Photoluminescence Emission Research Articles

A Cr3+-triggered near-infrared tungstate phosphor for organic compound non-destructive detection

Cr3+-doped near-infrared (NIR) luminescent materials have become a research hotspot in luminescence functional materials. However, developing NIR phosphors with emission wavelengths exceeding 1000 nm, suitable for organic compound non-destructive analysis, remains a significant challenge. In this study, LiSc(WO4)2:Cr3+ NIR phosphors were synthesized using a simple solid-state reaction method. Low temperature photoluminescence emission spectrum, electron paramagnetic resonance spectrum, and fluorescence decay curve confirmed that Cr3+ ions occupied both LiO6 and ScO6 octahedron sites, forming two luminescence centers. The sample exhibited an emission wavelength of 1082 nm under 523 nm excitation, with a full width at half maximum (FWHM) of 290 nm. As the Cr3+ concentration increased, the emission peak showed a blue shift. The sample LiSc(WO4)2:0.3Cr3+ with optimal optical performance exhibited an emission wavelength of 1023 nm and an FWHM of 228 nm. Its luminescence intensity retained 38.4% of room temperature value at 380 K, and the internal and external quantum efficiency were 33.2% and 18.9%, respectively. When packaged with a 525 nm green LED, the device as a NIR light source is capable of accurately identifying water, ethanol, ammonia, and silicone oil. This work demonstrates that tungstate materials have great potential in the field of optical materials and offers a new perspective for selecting matrix materials in the development of Cr3+-doped long-wavelength broadband NIR phosphors.

Photoluminiscence and absorption of emission by phonons of indirect transitions in layered GaS single crystals

Absorption in E||b and E⊥c polarizations and photoluminescence at the absorption edge were studied at temperatures range 10–300 K. It was found that the smallest indirect transitions take place from the minimum of conduction band C1 (point M) to the maximum of valence band V1 in the Brillouin zone center (point Γ or nearby). A distance between these extrema is 2.4484 eV at 10 K. In addition, the magnitude of indirect transitions from the second band C2 (point M) to valence band V1 (Brillouin zone center) is 2.4912 eV at 10 K. The splitting of C1–C2 bands in M point of the Brillouin zone is equal to ∼43 meV. The indirect transitions from third conduction band C3 (point K) to valence band V1 in the nearby of Γ point are equal to 2.7683 eV at 10 K. The splitting of conduction bands C2 (point M) and C3 (point K) is higher than one for the splitting C1–C2. It was observed bands associated with self-absorption of photoluminescence emission by phonons with symmetries E1g1+A1g2, A1g2+A1g1 and A1g2+E2g2 involved in indirect transitions.

The Hidden Mechanism: Excited-State Proton-Electron Pair Transfer in Metal Nanocluster Emission.

Comprehending the underlying factors that govern photoluminescence (PL) in metal nanoclusters (NCs) under physiological conditions remains a highly intriguing and unresolved challenge, particularly for their biomedical applications. In this study, we evaluate the critical role of excited-state proton-coupled electron transfer in the emission of metal NCs. Our findings demonstrate that hydronium ion (H3O+) binding can trigger a nonlinear, pH-dependent excited-state concerted electron proton transfer (CEPT) reaction. This involves simultaneous electron transfer from the Au(0) core to the Au(I)-ATT (ATT denotes 6-aza-2-thiothymidine) surface and proton transfer from H3O+ to the ATT ligand in a single step, greatly promoting vibrations and rotations of the Au(I)-ATT surface, resulting in substantial PL quenching of Au10(ATT)6 NCs. Further analyses show that the unique CEPT dynamics are strongly influenced by the opposing effects of increased reorganization energy and a larger pre-exponential factor on the electron transfer rate. Moreover, the proposed excited-state CEPT process is found to be prevalent in core-shell relaxation metal NCs, such as Au25(SR)18 (SR denotes thiolate) NCs, and serves as an important factor in limiting their PL emission. By simply controlling the pKa of the ligands, the emission performance of Au25(SR)18 can be easily regulated in physiological environments.

