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The synthesis and characterization of novel luminescent amorphous POSS-based polysilsesquioxanes (PSQs) with Tb3+ and Eu3+ ions directly integrated in the polysilsesquioxane matrix is presented. Two different Tb3+/Eu3+ molar ratios were applied, with the aim of disclosing the relationships between the nature and loading of the ions and the luminescence properties. Particular attention was given to the investigation of site geometry and hydration state of the metal centers in the inorganic framework, and of the effect of the Tb3+ → Eu3+ energy transfer on the overall optical properties of the co-doped materials. The obtained materials were characterized by high photostability and colors of the emitted light ranging from orange to deep red, as a function of both the Tb3+/Eu3+ molar ratio and the chosen excitation wavelength. A good energy transfer was observed, with higher efficiency displayed when donor/sensitizer concentration was lower than the acceptor/activator concentration. The easiness of preparation and the possibility to finely tune the photoluminescence properties make these materials valid candidates for several applications, including bioimaging, sensors, ratiometric luminescence-based thermometers, and optical components in inorganic or hybrid light-emitting devices. [ABSTRACT FROM AUTHOR]

Two new organo-europium complexes (OEuCs) [Eu(tfac)3(TB-Im)] (Eu1) [Eu(hfac)3(TB-Im)] (Eu2) incorporating fluorinated (hexafluoroacetylacetone; Hhfaa) or hemi-fluorinated (trifluoroacetylacetone; Htfac) β-diketones together with the large bite angle N^N ligand (2-(4-thiazolyl)benzimidazole; TB-Im) have been synthesized and characterized. The structure of the complexes has been established by single crystal X-ray diffraction (SC-XRD) analysis and shows that the coordination sphere is composed of a EuO6N2 core (octacoordinated). Continuous shape measures (CShMs) revealed that the geometry around Eu(III) is trigonal dodecahedral with approximate D2d-symmetry. Efficient red emission is observed for both the complexes in solution with a fairly large photoluminescence quantum yield (PLQY (Q LEu) = 39.00–47.00%). Furthermore, by utilizing the experimental photoluminescence (PL) data and theoretical modelling employing density functional theory (DFT) in conjunction with LUMPAC, energy transfer (ET) and back energy transfer rates were calculated, and an ET mechanism for the sensitized PL is proposed and discussed in detail. Finally, the complexes were used as an emitting layer (EML) to fabricate 20 organic light emitting diodes (OLEDs) by varying the doping concentration. Interestingly, both the complex-based OLEDs at 4 wt% doping concentration display white electroluminescence (EL) with the brightness (B) = 100.5–364.1 cd m−2 at very low turn-on voltage (Vturn-on) = 3.9–4.6 V. The overall electroluminescence performance of Eu1 and Eu2 is higher than that of the reported europium based single component white-OLEDs. [ABSTRACT FROM AUTHOR]

Gallium nitride co-doped with magnesium and europium shows great potential for active layers in red light emitting diode structures due to strong and sharp luminescence emission around 620 nm. In this work, sharp and intense Eu3+ luminescence lines from the excited states of the 5D J (J = 0, 1) multiplets to the ground states of the 7F J (J = 0, 1, 2) multiplets have been analyzed using a C 2 v crystal-field equivalent operator Hamiltonian. A model of Eu centers with the C 2 v symmetry has been proposed to be an Eu3+ complex accompanied by either a pair of nitrogen and gallium vacancies (V N - V Ga) or a pair consisting of a nitrogen vacancy and magnesium impurity (V N - Mg Ga) in the vicinity of the Eu ion based on the crystal-field analysis, the selection rules and the observed polarization of the Eu3+ luminescence lines. Energy transfer from the host to the Eu ions under band-to-band excitation occurs through electron-hole recombination between V N with the electron-like state and V Ga or Mg Ga with the hole-like state; these may be associated with the shallow-trapped or deep-trapped states, respectively, proposed as the energy transfer mechanism in previous literature. • Polarized photoluminescence/cascade-luminescence from ex situ Eu-doped GaN(Mg). • Energy levels/states of 7F 0 ,7F 1 and 7F 2 multiplets of Eu3+ experimentally estimated. • Model of Eu centers in GaN(Mg) with C 2 v (orthorhombic) symmetry proposed. • Eu complex with N/Ga vacancy pair, or a pair consisting of N vacancy and Mg impurity. • Energy transfer GaN.→Eu via recombination between these electron-like/hole-like states [ABSTRACT FROM AUTHOR]

