Band Gap Excitation Research Articles

Defects control and origins of blue and green emissions in sol-gel ZnO thin films

ZnO has broad application prospects in the field of LED lighting and display. However, the unclear luminescence mechanism limits the improvement of luminous efficiency and the realization of controllable luminescence. Herein, intrinsic defects (Zni and VO) in sol-gel ZnO thin films were controlled by post-annealed in different atmospheres (air, N2 and vacuum). The effect of annealing atmospheres on the intrinsic defects were quantitatively studied by XRD, Raman, XPS and EPR spectra, and the relationship between intrinsic defects and visible emissions were systematically investigated by excitation-dependent PL spectra under above bandgap and below bandgap excitations. Results show that N2-annealed ZnO film with more Zni defects and fewer Vo defects exhibits much stronger blue (∼440 nm and ∼450–480 nm) and green emissions (∼510–540 nm). Zinc interstitials states (including Zni and ex-Zni states) are the initial states of the electronic transitions for the blue (∼440 nm and ∼450–480 nm) and green emissions (∼510–540 nm). In addition, transitions from the conduction band to the VO level also emit a green peak at 525 nm, which can only be observed under above bandgap excitation. This work contributes to a better understanding of defect-induced blue and green emission in ZnO, which will help to achieve controllable luminescence and facilitate its commercial application as a luminescent material.

Photocatalytic reduction of Cr(VI) by Bi2.15WO6 complexed with polydopamine: Contribution of the ligand-to-metal charge transfer path

Photocatalytic reduction of Cr(VI) in water environments attracts more attention; however, the mechanisms involved in this process have not been clearly elucidated yet. In this study, the photocatalytic reduction of Cr(VI) by polydopamine modified Bi2.15WO6 (PDA/BWO) under visible light was conducted. Kinetics results show that PDA apparently accelerates the reduction of Cr(VI). The quasi-first-order kinetic constant of Cr(VI) reduction by 5PDA/BWO is 70.0 times that of the original BWO, reaching 0.070 min−1. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman analyses confirm the formation of ligand-to-metal charge transfer (LMCT) complex [Bi(III)OC] between PDA and BWO. The formed Bi(III)OC complex enhances visible light response and narrows the bandgap of PDA/BWO. The photoelectrochemical and photoluminescent characterization further reveals that the formed Bi(III)OC complex inhibits the recombination of carriers, thus enhancing the photocatalytic reactivity of PDA/BWO. Electrons, are derived from three paths, including dye sensitization, LMCT and bandgap excitation, contribute to Cr(VI) reduction by PDA/BWO. This study provides new insights on the paths of Cr(VI) reduction by PDA/BWO under visible light.

Photocharging of Semiconductor Materials: Database, Quantitative Data Analysis, and Application in Organic Synthesis

AbstractPhotocharging or photodoping is a process in which electrons are accumulated in a semiconductor upon bandgap excitation followed by quenching of the photogenerated holes by reductants. In semiconductors with excess of electrons, negative charge is compensated by cations, of which the most ubiquitous is H+. Photocharging of semiconductors has been studied since 1980s both from a fundamental perspective and application—as source of electrons and protons for reduction of organic compounds in the dark, solar‐to‐electric energy conversion, and recently also in the design of autonomous microswimmers. In this review, experimental data collected over 40 years of research are summarized and quantified. Maximum specific concentration of electrons stored in 1 g of a semiconductor, maximum average number of electrons stored per semiconductor particle, initial rate of photocharging, and initial rate of discharging are calculated for six classes of semiconductor materials, Ti‐, Zn‐, Cd‐, In‐, W‐based and graphitic carbon nitrides. Dependence of these parameters on material specific surface area, particle volume, and other properties is analyzed and trends are derived. A public database of photocharged materials is created to facilitate design of high‐performing materials with photocharging function, their application as rechargeable reductants in organic synthesis and development of devices.

