built-in polarization field is a fingerprint of III-nitride heterostructures. Alloy composition and doping profile significantly affect the magnitude of the electric field present in subsequent layers, but the sign of the electric field is usually defined by substrate polarity and external bias. Here, we propose to utilize acceptor and donor doping concentrations exceeding 1020 cm−3 to obtain a high junction field that can solely abolish built-in polarization for a polar (0001) InGaN/GaN quantum well (QW). We have used photoluminescence (PL), time-resolved PL (TRPL), and contactless electroreflectance in order to gain insight into the strength of the electric field present in the grown heterostructures. Good match between expected and measured electric field values was obtained. A dramatic decrease in the luminescence lifetime for a flat QW was confirmed using TRPL. The presented results open a way to realize devices that profit from the low built-in field, like photodetectors, using abundant polar substrates.

Doping level dependence of the structure and luminescence properties of LaBO3: Tb3+ phosphors

Tb3+ doped LaBO3 phosphors with various doping levels were synthesized by hydrothermal and post-calcination methods. The structure, morphology, chemical composition, and optical properties of the samples were studied by X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), Photoluminescence spectroscopy (PL). XRD patterns reveal that Tb3+ doped LaBO3 crystals with monoclinic or orthorhombic structures can be obtained by adjusting the doping content of Tb3+. The XPS and EDS results indicate that the elements of La, O, B, and Tb were uniformly distributed in the samples, and some doping Tb3+ were oxidized to Tb4+. The prepared Tb3+ doped LaBO3 phosphors emit green emission at 543 nm under 271 nm excitation. The luminescence intensity is affected by the Tb3+ doping level, and concentration quenching will be observed due to an electric quadrupole-electric quadrupole interaction (p-p) process when the Tb3+ doping amount rises above 22 %. In particular, the luminescence properties of the Tb3+ doped LaBO3 phosphors are dramatically affected by the structure of the samples, and the luminescence intensity of the samples with orthorhombic structure is significantly higher than those with monoclinic structure. The decay curves of samples exhibit a double exponential behavior, and the average luminescence lifetime decreases with an increase in Tb3+ doping levels.

Synthesis, structures and optical properties of mononuclear La, Eu and Tb complexes supported by calix[4]arene ligands bearing three pendant salicylaldiminato arms

AbstractThe synthesis and complexation behaviour of a new calix[4]arene ligand H4L3 bearing three pendant salicylaldimine arms towards selected lanthanide ions has been investigated. Reaction of H4L3 with Ln(NO3)3⋅6H2O in MeOH in the presence of NEt3 provides monomeric complexes of composition [Ln(HL3)] (Ln=La3+ (4), Eu3+ (5), Tb3+ (6)). An X‐ray crystallographic analysis for 4 reveals that only two of the three ligand arms are involved in the coordination of the lanthanide ions, to give eight‐coordinated Ln3+ ions in a distorted square‐antiprismatic N2O6 environment. UV‐vis spectrophotometric titrations show that such monomeric species prevail in CH2Cl2/MeOH (1/1 v/v) solution. The apparent stability constants determined by UV‐vis spectrophotometric titration are log K=6.8(2) for 5 and log K=5.8(1) for 6. The Eu and Tb complexes luminesce only weakly at 77 K with luminescence lifetimes of 0.469 and 0.306 s.

Highly Efficient Red Thermally Activated Delayed Fluorescence Nanoparticles for Real‐Time in Vivo Time‐Resolved Luminescence Imaging

AbstractThermally activated delayed fluorescence (TADF) nanoparticles are used importantly in time‐resolved luminescence imaging for eliminating the background signals from scattering and short‐lived autofluorescence. However, TADF nanoparticles are seldom used for real‐time time‐resolved luminescence imaging, due to their limited luminescence efficiency and lifetimes. To detect delayed fluorescence, multiple excitation cycles with adequate delay times are usually required, leading to long detecting durations and low imaging speed. Herein, highly efficient red TADF nanoparticles are developed through doping a guest molecule, TPAAQ (2,6‐bis[4‐(diphenylamino) phenyl] anthraquinone), in a host (4,4′‐bis(carbazol‐9‐yl)biphenyl, CBP) matrix. With a low doping concentration, the nanoparticles can exhibit obvious TADF with luminescence lifetimes over 0.1 ms and photoluminescence quantum yield up to 35%. A cell‐penetrating peptide is used together with the amphiphilic compound for assembling nanoparticles, which can easily penetrate cells and greatly increase the TADF signals for luminescence lifetime imaging. Thanks to the long‐lived and highly efficient TADF, real‐time in vivo time‐gated luminescence imaging of zebrafish is realized on a chopper‐based wide‐field microscope. This low‐cost time‐resolved luminescence imaging method showed a great potential for real‐time detection of life activities in many organisms with high autofluorescence.

