Search

The article explores the photoluminescence properties of UV, near-UV and blue excited BaWO 4 : Eu3+ red phosphors. The optical band gap narrowing is observed after adding Eu3+ ions. The excitation spectra exhibit a broad peak centred at 255 nm and several narrow peaks of Eu3+ ions at 362, 382, 395, 415 and 465 nm. The three peaks located at 255 (UV), 395 (near-UV) and 465 nm (blue) are the most intense and suitable for the excitation of the sample. The spectral profile of the emission spectra irradiated at 255, 395 and 465 nm are identical. The brightest emission is realized at 18 mol% doping of Eu3+ ions at 255 and 465 nm excitations. However, the optimum concentration is 16 mol% at 395 nm excitation. The phosphors emit highly pure red lights with color purity 98.192%, 97.794% and 98.693% for the optimised concentration under UV, near-UV and blue excitations of 255, 395 and 465 nm, respectively. The quantum efficiency of BaWO 4 : 16 mol% Eu3+ phosphor is calculated as∼48.234% at 395 nm excitation. The emission intensity parameters are calculated in view of the Judd-Ofelt theory. The spectroscopic parameters like radiative transition probability, radiative lifetime, branching ratio and stimulated emission cross-section are further evaluated from the three emission spectra recorded at 255, 395 and 465 nm excitations. The derived results advocate the use of synthesized material as a red phosphor in white-LED, laser and display devices. [ABSTRACT FROM AUTHOR]

A spectroscopic study of Eu3+, Tb3+ and Eu3+/Tb3+ ions-doped zinc sodium borotellurite (ZNB) glass synthesized by a melt-quenching method was performed via photoluminescence spectra and luminescence decay. The results of X-ray diffraction showed the amorphous materials of the prepared glass, and also indicated the difference in absorption spectra between glass samples doped by Eu3+ and Tb3+ ions. Three phonon energies of the ZNB host lattice were found around 932 cm−1, 1282 cm−1 , and 1892 cm−1 through the excitation spectra of Eu3+ and Tb3+ ions. The multiphonon relaxation rate (Wmp) was estimated for each phonon sideband and compared with previously reported results. Intensity parameters (Ωλ) were determined by the Judd–Ofelt theory and their values were used to evaluate the radiative transition of Eu3+ ions in ZNB glass, such as calculated lifetime (τcal), transition probability rate (A), effective line width (Δλeff), stimulated emission cross-section (σp), and branching ratio (βR). Eu3+/Tb3+ co-doped in ZNB glass exhibited multicolor emissions and the energy transfer process between Tb3+ and Eu3+ ions was confirmed based on the analysis of excitation spectra and decay time. [ABSTRACT FROM AUTHOR]

In this study, the optical and structural properties of carbon dots (CDs) synthesized using a hydrothermal method were investigated. CDs were prepared from various precursors such as citric acid (CA), glucose, and birch bark soot. The SEM and AFM results show that the CDs are disc-shaped nanoparticles with dimensions of ~7 nm × 2 nm for CDs from CA, ~11 nm × 4 nm for CDs from glucose, and ~16 nm × 6 nm for CDs from soot. The TEM images of CDs from CA showed stripes with a distance of 0.34 nm between them. We assumed that the CDs synthesized from CA and glucose consisted of graphene nanoplates located perpendicular to the disc plane. The synthesized CDs contain oxygen (hydroxyl, carboxyl, carbonyl) and nitrogen (amino, nitro) functional groups. CDs have strong absorption in the ultraviolet region in the range of 200–300 nm. All CDs synthesized from different precursors displayed bright luminescence in the blue-green region of the spectrum (420–565 nm). We found that the luminescence of CDs depended on the synthesis time and type of precursors. The results show that the radiative transitions of electrons occur from two levels with energies ~3.0 eV and ~2.6 eV, which are due to the presence of functional groups. [ABSTRACT FROM AUTHOR]

As promising luminescent materials for organic light-emitting diodes (OLEDs), thermally activated delayed fluorescence materials are booming vigorously in recent years, but robust blue ones still remain challenging. Herein, we report three highly efficient blue and deep-blue delayed fluorescence materials comprised of a weak electron acceptor chromeno[3,2-c]carbazol-8(5H)-one with a rigid polycyclic structure and a weak electron donor spiro[acridine-9,9'-xanthene]. They hold distinguished merits of excellent photoluminescence quantum yields (99%), ultrahigh horizontal transition dipole ratios (93.6%), and fast radiative transition and reverse intersystem crossing, which furnish superb blue and deep-blue electroluminescence with Commission Internationale de I'Eclairage coordinates (CIEx,y) of (0.14, 0.18) and (0.14, 0.15) and record-beating external quantum efficiencies (ηexts) of 43.4% and 41.3%, respectively. Their efficiency roll-offs are successfully reduced by suppressing triplet-triplet and singlet-singlet annihilations. Moreover, high-performance deep-blue and green hyperfluorescence OLEDs are achieved by utilizing these materials as sensitizers for multi-resonance delayed fluorescence dopants, providing state-of-the-art ηexts of 32.5% (CIEx,y = 0.14, 0.10) and 37.6% (CIEx,y = 0.32, 0.64), respectively, as well as greatly advanced operational lifetimes. These splendid results can surely inspire the development of blue and deep-blue luminescent materials and devices. Thermally activated delayed fluorescence materials are important for the development of OLED materials but the development of robust blue emitting materials remains challenging. Here, the authors report three highly efficient blue and deepblue delayed fluorescence materials demonstrating excellent electroluminescence performance. [ABSTRACT FROM AUTHOR]