Kinetic Study of the Thermal Quenching of the Ultraviolet Emission in Zn2GeO4 Microrods

Zn2GeO4 microrods obtained by thermal evaporation of a compacted powder mixture of ZnO and Ge exhibit quite intense UV luminescence at low temperatures. Herein, the luminescence properties of Zn2GeO4 microrods are studied for 2:1 and 1:1 ZnO:Ge ratio in the precursor mixture. In both cases, Zn2GeO4 microrods of high crystal quality produce a 355 nm emission under aforementioned bandgap excitation conditions at low temperatures. However, this emission vanishes at room temperature (RT) in the 1:1 samples while it is kept in the 2:1 ones. Herein this work, the thermal quenching of the UV luminescence is studied by means of steady and time‐resolved photoluminescence techniques from 4 K up to RT for both Zn2GeO4 microrods. The analysis of the results leads us to conclude that although the luminescence mechanisms are the same in both cases, a higher decay rate is observed in the 1:1 in both intensity and lifetime, which explain the observed thermal quenching at RT.

Synergistic Effect of Au-PdO Modified Cu-Doped K2W4O13 Nanowires for Dual Selectivity High Performance Gas Sensing.

Both 3-hydroxy-2-butanone and triethylamine are highly toxic and harmful to human health, and their chronic inhalation can cause respiratory diseases, eye lesions, dermatitis, headache, dizziness, drowsiness, and even fatality. Developing sensors for detecting such toxic gases with low power consumption, high response with superselectivity, and stability is crucial for healthcare and environmental monitoring. This study presents a typical gas sensor fabricated based on AuPdO modified Cu-doped K2W4O13 nanowires, which can selectively detect 3-hydroxy-2-butanone and triethylamine at 120 and 200 °C, respectively. The sensor displays excellent sensing performance at reduced operating temperature, high selectivity, fast response/recovery, and stability, which can be attributed to a synergistic effect of Cu dopants and AuPdO nanoparticles on the K2W4O13 host. The enhanced sensing response and selectivity could be attributed to the oxygen vacancies/defects, bandgap excitation, the electronic sensitization, the reversible redox reaction of PdO and Cu, the cocatalytic activity of AuPdO, and Schottky barrier contacts at the interface of tungsten oxide and Au. The significant variations in the activation capacities of Cu-doped K2W4O13, Pd/PdO, and Au nanoparticles toward 3H-2B and TEA, and the diffusion depth of the two gases in the coated sensing layer may cause dual selectivity. The designed gas sensor materials can serve as a sensitive target for detecting toxic biomarkers and hold broad application prospects in food and environmental safety inspection.

Structure, Stability, and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange.

A new strategy to incorporate the Sn(II) cation and its stereoactive lone pair into the structure of a photocatalytic oxide has been achieved by leveraging the asymmetric coordination environments within the (111)-oriented perovskite-type layers of Ba5Nb4O15. This layered perovskite represents one of the few known photocatalysts capable of efficiently splitting water, but its activity is restricted to ultraviolet radiation owing to its large band gap. By reacting this layered niobate at 350 °C for 24 h within a low-melting SnCl2/SnF2 salt, the new (Ba1-xSnx)Nb4O15 (x = 0-0.5; P3̅m1; a = 5.79650(5) Å, c = 11.79288(8) Å; Z = 2) has been prepared in high purity with up to ∼50% Sn(II) cations. Statistical disordering of the Sn(II) cations was probed by neutron diffraction Rietveld refinements and found to occur predominantly over the asymmetric cation sites, Ba2 and Ba3, for the 40% Sn(II) composition of x = 0.4. An increasing Sn(II) amount significantly red-shifts the band gap (Eg) from 0% Sn for x = 0 (3.78 eV; ultraviolet, indirect) to 40% Sn for x = 0.4 (Eg = 2.35 eV; visible, indirect), as found by UV-vis diffuse reflectance. Density functional theory calculations show an increasing metastability, i.e., a thermodynamic instability toward decomposition to the simpler oxides SnO, Nb2O5, and SnNb2O6. A synthetic limit of ∼50% Sn(II) cations can be kinetically stabilized under these reaction conditions. For the highest Sn(II) amounts, photocatalytic rates are observed for the production of molecular oxygen from water of up to ∼77 μmol O2 h-1 g-1 (visible irradiation) and ∼159 μmol O2 h-1 g-1 (UV-vis irradiation), with apparent quantum yields of ∼0.35 and 0.52%, respectively. By comparison, pure Ba5Nb4O15 exhibits no measurable photocatalytic activity under visible-light irradiation. Electronic structure calculations show that the decreased band gap stems from the introduction of the Sn(II) cations and the formation of a higher-energy valence band arising from the filled 5s2 valence orbitals. Thus, visible-light bandgap excitation occurs from electronic transitions predominantly involving the Sn(II) (5s2) to Nb(V) (4d0) cations. This study demonstrates the new and powerful utility of low-temperature Sn(II)-exchange reactions to sensitize layer-type oxide photocatalysts to the visible region of the solar spectrum, which is facilitated by exploiting their asymmetric cation environments.