Tuning the emissive color changes of lanthanide (Ln) complexes is an important and appealing project for promoting the applications of Ln-complexes. A solvothermal reaction of 4-cyano-3-methylbenzoic acid (HL) and Ln(NO3)3·6H2O affords three isostructural Ln-complexes [Eu(L)3(H2O)2]n (1-Ln) (Ln = Eu, Gd and Tb) with one-dimensional chain structures. 1-Eu and 1-Tb show bright red and green emissions with absolute quantum yields of 3.06% and 11.96%, respectively, and the energy transfer was analyzed in detail through combined calculations. Interestingly, a series of heterometallic doped 1-TbxEu1−x coordination polymers were also obtained by mixing different ratios of Eu3+ and Tb3+ ions, which possess continuous luminescent color changes from green to yellow, orange and red. In addition, 1-Eu exhibits high quenching efficiency and low detection limit (∼10−4 M) for the simultaneous sensing of MnO4−, CrO42− and Cr2O72− ions in water. [ABSTRACT FROM AUTHOR]

SrB2Si2O8: Eu2+/Ce3+ co-doped phosphors were synthesized via conventional high temperature solid state reaction method. The best rare earth doping SrB2Si2O8 phosphors were obtained at 950 °C for 6 h. For SrB2Si2O8: Eu2+, a large broad band locating at 440 nm corresponding to the 4f65d-4f7 (8S7/2) transition. The optimal concentration of Eu2+ is 8 at.%, its concentration quenching is due to dipole-dipole interaction. Under UV excitation of 320 nm, SrB2Si2O8: Ce3+ phosphor demonstrates a strong emission peak located at 373 nm. By Gaussian fitting, the emission of the sample peaking at 367 nm (27223 cm−1) and 396 nm (25270 cm−1) corresponding to the transition 5d-4f (2F5/2) and 5d-4f (2F7/2), respectively, the best doping concentration of Ce3+ is 0.6 at.%. Simultaneously, a series of Sr1−xB2Si2O8: xEu2+, Ce3+ phosphors were studied, results indicating that the emission intensity of Ce3+ ions decreases with the increasing of Eu2+ concentration, when the doping concentration of Eu2+ reaches 1.0 at.%, the emitting intensity is 2.1 times higher than that of the single doped Eu2+. The energy transfer efficiency among Ce3+ and Eu2+ ions is calculated to be as high as 93.4%, which is caused by the dipole-dipole resonant type from Ce3+ to Eu2+. [ABSTRACT FROM AUTHOR]

A series of LiLaMo 2 O 8 :Eu 3+ , R (R = Bi 3+ and Sm 3+ ) phosphors are synthesized by a high temperature solid-state reaction method in air. The crystal structures, fluorescence lifetimes, and luminescence properties are investigated in detail. LiLaMo 2 O 8 :Eu 3+ phosphor with excitation 395 nm shows red light in the range of 525–725 nm and it photoluminescence intensity may be enhanced ∼2.35 times due to energy transfer (ET) from a sensitizing species (Bi 3+ or Sm 3+ ) to Eu 3+ ion after Bi 3+ or Sm 3+ ion is co-doped. The optimal Eu 3+ , Bi 3+ , and Sm 3+ ion concentrations are 4%. Luminous mechanism of LiLaMo 2 O 8 :Eu 3+ , R (R = Bi 3+ and Sm 3+ ) phosphors and ET processes between Eu 3+ and Bi 3+ /Sm 3+ ions are analyzed and explained by their excitation and emission spectra and energy level diagrams of Eu 3+ , Bi 3+ , and Sm 3+ ions. The experimental results indicate that LiLaMo 2 O 8 :Eu 3+ , R (R = Bi 3+ and Sm 3+ ) phosphors may be used as potenial red emitting materials for white light emitting diodes (LEDs) based on either a near ultraviolet (∼395 nm) or blue (∼465 nm) chip. [ABSTRACT FROM AUTHOR]

