Photoluminescence Emission Intensity Research Articles

Photoluminescence properties of rare-earth ion-doped Na5YSi4O12-based glass ceramics

We developed herein photoluminescent glass ceramics based on rare-earth ion-doped Na5YSi4O12-type materials according to the Na3+3xY1−x−yRySi3O9 (R: Sm3+, Eu3+, Dy3+, Tb3+) composition. Glass ceramics generally have the advantages of excellent chemical durability, heat resistance, and moldability over sintered ceramics. Upon irradiation with near-ultraviolet light, Sm3+-, Eu3+-, Dy3+-, and Tb3+-doped glass ceramics emit purplish orange, reddish orange, yellow, and green lights, respectively. The photoluminescent emission intensity of glass ceramics is higher than that of the original glasses, and the emission intensity depends on the crystalline phase. The highest emission intensity of various rare-earth ion-doped glass ceramics is obtained when the parameter y is equal to 0.03, 0.16, and 0.02 for the Sm3+-, Eu3+-, and Dy3+-doped glass ceramic samples, respectively. The internal quantum efficiency is 3%, 37%, 7% and 23% for the Sm3+-, Eu3+-, Dy3+-, and Tb3+-doped samples, respectively. Thus the Na superionic conducting Na5YSi4O12-type glass-ceramics were proved to have potentiality as novel phosphors.

Nitrogen-doped carbon quantum dots conjugated isoreticular metal-organic framework-3 particles based luminescent probe for selective sensing of trinitrotoluene explosive.

Amine group-containing isoreticular metal-organic framework (IRMOF-3) particles are utilized for the first time as a trinitrotoluene (TNT) sensing material. IRMOF-3 particles are synthesized using zinc nitrate as a metal precursor and 2-amino-1,4-benzenedicarboxylic acid as a linker. The nitrogen-doped carbon quantum dots (NCQDs) are synthesized from citric acid and ethylenediamine as carbon and nitrogen precursor, respectively. The NCQDs are conjugated with IRMOF-3 particles as IRMOF-3/NCQDs. The TEM micrograph revealed the average size of IRMOF-3 particles to be 363.66nm. The photoluminescence emission intensity of IRMOF-3 particles at λem 430nm is highly increased in the presence of NCQDs (λex 330nm). Both the as-synthesized IRMOF-3 and IRMOF-3/NCQD particles are explored for TNT detection to compare the effect of NCQDs on the IRMOF-3 particle surface. Lower limit of detection (7.5 × 10-8M) and higher Stern-Volmer constant (4.46 × 106M-1) are achieved by IRMOF-3/NCQD particles. The association constant also increased from 5.3 × 104 to 2.78 × 106M-1 after the conjugation of IRMOF-3 particles with NCQDs. Moreover, enhanced selectivity for TNT over trinitrophenol is achieved using the IRMOF-3/NCQD particles. Graphical Abstract.

Effects of Y2O3 and transition-metal nitrates on phase, microstructures and PL properties of N-containing Ce2Si2.5Al0.5O3.5N3.5 melilite

N-containing Ce2Si2.5Al0.5O3.5N3.5 (CeSiAlON) melilite was synthesized at 1550 and 1600 °C for 5 h from CeO2, Si, Al, and Al2O3 in nitrogen by using Y2O3 and transition-metal nitrates (Co(NO3)2∙6H2O and Ni(NO3)2∙6H2O) as additives. The effects of Y2O3 and transition-metal nitrates on the phase, microstructures and photoluminescence properties of CeSiAlON melilite were studied. The incorporation of Y2O3 can promote the reaction of raw materials to a low degree, and results in a unit cell shrinkage of CeSiAlON due to the smaller radius of Y atom than that of Ce atom. The transition-metal nitrates can accelerate the reaction clearly and facilitate the formation of CeSiAlON fibers. The photoluminescence (PL) properties of CeSiAlON melilite presents a board violet emission band because of the 5d-4f transitions of Ce3+, and the additives can enhance the PL emission intensities of specimen significantly.