Optical Studies in Red/NIR Persistent Luminescent Cr-Doped Zinc Gallogermanate (ZGGO:Cr)

Zn1+xGa2−2xGexO4 (ZGGO:Cr)-persistent phosphor, with a molar fraction, x, of x = 0.1, doped with a 0.5% molar of chromium, was synthesised via solid-state reaction at 1350 °C for 36 h. X-ray diffraction measurements and Raman spectroscopy evidence a single crystalline phase corresponding to the cubic spinel structure. Room temperature (RT) photoluminescence (PL) and afterglow decay profiles were investigated using above and below bandgap excitation. In both cases, persistent PL was observed for almost 8 h, mainly originating from a Cr3+ defect, the so-called N2 optical centre. RT PL excitation and diffuse reflectance allow identification of the best pathways of Cr3+ red/NIR emission, as well as estimation of the ZGGO bandgap energy at 4.82 eV. An in-depth investigation of the observed luminescence at 15 K and temperature-dependent PL under site-selective excitation reveals the spectral complexity of the presence of several optically active Cr3+ centres in the ZGGO host that emit in almost the same spectral region. Furthermore, the temperature dependence of the R-lines’ intensity indicates the existence of thermal populating processes between the different optical centres. Such observations well account for a wide distribution of defect trap levels available for carrier capture/release, as measured by the persistent luminescence decay, from which the carriers are released preferentially to the N2 Cr3+-related optical centre.

Distinctive optical transitions of tunable multicolor carbon dots.

Three types of carbon dots (CDs) are synthesized from isomers of phenylenediamine to develop multicolor nanomaterials with low toxicity, high stability, and high quantum yield. The distinctive electronic structures of CDs lead to the characteristic optical transitions, such as three colors of blue, green, and red, which are primarily attributed to the difference in configurations, despite the similar basic structures of conjugated systems. The excitation-independent emission and the single exponential decay of CDs indicate the single chromophore-like nature in each type of CD. In addition, the two-photon luminescence of CDs exhibits a comparable shape and time profile to the typical photoluminescence with high photostability. Although the surface-related defect states are observed by intragap excitation, the contribution of defect states is barely observed in the emission profile upon band gap excitation. Consequently, the controllability of optical transitions in CDs enhances the potential of tunable multicolor nanomaterials for various applications as alternatives to quantum dots containing toxic elements.

Engineering of W-shaped benzodithiophenedione-based small molecular acceptors with improved optoelectronic properties for high efficiency organic solar cells.

