Critical Transfer Distance Research Articles

Concentration quenching of Eu2+ doped Ca2BO3Cl

With the aim of determining the concentration quenching mechanism of Eu2+ doped Ca2BO3Cl, a series of phosphors with a varied Eu2+ concentration (Ca2−xBO3Cl:xEu2+) was synthesized by the solid state reaction method. The phase structure was determined by X-ray diffraction. Photoluminescence (PL) measurements showed broad excitation and emission signatures of the allowed f–d transition of Eu2+ ions. The PL emission intensity was found to be increased by increasing the concentration of Eu2+ ions up to x=0.03 and then decreased as a result of the concentration quenching effect. The lifetime of the emission from the Eu2+ ions was measured and the decrease in the lifetime with increasing Eu2+ concentration confirmed that non-radiative energy transfer occurred between Eu2+ ions. From the luminescence data, the value of the critical transfer distance was calculated as 1.5nm and the corresponding concentration quenching mechanism was verified to be a dipole–dipole interaction.

An intense red-emitting phosphor Sr3Lu(PO4)3:Eu3+ for near ultraviolet light emitting diodes application

A series of Sr3Lu(PO4)3:Eu3+ phosphors were successfully prepared via the solid-state method, and their luminescence properties were investigated. The excitation and emission spectra show that this phosphor can be effectively excited by near ultraviolet (NUV) light, and produces strong and prevailing red emissions at 612nm belonging to the 5D0→7F2 electric dipole transition. Eu3+ ion was heavy doped in Sr3Lu(PO4)3 host and the optimal concentration of Eu3+ was found as 0.8. The critical transfer distance of Eu3+ was determined to be 8.5Å. The concentration quenching was demonstrated to be caused by the energy transfer among the nearest-neighbor ions in the Sr3Lu(PO4)3:Eu3+ phosphor. Under excitation of 394nm, the integral emission intensity of Sr3Lu0.2(PO4)3:0.8Eu3+ is about 6 times that of Y2O3:Eu3+. The CIE color coordinates of Sr3Lu0.2(PO4)3:0.8Eu3+ was (0.636, 0.354) located in red region. In addition, good thermal stability was also identified in Sr3Lu0.2(PO4)3:0.8Eu3+ and its emission intensity was reduced to 88% of its initial value at 100°C and 70% at 200°C. The current research suggests that Sr3Lu(PO4)3:Eu3+ could be a promising red phosphor for white LEDs and display devices.

Combined Spectroscopic And Molecular Docking Study Of Binding Interaction Of Pyrano [3, 2-f] Quinoline Derivatives With Bovine Serum Albumins And Its Application In Mammalian Cell Imaging

The interaction between pyrano [3, 2-f] quinoline derivatives (TPQ) and bovine serum albumin (BSA) was studied using spectroscopic techniques. The TPQ quench the fluorescence of BSA through dynamic quenching. According to Van’t Hoff equation, the thermodynamic parameters were calculated and which indicated hydrogen bonds and van der waals forces played a prime role in stabilizing the BSA–TPQ complexes. Also, the average binding distance (r) and the critical energy transfer distance (Ro) between TPQ and BSA were also evaluated according to Förster’s non-radiative energy transfer (FRET) theory. What is more, UV-visible and circular dichroism results showed that the addition of TPQ changed the secondary structure of BSA and led to a reduction in content α-helix (%) content. It was also observed that TPQ shows cell staining property to the cultured HeLa cell line. Theoretical docking study of interaction between BSA and TPQ also supported the experimental results. All the results suggested that BSA experienced substantial conformational changes induced by TPQ; this may be useful to study synthetic organic molecules for their application as pharmaceuticals.

Luminescent properties of novel red-emitting phosphor: Gd_2O_2CN_2:Eu^3+

Eu3+-doped Gd2O2CN2 was firstly synthesized by a classical solid-state reaction of Li2CO3, Eu2O3 and GdF3 under NH3 gas flow in the presence of graphite at low firing temperature. Powder X-ray diffraction (XRD) analysis indicated that Gd2O2CN2: Eu3+ crystallizes in a trigonal-type structure with space group P-3m1. Gd2O2CN2: Eu3+ shows a sharp red emission band peaking at 626 nm under excitation at 300 nm at room temperature. PL spectra indicates that Eu3+ doped Gd2O2CN2 samples emit the typical emission peaks at 614 nm and 626 nm originated from the hypersensitive electric dipole transition (5D0→7F2) of Eu3+ ions. The optimized doping concentration of Eu3+ ions was found to be 7.5 at. %, and the critical transfer distance was calculated to be 10.907 A.

