Electric Dipole-dipole Interaction Research Articles

Multicolor emission in [formula omitted] clusters and Eu3+ activated ZnO–P2O5 glasses achieved under near ultraviolet light excitation

The structural and photoluminescence properties of zinc phosphate glasses activated with Agmn+ clusters and Eu3+ are studied. The addition of Ag+ and Eu3+ does not significantly modify the glassy structural properties evaluated by X-ray diffraction (XRD) patterns and Raman spectroscopy. The only change observed by Raman spectroscopy, is ascribed to the creation of molecular oxygen. The photoluminescence spectra, recorded under near ultraviolet (NUV) light excitation, display the feature broad band attributed to Agmn+ clusters. With the Eu3+ addition, Eu3+ bands located at 578, 591, 611, 652 and 701 nm, appear on the Agmn+ cluster emission, achieving the highest intensity at 0.8 mol% of Eu3+. This behavior is accompanied by a gradual reduction of the Agmn+ cluster emission. Sinks related to Eu3+ absorption on Agmn+ cluster emission and shortening of Agmn+ cluster: S1 → S0 and T1,T2 → S0 emission decays, suggest respectively the existence of radiative and non-radiative energy transfers from Agmn+ clusters to Eu3+. The Burstein model points out that the non-radiative energy transfer processes are predominantly mediated by electric dipole-dipole interaction for the Agmn+ :S1 → S0 transition. The emission tonality, estimated from the CIE1931 chromaticity coordinates and correlated color temperature (CCT) can be tuned from the cold white region to the warm white one, with effective quantum yield measurements up to 48%, depending on the excitation wavelength and Eu3+ doping content. Emission tonalites out of the white light region (orange-pink, purple-pink and pink) are obtained at higher amounts of Eu3+ (0.8 and 1.0 mol%) as well.

Luminescence properties of Tb3+/Eu3+ co-doped glass based on GSBR system

In this work, a series of Tb3+/Eu3+ co-doped GeO2-SiO2-BaO-R2O3 (GSBR) glass were synthesized through high temperature melt cooling method. Luminescence properties of Tb3+/Eu3+ co-doped glass were studied by fluorescence spectrum, fluorescence lifetime and CIE coordinate. The energy transfer efficiency and probability were calculated by average donor distance and lifetime data, revealing that the type of energy transfer is the electric dipole-electric dipole interaction for Tb3+→Eu3+. And the efficiency of energy transfer from Tb3+ to Eu3+ increased greatly by increasing Eu3+ concentrations, which play an important role in adjusting the color at the excitation of 378 nm. The effects of different R2O3 (Gd2O3, Al2O3, Ga2O3) in the matrix on the luminescence intensity of the glass samples were compared. It was found that the luminescence intensity order of samples was Al2O3>Ga2O3>Gd2O3. Through the analysis of infrared and fluorescence spectra, the effects of different matrices components on the structure and luminescence properties of glass were revealed.

Enhanced crystallinity and photoluminescence properties of Yb2+ doped SrSi2O2N2 phosphor for image storage applications

A series of Yb2+ and Dy3+ doped SrSi2O2N2 phosphors with enhanced crystallinity and photoluminescence properties have been successfully synthesized by two-step method using Sr2SiO4 as precursor. It is clearly indicated from XRD results that Yb2+ ions can substitute Sr sites in SrSi2O2N2 crystal and exhibit pure phase and well-crystalline in comparison with the samples prepared by traditional solid-state reaction. The excessive amount of Si3N4 in the reactants promoted the formation of pure SrSi2O2N2 phosphors phase. SrSi2O2N2: Yb2+ phosphors show emission band at 583 nm and the broad excitation peaks located at 308 nm, 384 nm and 447 nm, covering the emission wavelength of NUV and blue chips. Compared with the sample prepared by traditional one-step solid-state reaction method, a dramatic enhancement of photoluminescence emission intensity (∼1.75 times) can be observed for SrSi2O2N2: 0.01 Yb2+ phosphor synthesized by two-step method. Due to the concentration quenching, the luminescence intensity reaches the maximum when doping concentration of Yb2+ ions is 1 mol%, which is identified as the electric dipole-electric dipole interaction. Notably, Yb2+ and Dy3+ co-doped SrSi2O2N2 phosphors with pure phase exhibit a unique thermal-stimulated luminescence property under NUV excitation, indicating the potential application in optical information storage. Furthermore, the mechanism of thermal-stimulated luminescence has been proposed.

