Synergistic effects of Tb doping in long-persistent luminescence in Ca3Ga4O9: xBi3+, yZn2+ phosphors: Implications for novel phosphorescent materials

Long afterglow phosphors constitute an emerging class of compounds with wide application in several fields, from photonic to dosimetry, solar energy storage and photocatalysis. In this study, we synthesized and thoroughly characterized a new class of persistent emitting materials, Ca3Ga4O9: xBi3+, yZn2+, zTb3+. Through the utilization of X-ray and Raman spectroscopy, as well as optical measurements including static and time-resolved luminescence, thermoluminescence, and phosphorescence, the effects of the Tb concentration on the optical and structural properties of the material has been deeply studied. A suitable mechanism was proposed to account for the long afterglow emission, wherein Tb3+ and Bi3+ ions occupying the Ca2+ sites serve as recombination centers, facilitating the generation of oxygen defects. Zn2+ in the Ga3+ sites, contribute to the charge balance and generates hole traps in the matrix. The enduring phosphorescence persists for over 3 h following the cessation of UV irradiation, discernible to the naked eye in low-light conditions.

Unveiling Hidden Prints: Optically stimulated luminescence for latent fingerprint detection

Fluorescent lighting and optical techniques have been widely utilized to enhance the detection of latent fingerprints. However, the development of new techniques is imperative to expand the range of surfaces from which latent fingerprints can be detected. When relying on traditional methods, fingerprint evidence can remain undetected or even disregarded due to insufficient detection and limited detail, especially when dealing with a luminescent background. In this study, we propose the utilization of optically stimulated luminescence (OSL) applied to a Ba2SiO4 matrix, co-doped with Eu2+ and Dy3+, as a powerful method for visualizing latent fingerprints on various surfaces, including thin plastic bags, rigid duct tape, thin aluminum foil, and glass slices. This technique effectively eliminates any luminescent background and significantly enhances optical imaging. This represents the first successful application of OSL in the development of latent fingerprints, thus paving the way for more efficient and effective forensic techniques in the future.

Optimizing the Mechanoluminescent Properties of CaZnOS:Tb via Microwave-Assisted Synthesis: A Comparative Study with Conventional Thermal Methods

Recent developments in lighting and display technologies have led to an increased focus on materials and phosphors with high efficiency, chemical stability, and eco-friendliness. Mechanoluminescence (ML) is a promising technology for new lighting devices, specifically in pressure sensors and displays. CaZnOS has been identified as an efficient ML material, with potential applications as a stress sensor. This study focuses on optimizing the mechanoluminescent properties of CaZnOS:Tb through microwave-assisted synthesis. We successfully synthesized CaZnOS doped with Tb3+ using this method and compared it with samples obtained through conventional solid-state methods. We analyzed the material's characteristics using various techniques to investigate their structural, morphological, and optical properties. We then studied the material's mechanoluminescent properties through single impacts with varying energies. Our results show that materials synthesized through microwave methods exhibit similar optical and, primarily, mechanoluminescent properties, making them suitable for use in photonics applications. The comparison of the microwave and conventional solid-state synthesis methods highlights the potential of microwave-assisted methods to optimize the properties of mechanoluminescent materials for practical applications.

Exploring the Impact of Nitrogen Doping on the Optical Properties of Carbon Dots Synthesized from Citric Acid

The differences between bare carbon dots (CDs) and nitrogen-doped CDs synthesized from citric acid as a precursor are investigated, aiming at understanding the mechanisms of emission and the role of the doping atoms in shaping the optical properties. Despite their appealing emissive features, the origin of the peculiar excitation-dependent luminescence in doped CDs is still debated and intensively being examined. This study focuses on the identification of intrinsic and extrinsic emissive centers by using a multi-technique experimental approach and computational chemistry simulations. As compared to bare CDs, nitrogen doping causes the decrease in the relative content of O-containing functional groups and the formation of both N-related molecular and surface centers that enhance the quantum yield of the material. The optical analysis suggests that the main emission in undoped nanoparticles comes from low-efficient blue centers bonded to the carbogenic core, eventually with surface-attached carbonyl groups, the contribution in the green range being possibly related to larger aromatic domains. On the other hand, the emission features of N-doped CDs are mainly due to the presence of N-related molecules, with the computed absorption transitions calling for imidic rings fused to the carbogenic core as the potential structures for the emission in the green range.