Role of oxygen vacancies on the green photoluminescence of microwave-assisted grown ZnO nanorods

Mechanism of commonly seen defect mediated photoluminescence (PL) from ZnO nanostructures is a topic of much discussion mainly due to its broad nature originating from several types of defects. Identification of such surface related defects requires suitable specimen having high surface to volume ratio characterized by complimentary techniques. Here, ZnO nanorods of different aspect ratio within the quantum confinement regime have been prepared using microwave-assisted synthesis method by varying time in the range of 1–4 min. The band gap as well as intensity of visible PL emission is found to decrease with the increase in size of nanorods obtained by allowing longer preparation time. Excitation wavelength dependent PL shows a strong green emission at ∼540 nm for above the band gap excitation (ABE) as well as below the band gap excitation (BBE) near to the band edge. Whereas a blue emission at ∼485 nm is seen for excitations far below the band gap. A systematic shift in emission from green to blue is observed for decreasing values of BBE, whereas almost no shift was seen for green emission with the variation of ABE. It is proposed that the green PL can be seen when ABE generated electrons in the conduction band transit rediatively to singly ionized oxygen vacancy (Vo+) and finally to reach the valence band whereas the blue emission may appear by direct excitation of electrons to a sub-band within the band gap by BBE. The presence of Vo+ in ZnO nanorods is confirmed by x-ray photoelectron spectroscopic studies and correlated with the green PL that shows increased intensity for higher concentration of Vo+ in smaller nanorods.

Spectroscopic and color chromaticity analysis of rhodamine 6G dye-doped PVA polymer composites for color tuning applications

Herein we report the successful fabrication of highly flexible, reversibly stretchable and transparent rhodamine 6G/poly(vinyl alcohol) (Rh6G/PVA) polymer composite (PC) films using a user-friendly solution casting method by adding different amounts, viz. 0, 0.5, 1, 1.5 and 2 wt%, of Rh6G dye. The FTIR studies reveal that an interaction between PVA matrix and added Rh6G dye and room-temperature photoluminescence (RTPL) emission intensity is decreased with the increase in the Tg is observed from DSC thermograms. The developed films show appreciable optical and RTPL properties as established by a UV–visible and fluorescence techniques such that the electronic spectral studies substantiate the changes in electronic band structure of PC films, leading to appreciable changes in the optoelectronic properties. These prepared films with excellent optoelectronic properties alongside appreciable flexibilities and stretchabilities aid their applications to organic light emitting diodes (OLED) with enhanced RTPL studies.

Laser-assisted synthesis of ZnO/ZnSe hybrid nanostructured films for enhanced solar-light induced water splitting and water decontamination

In this work, a novel method was developed to synthesize visible light-responsive ZnO/ZnSe photocatalysts, using rapid, simple Pulsed Laser Ablation of Solids in Liquids (PLASL) method. Using this method, we synthesized high-purity ZnO/ZnSe hybrid nanostructures with an optimum weight ratio of 10:4, which exhibited better photocatalytic activity. The addition of ZnSe on the ZnO semiconductor surface improved the light absorption of the composites and simultaneously decreased the photoluminescence emission intensity, which is an indicator of the inhibition of the electron-hole recombination rate. The nanostructured composites synthesized using the PLASL method were applied for photo-electrochemical water splitting and photo-degradation studies. The synthesized ZnO/ZnSe hybrid nanocomposites exhibited excellent visible-light-driven photocatalytic activity, which is highly desirable for water decontamination and photo-electrochemical water oxidation. This work, therefore, empirically demonstrates how this simple, cost-effective laser-based technique can be employed to rapidly synthesize high-purity, visible-light responsive photocatalysts expanding the potential for future solar energy conversion technologies.