In the present study, structural and photo-luminescence studies of Eu 3+ and Tb 3+ co-doped ZnMoO 4 host matrix has been investigated in detail. ZnMoO 4 :Eu 3+ /Tb 3+ have been synthesized via a simple and cost effective co-precipitation method. XRD, Raman and FTIR studies confirmed its triclinic structure of Eu 3+ /Tb 3+ co-doped ZnMoO 4 host. Emission spectra of the measured samples corroborate the dominant electric dipole transition emission ( 5 D 0 - 7 F 2 ) intensity over magnetic dipole transition emission ( 5 D 0 - 7 F 1 ) intensity. Moreover, the improvement in red emission ( 5 D 0 - 7 F 2 ) for Eu 3+ (3 at%) and Tb 3+ (2 at%) and high asymmetric ratio ∼10.4 is observed which dictates it as a highly red emitter. Additionally, commission international de-I′ Eclairage (CIE) values approaches to NSTC. Color purity of red emission improves after Tb 3+ co-doping. Photoluminescence studies reveals that Tb 3+ acts as a sensitizer for the Eu 3+ activated ZnMoO 4 host matrix. Study reveals that Eu 3+ /Tb 3+ co-doped ZnMoO 4 can be excited by near UV device, which is bottleneck in the advancement of LEDs technology. [ABSTRACT FROM AUTHOR]

Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na 2 O-Al 2 O 3 -SiO 2 glasses were developed to dope Eu 2+ and Mn 2+ with well controlled valence states by heating in H 2 gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu 3+ , Mn 3+ and Mn 2+ ions incorporated in the as-prepared glasses, the Eu 3+ and Mn 3+ ions were reduced to Eu 2+ and Mn 2+ ions, respectively, by heating in H 2 gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H 2 exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu 2+ and Mn 2+ , respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn 2+ ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu 2+ to Mn 2+ ions and the energy transfer efficiency was estimated with a concentration of Eu 2+ and Mn 2+ ions. [ABSTRACT FROM AUTHOR]

Tb 3 + and Eu 3 + single- and double-doped barium borate glasses are analyzed for their temperature-dependent luminescence and energy transfer properties. The glasses are investigated in the temperature range from 15 K to 700 K. The Tb 3 + doped glass has a higher temperature stability than the Eu 3 + doped one. Increasing the temperature leads to an enhanced energy transfer from Tb 3 + to Eu 3 + in the double-doped glass. The energy transfer mechanism is investigated in detail. [ABSTRACT FROM AUTHOR]