VIS/NIR double-domain luminescence sensing with anti-interference performance by a lanthanide-organic framework nanosheet loaded with atomically dispersed Cu sites

Fluorescence/luminescence detection has garnered extensive attention due to its remarkable sensitivity and selectivity within the visible (VIS) and near-infrared (NIR) spectrum. However, detection in the VIS domain is susceptible to interference from background fluorescence and internal quenching effects; the reliability and stability of NIR detection are constrained by its luminescence efficiency and lifetime. In this context, we introduce a dual-domain detection strategy under both VIS and NIR illumination, leveraging the advantages of both domains to achieve anti-interference luminescence detection of tetracycline hydrochloride (TC). Specifically, Cu2+ ions were incorporated into Yb-TCPP nanosheets (H2TCPP = 5,10,15,20-tetra-(4-carboxyphenyl) porphyrin) and anchored at the porphyrin core of the TCPP2- ligand, forming highly dispersed Cu-N4 sites. Notably, the Cu@MOF luminescent material exhibited a picomolar level dual-domain fluorescence/luminescence response towards TC: it activates detection in the VIS domain and turns off in the NIR domain. Largely due to this dual-domain response, the sensor showcases excellent anti-interference capabilities and reliability. When the VIS domain is perturbed, the sensor's detection in the NIR domain remains unaffected; conversely, interference in the NIR domain barely impacts the sensor's behavior in the VIS domain. Furthermore, a systematic mechanistic analysis suggests that the introduction of atomically dispersed Cu2+ sites not only enhances the acid-base interaction sites between the sensor and the analyte but also amplifies the adsorption capacity towards the analyte, effectively reducing detection limits and bolstering anti-interference capabilities. Anticipating the future, this detection strategy holds promise in offering a more cost-effective, reliable, and interference-resistant option for commercial detection, signaling a bright prospect for its development.

2-(2-Hydroxyphenyl) substituted benzimidazole derivatives: Suitable sensitizers for Tb3+ characteristic luminescence

Two series of 2-(2-hydroxyphenyl) substituted benzimidazole derivatives, (1-phenyl-2-(2-hydroxy-3-methoxyphenyl)benzimidazole, HL1; 1-methyl-2-(2-hydroxy-3-methoxyphenyl)benzimidazole, HL2) and their bimetallic complexes Zn–Ln(III)–L (Ln = Tb, Nd, Eu and Y) were prepared. The structures of ligands and complexes were characterized by 1H-NMR, FT-IR and single crystal X-ray diffraction. The UV–Visible absorption spectra, emission spectra and luminescent lifetime were measured. These results suggested that the ligands could efficiently sensitize the characteristic luminescence of Tb(III) and the photoluminescence quantum yield(PLQY) for Tb(III) complexes 3 and 7 were 74.8% and 55.3% respectively. While Nd(III) complexes 1 and 5 shown weak emission, and the Eu(III) complexes could not give the typical emission of lanthanide ions maybe due to the photo-induced electron transfer. In addition, the internal quantum yields of Nd(III) complexes were calculated utilizing luminescent lifetime.