Enhancing luminescent down-shifting of Eu-doped phosphors by incorporating plasmonic silver nanoparticles for silicon solar cells

This study experimentally demonstrated enhanced fluorescence emissions from luminescent down-shifting (LDS) Eu-doped phosphors under the effects of localized surface plasmon resonance (LPSR) from silver nanoparticles (Ag NPs). The plasmonic effects of the Ag NPs was examined in terms of plasmon-enhanced Raman scattering and plasmonic absorption. The fluorescence emission of the Eu-doped phosphors was examined in terms of photoluminescence (PL). Overlap between the plasmonic absorption band of Ag NPs and the PL emission band of Eu-doped phosphors increased fluorescence emissions by enhancing excitation. This study also developed an optical process model describing LSPR (Ag NPs), LDS (Eu-doped phosphors), and plasmon-enhanced fluorescence (PEF; Eu-doped phosphors with Ag NPs) on silicon solar cells. PEF was experimentally confirmed in terms of PL, external quantum efficiency (EQE), and photovoltaic current–voltage measurements. Compared to the cell with only an anti-reflection layer of SiO2/SOG, the inclusion of Ag NPs with the Eu-doped phosphors enhanced the PL emission intensity by 1.1243 times at a wavelength of 514 nm and also improved the EQE response by 8.3% (from 57.28% to 62.05%) and conversion efficiency by 7.1% (from 12.04% to 12.89%).

Sintering Temperature Effect on the Luminescence Properties of Y2O3:Tb3+ Phosphors Synthesized using a Liquid-Phase Reaction

The photoluminescence properties of crystalline Y2O3:Tb3+ nanoparticles fabricated using a liquid-phase reaction have been examined over a certain sintering temperature range for dopant activation. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to examine the size and the morphology of Y2O3:Tb3+ particles and disclosed the cubic Bragg peaks of the Y2O3:Tb3+ particles regardless of the sintering temperature with no substantial peak shift. The maximum photoluminescence (PL) emission intensity was observed from the Y2O3:Tb3+ phosphors sintered at 400 °C. The photoluminescence excitation (PLE) spectra of the Y2O3:Tb3+ phosphors are composed of broad bands at ∼260 nm (∼4.7 eV) and shoulder bands at ∼306 nm (∼4.05 eV). The experimental results revealed that the particle size and the crystallinity of the Y2O3:Tb3+ phosphors played a critical role in the luminescence. Over the entire range of sintering temperatures, the room-temperature decay time was found to be ∼2.81 ms.

Facile pH-sensitive optical detection of pathogenic bacteria and cell imaging using multi-emissive nitrogen-doped carbon dots

Rapid detection of lethal pathogens is critical to abate the mortality rate of patients suffering from infectious diseases. Herein, we report a pH-sensitive detection of the pathogenic bacteria using multicolor emissive Nitrogen-doped Carbon Dots (NtCD) synthesized by a one-step hydrothermal method. The unique pH-sensitive interaction of NtCD with bacteria was best studied at pH 2. NtCD was competent to detect several pathogenic bacteria such as; Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Proteus vulgaris (P. vulgaris). The fluorescence spectral investigations of NtCD revealed the excitation dependent emission property with a red-shift. It shows an intense photoluminescent (PL) emission at λex/λem = 340/435 nm. The calculated quantum yield of NtCD was 27.2%. It also possesses multicolor emission at different excitation wavelengths. TEM analysis displayed the uniform spherical morphology of NtCD particles with an average hydrodynamic diameter of 3.11 ± 0.75 nm. The zeta potential of NtCD was measured as −8.4 mV at pH 2. The interaction between NtCD and bacteria was explained on the basis of their zeta potential values. The PL emission response of NtCD tagged bacteria was investigated at λex = 340 nm. It was potentially tagging to both E. coli and S. aureus but with a better response towards E. coli cells. The human squamous epithelial cells (SEC) were deployed as a fitting substitute for achieving NtCD-mammalian cell imaging. Both NtCD tagged bacterial cells and SEC exhibited multicolor emission as well. Mechanistic implications of pH-dependent PL emission property of NtCD and its bacterial interaction were discussed extensively.