In the current study, with the objective to improve the overall performance of organic solar cells, seven new W-shaped small molecular acceptors – were developed theoretically by the end-group alteration of the reference (WR) molecule. The MPW1PW91 functional with the basis set 6-31G(d,p) was used to explore the optoelectronic properties of the WR and W1–W7 molecules and the time-dependent self-consistent filed (TD-SCF) simulation was used to investigate the solvent-state calculations. The several explored photovoltaic attributes were the absorption spectra, excitation energies, bandgap between the FMOs, oscillator strength, full width at half maximum, light-harvesting efficiency, transition density matrices, open-circuit voltage, fill factor, density of states, binding energy, interaction coefficient, etc. Overall, the results revealed a bathochromic shift in the absorption maxima (λmax), a reduced HOMO–LUMO gap (Egap), and smaller excitation energy (Ex) of the altered molecules as compared to the WR molecule. Some of the optoelectronic aspects of a well-known fused ring based acceptor named Y6 are also compared with the studied W-shaped molecules. Additionally, the W1 molecule presented the smallest Egap, along with highest λmax and the lowest Ex, amongst all, in both the evaluated media (gas and solvent). The open circuit voltage (VOC) of all the considered small molecular acceptors was calculated by pairing them with the PTB7-Th donor. Here, W6 and W7 displayed the best results for the VOC (1.48 eV and 1.51 eV), normalized VOC (57.25 and 58.41) and FF (0.9131 and 0.9144). Consequently, in light of the results of this research, the altered molecules could be considered for practical implementation in the manufacturing of OSCs with improved photovoltaic capabilities.

Defect-Interceded Cascading Energy Transfer and Underlying Charge Transfer in Europium-Doped CsPbCl3 Nanocrystals.

Rare-earth ion (RE3+) doping in cesium lead chloride (CsPbCl3) has unlocked novel prospects to explore changes in optical, magnetic, and charge carrier transport properties. This leads to a huge advancement in optoelectronic applications, yet deep understanding of the photophysics governing the energy transfer processes is lacking and demands vital attention. Herein, we probe into the mechanistic transfer processes from the band edge of the host (CsPbCl3) to the dopant europium ion (Eu3+) with the aid of femtosecond fluorescence upconversion and transient absorption (TA) spectroscopy. The upconversion measurement portrays a defect-mediated cascading energy transfer from CsPbCl3 to Eu3+ and further cross-relaxation among Eu3+ states. Moreover, TA studies reveal that there is charge transfer from the band edge of CsPbCl3 to doping-induced shallow defect states. Furthermore, two-photon absorption study establishes no compromise in the transfer mechanism even upon bandgap excitation. This work validates that Eu-CsPbCl3 is an apt entrant for optoelectronic applications.

Sample Concentration Affects Optical Gain Results in Colloidal Nanomaterials: Circumventing the Distortions by Below Band Gap Excitation

Ultrafast spectroscopy studies have been key to the development of optical materials, including colloidal semiconductor nanocrystals (NCs) engineered for lighting and light-harvesting technologies. Several physical processes, which are revealed by ultrafast spectroscopy in NCs, are highly dependent on the average number of excitons created per NC, including optical gain properties and multiexciton interactions. Consequently, proper considerations regarding NC populations are necessary to avoid misinterpretations. In this paper, we present an experimental and theoretical analysis of the influence of the sample optical density (OD) at the excitation energy on the results of ultrafast spectroscopy studies in NCs. We show that the pump beam depletion caused by high ODs can drastically change the results from transient absorption (TA) experiments leading to data misinterpretations, such as the overestimation of the optical gain threshold. Based on that, we propose a robust modification on the TA technique, which allows for an OD-independent characterization, free of distortions. The modification consists of pumping the sample below its band gap energy, limiting the electronic excitation to a two-photon absorption process, resulting in an effectively zero OD for the pump beam and a uniform excitation in the direction of the beam propagation. Consequently, an undistorted TA signal is produced, allowing for precise characterization of NCs, including the gain/absorption cross section, gain coefficient, and gain threshold. Furthermore, the uniform excitation allows for higher signal-to-noise ratio, independent of the sample concentration.