Formation of Complexes of f-Elements with Electron-Withdrawing N-Heterocyclic Diamides: Extraction and Solution Photophysics

To examine the scope of the abnormal aryl strengthening effect (an increase in the extraction of metal ions when an aromatic substituent is introduced into the amide group) on f-metal extraction, a series of tetradentate diamide-type extragents bearing electron-withdrawing pyridine rings in amide moieties of the molecules were tested. The solvent extraction of Am(III)/Eu(III) pairs was investigated under various conditions, the solution chemistry of the lanthanide-extragents systems was studied, and the bonding constants were calculated for complexes of Eu(III) and Tb(III) ions with diamides. The photophysical properties of chemically synthesized ligand/metal (LM) complexes with various LM compositions were additionally studied in depth. The replacement of a phenyl ring by a pyridine one led to a critical reduction in metal affinity, showing the major contribution of electronic nature to the abnormal aryl strengthening effect. However, the pyridine group in the amide side chain provided additional coordination positions for metal ion binding; corresponding complexes with LM2 composition were detected in the system and their stability was calculated. Due to the low stability of the corresponding LM2 complexes, chemical synthesis of the complexes led to the formation of only one metal-containing species with LM composition. The luminescence spectra of europium and terbium complexes of the LM composition were studied. Differences were discovered in the luminescence excitation spectra of europium and terbium complexes with the same ligand. The luminescence quantum yields and luminescence lifetimes of solutions of europium and terbium complexes were determined.

Energy transfer and laser gain cross-section analysis in Nd-Yb-Gd doped CaF2 crystals

A detailed spectroscopic characterization of CaF2 co-doped with neodymium and ytterbium ions is presented. The higher Nd3+ absorption cross-section around 791 nm than Yb3+ around 980 nm enables an efficient excitation of Yb3+ ions by pumping Nd3+ with a subsequent energy transfer (ET) from Nd3+ to Yb3+ ions. By combining Nd3+ and Yb3+, along with Gd3+ buffer ions Nd3+,Yb3+,Gd3+:CaF2 crystals exhibit very large emission bands extending the usual Yb3+ emission spectrum by adding the Nd3+ emission contribution at longer wavelengths. The Nd3+ ⟶ Yb3+ energy transfer efficiency is estimated using two different approaches based on luminescence intensity measurements and lifetimes, giving consistent results. An energy transfer efficiency of 80 % is achieved in CaF2:0.5%Nd,3%Yb,2%Gd illustrating the ET strength within Nd3+-Yb3+ clusters. Finally, a detailed study of the gain cross-sections and laser emission spectra, and their dependence with Yb3+ doping concentration and population inversion is carried out, providing a detailed model of the laser spectral dynamics in such crystals. The gain cross-section is either dominated by one of the Nd3+ peaks at 1065 nm or 1048 nm or exhibits a flat profile covering the 1045–1067 nm range, in which case the laser oscillates randomly over this spectral range. The results highlight the specifics of the Nd3+ four level laser coupled by energy transfer to the Yb3+ quasi three level laser. Among others, this study shows how a large Nd3+ inversion ratio initiates the depletion of the Yb3+2F7/2 ground state through the ET. This depletion then has two effects as it saturates the energy transfer since the number of Yb3+ acceptors diminishes and it also shifts the laser wavelength towards shorter wavelength as the Yb3+ laser reabsorption is weakened.

Polymer-ceramic pressure-sensitive paint with high pressure sensitivity and pressure-sensitivity constancy in low-pressure environments

The accurate measurement of tiny pressure variations in low-pressure environments requires pressure-sensitive paint (PSP) with high pressure sensitivity and pressure-sensitivity constancy for aerodynamics testing. In this study, polymer-ceramic pressure-sensitive paints (PC-PSPs) were developed using platinum(II) meso-tetra(pentafluorophenyl) porphyrin (PtTFPP) and palladium(II) meso-tetra(pentafluorophenyl) porphyrin (PdTFPP) as luminophores; titanium dioxide (TiO2) and mesoporous silica (mSiO2) as particles; and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), poly(isobutyl-methacrylate) (PIBM), ethylene-vinyl acetate copolymer (EVA), and polyacrylate (B1000) as polymers. The static characteristics were calibrated and evaluated under low-pressure conditions. The results showed that PC-PSPs using PtTFPP with a short-lifetime and high oxygen-permeable polymer led to high pressure sensitivity. By contrast, if PdTFPP with a long-lifetime was used, the pressure sensitivity was dominated by the luminescence lifetime rather than the oxygen permeability of the polymer. PdTFPP/mSiO2-PTMSP exhibited a remarkable pressure sensitivity of 78.46%/kPa. PC-PSPs employing PIBM, EVA, and B1000, respectively, exhibited excellent pressure sensitivity constancy above 96% after near-vacuum storage for one hour. However, PTMSP-based PC-PSPs exhibited poor pressure-sensitivity constancy owing to the aging of the polymer in vacuum, which can be improved by employing the long-lifetime PdTFPP luminophore and mSiO2 particles. Furthermore, PC-PSPs using mSiO2 particles exhibited lower signal levels, higher pressure sensitivities, lower temperature dependencies and photodegradation than those using TiO2 particles. PdTFPP/mSiO2-PIBM and PdTFPP/mSiO2-B1000 exhibited application potential under low-pressure conditions owing to their favorable static characteristics.