In this work, efficient red phosphorescent OLEDs (PHOLEDs) were designed and fabricated by solution processing method. Based on well optimized doping concentrations of emitter and ratio of mixed host materials, Eu(DBM) 3 Phen (DBM = 1,3-diphenylpropane-1,3-dion, Phen = 1,10-phenonthroline) was doped into the light-emitting layer (EML) which plays the role of sensitizer. Experimental results indicated that the incorporation of Eu(DBM) 3 Phen molecules can effectively trap the superfluous electrons within EML, which is helpful for balancing charges' distribution and widening the recombination zone. Besides, the presence of Eu(DBM) 3 Phen molecules can accelerate the transfer of triplet energy from hosts to red emitters, therefore remarkably enhances device performance. By optimizing the doping concentrations of emitter and sensitizer, ratio of co-hosts and the functional layer thickness, recombination center was accurately adjusted to further broaden recombination zone, therefore causing decreased excitons density and suppressed excitons quenching. Eventually, the optimal solution-processed red PHOLED obtained the maximum current efficiency (47.12 cd/A) and external quantum efficiency (27.3%). High performance solution-processed red phosphorescent organic light-emitting diodes by incorporating trivalent rare earth europium complex Eu(DBM) 3 Phen (DBM = 1,3-diphenylpropane-1,3-dion, Phen = 1,10-phenonthroline) into light-emitting layer as sensitizer. [Display omitted] • High performance solution-processed red phosphorescent OLED was designed by utilizing Eu(DBM) 3 Phen into EML as sensitizer. • Co-doped sensitizer molecules function as electron trappers. • The optimal solution-processed red PHOLED obtained the maximum CE up to 47.12 cd/A and EQE up to 27.3%. • This work firstly demonstrated the efficacy of utilizing rare earth complex as sensitizer in solution-processed OLEDs. [ABSTRACT FROM AUTHOR]

A series of green-to-red color-tunable Sr 3 La(PO 4 ) 3 :Tb 3+ , Eu 3+ phosphors were prepared by high temperature solid-state method. The crystal structures, photoluminescence properties, fluorescence lifetimes, and energy transfer of Sr 3 La(PO 4 ) 3 :Tb 3+ , Eu 3+ were systematically investigated in detail. The obtained phosphors show both a green emission from Tb 3+ and a red emission from Eu 3+ with considerable intensity under ultraviolet (UV) excitation (~377 nm). The emission colors of the phosphors can be tuned from green (0.304, 0.589) through yellow (0.401, 0.505) and eventually to red (0.557, 0.392) due to efficient Tb 3+ -Eu 3+ energy transfer (ET). The Tb 3+ →Eu 3+ energy transfer process was demonstrated to be quadrupole-quadrupole mechanism by Inokuti-Hirayama model, with maximum ET efficiency of 86.3%. The results indicate that the Sr 3 La(PO 4 ) 3 :Tb 3+ , Eu 3+ phosphors might find potential applications in the field of lighting and displays. [ABSTRACT FROM AUTHOR]

A series of Dy 3+ or/and Eu 3+ doped Y 2 Mo 4 O 15 phosphors were successfully synthesized at a low temperature of 600 °C via solid state reaction. The as-prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence (PL) excitation, emission spectra and PL decay curves. XRD results demonstrate that Y 2 Mo 4 O 15 : Dy 3+ , Eu 3+ has the monoclinic structure with the space group of p21/C(14). Under the excitation of ultraviolet (UV) or near-UV light, the Dy 3+ and Eu 3+ ions activated Y 2 Mo 4 O 15 phosphors exhibit their characteristic emissions in the blue, yellow and red regions. The emitting light color of the Y 2 Mo 4 O 15 : 0.08Dy 3+ , y Eu 3+ phosphors can be adjusted by varying the concentration ratio of Dy 3+ to Eu 3+ ions and a white light is achieved when the doping concentration of Eu 3+ is 5%. In addition, the energy transfer from Dy 3+ to Eu 3+ is also confirmed based on the luminescence spectra and decay curves. [ABSTRACT FROM AUTHOR]