A series of Eu3+ and Eu3+/Gd3+ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd3+ to Eu3+ ions. The density of glasses increased with increasing of Gd3+ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu3+-Gd3+ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu3+: 5D 0 → 7F 2 transition. Less intense emissions centered at 577 nm (7F 0), 590 nm (7F 1), 651 nm (7F 3) and 700 nm (7F 4) are also observed from the radiative transitions of the excited state 5D 0 of Eu3+ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu3+ and 3.0 mol% Gd3+ co-doped glass under λ Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications. [ABSTRACT FROM AUTHOR]

In the optical energy gap, visible and near-IR emission of halide phosphate glasses with a composition of 40P2O5-30ZnO-20LiCl-10BaF2 in mol% doped with 3.5 × 104 ppm Pr2O3, referred to as PZLBPr, were synthesized. The UV-VIS-NIR and spectroscopic properties of these glasses were also predicted. The current glasses had broadband emission photoluminescence covering a wavelength range of 1250 to 1700 nm when excited at 455 nm. These bands for near-infrared emission luminescence relate to the transitions 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3, 3F4 in the optical telecommunication window. The significant PL emission wideband was caused by the radiative transition from Pr3+: 1D2 to 1G4. At 445 nm excitation, these glasses exhibited emission bands that corresponded to blue/reddish orange spectral ranges in visible ranges. The prepared glass has a high lasing quality factor (Ω4/Ω6 = 0.9), high optical energy (4.72 eV), and quantum efficiency = 87.3% with FWHM = 156 nm of transition emission from the 1D2 → 1G4 level. As a result, broadband near infrared optical amplifiers can be fabricated from the prepared glasses. [ABSTRACT FROM AUTHOR]

The effect of irradiation with different doses of 4-MeV electrons on radiative recombination of nonequilibrium charge carriers in Cu(In,Ga)(S,Se)2 thin films of solar cells was studied. Near-edge photoluminescence (PL) in the energy range ~0.9–1.2 eV in nonirradiated and irradiated direct-gap Cu(In,Ga)(S,Se)2 solid solutions was caused by optical interband transitions and radiative recombination through energy levels of acceptor- and donor-type structure defects in the presence of strong potential fluctuations. PL spectra measured in the temperature range 5–300 K exhibited energy shifts of the near-edge PL band maxima and redistributions of their intensities in thin films after irradiation with different doses of electrons. The activation energies of nonradiative recombination were determined from the quenching of PL band intensities. The possible nature of structural defects in nonirradiated and electron-irradiated Cu(In,Ga)(S,Se)2 solid solutions was discussed. [ABSTRACT FROM AUTHOR]

Recently, there have been significant interest in the wide potential of photoluminescence (PL) response of rare-earth doped perovskite oxide thin films in the field of optoelectronics. This work reports an effective method to modulate the PL properties of 0.8 mol%Sm3+-doped BaTiO 3 (BTO:Sm) thin films through static and dynamic strain. BTO:Sm films were epitaxially grown on LaAlO 3 (LAO), 0.7Pb(Mg 1/3 Nb 2/3)O 3 -0.3PbTiO 3 (PMN-PT), MgO, and Mica single-crystal substrates by pulsed laser deposition technique. Compared with the BTO:Sm/PMN-PT heterostructure which experiences minimal lattice mismatch effect, the PL intensity of BTO:Sm/LAO and BTO:Sm/MgO is enhanced by 818.1% and 1014.7%, respectively, due to static tensile/compressive strain (-0.429% and 0.461%) during the epitaxial growth process. In the flexible BTO:Sm/Mica heterostructure, dynamic strain is introduced through mechanical bending. Compared with the unbent state, the u-type and n-type bending modes increase the relative changes in PL intensity (Δ I / I) by 599.0% and 768.5%, respectively. Particularly, BTO:Sm/Mica also exhibits a remarkable optical transmittance exceeding 75% (500–2500 nm). The enhancement of PL intensity is closely related to the adjustment of lattice strain, which changes the crystal field strength of the BTO:Sm and the radiative transition probability. This work provides valuable insights for designing future optoelectronic devices and environmental monitoring equipment. It has the potential to advance photonics and sensor technologies, paving the way for innovation and exploration in these fields. • The enhancement of PL intensity in BTO:Sm thin films is achieved through static strain. • High-quality BTO:Sm thin film with high transmittance and low roughness is epitaxially grown on Mica substrates. • Dynamic tuning of the PL behavior in BTO:Sm thin film is achieved by applying bending induced dynamic strain. [ABSTRACT FROM AUTHOR]

A high-luminescent, blue-light excitable europium(III) coordination complex, [Eu(µ2-OC2H5)(btfa)(NO3)(phen)]2phen (1) {btfa = benzoyl trifluoroacetone, phen = 1,10-phenantroline}, has been synthesized and investigated. The complex was characterized by infrared (IR) and photoluminescence (PL) spectroscopy. The PL emission spectra of powder samples registered in a range of 10.7–300 K exhibit characteristic metal-centered luminescence bands, assigned to internal radiative transitions of the Eu3+ ion, 5D1→7Fj and 5D0→7Fj (j = 0–4). The high-resolution spectrum of the transition 5D0→7F0 shows that it consists of two narrow components, separated by 0.96 meV, which indicates the presence in the matrix of two different sites of the Eu3+ ion. The splitting pattern of 5D0→7Fj (j = 0–4) transitions indicates that europium ions are located in a low-symmetry environment. The absolute quantum yield and the sensitization efficiency were determined to be 49.2% and 89.3%, respectively. The complex can be excited with low-cost lasers at around 405 nm and is attractive for potential applications in optoelectronics and biochemistry. [ABSTRACT FROM AUTHOR]