Synthesis and characterization of a europium coordination polymer as a fluorescent sensor for the selective detection of PO43−, DTZ, and NFT

A new europium coordination polymer [Eu(2,3′-oba)(2,3′-Hoba)(IP)]n (Eu-CP) has been synthesized by hydrothermal reaction using 2,3′-oxbis (benzoic acid) (2,3′-H2oba) and 1H-imidazole [4,5-f] [1,10]-phenanthroline (IP). The semi-rigid ligand 2,3′-H2oba and large rigid ligand IP form a 1D chain structure of the Eu-CP, which is further stacked into a 3D supramolecular architecture through C–H⋯O and O–H⋯N hydrogen bonding. Below 400 °C, the Eu-CP does not decompose. It shows good chemical stability in common solvents and aqueous solutions with pH in the range of 3–12. The Eu-CP emits strong red luminescence, attributed to the 5D0→7FJ (J = 0–4) transitions of the Eu3+ ion. The luminescence quantum yield and lifetime are 61% and 0.94 ms, respectively. The Eu-CP has a broad absorption in the range of 200–400 nm, with a maximum excitation wavelength of 365 nm. Furthermore, Eu-CP is used as a sensor for the detection of PO43−, dimetridazole (DTZ), and nitrofurantoin (NFT) in aqueous systems, and NFT in biological samples (calf serum) based on the luminescence quenching effect. Notably, luminescent Eu-CP@film was prepared for sensing PO43−, NFT, and DTZ, which can be reused more than 20 times, facilitating a visually simple and rapid online detection platform. In addition, we also studied the luminescence quenching mechanism of Eu-CP by analytes.

THE EFFECT OF BARIUM CONTENT ON THE LUMINESCENCE PROPERTY OF DYSPROSIUM-DOPED BORATE GLASSES

Barium sodium borate glasses doped with Dy2O3 were fabricated in this work with the variation of barium oxide concentration. The excitation spectra, with 575 nm emission, show the highest excitation band at 349 nm. The emission spectra, with 349 nm excitation, show the emission bands at 482 and 575 nm. The highest emission light yield has occurred when the glass sample has 10 mol% of BaO. The (x,y) color coordinates of the emitted light from all the glass samples were (0.37,0.41) that point at the white light region in the CIE 1931 color space. The Y/B ratio indicates a high asymmetric environment around Dy3+ ions. The luminescence lifetimes are found to be 0.455 for all the glass samples.

Neural Networks Push the Limits of Luminescence Lifetime Nanosensing.

Luminescence lifetime-based sensing is ideally suited to monitor biological systems due to its minimal invasiveness and remote working principle. Yet, its applicability is limited in conditions of low signal-to-noise ratio (SNR) induced by, e.g., short exposure times and presence of opaque tissues. Herein this limitation is overcome by applying a U-shaped convolutional neural network (U-NET) to improve luminescence lifetime estimation under conditions of extremely low SNR. Specifically, the prowess of the U-NET is showcased in the context of luminescence lifetime thermometry, achieving more precise thermal readouts using Ag2 S nanothermometers. Compared to traditional analysis methods of decay curve fitting and integration, the U-NET can extract average lifetimes more precisely and consistently regardless of the SNR value. The improvement achieved in the sensing performance using the U-NET is demonstrated with two experiments characterized by extreme measurement conditions: thermal monitoring of free-falling droplets, and monitoring of thermal transients in suspended droplets through an opaque medium. These results broaden the applicability of luminescence lifetime-based sensing in fields including in vivo experimentation and microfluidics, while, hopefully, spurring further research on the implementation of machine learning (ML) in luminescence sensing.