Interaction mechanism for energy transfer from Ce to Tb ions in silica

Energy transfer phenomena can play an important role in the development of luminescent materials. In this study, numerical simulations based on theoretical models of non-radiative energy transfer are compared to experimental results for Ce, Tb co-doped silica. Energy transfer from the donor (Ce) to the acceptor (Tb) resulted in a decrease in the Ce luminescence intensity and lifetime. The decrease in intensity corresponded best with the energy transfer models based on the exchange interaction and the dipole-dipole interaction. The critical transfer distance obtained from the fitting using both these models is around 2nm. Since the exchange interaction requires a distance shorter than 1nm to occur, the mechanism most likely to account for the energy transfer is concluded to be the dipole–dipole interaction. This is supported by an analysis of the lifetime data.

Relationship between Eu3+ substitution sites and photoluminescence properties of SrIn2O4:Eu3+ spinel phosphors

Eu3+-doped SrIn2O4 phosphors were synthesized by the solid solution method at 1400°C in air. The chemical composition of the phosphors was systematically changed to study the relation between the Eu3+ substitution site and photoluminescence (PL) properties. Under excitation of the 7F0→5L6 transition of Eu3+ at 393nm, the SrIn2O4:Eu3+ exhibited dominant red emission peaks at 611, 616 and 623nm, which are attributed to the electric dipole transition 5D0→7F2 of Eu3+. The results of X-ray diffraction analysis combined with PL spectroscopic analysis revealed that Eu3+ ions occupied two different crystallographic In3+ sites in the host SrIn2O4, while it was found to be impossible to substitute Sr2+ with Eu3+ prior to the Eu3+ substitution at the In3+ sites in the SrIn2O4. The intensity of the red emission peaks increased with the total amount of dopant Eu3+ ion at the two In3+ sites, and reached a maximum at 25mol% Eu3+-doping (SrIn2−xO4:xEu3+, x=0.25). Moreover, a small amount (<10mol%) of Eu3+ at the Sr2+ site in the SrIn2−xO4:xEu3+ was found to contribute to enhance the red emission peak intensity at 616nm. As a result, the highest red emission intensity evaluated as the total emission peak intensities at the 611, 616 and 623nm was achieved for Sr0.92In1.75O4:0.33Eu3+ in which Eu3+ ion concentrations at the In3+ and Sr2+ sites were simultaneously optimized as 25 and 8mol%, respectively (Sr1−yIn2−xO4:(x+y)Eu3+, x=0.25, y=0.08). This red emission intensity was 2.2 times higher than that of the phosphor without contribution of the Eu3+ at the Sr2+ site (SrIn2−xO4:xEu3+, x=0.25). The critical energy transfer distance of Eu3+ ion in the Sr0.92In1.75O4:0.33Eu3+ phosphor was determined to be 0.817nm, and the electric multipolar interaction was suggested as the dominant mechanism for concentration quenching of PL emission due to Eu3+ ions in the Eu3+-doped SrIn2O4 phosphors investigated in this study.

Photoluminescence properties and thermal stability of RbBaPO4:Eu3+ phosphor

With the conventional solid state reaction method, a series of novel orange-red emitting Eu3+ doped RbBaPO4 phosphors were prepared. The crystal structures, photoluminescence properties and thermal properties of the phosphors were carefully investigated. The phosphors exhibit a dominant emission at 612 under 392 nm excitation. The optimal Eu3+ concentration and its critical energy transfer distance were determined to be 9 mol % and about 13 A, and the dominant concentration quenching mechanism of Eu3+ emission is the dipole–dipole interaction. The asymmetry ratio [I(5D0 → 7F2)/I(5D0 → 7F1)] was studied in detail. The band gap energy of RbBaPO4 host was estimated to be 5.39 eV from the Kubelka–Munk function. The phosphor shows excellent thermal stability and the activation energy for the thermal quenching process (ΔE) was calculated to be 0.292 eV. The results suggest that the phosphor could find potential application as orange-red phosphor for white light emitting diodes.