Antimony-lead-oxyfluoroborate (SbPbOFB) glasses doped with various concentrations of Eu3+ ions were prepared by employing melt quenching and their luminescence activity was characterized using different spectroscopic methods such as optical absorption, photoluminescence (PL) excitation, PL emission, and PL decay. The Raman spectrum was recorded for an un-doped SbPbOFB glass to identify various functional groups present. The optical absorption spectra recorded for Eu3+ ion-doped SbPbOFB glasses showed five bands corresponding to 7F0→5L6, 7F0→5D2, 7F1→5D1, 7F0→7F6 and 7F1→7F6 transitions. The PL spectra measured under 394-nm excitation wavelength show five peaks corresponding to 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 transitions at 578, 592, 613, 652 and 701 nm, respectively. Among them, that pertaining to the 5D0→7F2 transition appeared at 613 nm in the visible red region showing relatively high intensity. The Judd-Ofelt (J-O) parameters evaluated from the absorption spectral data are correlated with the prominent emission spectral features such as 5D0→7F1 (592 nm), 5D0→7F2 (613 nm) and 5D0→7F4 (701 nm) to estimate radiative properties such as transition probabilities (AR), branching ratios (βR) and emission cross sections (σ se). Quantum efficiency (η%) of the prepared glasses was estimated by correlating the radiative lifetimes with the experimental lifetimes measured from the PL decay spectral features. The PL emission spectral features are used to estimate the CIE color coordinates (x, y) of the studied glasses. The measured βR, σ se, η%, and the CIE coordinates estimated for the studied glasses revealed their suitability for visible red light-emitting device applications. [ABSTRACT FROM AUTHOR]

To experimentally identify the character of radiative transitions in trigonal Cu2BaSnS4, we conduct temperature and excitation intensity dependent photoluminescence (PL) measurements in the temperature range of 15–300 K. The low-temperature near band edge PL spectrum is interpreted as the free exciton at 2.11 eV and the bound exciton at 2.08 eV, coupled with associated phonon-assisted transitions. In the low energy region, we assign the dominant defect emission at 1.96 eV to donor–acceptor-pair recombination and the weak broad emission at 1.6 eV to the free-to-bound transition. The activation energies and temperature shift for the radiative transitions are determined and discussed. Above 90 K, the free exciton recombination becomes the dominant radiative transition, with its energy shift mainly governed by the contribution of optical phonons. [ABSTRACT FROM AUTHOR]

Results of studies by scanning electron microscopy and photoluminescence (PL) of structural features and radiative transitions of ZnO:Mg films grown by atmospheric pressure metal-organic chemical vapor deposition (APMOCVD) on silicon substrates are presented. Different ZnO:Mg microstructures from polycrystalline films with smooth morphology to columns and hexagonal rods are effectively formed in a wide temperature range 190-450 °C using two compositions of a mixture of zinc and magnesium (5 and 10 wt. %) acetylacetonates (ZnAA and MgAA, respectively) as precursors. The substrate temperatures have a drastic effect on the crystallinity and morphology of ZnO films. A column shaped ZnO microstructure is formed at a substrate temperature above 350 °C. The MgАА content in the mixture of precursors also affects the morphology of polycrystalline films. At lower substrate temperatures (200-320 °C), grown ZnO:Mg samples with MgAA content of 10 wt. % have a surface morphology characterized by enlarged grains compared to samples grown with MgAA 5 wt. %, whereas high substrate temperatures (350-450 °C) promote to form a surface morphology with rod-like structures in both cases: 5 and 10 wt. % of MgAA content. The growth rate of ZnO structures increases with increasing substrate temperatures. The PL emission spectra of samples with 10 wt. % MgAA demonstrate increased near band edge (NBE) emission and suppress defect level emission compared to samples with 5 wt. % MgAA. Therefore, we can conclude that magnesium acts as an isoelectronic impurity improving NBE PL emission due to gettering of defects. Mg also causes an increase in grain size, improving the crystalline perfection of ZnO:Mg polycrystalline films grown at low substrate temperatures, as well as helps to grow hexagonal rods at higher substrate temperatures. Thus, Mg-doped ZnO microstructures grown in the high temperature range could be an effective photocatalyst. [ABSTRACT FROM AUTHOR]

The relationships governing variation of the photoluminescence of graphitic carbon nitride synthesized by heat treatment of melamine in a closed air medium containing oxygen in the temperature range of 10–300 K were investigated. It was shown that the concentration of oxygen in the obtained material 4–5 at.% increases with increase of temperature and decreases with increase in the duration of the synthesis process. By measurements at reduced temperatures right down to 10 K it was possible to resolve bands due to radiative recombination processes in the photoluminescence spectra of the graphitic carbon nitride. It was found that increase of the synthesis temperature from 500 to 600°C and also increase of the duration at the given temperature from 30 to 240 min shift the maximum in the photoluminescence spectrum from 2.74 eV into the region of lower energies to 2.71–2.67 eV. This is due to the bigger role of the molecular system formed by the π bonds of carbon and nitrogen atoms with sp2 hybridization and characterized by a smaller forbidden band width in the emission of light. Transitions due to recombination through oxygen-induced levels in the forbidden band of the semiconductor lead to the appearance of a "tail" in the photoluminescence spectra in the region of low energies (2.40–2.33 eV). Increase of the carbon nitride synthesis temperature to 600°C leads to a change in the structure of the energy bands and to increase of the energy of the radiative transitions as a result of increase in the degree of doping with oxygen atoms and thermal stratifi cation. [ABSTRACT FROM AUTHOR]