Optimization of LPCVD Deposition Conditions of Silicon-Rich Silicon Nitride to Obtain Suitable Optical Properties for Photoluminescent Coating

Silicon nitride is a commonly used material for ceramic applications and in the fabrication processes of integrated circuits (ICs). It has also increased in interest from the scientific community for use as a functional coating due to its physical, mechanical, electrical, and optoelectronic properties. In particular, silicon-rich silicon nitride (SRSN) has been considered in the photovoltaic industry as a down-conversion film for solar cells. In this work, SRSN films have been obtained by the Low-Pressure Chemical Vapor Deposition (LPCVD) technique at low to moderate deposition temperatures with a variation in the precursor gas pressure ratio. The SRSN films showed a wide photoluminescence (PL) in the visible region (without a high-deposition temperature or annealing process) and suitable optical properties (refractive index and absorption in the UV) to be used as photoluminescent coating on silicon solar cells. The absence of high-deposition temperatures could preserve the original structure of silicon solar cells, once the SRSN layer was applied. In addition, control of the reactive gas pressure ratio and deposition temperature showed an influence on the refractive index, the surface roughness, and the PL emission.

MORPHOLOGICAL AND OPTICAL PROPERTIES OF ZNO NANORODS GROWN ONTO SILICON SUBSTRATES: THE IMPACT OF GROWTH TEMPERATURE

ZnO nanorods (NRs) have been successfully grown onto Silicon (Si) substrates. The properties of ZnO NRs have been characterized using field emission scanning microscopy, Photoluminescence, and X-ray diffraction. Results showed that the growth temperature (85, 90, 95, and 100oC) significantly affected the properties of ZnO NRs. At a temperature of 95oC, the structural and optical properties have been significantly enhanced, besides, well-aligned ZnO NRs have been obtained. With the rise of growth temperature from 85 to 95oC, the crystallite size increases (52 to 94 nm), and the near band edge emission to deep level emission ratio is enhanced. Besides, the aspect ratio for the prepared ZnO NRs has increased significantly reaching 19.42. This study emphasizes the significance of growth temperature in tunning the structural and microstructural and subsequently the physicochemical properties of ZnO NRs by fine control of the growth temperature. Moreover, a facile and cost-efficient method for fabricating ZnO nanorods for electronic applications based on silicon is presented in this study.

A novel red emitting Eu3+ doped CaSiO3 nanophosphor derived from agro-wastes for advanced forensic applications

The modified sol–gel approach was utilised to synthesise Eu3+ (1–5 mol%) doped CaSiO3 nanophosphors (NPs) using eggshell (ES) and rice husk ash (RHA) as precursors for SiO2 and CaO, respectively. Powder X-ray diffraction (PXRD) peaks confirm the monoclinic structure of the powdered samples. The photoluminescence (PL) emission spectra display distinct emission peaks corresponding to Eu3+ ions. After optimizing the Eu3+ ion concentration, the highest intensity (CaSiO3:3Eu3+) was achieved at 3 mol%. As the concentration increased beyond this point, the emission intensity decreased due to concentration quenching (CQ). Temperature-dependent photoluminescence (TDPL) was investigated in the range of 303 to 443 K. The results demonstrated that emissions at elevated temperatures are significantly stronger than those at ambient temperature. TDPL studies revealed excellent thermal stability, with emission intensity remaining at 87.5 % even at 423 K. Additionally, the phosphor’s absolute sensitivity of 0.003 K−1 and relative sensitivity of 1.44 % K−1 highlight its strong potential for temperature sensing applications. The suitability of the phosphor for the powder dusting method in fingerprint (FP) detection on various surfaces was also assessed. Under 365 nm UV light, the CaSiO3:3Eu3+ phosphor clearly reveals the level 1–3 structure of LFPs.