On the optical properties of gallium based garnet phosphors according to Ca2Ln1-xCexZr2Ga3O12 (with Ln = Y, La, Gd, Lu)

Several samples of a gallium based garnet phosphor activated by cerium were investigated and reported upon in this work. Firstly, a solid solution corresponding to Ca2Lu1-xCexZr2Ga3O12 (x = 0.001–0.1), in which a doping level of 1 atom-% was revealed as the optimal activator concentration for high efficiency. Secondly, a range of samples according to the general composition Ca2(Y,La,Gd,Lu)0.99Ce0.01Zr2Ga3O12 was investigated to study the effect of different non emitting lanthanide ions on the optical properties. For this work various polycrystalline samples were synthesized and investigated by X-ray powder diffraction to determine the phase purity of the prepared samples. Fluorescence properties were examined employing excitation, emission, and diffuse reflectance spectroscopy. Temperature dependent emission spectra and fluorescent lifetimes were investigated to gain insight into the thermal quenching behaviour. From the spectroscopic investigation it was confirmed that the crystal field splitting of the cerium 5di components is strongly influenced by the size of the non-emitting lanthanide ion and the molar concentration of cerium. The change in crystal field splitting consequently shaped the excitation and emission wavelengths. Additionally, T1/2 values were determined from temperature dependent emission spectra and found to be between 230 and 250 K. Furthermore, luminescent lifetimes were calculated from pulsed laser excited decay curves. On the basis of the spectroscopy results potential applications of these phosphors are discussed.

Growth, Structure, Spectroscopy, and Laser Operation of a “Mixed” Yb:(Y,Lu)3Al5O12 Garnet Crystal

A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y0.601Lu0.233Yb0.166)3Al5O12 was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The stimulated-emission cross-section for Yb3+ ions was maximized to 2.53 × 10−20 cm2 at 1031 nm. The emission bandwidth was ~8 nm, and the reabsorption-free luminescence lifetime of the 2F5/2 state was 1.063 ms. Pumped at 941 nm, the Yb laser generated a maximum output power of 1.04 W at 1.03 and 1.05 μm with a high slope efficiency of 76.4% and a laser threshold of 76 mW. A continuous wavelength tuning over a range of 51.6 nm (1026.4–1078.0 nm) was also achieved. Power scaling was achieved using a 969 nm diode-pumped microchip cavity. A maximum output power of ~9 W was obtained at 1.05 μm with a slope efficiency of 76% and an almost circular laser beam profile.

On the optical properties of monoclinic Na3AlF6 and Na3AlF6:Mn4+

Mn4+ activated luminescent materials have attracted much attention as colour converters for light sources and displays. In particular, alkali metal hexafluorometallates, such as K2SiF6:Mn4+ or K2TiF6:Mn4+, emit light in the red spectral region if pumped by phosphor converted LEDs (pcLED). In accordance with Zhu et al. we applied the cation-exchange method in order to synthesize Mn4+ doped Na3AlF6. Na3AlF6:Mn4+ exhibits efficient red photoluminescence peaking at 627 nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d.3 configuration) within the [MnF6]2- octahedra on the aluminum site in the cryolite host structure. Photoluminescence properties, such as temperature dependence of the PL intensity and luminescence lifetime are presented. Additionally, the band structure of the undoped host material has been treated with Density Functional Theory (DFT). The theoretical results have been evaluated experimentally with diffuse UV reflectance spectroscopy. Finally, luminous efficacy and color rendering values of simulated warm white emitting pcLEDs comprising a dichromatic phosphor blend employing Na3AlF6:Mn4+ as the red emitting component are calculated and compared to the performance of warm white emitting pcLEDs comprising K2SiF6:Mn4+ as red emitting component.

Flour moisture detection with an europium-based luminescent probe

In this work, we describe the application of the self-assembled europium complex 1:Eu(III) (where 1: diethyl 8-methoxy-2-oxo-1,2,4,5-tetrahydro-cyclopenta[de]quinolin-3-yl)phosphonate) for the analysis of water content of wheat flour. The methodology herein described represents a robust and accurate way for the detection of small amounts of water in food, providing comparing results with well-established methods such as thermogravimetry and Karl-Fischer titration. Interestingly, as an advantage over other methods, our luminescence-based approach can be implemented in lab-on-a-chip microfluidic devices for real-time and on-line detection of water content of food samples. Additionally, the remarkably long luminescence lifetime of Eu(III) allows the use of state-of-the-art imaging strategies based on PLIM microscopy for the direct visualization of unique water content maps of wheat flour particles.