Photo-assisted degradation of organic pollutant by CuFeS2 powder in RGB-LED reactors: A comprehensive study of band gap values and the relation between wavelength and electron-hole recombination

This work investigated the relation between direct band-gap conversion and excitation wavelength towards catalysis efficiency in red, green, and blue (RGB) light-emitting diode (LED) reactors. An integrating sphere and spectroradiometer system obtained the emission wavelengths of the operating modes spectra of the RGB-LED reactors. The effects of pH, catalyst, and H2O2 dosage were investigated, and the optimal photocatalysis conditions were found to be at pH 3, catalyst loading of 0.25 g L−1, 0.25 mmol L−1 of H2O2(aq) (30% v/v) for an initial model pollutant concentration of 75 mg L−1 and reaction time of 60 min. Under the higher intensity red mode (R1), the highest color removal rate was reached (88.1%), while in the conventional white light mode (WL), the decolorization efficiency remained 64.3%. Furthermore, the R1 mode showed a superior TOC removal than the WL mode, reaching the final removal efficiencies of 91.86% and 61.06%, respectively. Contrary to what has been reported, as the dominant wavelength of the irradiation source decreased, the efficiency also tended to decrease. The electron-hole recombination increased as the irradiation mode decreased, and a work function (φ) representing this phenomenon was obtained by the deduction of the relation between energy (E) and frequency (f) of the photons involved. Therefore, the insights presented in this work are valuable tools in increasing LED photocatalysis efficiency.

Activation of bismuth aluminate for obtaining near infrared emission

New results on NIR emission in Bi2Al4O9 phosphors activated with Cr3+, Er3+or Nd3+ are presented. These phosphors were prepared by a simple two step method consisting of combustion followed by annealing at 800C. Annealing step was necessary to obtain powders with good crystallinity; as-combusted powders being amorphous. Host sensitization was observed in all the phosphors. An excitation band around 279 nm corresponds to bandgap excitation of the host1So→ 3P1 transition of the Bi3+ ion, while that at 360 nm to the defect absorption. Apart from the excitation in these host related bands, characteristic excitations also produced intense emission lines. It is suggested that these phosphors can be useful for making low cost NIR sources needed in various applications.

Observation of negative photoconductivity at bandgap and super bandgap excitations in GaN nanorods

We report on the surprising observation of negative photoconductivity (NPC) in GaN nanorods (NRs) by bandgap and super bandgap excitations. A metal-semiconductor-metal (MSM) type of device configuration using Ni/Au as an electrode at both ends, has been used to study the NPC phenomenon. On exposing the device to the light sources with 363 nm (bandgap excitation) and 250 nm (super bandgap excitation) wavelengths, NPC with a drop of approximately 50 and 60% was observed, respectively. To explain this phenomenon, a model of trapping of photogenerated electrons by the trap states is proposed. Interestingly, a significant drop in the illumination current is observed at low values of power density (up to 3 μW/mm2) of the incident light. It has been interpreted that on increasing the power density, the density of trapped electrons starts approaching the density of available trap states. The de-trapping process is observed to be very slow as the illumination current reached the dark current value in nearly 2 h after switching off the incident light. The observation of NPC and saturation of trap states with high intensity of incident light are also validated by Kelvin Probe Force Microscopy (KPFM) characterization performed in the dark and on illumination with varying intensity of the incident light. Furthermore, on increasing the temperature from room temperature (RT) to 300 °C, the NPC was found to reduce to almost zero, which indicates the de-trapping of trapped electrons on increasing the temperature.