A series of Eu 2+ doped and Eu 2+ /Mn 2+ co-doped Ca 3 Y(PO 4 ) 3 phosphors have been synthesized by high temperature solid-state route. In the Eu 2+ -doped samples, an intense and broad green emission band is presented under the excitation of 370 nm light. Emission color changing from green to warm white light is observed when different concentrations of Mn 2+ ions were introduced into the lattice of Ca 3 Y(PO 4 ) 3 :Eu phosphor, originating from an efficient energy transfer from Eu 2+ to Mn 2+ ions. The energy transfer mechanism from Eu 2+ to Mn 2+ is demonstrated to be a quadrupole–quadrupole interaction based on the concentration quenching as well as the energy transfer efficiency of 90%. The temperature-dependent luminescence of Ca 3 Y(PO 4 ) 3 :Eu 2+ ,Mn 2+ phosphor reveal that 52% of initial intensity can be kept at 150 °C, suggesting good thermal stability of the phosphor. Our results indicate that the Ca 3 Y(PO 4 ) 3 :Eu 2+ ,Mn 2+ phosphor may be a potential candidate for use as near ultraviolet pumped white light-emitting diodes phosphor. [ABSTRACT FROM AUTHOR]

Dy-doped and Dy/Eu-codoped GdMoO phosphors were synthesized by hydrothermal method. The results of X-ray diffraction indicate that the GdMoO phosphors have crystallized with the monoclinic structure. The emission spectra exhibit emissions at 577 nm and 488 nm that corresponded to the yellow and blue emissions, respectively. The emission intensity of these bands increases with the rise of the Dy up to a particular concentration and then reduces at a higher level. The observed behaviour was explained on the basis of concentration quenching phenomena. The enhancement in the emission intensity of the Dy with the addition of Eu along with the red emission at 617 nm for Eu was noted. The energy transfer between the two rare earth ions was studied. Codoping with the trivalent Eu ions neutralized the red emission part of the phosphor. Thus, by incorporating the adequate quantity of Eu the photometric characteristics of the phosphors can be adjusted. [ABSTRACT FROM AUTHOR]

A new approach to calculate the effective Ln–Ln energy transfer rates in a doped crystal matrices was proposed and successfully applied to the YVO 4 :Yb 3+ ,Er 3+ upconversion system. This approach is based on the known set of Ln–Ln distances obtained from the crystal structure of the matrix and the probabilities of their occurrence. The non-radiative energy transfer rates were calculated in the intermediate coupling scheme taking into account the shielding of the 4f electrons. The required partial (that is, forced electric dipole-only, lacking the dynamic coupling contribution) Judd–Ofelt Ω λ parameters were calculated using the Simple Overlap Model (SOM). The spectral overlap factor F was estimated from optical absorption measurements. A simplified “one level-one manifold” energy level scheme was applied. The F 7 / 2 4 , H 11 / 2 2 and S 3 / 2 4 states of Er 3+ were treated as an effective level. The set of rate equations containing radiative, non-radiative and energy transfer processes was solved numerically using fourth-order Runge–Kutta method. Both continuous and pulsed excitation modes were simulated. The dependence of the upconversion intensity upon the pump power was found. The simulations resulted in good agreement with the experimental results and provided new insights into the dynamics of the upconversion process and a connection between the macroscopic properties and the microscopic description. [ABSTRACT FROM AUTHOR]

In this study, a series of Gd 2 O 3 : Ln 3+ (Ln = Dy, Eu) submicrospheres were successfully prepared by a hydrothermal method and a subsequent higher temperature pyrolysis. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectrometer (EDS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM) were utilized to characterize the as-prepared samples. The precursor sample thoroughly decomposed into Gd 2 O 3 submicrospheres with a diameter of about 550 nm after calcination. Under UV excitation, the samples exhibit multicolor emissions including yellow-green, yellow, red as well as white, moreover, the Dy 3+ ions acted as donors can transfer the energy to Eu 3+ served as acceptors in Gd 2 O 3 : Dy 3+ , Eu 3+ system. The interaction between Dy 3+ ions and Eu 3+ ions is verified to be phonon-assisted electric quadrupole–quadrupole interaction. Multicolor luminescence including white light emission can be obtained through varying the content of Eu 3+ or adopting different excitation wavelengths in Dy 3+ and Eu 3+ co-doped Gd 2 O 3 system. The energy transfer efficiency reaches 88.2% when the doped concentration of Eu 3+ is 0.035. The CIE chromaticity diagram directly reveals the variability of the hue of the as-prepared samples. Besides, the as-prepared samples exhibit paramagnetic properties at room temperature. This type of color-tunable luminescence phosphors has promising applications in the fields of photoelectronic devices and biomedical science. [ABSTRACT FROM AUTHOR]