Substrate effect on the photoluminescence of chemical vapor deposition transferred monolayer WSe2

The substrate effect is an important issue in the properties of two-dimensional transition metal dichalcogenides (2D TMDs). Quantitatively determining the dependence of the photoluminescence (PL) emission properties and the excitonic behavior of single-layer 2D materials in a specific dielectric environment would provide helpful guidance for the rational design of substrates for high performance 2D TMD PL emission devices. Here, using a WSe2 monolayer on different substrates as a model system, it is demonstrated that the PL emission intensities can drastically change depending on the substrate effect. From the analysis of the excitonic behavior, the results reveal that the spectral weight between the neutral and charged excitons in the PL spectra is significantly modified by the substrate types, and the weight factor is dependent on the laser excitation density. The charged exciton binding energy is obviously negatively related to the substrate dielectric constant. Furthermore, the change trends of the binding energy of the monolayer WSe2 on different substrates are basically the same for the increase of the excitation density. These results suggest that the choice of the substrate plays a significant role in the modulation of the PL properties and exciton states of atomically thin WSe2; hence, substrate engineering should be carefully considered in the design of future 2D devices.

Positive temperature dynamics of near-band-edge photoluminescence in Nb-doped SrTiO3

The positive temperature dynamics in the near-band-edge (NBE) photoluminescence (PL) of Nb-doped SrTiO3 single crystal have been investigated in the temperature range of 10 K–120 K. Intensity of the NBE PL emission with a peak at 3.21 eV has shown increase with increasing temperature. This NBE PL consists of two emission lines with peaks at 3.208 and 3.167 eV. The thermal dynamic in the intensity of the 3.21 eV emission was mainly defined by the temperature behavior of the 3.208 eV transition. The increase in the intensity of the 3.208 eV line with increasing temperature was associated with an increase in the number of electrons thermally excited from the surface. Additionally, a critical point in intensity of the PL at 3.21 eV can be caused by the phase transition, which occurs in Nb-doped SrTiO3 at 115 K.

A facile microwave synthesis of Cr-doped CdS QDs and investigation of their physical properties for optoelectronic applications

Herein, we present the facile synthesis of different content of chromium (Cr)-doped CdS quantum dots (Cr@CdS QDs) using microwave route within 15 min. The synthesized Cr@CdS QDs were investigated for structural, morphological, opto-dielectric, and electrical natures. X-ray diffraction confirms the monophasic hexagonal system of Cr@CdS and the sizes of crystallites are calculated to be 8.72, 7.04, 8.84, 6.56, 5.96, 6.52 and 6.99 nm for 0.0, 0.5, 1.0, 5.0, 10.0, 15.0, and 20.0 wt% Cr@CdS samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal the quantum dots size spherical shape morphology of synthesized Cr@CdS samples and the size is noted in range of 8.5–8.1 nm. The lattice spacing and orientation of grown QDs was also evaluated by high-resolution TEM and Selected Area Electron Diffraction (SAED) pattern. Diffused reflectance spectra were recorded and Kubelka–Munk theory is employed to estimate the energy gap. The energy gap was estimated between 2.4 and 2.46 eV for Cr@CdS QDs. Photoluminescence (PL) emission spectra own an strong emission peak in both spectra recorded at two different excitation wavelengths and revealed that the PL emission intensity is quenched with Cr doping in CdS. Dielectric and ac electrical studies shows the dependence on frequency and Cr content doping, and constant values are enhanced from 14 to 17 at 4 MHz. The prepared Cr@CdS QDs will be highly useful as sensitizers in solar cell, spintronics, and optoelectronics.

Correlation between experimental and theoretical study of scheelite and wolframite-type tungstates

Structural and optical properties of AWO4(A=Ba, Sr, Ca, Mg, and Zn) ceramics were investigated. The structural analysis confirmed the scheelite-type tetragonal structure for (A=Ba, Sr and Ca)WO4 and wolframite-type monoclinic structure for (A=Zn and Mg)WO4 compounds. The experimentally observed optical band gap (Eg) found to be in the range of 4.17–5.92 eV agree with those calculated with the help of density functional theory. A decrease in band gap value with the decrease in ionic radii of A2+ in the AWO4 compound was observed. An intense blue-green photoluminescence emission was observed for these materials and correlated with Eg. The environmental factor he calculated by complex chemical bond theory has been correlated with the broadening of PL excitation bands. The excitation spectra revealed that there subsists a negative relation between he and position of energy levels.