Tail state mediated conduction in zinc tin oxide thinfilm phototransistors under below bandgap optical excitation

We report on the appearance of a strong persistent photoconductivity (PPC) and conductor-like behaviour in zinc tin oxide (ZTO) thinfilm phototransistors. The active ZTO channel layer was prepared by remote plasma reactive sputtering and possesses an amorphous structure. Under sub-bandgap excitation of ZTO with UV light, the photocurrent reaches as high as ~ 10−4 A (a photo-to-dark current ratio of ~ 107) and remains close to this high value after switching off the light. During this time, the ZTO TFT exhibits strong PPC with long-lasting recovery time, which leads the appearance of the conductor-like behaviour in ZTO semiconductor. In the present case, the conductivity changes over six orders of magnitude, from ~ 10−7 to 0.92/Ω/cm. After UV exposure, the ZTO compound can potentially remain in the conducting state for up to a month. The underlying physics of the observed PPC effect is investigated by studying defects (deep states and tail states) by employing a discharge current analysis (DCA) technique. Findings from the DCA study reveal direct evidence for the involvement of sub-bandgap tail states of the ZTO in the strong PPC, while deep states contribute to mild PPC.

Quantum Chemical Approach of Donor−π–Acceptor Based Arylborane–Arylamine Macrocycles with Outstanding Photovoltaic Properties Toward High-Performance Organic Solar Cells

A theoretical quantum chemical investigation of D−π–A conjugated molecules based on arylborane–arylamine is proposed with the motive of suggesting new organic materials for organic solar cells (OSCs). Optoelectronic properties and geometries of organic donor molecules MC1R–MC1M5 encompassing a caged ring as the donor, thiophene as the bridge, and end-capped moieties as the acceptor are characterized using DFT and TD-DFT. Study involved forecasting the photophysical descriptors such as frontier molecular orbitals, ionization potential, electron affinity, molecular electrostatic potential, transition density matrix, binding energy (Eb), dipole moment, reorganization energy, and open-circuit voltage (VOC) at ground state geometries using the MPW1PW91/6-31G(d,p) basis set. By modulation of end-capped acceptor groups, comprehensive analysis of newly tailored molecules is conducted to reveal insight about π-conjugation contribution on the performance of OSCs. The structure–property relationship of the reference (MC1R) is contrasted with newly organized molecules (MC1M1–MC1M5). The proposed strategy effectively enhanced the absorption (λmax) of all designed molecules. MC1M1 exhibited λmax at 530 nm in DCM (dichloromethane) solvent with the lowest band gap (2.86 eV) and lowest excitation energy of 2.34 eV. An elevated VOC of 2.27 eV is revealed by MC1M4. MC1M2 presented a lowest binding energy of 0.42 eV. The highest hole and electron mobility is ascertained in all newly designed molecules because of their low reorganization energy values which validated preferrable photovoltaic properties as compared to the reference MC1R. MC1M1 showed the lowest electron mobility (λe = 0.009301 eV), and MC1M2 demonstrated the lowest hole mobility (λh = 0.001 874 eV). Our comparative outcomes are proposed to be possible choices for designing efficient OSCs.

A carbon-doping related luminescence band in GaN revealed by below bandgap excitation

Carbon doped GaN grown by hydride vapor phase epitaxy was investigated by photoluminescence and photoluminescence excitation spectroscopy covering a broad range of carbon concentrations. Above bandgap excitation reveals typical transitions related to CN and CN−Hi that decrease with increasing carbon concentration. Besides the formation of nonradiative defects, the formation of complexes containing more than one carbon atom is proposed to be responsible for this reduction. Below bandgap excitation reveals an intense emission band around 1.62 eV for [C] >1018cm−3 that is shown by photoluminescence excitation spectroscopy to be most efficiently excited at 2.7 eV. The 1.62 eV transition thermally quenches above 80 K. A configuration-coordinate diagram model is proposed to explain the observed emission, excitation, and thermal quenching behavior. Based on the simultaneous increase in the concentration of tri-carbon complexes, this band is tentatively attributed to a transition involving a deep tri-carbon-related charge state transition level in the GaN bandgap.