Authors aim to study multicomponent barium bismuth borate glasses doped with Dy3+ (1 mol%) for white light-emitting diodes (WLEDs) application. All samples, synthesized through melt-quench approach, were characterized by XRD, optical absorption, excitation, emission, and decay lifetimes. Oscillator strengths and Judd–Ofelt intensity parameters (Ω2, Ω4, Ω6) for all glasses were computed from absorption spectra and further, radiative emission transition probability (AR), branching ratio (βR), and radiative lifetime (τR) were estimated for Dy3+ ion various excited states using J–O parameters. Upon 350 nm excitation, 4I15/2 → 6H15/2 [454 nm (blue)], 4F9/2 → 6H15/2 [483 nm (blue)], 4F9/2 → 6H13/2 [575 nm (yellow)], and 4F9/2 → 6H11/2- [663 nm (red)] emission transitions were observed among which 4F9/2 → 6H13/2 transition exhibits the highest intensity. Dy3+: Li glass showed relatively higher PL intensity and quantum efficiency than Dy3+: Na and Dy3+: K samples. Calculated CIE chromaticity (x = ~ 0.35, y = ~ 0.39) coordinates (λex.: 350 nm) and CCTs (4749‒4890 K) proclaimed overall neutral white light emission from all samples, implying their suitability for WLED applications. Decay lifetimes (τexp) were determined for Dy3+: 4F9/2 → 6H13/2 transition. Additionally, stimulated emission cross-section ( σ p E ) and gain bandwidth ( σ p E × Δλeff) were calculated for respective blue and yellow emission transitions. [ABSTRACT FROM AUTHOR]

The chemical composition of Pr3+-doped strontium–aluminum–bismuth–borate glasses with different concentrations, that is, (50 – x)B2O3 + 20Bi2O3 + 7AlF3 + 8SrO + 15SrF2 + xPr2(CO3)3 (where x = 0.1, 0.5, 1.0, and 1.5 mol.%), have been prepared by the melt quenching technique. XRD, SEM, and EDS studies reveal the structural and amorphous properties of the prepared glasses. Different borate groups are analyzed by FTIR measurements. Judd–Ofelt (J–O) intensity parameters, Ωλ (λ = 2, 4, and 6) are calculated from the absorption spectrum to identify the nature of Pr3+ ions with their surrounding ligands. Using the J–O parameters, the radiative properties such as radiative transition probabilities AR and radiative lifetimes τcal are evaluated for various excited transitions of Pr3+ ions. Stimulated emission cross sections σ p E and branching ratios βR for the emission transitions are evaluated by the photoluminescence spectra. The higher values of σ p E and βR are identified for the emission transitions 3P0 → 3H4 and 1D2 → 3H4 of SABiBPr15 and SABiBPr01 glasses; these glasses are suitable for light emitting materials. The chromaticity color coordinates are calculated to find the average color of the emission spectra. [ABSTRACT FROM AUTHOR]

Cu 2 ZnSnS 4 (CZTS) is an emerging quaternary semiconductor material to use as absorber layer for solar cells due its suitable band gap, high absorption coefficient, earth abundancy and less toxic nature. This work provides a comprehensive insight into the phase evolution of CZTS synthesized at a relatively lower process time. In this study, CZTS bulk polycrystals were synthesized using elemental pre cursors via melting route. The influence of soaking time on the structural, compositional and optical properties were investigated using XRD, EDS, Raman, DRS, PL and XPS measurements. XRD pattern revealed a highly crystalline tetragonal structure corresponding to kesterite phase. EDS mapping were performed over a large area of the sample revealed homogeneous distribution and near stoichiometric composition for the sample soaked for 14 h (S14). Raman spectra confirmed the existence of single phase CZTS without any secondary and ternary phases for S14. Diffuse reflectance spectroscopy gave a band gap value in the range 1.34–1.39 eV. PL analysis revealed that asymmetric band shape and higher energy shift is the characteristics of radiative transitions which are influenced by fluctuating potentials. XPS studies confirmed the oxidation states as Cu(I), Zn(II), Sn(IV) and S(II). Image 1 • Melting route is used to synthesize CZTS polycrystals. • Effect of soaking time on phase purity of CZTS is discussed in detail. • Crystallite size increased from 41.40 to 50.56 nm, which increased proportionally with increase in soak time. • Composition of 14 h soaked CZTS sample approached near to stoichiometry. • Temperature rate profile of 1 °C / minute and soaking of 14 h resulted in obtaining phase pure CZTS. [ABSTRACT FROM AUTHOR]

Ga doped ZnO nanostructures were synthesized by VLS mechanism in which Ga was simultaneously used as a catalyst as well as dopant with varied Ga layer thickness (1 nm, 3 nm, 5 nm and 10 nm). The synthesized ZnO NWs were studied for optical and UV light sensing characteristics. The morphology of grown nanostructures studied by SEM showed that the diameter of nanowires increased with the thickness of the Ga film increase. XRD patterns revealed that ZnO was present in Wurtzite (hexagonal) phase. In addition to ZnO an impurity phase of Ga2O3 was also observed in all synthesized ZnO NWs. The amount of Ga doping affected the position and intensity of ZnO (002) reflection peak in the XRD patterns. This was ascribed to two factors, one is substitution of Ga atoms at the Zn site in the ZnO crystal structure and secondly tendency of Ga to become interstitial. Room temperature and temperature dependent photoluminescence spectroscopy was performed to study the band edge and defected assisted luminescence. In the low temperature PL spectra, DAP transition at (3.30–3.32 eV) and neutral Ga donor bound exciton DoX lines were observed, which disappeared when the temperature was raised above 100 K, which confirmed the successful Ga doping in ZnO crystal structure. The PL intensity showed anomalous behavior as a consequence of tail edge states, which showed strong dependence on Ga content. It was observed that the activation energy for radiative transitions decreased rapidly while the activation energy for non-radiative did not decrease appreciably with the Ga content. This led to enhanced UV sensing characteristics of ZnO NWs with slow recovery time. It is demonstrated that the recovery time depended on the Ga content as it became slow for large Ga content. [ABSTRACT FROM AUTHOR]