Luminescent properties of Eu3+ doped NaY(WO4)2 nanophosphors prepared by molten salt method

Tetragonal phase NaY(WO4)2:Eu3+ phosphors were synthesized through a molten salt method. The X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were utilized to characterize the crystal structure and morphology. The emission and excited spectra were used to study the photoluminescence properties. The results of XRD and FE-SEM indicated that the samples prepared by this method were pure phase and the particle size was about 50 nm. The PL results showed that Eu3+5D0→7F2 red luminescence at 616.5 nm could be excited by 394.5 nm near-UV light and 465 nm blue light in NaY(WO4)2 host effectively, and the quenching concentration was 30 mol.%. The critical energy transfer distance and J-O parameters were calculated. The energy transfer type between Eu3+ was proved. What's more, the quantum efficiencies of the 5D0 level of Eu3+ were calculated as well.

Investigation of UV-emitting Gd(3+)-doped LiCaBO3 phosphor.

Incorporating the Gd(3+) rare earth ion in the LiCaBO3 host lattice resulted in narrow-band UV-B emission peaking at 315 nm, with excitation at 274 nm. The LiCaBO3:Gd(3+) phosphor was synthesized via the solid-state diffusion method. The structural, morphological and luminescence properties of this phosphor were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. Electron paramagnetic resonance (EPR) characterization of the as-prepared phosphors is also reported here. XRD studies confirmed the crystal formation and phase purity of the prepared phosphors. A series of different dopant concentrations was synthesized and the concentration-quenching effect was studied. Critical energy transfer distance between activator ions was determined and the mechanism governing the concentration quenching is also reported in this paper.

Fluorescence properties of Tb3+ and Sm3+ activated novel LiAl7B4O17 host via solution combustion synthesis

Novel LiAl7B4O17 (LABO) phosphor activated with trivalent rare earth ions (RE=Tb, Sm) was synthesized by using solution combustion synthesis. The powder X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), photoluminescence (PL), critical transfer distance (Rc) and quenching mechanism studies were employed to characterize the samples. Under ultraviolet irradiation of the LiAl7B4O17: Tb3+, Sm3+ phosphors exhibit the typical green (5D4→7Fj=6, 5, 4 and 3) emission band of the Tb3+ ions, as well as an orange-red and red (4G5/2→6HJ=5/2, 7/2, 9/2) emission bands of the Sm3+ ions. These results suggest that Tb3+ and Sm3+ activated LABO phosphor could be promising in vision of the necessity for solid state lighting applications.

Electron-phonon coupling properties and energy transfer in NaY(WO4)2:Eu3+ phosphor

NaY(WO4)2 phosphors with various Eu3+ concentrations were prepared via a molten salt method. The crystal structure and morphology of the phosphors were characterized by means of XRD and field emission scanning electron microscope. The excitation spectra and emission spectra were measured. The energy transfer type between Eu3+ was proved. What's more, the critical energy transfer distance (Rc) and Huang-Rays factor were calculated. The self-generated quenching process of Eu3+ was explained based on Auzel's model, and the intrinsic radiative transition lifetime for 5D0 level was confirmed. The energy transfer rate between Eu3+ ions was derived on the basis of the fluorescence lifetime. Finally, the refractive index n was calculated.

Temperature-dependent nonradiative energy transfer from Gd3+ to Ce3+ ions in co-doped LuAG:Ce,Gd garnet scintillators

Energy transfer from donor Gd3+ to acceptor Ce3+ ions was studied in low doped lutetium aluminum garnet, LuAG:Ce,Gd. High purity single crystalline films were prepared by liquid phase epitaxy. The mechanism of nonradiative energy transfer from 6PJ (Gd3+) multiplet to crystal field split 5d2 (2D) states of Ce3+ was established as long-range dipole–dipole interaction and the average critical transfer distance between Gd3+ and Ce3+ ions was found ~14Å at room temperature. It is shown that the single step energy transfer between donor–acceptor pairs is dominant while migration of excitation energy within the donor Gd3+ subsystem is only a small perturbation in the energy transfer mechanism in the studied low doped garnets.