Role of hydrogen species in promoting photoluminescence from Eu3+-doped ZnO thin films via bandgap excitation

We studied the role of hydrogen-containing species (OH and/or H) in promoting photoluminescence (PL) from 1 at. % Eu3+ ions doped in ZnO thin films. The hydrogen concentration in the films was systematically changed by varying the substrate temperature and the vapor pressure of H2O gas supplied during sputter deposition. The correlation between the PL spectra via bandgap excitation and the degree of oxidization/hydrogenation was investigated by x-ray diffraction and Fourier-transform infrared spectroscopy. Films deposited at room temperature under H2O partial pressures higher than 10−2 Pa were sufficiently hydroxylated, as confirmed by the appearance of diffractions peaks from Zn(OH)2 coexisting with ZnO(002). Eu3+ emissions were observed after post-annealing in a vacuum or O2 atmosphere. When the H2O pressure was lower than 10−2 Pa, the ZnO:Eu films were so oxygen-deficient as to exhibit a metallic character, which deactivated the Eu3+ emission. Deposition at temperatures above 200 °C reduced the OH and/or H species incorporated in the ZnO films and only a faint Eu3+ emission was observed. The H2O pressure under which a sharp Eu3+ emission could be obtained was between 1.0 and 2.5 × 10−2 Pa if subsequent post-annealing was done in a vacuum. For more oxidized films deposited at 3.5 × 10−2 Pa, reduction by post-annealing in an H2 atmosphere was effective to generate a sharp and intense Eu3+ emission signal through reduction and hydrogenation, confirming that a moderate oxidization/hydrogenation state is a necessary condition. Codoped hydrogen species will facilitate substituting Zn2+ sites with emission-active Eu3+ ions and stabilize them.

Size-Resolved Electron Solvation in Neutral Water Clusters.

Cluster-size-resolved ultrafast dynamics of the solvated electron in neutral water clusters with n = 3 to ∼200 molecules are studied with pump–probe time-of-flight mass spectrometry after below band gap excitation. For the smallest clusters, no longer-lived (>100–200 fs) hydrated electrons were detected, indicating a minimum size of n ∼ 14 for being able to sustain hydrated electrons. Larger clusters show a systematic increase of the number of hydrated electrons per molecule on the femtosecond to picosecond time scale. We propose that with increasing cluster size the underlying dynamics is governed by more effective electron formation processes combined with less effective electron loss processes, such as ultrafast hydrogen ejection and recombination. It appears unlikely that any size dependence of the solvent relaxation dynamics would be reflected in the observed time-resolved ion yields.

SrAl2O4: Eu2+, Dy3+ persistent luminescent materials functionalized with the Eu3+(TTA)-complex by microwave-assisted method

Recently, several classes of rare-earth-doped luminescent materials have been drawing attention due to structurally engineered energy converting systems, capable of tuning absorption and emission spectral ranges, outlining new materials and applications in photonics. In this scenario, this work presents the development of SrAl2O4:Eu2+,Dy3+ phosphors prepared by the Pechini method, which were further APTMS-functionalized (3-aminopropyltrimethoxysilane) by microwave-assisted synthesis, incorporating a Eu3+ β-diketonate complex embedded within a SiO2-R network to increase light absorption and promote energy transfer processes. Powder X-ray diffraction data revealed a stable characteristic monoclinic phase of the SrAl2O4 host matrix, which undergoes structural changes after functionalization. Particle morphology and elemental distribution were probed by scanning electron microscopy technique, exhibiting surface alteration effects. Photoluminescence spectra displayed a characteristic broad green emission band assigned to the 4f65d1(2D) → 4f7(8S7/2) interconfigurational transition of the Eu2+ ion. Functionalized materials presented absorption shifts coupled with an emission band intensification suggesting effective interactions between the β-diketonate complex, the SiO2-R network, and the inorganic host matrix. Increased absorption range and persistence decay time under near band gap excitation on modified materials were also observed.