The europium (Eu) and ytterbium (Yb) co-doped SiO 2 –Al 2 O 3 –MF 2 (M = Ca, Sr) oxyfluoride glasses were prepared by the melting-quenching method, in which the partial reduction of Eu 3+ ions during high temperature fabrication in air atmosphere was explained by optical basicity model. In this system, the near-infrared emission of Yb 3+ at 974 nm can be observed upon the excitation of both Eu 3+ and Eu 2+ , as well as charge transfer state absorption of Yb 3+ . The steady and time-resolved luminescence spectra measurements were carried out to further prove the energy transfer from Eu 3+/2+ ions to Yb 3+ . Based on the measured luminescence decay of Eu 3+ and Eu 2+ , the energy transfer efficiency and the quantum efficiency are much higher in the glass containing SrF 2 due to the efficient energy transfer from both Eu 3+ and Eu 2+ to Yb 3+ . [ABSTRACT FROM AUTHOR]

A series of Eu 2+ and Eu 2+ /Tb 3+ co-doped Ba 3 GdNa(PO 4 ) 3 F phosphors have been synthesized via a high temperature solid-state reaction. The relative intensity of PL spectra of Ba 3 GdNa(PO 4 ) 3 F: x Eu 2+ increases with increasing x value, and reaches a maximum at x =0.04. Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ phosphors exhibit a broad excitation band ranging from 220 to 450 nm, which matches perfectly with the characteristic emission of n -UV light-emitting diode (LED) chips. Upon 365 nm excitation, the Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ phosphors show two dominating bands peaked at 466 and 543 nm, which are assigned to the 4f 7 →4f 6 5d 1 transition of the Eu 2+ ions and the 5 D 4 → 7 F 5 transition of the Tb 3+ ions, respectively. In view of the energy transfer mechanism between Eu 2+ and Tb 3+ , the Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ emission color can adjust from blue to green, and their chromatic coordinates ( x , y ) vary from (0.16, 0.135) to (0.254, 0.398). The critical distance was also calculated to be 16.90 Å. The above results indicate that the Ba 3 GdNa(PO 4 ) 3 F: Eu 2+ , Tb 3+ phosphors are a candidate for blue–green components in the application of n -UV w -LEDs. [ABSTRACT FROM AUTHOR]

KLuS 2 single crystals doped with divalent europium and co-doped with trivalent praseodymium, samarium or cerium were synthesized in the form of crystalline hexagonal platelets as interesting candidates for white LED solid state lighting. Luminescence characteristics in UV/Vis, including radioluminescence, photoluminescence excitation and emission spectra and photoluminescence decays, were measured in the broad concentration and temperature interval revealing presence of thermally stable emission features of both Eu 2+ and co-dopants in a single KLuS 2 host. Energy transfer from Eu 2+ to Pr 3+ , Sm 3+ and Ce 3+ is identified. CIE xy -coordinates are used to compare effects of dopants on resulting spectrum. The application potential in white LEDs phosphors is discussed. [ABSTRACT FROM AUTHOR]