A single host white light emitting Zn2SiO4:Re3+ (Eu, Dy, Sm) phosphor for LED applications

We report photo and thermoluminescence properties of Zn2SiO4:Re3+ (Eu, Dy, Sm) phosphors prepared by low temperature solution combustion technique. The hexagonal phase was confirmed by PXRD patterns. SEM micrographs revealed that morphological features were highly dependent on type of the dopant ion. Characteristic excitation and emission peaks of Eu3+, Dy3+ and Sm3+ were observed from PL studies. The concentration quenching occurred for 3mol% Re3+ doped lanthanide ions, whose critical energy transfer distance (Rc) was found to be ∼13Ǻ. The corresponding concentration quenching was verified to be dipole–dipole interaction. The chromaticity co-ordinates of Zn2SiO4:Eu3+/Dy3+/Sm3+ phosphors were located in white region suggests them to be a potential candidate for the production of white light emitting phosphors. Three TL glow peaks in Eu3+, Dy3+ doped and two glow peaks in Sm3+ doped Zn2SiO4 nanophosphor observed in TL studies indicated that more than one type of traps were created in these phosphors. TL intensity increases linearly in Sm3+ doped Zn2SiO4 up to 4kGy and thereafter, it decreases. Up to 4kGy, the phosphor was quite useful in radiation dosimetry.

The local field dependent effect of the critical distance of energy transfer between nanoparticles

The fluorescence resonance energy transfer between various types of fluorophore pairs was investigated. Dye molecules, quantum dots, fluorescent nanoparticles (dye molecules encapsulated in polymer matrices) were used as donor D. Dye molecules and gold nanoparticles were used as acceptor A. We found that the experimental Förster critical transfer distance R0 is 1–10nm when both D and A are dye molecules, and becomes larger than 10nm when the donor is fluorescent nanoparticles. When the acceptors A are gold nanoparticles, the case is considered as localized plasmon coupled nanosurface energy transfer (NSET), the experimental critical distance d0 increases up to few ten nanometers when D are dye molecules or quantum dots. For the first time, un-expected giant resonance energy transfer (G-RET) phenomenon is observed in our experiments with very large critical transfer distance d0, which increases from few ten nanometers to micrometers when the donors are fluorescent and the acceptors are gold nanoparticles. A model “nanowave emitter station and antenna” is given to explain the local field dependence of the critical distance of energy transfer between those nanoparticles. Moreover, a simple theoretical model with size–number contribution (for fluorescent nanoparticles) and surface plasmon coupled enhancement effect (for gold nanoparticles) is proposed to explain these obtained experimental results.

Photoluminescence properties of a new orange–red emitting Sm3+-doped Y2Mo4O15 phosphor

A series of novel Y2Mo4O15:xSm3+ ( (0.01 ≤ x ≤ 0.20) phosphors for white light-emitting (W-LEDs) were successfully prepared by the solid state reaction technology at 973K for 12h. X-ray diffraction and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. The emission spectra of the Y2Mo4O15:Sm3+ phosphors consisted of some sharp emission peaks of Sm3+ ions centered at 565nm, 605nm, 650nm, and 712nm. The strongest one is located at 605nm due to 4G5/2–6H7/2 transition of Sm3+, generating bright orange–red light. The optimum dopant concentration of Sm3+ ions in Y2Mo4O15:xSm3+ is around 5mol% and the critical transfer distance of Sm3+ is calculated as 23.32Å. The CIE chromaticity coordinates of the Y2Mo4O15:0.05Sm3+ phosphors were located in the orange reddish region. The Y2Mo4O15:Sm3+ phosphors may be potentially used as red phosphors for white light-emitting diodes.

Preparation and luminescence properties of Sr7Zr(PO4)6:Dy3+ single-phase full-color phosphor

Novel single-phase white-light-emitting Sr7Zr(PO4)6:Dy3+ phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reactions. The phases and luminescent properties of the obtained Sr7Zr(PO4)6:Dy3+ phosphors were characterized. The results show that the luminescence spectra excited by 350 nm consist of two characteristic blue and yellow bands, corresponding to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. When x > 0.02, the concentration quenching effect occurred, and the critical transfer distance (Rc) was ~19.247 A. The energy transfer of the Dy3+ ions is the electric dipole–dipole interaction mechanism. The International Commission on Illumination chromaticity coordinates for Sr7−xZr(PO4)6:xDy3+ phosphors were located in the white region. The developed phosphor has great potential as a single-component white-light-emitting phosphor for UV-LEDs.