Powders of ZnO and ZnO:M (M = Al3+ and Sr2+) with 1 and 4% of M nominal content were synthetized by a hydrothermal method in a diethanolamine (DEA) medium. The samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), micro-Raman and photoluminescence (PL). The powder particles were spherical with average radius decreasing from 1 μm down to 70 nm with increasing Al3+ nominal content but nearly independent on the Sr2+ nominal content. The XRD and micro-Raman results indicate that both Al3+ and Sr2+ mostly incorporated substitutionally into the ZnO lattice, giving rise to compressive and tensile strain, respectively, as a result of ionic radii differences. The PL spectra for ZnO:Al exhibit a dopant-induced contribution at ∼3.1 eV, which is not observed for ZnO:Sr, due to radiative transitions involving trapping of photocarriers at theoretically expected substitutional Al3+ donor states or at Zn interstitial defects. • ZnO and ZnO:M (M = Al3+ and Sr2+) powders were synthetized by a hydrothermal method • The particles radius decreased from 1 μm down to 70 nm with Al dopant incorporation • Both Al3+ and Sr2+ are mainly incorporated substitutionally • Al3+ and Sr2+ additions to ZnO induce compressive and tensile strain respectively • Al3+ incorporation induced a PL component at ∼3.1 eV related with Zn interstitial [ABSTRACT FROM AUTHOR]

In this work, porous silicon surface was modified by aqueous solutions of nucleic acids and the effect of such modification on the porous silicon photoluminescence was studied. The treatment of porous silicon with the nucleic acid solutions was found to cause an increase in the photoluminescence intensity, the change being greater with DNA rather than RNA (homopolymer poly(A)). By means of infrared spectroscopy, it was found that the number of Si-O bonds at the silicon surface after treatment by nucleic acid solutions is much higher than that after treatment by distilled water. It is found that the porous silicon photoluminescence weakly depends on the concentration of the molecular oxygen in the DNA solution. At the same time, illumination of the DNA-treated porous silicon samples by the visible light enhances the porous silicon photoluminescence intensity. Nucleic acid stimulated increase in the porous silicon photoluminescence is attributed to thinning of the silicon skeleton, which, according to the quantum-size model of photoluminescence, leads to a radiative transition probability increase. The thinning could be related to enhancement of dissolution and, to a greater extent, to oxidation of porous silicon in aqueous solution by the nucleic acids. The effect of nucleic acids in aqueous solutions on the porous silicon modification was assumed to be twofold. Firstly, nucleic acids, being polyanions in aqueous solutions, can enhance the corrosion of porous silicon by water. Secondly, an increased concentration of reactive oxygen species is generated in aqueous solutions of nucleic acids under visible light illumination. The latter is supposed to be the main reason of porous silicon oxidation. The results of the work can be useful for the development of PSbased biosensors. [ABSTRACT FROM AUTHOR]

Abstract A series of different Eu3+ ions incorporated La 2 Mo 2 O 9 phosphors exhibiting photoluminescence (PL) peaks in the red region (613 nm; 5D 0 →7F 2) were successfully synthesized by a citrate sol-gel method. Under the 351 nm excitation, the optimal doping concentration of Eu3+ ions was identified to be 25 mol% with higher PL emission intensity and further the concentration quenching mechanism was governed by electric diploe-diploe interaction. More importantly, the optimized phosphor was demonstrated high color purity while the Commission Internationale de I'Eclairage chromaticity coordinates were (0.661, 0.339). The intrinsic radiative transition lifetime for the optimized red phosphor was calculated to be 530.7 μs and the local structure environment of Eu3+ ions in the La 2 Mo 2 O 9 host matrix was also analyzed by the Judd-Ofelt theory. Moreover, a red-emitting light-emitting diode (LED) device was fabricated by combing a near-ultraviolet LED chip with the optimized red phosphor, which exhibits a dazzling red light. Based on the obtained results, the Eu3+ ions activated La 2 Mo 2 O 9 phosphors are expected to be as a promising red-emitting phosphor for solid-state lighting. Graphical abstract Image 1 Highlights • A series of La 2 Mo 2 O 9 :Eu3+ phosphors were synthesized by a facile sol-gel method. • All the samples emitted bright red emissions from the Eu3+ ions pumped by 351 nm light. • Optimized phosphors had high color purity of 96.3% while CIE values were (0.661, 0.339). • The refractive index was 2.48 while the Ω 2 and Ω 4 were obtained by Judd-Ofelt theory. [ABSTRACT FROM AUTHOR]

Nd3+‐doped phosphate laser glasses have been attracting much attention and widespread investigation due to their high solubility of rare earth (RE) ions, excellent spectroscopic properties, and large damage threshold. However, the narrow NIR emission bandwidth (less than 30 nm) of these Nd3+‐doped phosphate glasses limits their further application toward ultrahigh power field and efficient fiber laser in new region. Here, we demonstrate the broadening and enhancing of Nd3+NIR emission in laser glass of zinc aluminophosphate through tuning the glass structure and covalency of Nd‐O bond without limiting the radiative properties of Nd3+. The maximum bandwidth of 1.05 μm emission is broadened to 50 nm, which is comparable to that of Nd3+‐doped aluminate laser glasses. Simultaneously, the lifetime of 4F3/2 level is elongated nearly by two times. Structural and optical properties of prepared glasses were discussed systematically to reveal the mechanism. Detailed analysis on optical spectra and glass structure indicates that the bandwidth is affected by not only the covalency of Nd‐O but also the compactness of glass structure. Our results could enrich our understanding about the relationship between local glass structure and luminescence behaviors of active centers, and may be helpful in designing new RE‐doped laser glass systems. [ABSTRACT FROM AUTHOR]