Hydrothermal synthesis and optical luminescence center attribution in samarium-doped zirconia nanocrystals

Sm[Formula: see text] -doped ZrO2 (SDZ) nanocrystals were prepared via a hydrothermal route without subsequent calcination. These samples underwent a series of characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) spectroscopy, and photoluminescence (PL) spectral. The results showed pure cubic ZrO2 nanocrystals, with a crystallite size of 8.4 nm, were achieved by doping 8 mol% Sm[Formula: see text]. It was observed that the concentration of Sm[Formula: see text] had a significant impact on the crystallite structure of the samples, which exhibited an array of spherical shape and irregular aggregates. The inclusion of PL emission bands, spanning from the ultraviolet to blue-green range, highlighted three distinct bands. These were analyzed using Gaussian fittings and were attributed to three different types of defects, referred to as the F, F1, and F2 centers, respectively.

Visible Light Driven Defect Mediated Photocatalytic Activity of Spray Pyrolyzed Ga and Al Doped ZnO Thin Film Electrodes

AbstractGa and Al doped ZnO thin film electrodes are spray deposited and explored for photocatalytic deterioration of methylene blue dye. X‐ray diffraction unveils both films to have highly textured growth along the (002) plane. The surface morphology is found to have near spherical and distorted rectangular particles for Ga and Al dopants, respectively. Photoluminescence emission study reveals that both films have visible light emissions in the violet, blue, and green regions due to oxygen vacancy defects. The deposited films exhibit a reasonably higher transmittance of 89 and 77 % with mobility of 30.5 and 29.6 cm2/Vs for Ga and Al doped ZnO, respectively. Cyclic test and photo‐corrosion studies performed for selected samples were indicating significant stability. Based on these findings the electrodes are explored for the photocatalytic degradation of methylene blue dye and are found to have significant efficiency upon LED and sunlight irradiation.

Self‐assembled small molecule spherulites under mild conditions: High solid‐state quantum yield and unique interconnected structural and fluorescent colors

AbstractSpherulites are generally fabricated from cooling polymer melts, while their fabrication under mild conditions or from small molecule materials has been barely reported. Besides, organic luminescent molecules typically suffer from low quantum yields in a solid state. Moreover, preparing material with interconnected and simultaneous changes in structural and fluorescent colors is challenging. Here, we present the first solution‐derived spherulites with unique interconnected structural and fluorescent colors, self‐assembled from stearoylated monosaccharides at room temperature. D‐galactose stearoyl ester self‐assembled into banded spherulites, containing twisted nanoplates and interconnected simultaneously changing structural and fluorescent colors. In comparison, D‐mannose stearoyl ester can only form non‐banded spherulites, which contain oriented nanoplates and uniform structural and fluorescent colors. Such materials revealed a novel negative correlation between fluorescence and birefringence, termed alignment‐promoted quenching propensity. Remarkably, the solid‐state fluorescence quantum yields of galactose and mannose‐derived spherulites are as high as 49 ± 2% and 51 ± 2% respectively, approximately ten times higher than those of unmodified monosaccharides. These quantum yield values are among the highest of reported organic nonconventional fluorophores and even comparable to those of conventional aromatic chromophores. Moreover, these spherulites manifested an unexpected excitation‐dependent multicolor photoluminescence with a broad‐spectrum emission (410−620 nm). They show multiple peaks in the photoluminescent emission spectra and broad fluorescence lifetime distributions, which should be attributed to the clustering of a variety of oxygen‐containing functional groups as emissive moieties.

Optimization of carrier mobility in Pr-doped SrTiO3 thin films through controlled Sr-segregation for optoelectronic applications

Functional oxides employed in electronic components hold significant promise for future electronic devices. Strontium titanate based thin films have several emergent features due to unsaturated bonds, dimension restriction, production of oxygen vacancies and point defects that make them attractive for optoelectronic applications. Here we prepared Pr-doped strontium titanate thin films via RF magnetron sputtering in a pure Argon environment at various gas pressures followed by heat treatment. The structural parameters, analyzed via XRD and Raman spectroscopy, were correlated with the electrical transport properties. Intriguing morphological features such as Stranski–Krastanov (SK) growth and cation segregation observed by FESEM and AFM analysis were further examined to elucidate the conduction mechanism in the films. The optical studies unveiled significant transparency in the visible spectrum. Photoluminescence emission studies at specific wavelengths shed light on the involvement of oxygen vacancies. By carefully controlling annealing conditions and optimizing sputtering parameters, thin films devoid of Sr segregation with highest reported carrier mobility of 33.9 cm2/V s were prepared. The high mobility leading to enhanced conductivity render the films suitable for a wide range of optoelectronic applications.