Effects of annealing temperature and neodymium concentration on structural and photoluminescence properties of Nd3+-doped Y2O3-SiO2 powders

We report the structural and photoluminescence (PL) properties of Nd3+-doped Y2O3-SiO2 powders (Y2O3-SiO2:Nd3+) as functions of annealing temperature and Nd3+ ion doping concentration. Y2O3-SiO2:Nd3+ powders were prepared using the high-energy ball-milling (HEBM) method, and their structural and PL properties were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and PL spectroscopy. The XRD results reveal a cubic phase without impurities, and the peak broadening decreases with an increase in annealing temperature due to the increase in the crystallite size. The PL emission intensity increases with an increase in annealing temperature. The highest PL emission intensity is observed for the 300-min milled mixture annealed at 1000 °C for 1 h with a Nd3+ concentration of 1 mol%. The PL peaks excited by 800 nm radiation were detected, centered at 1080 nm (4F3/2 → 4I11/2) and 1350 nm (4F3/2 → 4I13/2).

Enhanced photocatalytic activity of ethylenediamine-assisted tin oxide (SnO2) nanorods for methylene blue dye degradation

Ethylenediamine (EDA) assisted tin oxide (SnO2) nanorods were successfully prepared using the solvothermal method. The prepared samples were characterized using X-ray diffraction, Fourier transforms infrared analysis, field emission scanning electron microscopy, ultraviolet–visible spectroscopy and photoluminescence spectroscopy analysis. The EDA significantly influences the crystallite size and crystallinity of the prepared SnO2. The optical absorption spectra after the addition of EDA showed the absorption edge red-shifted, which improves the absorption toward the visible-light region. Similarly, the spectral intensity of photoluminescence emission was decreased after the addition of EDA. The photocatalytic activity of the prepared samples was investigated by monitoring the degradation of methylene blue dye under UV–visible light irradiation. The highest photocatalytic activity was attained for the nanorods structured with SnO2, which is higher than that of pristine SnO2 due to the effective visible-light absorption and high charge separation of the photogenerated electron-hole pairs.

Exciton recombination mechanisms in solution grown single crystalline CsPbBr3 perovskite

Lead halide perovskites have attracted tremendous attention recently due to their great success in the fields of photovoltaic technologies and light-emitting devices. In this work, the excitonic photoluminescence (PL) properties of all-inorganic perovskite CsPbBr3 were investigated in detail via temperature-dependent PL and Raman spectroscopy in the range of 87 K–297 K, benefiting from our recent work on solution growth of high-quality CsPbBr3 single crystals. The exciton binding energy was extracted as 37 ± 2.7 meV from temperature-dependent PL emission intensity. Furthermore, the PL emission peak energy showed complicated behaviors compared to common semiconductors. With the increase of temperature, the PL emission spectrum blueshifted below 223 K, while it was redshifted in the range of 223 K–293 K. Theoretical research indicated that the thermal expansion governs the energy bandgap evolution of CsPbBr3 below 223 K, while for higher temperatures, the contribution of electron-phonon interaction became dominant. Meanwhile, the broadening of the PL emission spectrum was mainly attributed to the exciton-longitudinal optical phonon scattering. Our results may contribute to a better understanding of the luminescence behaviors in all-inorganic perovskite CsPbBr3-based light-emitting devices in the future.

Novel Hierarchical YBO3:Eu3+ Nanocrystals Synthesized by Folic Acid Assisted Hydrothermal Process

ABSTRACTYBO3:Eu3+ crystals with flower-like hierarchitecture are readily synthesized through a folic acid assisted hydrothermal process using polyborate precursors in the aqueous solution. It was found that the pH value , borate/yittrium ratio and the mass of folic acid take effects on the morphology and photoluminescence emission intensity of YBO3:Eu3+ crystals. The product with the small flower-like hierarchitecture was obtained under the conditions of pH value at 9, borate/yittrium ratio at 2 and the mass of folic acid at 0.44 g, showing the strongest photoluminescence intensity. The growth process of the YBO3:Eu3+ flowers and microflowers was invesitgated based on the time-dependent experiments, which showed that the growth mechanism of the flower-like hierarchitecture follows an in situ growth rather than self-assembly process as reported previously. Such a hydrothermal route using folic acid as a capping agent may provide a green and effective method for fabricating useful and complex 3D architectures of LEDs phosphors.