Synthesis and Photophysical Properties of Fluorescent 6-Aryl-D-π-A Coumarin Derivatives

A series of 6-aryl coumarin dyes were synthesized in satisfactory yields by Pd-catalyzed Suzuki cross-coupling reactions with a panel of boronic acids and coumarin bromides. Photophysical studies highlighted a large Stoke shift and interesting fluorescence quantum yield for these compounds. Optical properties were also investigated with the aid of quantum chemical calculations. The treatment of selected coumarin dyes with increasing amounts of trifluoroacetic acid showed that their fluorescence can be strongly influenced by pH (fluorescence quenching at high acid concentrations), while the addition of Fe³⁺ and Al³⁺ metal ions allowed to highlight dichotomous behavior with the corresponding reduction in fluorescence with the increase of [Fe³⁺] or [Al³⁺]. Finally, biological assays and fluorescence microscopy imaging investigations indicated that these compounds can be used as potential biomarkers in living and fixed cells.

Formation of Citrazinic Acid Ions and Their Contribution to Optical and Magnetic Features of Carbon Nanodots: A Combined Experimental and Computational Approach

The molecular model is one of the most appealing to explain the peculiar optical properties of Carbon nanodots (CNDs) and was proven to be successful for the bottom up synthesis, where a few molecules were recognized. Among the others, citrazinic acid is relevant for the synthesis of citric acid-based CNDs. Here we report a combined experimental and computational approach to discuss the formation of different protonated and deprotonated species of citrazinic acid and their contribution to vibrational and magnetic spectra. By computing the free energy formation in water solution, we selected the most favoured species and we retrieved their presence in the experimental surface enhanced Raman spectra. As well, the chemical shifts are discussed in terms of tautomers and rotamers of most favoured species. The expected formation of protonated and de-protonated citrazinic acid ions under extreme pH conditions was proven by evaluating specific interactions with H2SO4 and NaOH molecules. The reported results confirm that the presence of citrazinic acid and its ionic forms should be considered in the interpretation of the spectroscopic features of CNDs.

Assembly of Multicomponent Nano-Bioconjugates Composed of Mesoporous Silica Nanoparticles, Proteins, and Gold Nanoparticles

The purpose of this work was the assembly of multicomponent nano-bioconjugates based on mesoporous silica nanoparticles (MSNs), proteins (bovine serum albumin, BSA, or lysozyme, LYZ), and gold nanoparticles (GNPs). These nano-bioconjugates may find applications in nanomedicine as theranostic devices. Indeed, MSNs can act as drug carriers, proteins stabilize MSNs within the bloodstream, or may have therapeutic or targeting functions. Finally, GNPs can either be used as contrast agents for imaging or for photothermal therapy. Here, amino-functionalized MSNs (MSN-NH2) were synthesized and characterized through various techniques (small angle X-rays scattering TEM, N2 adsorption/desorption isotherms, and thermogravimetric analysis (TGA)). BSA or lysozyme were then grafted on the external surface of MSN-NH2 to obtain MSN-BSA and MSN-LYZ bioconjugates, respectively. Protein immobilization on MSNs surface was confirmed by Fourier transform infrared spectroscopy, ζ-potential measurements, and TGA, which also allowed the estimation of protein loading. The MSN-protein samples were then dispersed in a GNP solution to obtain MSN-protein-GNPs nano-bioconjugates. Transmission electron microscopy (TEM) analysis showed the occurrence of GNPs on the MSN-protein surface, whereas almost no GNPs occurred in the protein-free control samples. Fluorescence and Raman spectroscopies suggested that proteins-GNP interactions involve tryptophan residues.

Exploiting combined absorption and front face fluorescence spectroscopy to chase classification: A proof of concept in the case of Sardinian red wines

We present the analysis of optical spectroscopy fingerprints of three different varieties of Sardinian red wine, Carignano, Cannonau and Monica, belonging to Italian DOC (Controlled Origin Designation) red wines family. We selected 15 commercial wines (five for each variety), produced in the middle and south regions of Sardinia form monovarietal grapes. Despite different grapes, farming and tasting, all the samples share common absorption and fluorescence features. A two steps analysis is applied to achieve good classification of the wines. We recorded typical absorbance spectra with a large absorption below 300 nm and a visible absorption band at about 520 nm. Colour attributes according to chromaticity coordinates were evaluated by means of transmittance data and coupled to wine aging data to achieve classification. Despite similar values of lightness (L*), chroma (C*_ab), and hue angle (h°_ab) for the three varieties, good clustering was gathered for Carignano and Cannonau wines, whilst Monica variety has wide spread chromatic coordinates. UV excited fluorescence spectra display large and composite emission bands from the near UV down to the whole visible range. We performed multivariate analysis in the framework of the principal component analysis of fluorescence spectra coupled with absorption ones being able to achieve good clustering between the three varieties. One anomaly among Cannonau wines is discussed.