Rapid microwave preparation of nitrogen doped carbon dots and their applications as highly sensitive nanoprobe for hematin

In this work, nitrogen-doped carbon dots (NCDs) were obtained by microwave rapid preparation method with lipase and guanidine hydrochloride as precursors in only 6 min. In order to achieve high sensitivity detection of hematin, based on obtained NCDs as a nanoprobe, a new detection method based on photoluminescence (PL) change was developed. Further studies have shown that the sensing strategy relied on the inner filter effect to selectively quench the PL emission of NCDs at 379 nm by hematin under 320 nm excitation. The nanoprobe had a wide linear range (0.2–13 μmol/L) and a detection limit of 0.07 μmol/L. The method was effectively applied to the identification of hematin in human blood samples. The proposed nanoprobe has the characteristics of simple and efficient design. It can achieve rapid and accurate detection, which is very suitable for real-time analysis of blood samples to facilitate diagnosis.

The impact of charge carrier dynamics on the outdoor performance of cesium-lead-halide perovskite photovoltaics

We investigated the optoelectronic characteristics of cesium-based perovskite using various techniques. The steady-state photoluminescence (PL) spectroscopy of this perovskite solar cell composition shows the presence of strong peaks at a wavelength of 759 nm, which that corresponds to a band gap energy 1.63 eV. This band gap energy was estimated using two complementary methods, the PL emission spectra and the UV–vis absorption spectra. The study describes the dependence of photon energy on wavelength using a Gaussian mathematical model. Real-outdoor performance testing was conducted in Ethiopia’s climate during the hottest seasons to study the device performance under outdoor conditions at varying irradiances. Moreover, we investigated power generation from the devices using current–time measurements and analyzed charge carrier dynamics through transient photocurrent measurements.

UV-enhanced O2 sensing using β-Ga2O3 nanowires at room temperature

Oxygen sensors based on β-Ga2O3 nanowires were prepared by a chemical vapor deposition method and investigated in detail. β-Ga2O3 nanowires grew on sapphire substrate at 1100 °C with Au as a catalyst. The polycrystalline structure was confirmed according to the X-ray diffraction (XRD) patterns. Scanning electron microscope (SEM) images revealed the average diameter of the nanowires was 150 nm. The ratio of Ga to O was 0.765 according to energy dispersive spectroscopy (EDS) results. Photoluminescence emissions at 445 and 484 nm originated from oxygen vacancies and gallium-oxygen vacancy pairs. Both EDS results and photoluminescence revealed intrinsic oxygen vacancies in β-Ga2O3 nanowires. We coated the β-Ga2O3 nanowires on an interdigitated electrode to fabricated an oxygen sensor. Under ultraviolet light irradiation, at room temperature, the sensor’s response rise time and recovery time were 1034 s and 1283 s to 600 ppm oxygen, those were 1290 s and 1709 s to 1200 ppm oxygen. The mechanism of oxygen sensing was discussed.

Investigating the multifunctionality of Cu2+ doped LaSrMnO3: understanding structural, optical, and magnetic responses

Abstract This study examines the impact of copper ions (Cu2+) on the structural, optical, and magnetic, characteristics of La0.6Sr0.4Mn1-xCuxO3 (LSMCO) manganites. Various techniques, including X-ray diffraction, field emission scanning electron microscopy, Raman spectroscopy, DC magnetization, and photoluminescence measurements were employed for a comprehensive analysis. Structural examinations revealed that all compositions exhibit a single-phase orthorhombic structure. Raman spectroscopy reveals the structural distortion due to the inclusion of Cu at Mn site. The photoluminescence properties of the manganite were found to be influenced by the excitation wavelength, demonstrating energy transfer from Mn ions. Magnetic investigations indicated that the introduction of Cu leads to a reduction in the saturation magnetization of the manganite.