Nd3+‐doped phosphate laser glasses have been attracting much attention and widespread investigation due to their high solubility of rare earth (RE) ions, excellent spectroscopic properties, and large damage threshold. However, the narrow NIR emission bandwidth (less than 30 nm) of these Nd3+‐doped phosphate glasses limits their further application toward ultrahigh power field and efficient fiber laser in new region. Here, we demonstrate the broadening and enhancing of Nd3+NIR emission in laser glass of zinc aluminophosphate through tuning the glass structure and covalency of Nd‐O bond without limiting the radiative properties of Nd3+. The maximum bandwidth of 1.05 μm emission is broadened to 50 nm, which is comparable to that of Nd3+‐doped aluminate laser glasses. Simultaneously, the lifetime of 4F3/2 level is elongated nearly by two times. Structural and optical properties of prepared glasses were discussed systematically to reveal the mechanism. Detailed analysis on optical spectra and glass structure indicates that the bandwidth is affected by not only the covalency of Nd‐O but also the compactness of glass structure. Our results could enrich our understanding about the relationship between local glass structure and luminescence behaviors of active centers, and may be helpful in designing new RE‐doped laser glass systems. [ABSTRACT FROM AUTHOR]

Results of XPS characterization, theoretical modeling and photoluminescence study of bismuth-implanted gadolinium oxide (Gd 2 O 3 :Bi) films are presented. Scenarios for the introduction of bismuth ions into amorphous-crystalline Gd 2 O 3 host and mechanisms for the formation of optically active centers are considered. It has been demonstrated that the optical properties of Gd 2 O 3 :Bi films are guided by the interplay of a quite complex system of single Bi2+ ions, (Bi3+–Bi3+) pairs and single Bi3+-ions, oxygen vacancies and "defective" gadolinium ions. Photoinduced excitation-relaxation processes involving various Bi-related centers and defect states of the host are observed. Due to the multicolor emission (red, green and blue) of single Bi2+ ions, (Bi3+- Bi3+) pairs and single Bi3+ ions excited in the ultraviolet spectral range, the UV–VIS energy conversion in a wide spectral range is realized. The advantage of Gd 2 O 3 :Bi as a material for energy conversion lies in the fact that due to the polyvalence of bismuth and the variety of different optical centers, a wide range of both absorbed UV light and emitted VIS light is involved in the conversion. This indicates the prospects for practical use of Gd 2 O 3 :Bi films as multifunctional material for energy conversion and photo-detection systems. • The evolution of the formation of defects and clusters in Bi-implanted Gd2O3 films has been established. • Radiative transitions in single Bi2+ ions, (Bi3+- Bi3+) pairs and single Bi3+ ions provide multi-color emission. • Energy transfer from defective Gd3 + host ions to Bi-related emission center is observed. • Wide spectral ranges of both absorbed UV light and emitted VIS light are involved in energy conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Red emissive complexes with [Eu(TFFB) 3 L] stoichiometry were synthesized and investigated by spectroscopic studies. • Red emissive behavior of the complexes was characterized by photoluminescence study. • Photophysical characteristics of the mononuclear Eu(III) complexes were analyzed theoretically (JOES) and experimentally. • Probability amplitude distribution and the energy of HOMO and LUMO were estimated through DFT. Heteroleptic trivalent complexes of europium were prepared on reaction of EuCl 3 ·6H 2 O, fluorinated 1,3-diketone and 2,2′-bipyridine or its derivatives in the molar ratio of 1:3:1 respectively. Structural analysis of prepared complexes was done via spectral study. Luminescence features of synthesized complexes have been explored by the photoluminescence and decay spectral profile. Strong emission in the red spectral region was observed for Eu3+ ion corresponding to the electric dipole 5D 0 → 7F 2 hypersensitive transition. The radiative transition probabilities as well as the Judd-Ofelt parameters were computed and discussed. Complexes emit red light in the visible spectrum as illustrated by their CIE color coordinates are essential for creating effective display and lighting devices. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra of CuInS single crystals grown by Bridgman method have been studied in the wavelength region of 720-1020 nm and in the temperature range of 10-34 K. A broad PL band centred at 861 nm (1.44 eV) was observed at T = 10 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.5- 60.2 mW cm range. Radiative transitions from shallow donor level located at 17 meV below the bottom of the conduction band to the acceptor level located at 193 meV above the top of the valence band were suggested to be responsible for the observed PL band. An energy level diagram showing transitions in the band gap of the crystal has been presented. [ABSTRACT FROM AUTHOR]

A detailed analysis of the radiative recombination processes in Ag(InGa)Se2 thin films grown by a three-stage method was carried out by photoluminescence. The temperature and excitation dependence of the photoluminescence spectra was used to identify the recombination types and determine the ionization energy of the defects in the films. Significant differences were observed between the spectra of the Ag-rich and Ag-poor samples. The Ag-rich films were dominated by two emission peaks of donor acceptor pairs (DAPs). The DAP at lower energy level is attributed to recombination of donor level 13.8 meV (Agi) with acceptor level 70.3 meV (AgIn), while the one at high energy level is assigned to recombination of donor level 18.5 meV (Agi) with acceptor level 108.9 (Ag