Eu 3+ and Gd 3+ ions co-doped amorphous silica nanorods were prepared using a simple sol–gel method, and their luminescent properties were studied under the excitation of ultraviolet light. X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared spectrum (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), and Photoluminescence (PL) spectra were employed to characterize the products in detail. The nanorods are uniform and their diameters and lengths are in the range of 200–300 nm and 500–700 nm, respectively. Energy transfer process in Gd 3+ and Eu 3+ co-doped silica, where a ground state of Gd 3+ , 8 S 7/2 , was selectively excited to a 6 I J state under the excitation of 274 nm, was studied in terms of luminescence spectra, which indict that the energy transfer of Gd 3+ –Eu 3+ is efficient. The mechanism of energy transfer from Gd 3+ to Eu 3+ is a resonant transfer, in which electric dipole–dipole interaction plays a leading role. Furthermore, the doping concentration-dependence of Eu 3+ ions on the energy transfer efficiency was also investigated. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) properties of singly doped (Dy3+) and codoped (Dy3+, Eu3+) fluoroaluminoborate glasses, with an emphasis on the white light generation, are studied. The γ-irradiation led to the formation of defects in Dy3+-doped glasses and photoreduction of Eu3+ to Eu2+ in codoped (Dy3+, Eu3+) glasses. The electron paramagnetic resonance spectra confirm the presence of divalent europium ions and defects in Dy3+, Dy3+-Eu3+-doped glasses. The FTIR spectra mainly establish the compaction of glass network due to γ-irradiation. From the PL spectra, the intensity ratio of Dy3+ emission bands yellow to blue (4F9/2-6H13/2/4F9/2-6H15/2) defines the site symmetry, covalency, and feasibility of extracting white light. The existence of an energy transfer (ET) from Dy3+ to Eu3+ ions are established due to the decrease in intensity of Dy3+ peaks with an increase of Eu2O3 content. Moreover, the non-exponential nature of decay curves was well fitted with the generalization of Yokota-Tanimoto model for electric dipole-quadrupole ( S = 8) interaction that is responsible for ET process from sensitizer (Dy3+) to activator (Eu3+). [ABSTRACT FROM AUTHOR]

We report Eu3+, Sm3+ co-doped La(OH)3 nano-crystalline red emitting phosphor prepared following combustion synthesis protocol. The structural and morphological information about the synthesized samples have been explored using X-ray diffraction (XRD) and transmission electron microscopic (TEM) techniques. The optical properties of the samples have been investigated under 355 nm laser excitations. The sample emits intense red emissions at 625 and 707 nm due to 5D0 → 7F2 and 5D0 → 7F4 transitions in Eu3+ ion, respectively. The concentrations of both, Eu3+ and Sm3+ in the samples were optimized at 1 mol% to get maximum fluorescence. The presence of Sm3+ in the Eu3+ doped sample enhances the emission intensity up to two times. The samples annealed at higher temperature show significant enhancement in the emission intensity. The life time studies show an efficient energy transfer from Sm3+ to Eu3+ ions and have been discussed with the help of schematic energy level diagram. This enhancement in the emission intensity is discussed in terms of the rare earth ion concentration, annealing temperature and energy transfer. [ABSTRACT FROM AUTHOR]

Low-toxic core-shell ZnSe:Eu/ZnS quantum dots (QDs) were prepared through two steps in water solution: nucleation doping and epitaxial shell grown. The structural and morphological characteristics of ZnSe/ZnS:Eu QDs with different shell thickness were explored by transmission electron microscopy (TEM) and X-ray diffraction (XRD) results. The characteristic photoluminescence (PL) intensity of Eu ions was enhanced whereas that of band-edge luminescence and defect-related luminescence of ZnSe QDs was decreased with increasing shell thickness. The transformation of PL intensity revealed an efficient energy transfer process between ZnSe and Eu. The PL intensity ratio of Eu ions (I613) to ZnSe QDs (IB) under different shell thickness was systemically analyzed by PL spectra and time-resolved PL spectra. The obtained results were in agreement with the theory analysis results by the kinetic theory of energy transfer, revealing that energy was transmitted in the form of dipole-electric dipole interaction. This particular method of adjusting luminous via changing the shell thickness can provide valuable insights towards the fundamental understanding and application of QDs in the field of optoelectronics. [ABSTRACT FROM AUTHOR]