Preparation and Characterization of Au Quantum Dots Using Laser in Benzene and Study of the Pulse Energy effect on Quantum Size

Here, findings from a study on pulsed laser ablating of noble Au targets submerged in benzene solvent and a study on the effect of pulse energy on quantum size are presented. Three samples of gold quantum dots (AuQDs) are synthesized at pulse fluence of 4, 8, and 12 J/cm2, which is referred to as F1, F2, and F3, respectively. The prepared AuQDs were characterized by UV-Vis, HR-TEM, XRD, XPS, EDX, FTIR, Raman spectroscopy and Photoluminescence measurement. AuQDs that were synthesized have monocrystalline and cubic (FCC) structure, according to XRD patterns. It was found that the direct optical energy gap of AuQDs is enhanced to 2.6 eV. The emission peak of AuQDs photoluminescence emission spectra is at roughly 481, 445, and 437 nm, for F1, F2, F3 samples, respectively. The quantum size was reduced to 2 nm for sample F3. This strategy has the ability to prepare pure AuQDs in one step, with promising biosensor and bioimaging applications.

Geometrically isomeric [Ir(C^N)(C’^N’)(N’’^O)-tris-heteroleptic [Ir(dFppy)(CN-ppz)(pic)] Ir(III)-complexes with blue-light: Forwards to efficient blue organic light-emitting diodes

Despite the great success of Ir(III)-complex-based green/red-light OLEDs (OLED = organic light-emitting diode), the realization of their efficient blue-OLEDs is far behind and challenging. Herein, using HdFppy (2-(2,4-difluorophenyl)pyridine) and CN-ppzH (4-(1H-pyrazol-1-yl)benzonitrile) as the HC^N/HC’^N’ ligands and Hpic (2-picolinic acid) as the N’’^O-ancillary ligand, the [Ir(C^N)(C’^N’)(N’’^O)]-tris-heteroleptic molecular design strategy was adopted, obtaining the two [Ir(dFppy)(CN-ppz)(pic)]-configured blue-emitting (λPL (photoluminescence emission peak) = 466, 496(sh) nm; ΦPL (photoluminescence quantum efficiency) = 0.41–0.46) geometrical isomers 1a and 1b. Further through the doped and vacuum-deposited fabrication, their blue-OLEDs-1A/1B with the LMax (maximum luminance) values up to 18090–22528 cd/m2 and the ηEQEMax (maximum external quantum efficiency) sizes of 7.99–8.42 %, were realized, respectively. This study result shows that [Ir(dFppy)(CN-ppz)(pic)]-included [Ir(C^N)(C’^N’)(N’’^O)]-tris-heteroleptic Ir(III)-complexes can be used as the attractive blue-phosphor candidates forwards to efficient blue-OLEDs.

Energy trapping to substitutional and charge compensation defects in persistent luminescent BaAl2O4:Tb3+

The holistic approach of the photoluminescence (PL), thermoluminescence (TL), and persistent luminescence properties at room temperature of BaAl2O4:Tb3+ were investigated in detail using a wide range of techniques. Materials were obtained using a solution combustion synthesis. The x-ray powder diffraction patterns of nondoped and Tb3+ doped BaAl2O4 indicated the hexagonal phase, and a Tb4O7 solid solution was observed at 4 and 5 mol% Tb doped aluminate. X-ray photoelectron spectroscopy revealed that Ba occupied one site and that Tb ions occupied this site as Tb3+ as well as TbIV. PL emission in blue, green, and red was observed under an excitation at 228 nm, that originated from the interconfigurational 4f8–4f75d1 transitions of Tb3+. Time-of-flight secondary ion mass spectroscopy, UV–vis diffuse reflectance, and PL revealed the presence of a Cr3+ impurity. The 0.5 mol% Tb3+ doped BaAl2O4 exhibited a strong TL band at 354, 437 and 598 K, which were attributed to the traps formed by Tb3+ doping and subsequent O2− charge compensation. A persistent luminescence mechanism was constructed for the Tb3+ doped BaAl2O4. After the energy was stored in thermally liberated Tb3+ in the Ba2+ substitution sites and charge compensation defects, the Tb3+ was the source of the continuous luminescence.