Luminescence dynamics and concentration quenching in Gd2−xEuxO3 nanophosphor

Gd2−xEuxO3 nanophosphor with enhanced luminescence has been synthesized by solution combustion method in diethylene glycol medium. The effect of Eu3+ content on the structure, morphology and luminescence dynamics has been investigated. The observed red shift in charge transfer band of the nanophosphor with increase in Eu3+content is attributed to the increase in covalency and Eu–O bond length. Excess europium content leads to reduction in intensity of photoemission as a result of concentration quenching. Transient characteristics exhibit single exponential behaviour and the fitted life time values get shortened with increase of Eu3+ content, due to increase in non-radiative transition rate. The observed quenching of luminescence in the phosphor is found to be in agreement with the energy transfer theory proposed by Dexter and Schulman and found that dipole–dipole interaction between Eu3+ ions is the key mechanism responsible for quenching. Critical energy transfer distance between Eu3+ ions in Gd2−xEuxO3 is determined to be 1.148nm. Judd–Ofelt intensity parameters and the radiative parameters of the phosphors were evaluated from the emission spectrum to analyse the crystal field environment and the degree of covalency between the rare-earth ion and the surrounding ligands. The value of Ω2 intensity parameter confirmed the hypersensitive nature of the 5D0–7F2 transition with larger asymmetry around Eu3+ ions.

Photoluminescence characteristics of high thermal stable fluorosilicate apatite Ba2Y3(SiO4)3F:Sm3+ orange-red emitting phosphor

A series of orange-red emitting Ba2Y3(SiO4)3F:xSm3+ (0.003≤x≤0.08) fluorosilicate apatite phosphors was synthesized by the convenient solid-state reaction. X-ray diffraction and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. The emission spectra of the Ba2Y3(SiO4)3F:Sm3+ phosphors consisted of some sharp emission peaks of Sm3+ ions centered at 564, 601, 648, and 710nm. The strongest one is located at 601nm due to 4G5/2–6H7/2 transition of Sm3+, generating bright orange-red light. The optimum dopant concentration of Sm3+ ions in Ba2Y3(SiO4)3F:xSm3+ is around 3mol% and the critical transfer distance of Sm3+ is calculated as 26Å. The quenching temperature is above 500K. The CIE chromaticity coordinates of the Ba2Y3(SiO4)3F:0.03Sm3+ phosphors is located in the orange reddish region. The Ba2Y3(SiO4)3F:Sm3+ phosphors may be potentially used as red phosphors for white light-emitting diodes.

Photoinduced electron transfer from phenanthrimidazole to magnetic nanoparticles.

The dynamics of photoinduced electron injection from (E)-1-(4-methoxyphenyl)-2-styryl-1H-phenanthro [9,10-d]imidazole (MPSPI) synthesised using nano TiO(2) as catalyst to Fe(2)O(3) nanocrystal has been studied by FT-IR, absorption, fluorescence and lifetime spectroscopic methods. The binding between nanoparticle and MPSPI is confirmed by binding constant and binding site. The distance between MPSPI and nanoparticle as well as the critical energy transfer distance has been obtained. The free energy change (ΔG(et)) for electron injection has also been deduced.

Blue-emitting SrB2O4:Eu2+ phosphor with high color purity for near-UV white light-emitting diodes

A blue-emitting SrB2O4:Eu2+ phosphor with high color purity was synthesized by conventional high-temperature solid state reaction method. Its crystal structure, luminescence properties and concentration quenching mechanism were investigated. This phosphor can be effectively excited within the broad near ultraviolet wavelength region from 270 to 350nm and feature a satisfactory blue-emitting performance.In particular, the color purity of the as-synthesized SrB2O4:Eu2+ phosphor is much better than that of the blue emitting, commercial compound BaMgAl10O7:Eu2+. The emission peaks located at 448nm, which can be attributed to the transitions of 4f65d1 to 4f7 of Eu2+ ions. It is shown that the 6.0mol% doping concentration of Eu2+ ions in SrB2O4:Eu2+ phosphor is optimum, and that the concentration quenching occurs when Eu2+ concentration is beyond 6.0mol%. The physical mechanism of concentration quenching mechanism can be explained by the dipole–dipole interaction of Eu2+ ions, and the critical transfer distance was determined to be 13.98Å. The present work suggests that the SrB2O4:Eu2+ phosphor is a promising blue-emitting material for near-UV white light-emitting diodes.