The emission band spectra of Tl2Ga2Se3S layered crystals have been studied in the temperature range of 10- 50 K and in the wavelength region of 540-700 nm. A broad photoluminescence band centered at 626 nm (1.98 eV) was observed at T = 10 K. Variation of emission band has been studied as a function of excitation laser intensity in the 0.4-51.5 mW cm-2 range. The analysis of the spectra reveals that the peak energy position changes with laser excitation intensity (blue shift). This behavior of the emission band is in agreement with the idea of separation inhomogeneity of donor-acceptor pairs. Radiative transitions from the moderately deep donor level Ed = 270 meV to the shallow acceptor level Ea = 10 meV were suggested to be responsible for the observed photoluminescence band. [ABSTRACT FROM AUTHOR]

Strong-luminescence YVO4:Eu nanoparticles were prepared by wet chemical reaction at 155°C. Energy transfer processes from V–O and Eu–O to Eu3+andf–ftransition of Eu3+are identified. Luminescence intensity is highest when excited through V–O charge transfer band. Also, luminescence intensity increases with heat treatment temperature up to 900°C due to increase of radiative rate. The luminescence emission intensity could be improved after covering the nanoparticles with an undoped shell. Bi-exponential decay is found. [ABSTRACT FROM PUBLISHER]

Abstract: In this work, doped AlGaAs/GaAs parabolic quantum wells (PQW) with different well widths (from 1000Å up to 3000Å) were investigated by means of photoluminescence (PL) measurements. In order to achieve the 2DEG inside the PQW Si delta doping is placed at both side of the well. We have observed that the thickness of this space layer plays a major rule on the characteristics of the 2DEG. It has to be thicker enough to prevent any diffusions of Si to the well and thin enough to allow electrons migration inside the well. From PL measurement, we have observed beside the intra well transitions, indirect transitions involving still trapped electron on the delta doping and holes inside the PQW. For the thinness sample, we have measured a well defined PL peak at low energy side of the GaAs bulk emission. With the increasing of the well thickness this peak intensity decreases and for the thickest sample it almost disappears. Our theoretical calculation indicated that carriers (electron and holes) are more placed at the center of the PQW. In this way, when the well thickness increases the distance between electrons on the delta doping and holes on the well also increases, it decreases the probability of occurrence of these indirect optical transitions. [Copyright &y& Elsevier]

Results of Cd0:7Mn0:3Te magneto-photoluminescence investigations are analyzed. Photoluminescence was measured in a Voigt geometry at the temperature of 1.6 K. Two models describing radiative transition energy are compared with the experimental results of Cd0:7Mn0:3Te luminescence. The energy of recombination transition, employing the complete form of band states splitting description (term due to the Landau splitting included), shows deviation from experiment at B > 2 T. Two possible reasons of discrepancies from the experiment - exchange interaction constants dependence on magnetic field or band edge energies pinning in magnetic field - are discussed. Band edge energies pinning in magnetic field is related to the hybridization of Mn 3d5 levels with the band states of the host. We determine the corrected values of exchange interaction constants (N0α - N0β=3) at magnetic fields B < 5 T. [ABSTRACT FROM AUTHOR]

Abstract: Photoluminescence (PL) spectra of TlGaSeS layered single crystals have been studied in the wavelength region of 695–1010nm and in the temperature range of 20–56K. Two PL bands centered at 773 (1.605eV, A-band) and 989nm (1.254eV, B-band) were observed at T =20K. Variations of both bands have been investigated as a function of excitation laser intensity in the range from 4.2 to 111.4mWcm−2. These bands are attributed to recombination of charge carriers through donor–acceptor pairs located in the band gap of the crystal. Radiative transitions from deep donor levels located at 0.721 and 1.069eV below the bottom of conduction band to shallow acceptor levels located at 0.008 and 0.011eV above the top of the valence band are suggested to be responsible for the observed A- and B-bands in the PL spectra, respectively. [Copyright &y& Elsevier]

Abstract: This article presents the optical absorption and emission properties of Pr3+ and Nd3+ doped two different mixed alkali chloroborate glass matrices of the type 70B2O3·xLiCl·(30− x)NaCl and 70B2O3·xLiCl·(30− x)KCl (x =5, 10, 15, 20 and 25). The variation of Judd–Ofelt parameters (Ω 2, Ω 4 and Ω 6), total radiative transition probabilities (A T), radiative lifetimes (τ R) and emission cross-sections (σ p) with the variation of alkali contents in the glass matrix have been discussed in detail. The changes in the peak wavelengths of the hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes of certain excited states of Pr3+ and Nd3+ in these two glass matrices are reported. Peak stimulated emission cross-sections (σ P) are reported for the observed emission transitions of Pr3+ and Nd3+ ions. Branching ratios (β) of the observed emission transitions obtained from the Judd–Ofelt theory are compared with the values obtained from the emission spectra. [Copyright &y& Elsevier]

The positions of Stark levels have been determined, using a step-by-step procedure, in the 4I9/2 and 4F3/2 manifolds of Nd3+ ions from absorption and photoluminescence measurements in the 12–293 K temperature range. This data has been used to calculate the emission cross-section for which the maximum value turns out to be ∼2.3 × 10−20 cm2. The radiative recombination time, calculated using Judd–Ofelt analysis, of the 4F3/2 manifold is in close vicinity to the experimentally determined times that were measured by the conventional decay of PL after interruption of excitation and by QFRS. Moreover, the peak time defined by QFRS is independent of temperature. Therefore, the dominant relaxation mechanism from the 4F3/2 excited manifold of Nd3+ ions in GaLaS glass is believed to be by radiative emission. [ABSTRACT FROM AUTHOR]