Vibrational and optical characterization of s-triazine derivatives

The optical and electron properties of three different s-triazine derivatives are investigated to ascertain the role of the donor acceptor character in amine-triazine systems depending on the bridging radical of the ammine group. The three derivatives were obtained starting from three different ammine compounds allowing to achieve a structure with a triazine core, surrounded by three ammine group and terminated with cyano or methyl or oxy-methyl functional group. Experimental optical data were interpreted in view of the electronic insights gathered by means of density functional theory simulations on base compounds. As compared to the reference electron donating triazine core, the resulting compounds show different donor acceptor character, from electron accepting to electron donating feature. Among the analyzed derivatives, the cyano terminated ammino-triazine compound shows the most promising optical features for photonics and lighting applications.

A facile strategy for new organic white LED hybrid devices: design, features and engineering

A facile and ecofriendly strategy to design and engineer new organic white LEDs is tested.

Investigation of energy transfer in terbium doped Y (2)SiO(5) phosphor particles

The kinetics of luminescence of sol-gel synthesized terbium doped Y (2)SiO(5) (YSO) phosphor particles is investigated in detail with reference to Tb concentration in the 0.001%-10% range. By increasing the dopant concentration, the luminescence profile changes from a blue to a green peaked emission spectrum because of the energy transfer among centers. The inter-center energy transfer mechanism is well accounted for by the Inokuti-Hirayama (IH) kinetic model which is based on a statistical average of inter-center distance dependent decay modes of the donor luminescence. The distribution of the decay modes is implemented from the Förster-Dexter resonance theory of energy transfer by assuming a rate constant for the energy transfer by multipolar interactions between donors and acceptors. However, the experimental results recorded in the low concentration limit show the presence of green emission contributions in the luminescence spectrum which cannot be related to the Tb concentration; for this reason an additional internal energy transfer mechanism, occurring among levels of the same center, is proposed to account for the recorded emission properties. Thus, a new and more exhaustive model which includes both the internal and external energy transfer processes is considered; the proposed model allows a better explanation of the spectroscopic features of Tb related centers in YSO crystals and discloses the critical concentration and the quantum yields of the different energy transfer mechanisms.

Emission properties of Tb3+ ions in LYSO: evidence of a cross relaxation mechanism explained by a kinetic model

The optical properties of Tb(3+) ions in oxyorthosilicates of lutetium and yttrium (LYSO) are reported. The introduction of a small number of terbium ions (nominal content 10 ppm) generates, in the otherwise transparent absorption spectrum of the matrix, an ultraviolet absorption band peaked at about 240 nm. By exciting within the reported UV band, line shaped emissions in the 350-600 nm range are detected. These transitions are related to the (5)D(3) and (5)D(4) levels of the Tb(3+) ions and are characterized by decay times in the millisecond time domain. Analysis of the decay time measurements allows us to individuate a cross relaxation mechanism among terbium ions even at the low dopant concentration investigated. We propose a three-level kinetic model which is able to successfully reproduce the experimental data, allowing us to discriminate among the radiative and non-radiative contributions to the observed emissions.

Ultraviolet Photoluminescence of Silanol Species in Mesoporous Silica

The optical properties of sol-gel synthesized porous silica excited by synchrotron radiation in the 4-10 eV range of samples with different porosity at 8 K and room temperature are reported. The analysis of the ultraviolet photoluminescence indicate the contributions of two different emitting centers. The spectral and temporal characteristics of the two luminescence bands are reported: emission peaks at about 3.7 and 4.0 eV, excitation channels around 5.4-5.7 and 6.2-6.5 eV, and mean lifetimes of about 17 and 2 ns, respectively. The analysis of the optical properties in samples with different porosity allows us to propose a silanol-related model for the two centers.

Time Resolved Ultraviolet Photoluminescence of Mesoporous Silica

We studied the optical properties of sol-gel synthesized porous silica excited by synchrotron radiation in the 4-10 eV range. The spectral and temporal characteristics of the ultraviolet photoluminescence at about 3.7 eV are reported. The UV emission results from the contribution of two different centers: the first one centered at 3.7 eV with a decay time of 2.0 ns and the second one peaked at 3.9 eV with a decay time of 20 ns. We propose to assign the observed luminescence to different interacting surface silanols.