Evidencing the NIR luminescence and longer lifetime from ytterbium complex constructed from perfluorinated β-diketone and heteroatom based ancillary ligand

We have designed an ytterbium-based complex with perfluorinated beta-diketone and bidentate nitrogen-based heterocyclic base 2-(1H-Imidazol-2-yl) pyridine, [Yb(fod)3(impy)]. The octa-coordinate structure of [Yb(fod)3(impy)] was confirmed by means of various spectroscopic techniques and theoretical calculations. The photophysical behavior of [Yb(fod)3(impy)] demonstrated characteristic emission in NIR region centered at 978 nm with shoulders at 1006 nm and around 1032 nm. Interestingly, the lifetime obtained for the said complex is amounted to 15 µs and good intrinsic quantum yield 0.75 %. The significant spectroscopic measurements suggest that beta-diketone and ancillary ligand employed in the present work are functioning as an efficient sensitizer for ytterbium ion. The synthesized complex [Yb(fod)3(impy)] could find significant place in designing of NIR OLEDs, lasers, optical-electronic devices, cell imaging purpose owing to the biocompatible feature of Yb (III) complexes as their emission windows are transparent to body fluids.

Microwave-assisted fabrication of Sr2ZnMoO6:Sm2O3 phosphors in TeO2: ZnO: B2O3 glass matrix for high-efficiency solid-state lighting applications

The present work focuses on synthesizing Sr2ZnMoO6:Sm2O3 phosphor-mixed TeO2: ZnO: B2O3 glass by microwave synthesis technique at different times (16, 18, 20, 22, 24 min). These samples, after synthesizing they were characterized through XRD, FTIR, density, molar volume, refractive index, absorption spectra, luminescence properties, and lifetime analysis.The study of crystalline nature was studied using XRD spectra of Sr2ZnMoO6. Absorption spectra were evaluated in the wavelength region between 400 and 1800 nm and found seven peaks, which corresponded with the energy transitions of Sm3+ion from the ground level of 6H5/2 → 6F11/2, 9/2, 7/2, 5/2, 3/2, 6H15/2, and 6F1/2 at 944, 1083, 1238, 1383, 1485 and 1543 nm respectively. The photoluminescence in the wavelength region of 500–750 nm using the excitation wavelength at 403 nm. The emission intensity of the samples increased with sintering time until 20 min after which it decreased. The highest peak was observed at 597 nm, corresponding to 4G5/2 → 6H7/2 (orange) transitions of Sm3+ ion. The luminescence lifetime from the 4G5/2 to 6H7/2 level increased with increasing sintering time until 20 min, which had a lifetime of 0.431–0.711 ms when monitored at λex = 403 nm. The results obtained in photoluminescence properties showed that the samples could be potential candidates for orange light-emitting diodes for solid-state lighting applications.

Control upconversion decay dynamics from the perspective of collective response

Very recently, upconversion luminescence (UCL) lifetime, as a powerful optical dimension, has attracted tremendous research interest due to its advantages of high information capacity and high photophysical stability. With the implementation and emergence of endlessly fascinating UCL features, it is particularly meaningful to understand the photophysical mechanisms inside UCL materials to enable rational subdivision-level structure design, which is however currently far from sufficient. In this work, we take an ordinary upconversion nanoparticle as an example to prove that the UCL decay curves and corresponding lifetimes are indeed a collective response of the entire UCL system to excitations, that exhibits correlated, yet quite different properties from individual ions. A specially developed theoretical random walk model combined with an experimental lifetime control for Yb3+/Er3+ UCL demonstrates that energy diffusion principally alters the decay rate. Moreover, the different extent of the influence of energy diffusion on the emissions of 2H11/2/4S3/2 (green) and 4F9/2 (red) leads to an extremely uncommon cross-over comparison of decay rates. This work provides new ideas for understanding decay dynamics and practical UCL lifetime manipulation methods.