We have measured the photoluminescence (PL) lifetime of a freestanding GaN film using one- and two-photon excitations to demonstrate the dramatic difference in exciton recombination dynamics at the surface and in the bulk. An ultra-long exciton PL lifetime of 17.2 ns at 295 K is observed from a GaN freestanding film using two-photon excitation, whereas less than 100 ps lifetime is observed for one-photon excitation, suggesting that nonradiative processes from surface defects account for the short PL lifetime measured. The room temperature exciton lifetime of 17.2 ns is the longest ever reported for GaN film. A monotonic increase in two-photon excited PL lifetime with increasing temperature and the linear dependence of the exciton lifetime with emission wavelength show good agreement with the theoretical predictions, indicating that radiative recombination dominates for bulk excited state relaxation processes. [ABSTRACT FROM AUTHOR]

Spectroscopic and luminescent properties of the Nd-doped and Nd–Ag co-doped borate glasses with Li 2 B 4 O 7 (Li 2 O–2B 2 O 3) basic composition are investigated and analysed using optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics) experimental methods and Judd–Ofelt analysis. Optical absorption, photoluminescence spectra and decay kinetics of Nd3+ ions were registered and detailed analysed. Experimental and theoretical oscillator strengths (f exp and f theor), Judd–Ofelt intensity parameters (Ω 2 , Ω 4 , Ω 6), and important to laser applications radiative parameters such as probabilities of radiative transitions (A rad), branching ratios of luminescence (β), radiative lifetimes (τ rad), emission cross-sections (σ em), and quantum efficiency (η) of the Nd3+ luminescence in the Li 2 B 4 O 7 :Nd and Li 2 B 4 O 7 :Nd,Ag glasses have been calculated. Broad absorption band of surface plasmon resonance (SPR) related to silver nanoparticles was observed in the Li 2 B 4 O 7 :Nd,Ag glass. Presence of the Ag paramagnetic centres and aggregates in the Li 2 B 4 O 7 :Nd,Ag glass was confirmed by EPR spectroscopy. Photoluminescence emission and excitation spectra as well as decay kinetics of the Ag+ ions and small non-plasmonic Ag aggregates or nanoclusters were registered and discussed. Observed enhancement of the Nd3+ luminescence intensity in the Li 2 B 4 O 7 :Nd,Ag glass is explained by effects induced by SPR of the Ag nanoparticles as wells energy transfer from Ag+ ions and Ag aggregates to the Nd3+ ions. Image 1 • The Nd-doped and Nd–Ag co-doped Li 2 B 4 O 7 glasses of high optical quality were obtained. • Optical absorption, EPR, photoluminescence spectra and decay kinetics were studied. • Judd-Ofelt parameters (Ω 2 , Ω 4 , Ω 6) and radiative properties (A rad , β , τ rad , σ em , η) were calculated. • Enhancement of the Nd3+ luminescence in the Li 2 B 4 O 7 :Nd, Ag glass was obtained. • Silver co-doping improves luminescent and laser properties of the Nd3+-doped borate glasses. [ABSTRACT FROM AUTHOR]

Al 2 O 3 :Eu3+ nanophosphors were synthesized by the microwave assisted solvothermal technique. The structural and photoluminescence characteristics of alumina powders doped with 6.4 ​at.%, 7.5 ​at.%, 9.5 ​at.% and 13 ​at.% Eu, calcined at 900 ​°C, 1000 ​°C, 1100 ​°C and 1200 ​°C for 3 ​h, were investigated by X-ray diffraction, and reflectance, photoluminescent and X-ray fluorescence spectroscopies. The effects of the calcination temperature on the structure and, in turn of it on the photoluminescence properties are investigated. Luminescent decays curves were measured for the emission ascribed to the 5D 0 -7F 2 transition in all the samples and a non-exponential behavior is observed. An increase in the average lifetime correlates well with the formation of the EuAlO 3 perovskite phase as the calcination temperature increases. Judd-Ofelt analyses were performed and some additional quantities were derived from them such as the radiative and nonradiative transition rates and the emission quantum efficiency. The decrease in the Ω 2 parameter value as the calcination temperature increases is compatible with a higher symmetry around the Eu3+ site as well as with a reduction in the Eu3+ covalence bonding within this ion into EuAlO 3 perovskite. Short caption X-ray diffraction patterns and excitation spectra from 6.4 at.% and 13 at.% Eu-doped alumina nanophosphors annealed at 900 °C and 1200 °C, respectively. Long caption X-ray diffraction (XRD) patterns and excitation spectra of 6.4 at.% and 13 at.% Eu-doped alumina nanophosphors annealed at 900 °C and 1200 °C, respectively. The XRD pattern of 6.4 at.% Eu-doped alumina shows the amorphous and γ-Al 2 O 3 phases resulting in an excitation spectrum where the broad peak centered at 270 nm is ascribed to an Eu3+–O2- charge transfer (CT) state in Al 2 O 3 , unlike in the alumina sample doped with 13 at.% Eu annealed at 1200 °C this band is significantly reduced and a new band being associated with an O 2 --Eu3+- CT state in EuAlO 3 appears at around 300 nm. Image 1 • Al 2 O 3 :Eu3+ nanophosphors were synthesized by a microwave assisted solvothermal technique. • Annealing temperature and Eu concentration govern amorphous-Al 2 O 3 → γ-Al 2 O 3 → EuAlO 3 phase transformations. • Luminescent features of the nanophosphors strongly depend on crystal structure. • A new excitation band at 303 nm is plausibly associated with the O2- → Eu3+ charge transfer state of EuAlO 3. [ABSTRACT FROM AUTHOR]