Highly-increased photoluminescence of Pr3+ due to the Eu2+→ Pr3+ energy transfer in Al2O3 coatings formed by plasma electrolytic oxidation

In this paper, photoluminescence (PL) properties of Pr3+ single doped and Pr3+/Eu2+ co-doped Al2O3 coatings formed by plasma electrolytic oxidation of aluminum were investigated. The PL spectra of Al2O3:Pr3+ coatings feature bands ascribed to 4f-4f transitions of Pr3+. PL excitation spectra contain three broad bands in the violet and blue regions which correspond to the direct excitation of the Pr3+ ground state 3H4 into higher levels 3PJ (J = 0, 1, 2), while PL emission spectra contain several bands attributed to transitions of Pr3+ from excited levels 3P0 and 3P1 to the lower multiplets 3HJ (J = 4, 5, 6) and 3FJ (J = 2, 3, 4). Among these transitions, 3P0→3F2 transition in the red region (644 nm) is the most intense. PL emission intensity of Pr3+ increases by co-doping Eu2+ into Al2O3:Pr3+ coatings due to the energy transfer from Eu2+ to Pr3+, occurring due to the overlap between PL emission spectra of Eu2+, excited by middle ultraviolet radiation, and PL excitation spectra of Pr3+ in Al2O3 host. Under middle ultraviolet excitation, 3P0→3F2 transition of Pr3+ in Al2O3:Pr3+/Eu2+ coatings is 62 times more intense than without co-doping and 16 times if comparison is made with Al2O3:Pr3+ excited by 446 nm. The total luminescence intensity of Al2O3 co-doped with Pr3+/Eu2+ and doped with Pr3+ is 3.6 times more intense of the former if both samples are excited by 446 nm. The gains are linearly increasing with Eu2+ doping concentration. Al2O3:Pr3+/Eu2+ poses as an alternative phosphor to YAG:Ce3+ for the creation of neutral white LEDs by excitation with InGaN semiconductors.

Higher Intrinsic Quantum Yield of Eu3+-Doped Zn2sio4 Obtained by Sol-Gel Process, Calculated by Judd - Ofelt Theory

The sol-gel process allows the obtaining of Eu3+-doped Zn2SiO4with 1 mol% with different molar ratios between Zn2+ and Si4+. The materials reported here were obtained with a resistive furnace at 600, 900, 1000 and 1100°C degree, during 2 h. All the materials exhibited an intense photoluminescence emission with bands assigned to the Eu3+ transitions. Among the materials studied, the samples containing 70 and 80% of Si4+, exhibited higher Eu3+ lifetimes values. The predominance of the quartz phase decreases micro deformations and the location of the Eu3+ ions in higher symmetry sites, reducing the intensity of the photoluminescent materials. The increasing of annealing temperature contributes to the detrimental lifetime and luminescence materials due to the location of the Eu3+ in the site of high symmetry. Through Judd-Ofelt theory was possible to obtain higher values of intrinsic quantum yield (QLn Ln) between 32 and 66% dependent on the temperature of heat-treatment, in comparison with the same material reported in the literature. Keywords: Orthosilicates; Photoluminescence; Rare Earth; Europium;

Practical Applications of Quantum Sensing: A Simple Method to Enhance the Sensitivity of Nitrogen-Vacancy-Based Temperature Sensors

Nitrogen-vacancy centers in diamond allow measurement of environment properties such as temperature, magnetic and electric fields at nanoscale level, of utmost relevance for several research fields, ranging from nanotechnologies to bio-sensing. The working principle is based on the measurement of the resonance frequency shift of a single nitrogen-vacancy center (or an ensemble of them), usually detected by by monitoring the center photoluminescence emission intensity. Albeit several schemes have already been proposed, the search for the simplest and most effective one is of key relevance for real applications. Here we present a new continuous-wave lock-in based technique able to reach unprecedented sensitivity in temperature measurement at micro/nanoscale volumes (4.8 mK/Hz$^{1/2}$ in $\mu$m$^3$). Furthermore, the present method has the advantage of being insensitive to the enviromental magnetic noise, that in general introduces a bias in the temperature measurement.