Exploration of the Photoluminescence Behavior and Emission Mechanism of Thioester Polyacrylamide Tablets During the Gradual Increase of Molecular Weight.

To enhance the photoluminescence (PL) of unconventional luminescent compounds, particularly their persistent room temperature phosphorescence (p-RTP) performance, compressing the powder into tablets has been demonstrated as a viable approach. Nevertheless, the alterations in the emission capability of PL in compacted tablets have not been comprehensively investigated. In this study, four polyacrylamide (PAM) with controllable molecular weight (MW) are fabricated from powder to tablets, and their PL emission properties are thoroughly examined and compared with corresponding powders to elucidate the emission mechanism. As MW increases, both PL and p-RTP emissions of the tablets gradually intensify, exhibiting significant enhancement compared to the corresponding powder while retaining the characteristic blue shift. Through small angle X-ray scattering (SAXS), construction of molecular models for tablets, detailed analysis of molecular interactions, and theoretical calculations are conducted to reasonably explain these emission phenomena using clustering-triggered emission (CTE) and average packing density promoted emission (PDE) mechanisms. These findings not only advance the understanding of nonconventional luminogens' emission mechanisms but also offer new insights for preparing nonconventional luminescent polymers with controllable p-RTP emission performance.

Innovative synthesis and forensic applications of bio-mediated SrO–MgO–In[formula omitted]O[formula omitted] nanocomposites with blue photoluminescence

The first of its kind Strontium oxide–Magnesium Oxide–Indium oxide (SMI) nanocomposites were synthesized utilizing a bio-mediated method with Euphorbiatirucalli latex as a reducing agent, followed by calcination. Synthesis of SMI NCs is confirmed by Bragg reflections of SrO, MgO, and In2O3, among them peaks belonging to In2O3 are observed to be prominent. The crystallite size, and other parameters like dislocation density, strain, structural factor, and crystallinity were estimated. Due to lower surface energy and the adhesion of particles with weak forces, morphology of the surface contains a larger degree of agglomeration. The direct energy band gap was determined to be 3.18 eV. Furthermore, the PL (photoluminescence) emission spectra, CIE, and CCT coordinates strongly indicate high-intensity emission in the region of blue color. Dusting of powder reveals latent fingerprints. Synthesized SMI nanocomposite exhibits highly-resolved patterns in the form of ridges used to analyze specific latent fingerprints with clarity. Thus, the recently synthesized nanocomposite may have been used in forensics, fluorescence labeling, and blue light emission.

Remarkable NH3 gas sensing performance of spray deposited Tb doped WO3 thin films at room temperature

To evade potential health hazards associated with exposure to NH3, there has been an increasing demand for efficient gas sensors operating at room temperature (RT). In this study, thin films of Tb-doped (0–5 wt%) WO3 synthesized by spray pyrolysis technique are used as a novel material for sensing NH3 gas. The X-ray diffraction (XRD) pattern identified the hexagonal crystal system of WO3 films and increased crystallinity for the 2 wt% Tb-doing concentration. Field emission scanning electron microscopy (FE-SEM) unveiled the distinct surface morphology of mesh-like porous structures for Tb-doped films suitable for the target gas adsorption/desorption process. Multiple photoluminescence (PL) emission peaks indicate the presence of defect states, including defect energy levels created by oxygen vacancies (Ov). Optical analysis indicated shrinkage of the bandgap of WO3 thin films for doping levels up to 2 wt%. Among all gas sensors, 2 wt% Tb-doped WO3 exhibited exceptionally high response and low response time at 250 ppm NH3 concentrations measured at room temperature (RT). The sensor’s performance for NH3 gas sensing is compared with previous reports on WO3-based NH3 sensors. The gas sensing mechanism in WO3 is also briefly discussed.