Theory of Nonradiative Energy Transfer between Two Optical Ions Using the Proper Adiabatic Approximation

Using adiabatic approximation of polyatomic molecules and methods of molecular quantum electrodynamics, we have derived the Förster-Dexter theory of energy transfer between two optical ions. Although we have assumed a single configurational coordinate, the theory can be easily formulated for multiple normal coordinate system. This approach leads smoothly to the energy transfer rates originally derived by Dexter1 for electric dipole-electric dipole interaction without any additional assumptions regarding the normalization of the wavefunctions in the energy space. Using the transfer rates thus derived, and the band shape functions, Wp , a new function F(T) has been proposed to study the temperature dependence of energy transfer rates due to the overlap of the emission and absorption line shapes of the donor and acceptor ions, respectively. This function has been studied for various scenarios of the relative alignment of the zero phonon lines of these ions in order to understand the participation of phonons in the energy transfer process. We have also compared this quantum mechanically derived F(T) function with that derived using semiclassical theory. The agreements are very good at high temperatures. D. L. Dexter, J. Chem. Phys. 21, 836(1953)

Ethylene glycol associated facile preparation and luminescent behaviors of RE (RE = Sm3+, Dy3+) ions activated NaLuF4 nanoparticles

To achieve high quality luminescent nanomaterials, we synthesized series of rare-earth (RE; RE = Sm3+, Dy3+) ions activated NaLuF4 nanoparticles via a facile synthetic technique at room temperature. The phase category, microstructure and luminescent behaviors of the resultant samples were detailedly investigated. Under a certain excitation wavelength, these prepared nanoparticles can emit glaring visible light and the emission intensities are determined to be sensitive to the doping content. The optimal doping concentration for Sm3+ and Dy3+ ions in the NaLuF4 host lattices are 1 and 3 mol%, respectively, and the involved concentration quenching mechanisms are all contributed by the electric dipole-dipole interaction. The synthesized nanoparticles exhibit splendid thermal stability and the activation energies of the NaLuF:0.01Sm3+ and NaLuF4:0.03Dy3+ nanoparticles are 0.16 and 0.17 eV, respectively. Furthermore, the temperature-dependent decay time reveals that the thermal quenching mechanism of the designed nanoparticles is responsible by the crossover process between the excited level and ground state. These results indicate that the resultant nanoparticles with good luminescent materials and high thermal stability are potential candidates for white light-emitting diode.

Study on energy transfer in Ce3+/Sm3+ activated LaSi3N5 phosphor for warm white-light LED

Sm3+, Ce3+ singly doped and Ce3+-Sm3+ co-activated LaSi3N5 were synthesized by a solid-state reaction method. The crystal structure, morphology and luminescent properties of the corresponding samples are characterized. The photoluminescence results demonstrate that LaSi3N5:Ce3+ phosphor has a broad band excitation spectra and emission spectra with peak at 418 nm, while LaSi3N5:Sm3+ phosphor demonstrates characteristics of linear excitation spectra with main peak locating at 407 nm. An apparent spectral crossover between the emission spectrum of LaSi3N5:Ce3+ and excitation spectrum of LaSi3N5:Sm3+ can be observed, pointing to the possibility of energy transfer from Ce3+ to Sm3+, which is further proved by the investigations of diffuse reflectance spectra, emission spectra, and fluorescence lifetime decay curves. The energy transfer efficiency reaches the maximum of 65.5%. The mechanism of energy transfer was determined to be electric dipole-dipole interaction. This study provides a new example for the development of efficient phosphors in Ce3+- Sm3+ codoped nitrides.

Spectroscopic analysis of Nd3+-doped cadmium-vanadate invert glasses for near-infrared laser applications

Nd3+ activated CdO-V2O5 invert glasses were synthesized by the well-stablished melt quenching technique, using starting proportions of 95.0 and 5.0 mol% of CdO and V2O5, respectively. The XRD patterns revealed that the glass system remains amorphous up to 4.0 mol% of Nd3+. Such fact was mainly attributed to the low V2O5 content, which avoided the segregation of additional phases. The minimal addition of 0.1 mol% of Nd3+ reduced the direct and indirect glass bandgap energies from 2.79 to 2.66 eV, and from 2.48 to 2.13 eV, respectively. For higher Nd3+ contents, the bandgap energy was recovered, reaching values of 2.78 and 2.40 eV for direct and indirect allowed transitions, respectively. This fact was associated with a Burstein-Moss like effect, observed in semiconductors highly doped. The tail of the absorption edge revealed that the Urbach energy systematically grows with the addition of Nd3+, because of the creation of localized states into the bandgap. The Judd-Ofelt (JO) parameters obtained by least-square method from the experimental and theoretical oscillator strengths, were found in the Ω2 = 5.24-11.04 × 10−20 cm2, Ω4 = 2.26-4.47 × 10−20 cm2, and Ω6 = 2.85-6.28 × 10−20 cm2 range. Such values are close to those reported in other popular glass systems. The stimulated emission cross-section peak (σp) values calculated for the glass sample doped with 2.0 mol% resulted to be 0.26 × 10−20 cm2 (Nd3+: 4F3/2 → 4I9/2) and 0.81 × 10−20 cm2 (Nd3+: 4F3/2 → 4I11/2). The Nd3+ emission spectra, recorded upon 585 nm excitation (Nd3+: 4I9/2 → 4G5/2 + 2G7/2), showed the near-infrared Nd3+ emission bands at 881 nm (Nd3+: 4F3/2 → 4I9/2), 1063 nm (Nd3+: 4F3/2 → 4I11/2) and 1341 nm (Nd3+: 4F3/2 → 4I13/2), being dominated for that coming from the Nd3+: 4F3/2 → 4I11/2 transition. The overall emission reached the optimum intensity at 2.0 mol% of Nd3+, with a maximum quantum efficiency (ηQE) of 0.23. From the emission spectra important laser parameters such as gain bandwidth (σEMI(λp) × Δλem) and optical gain (σEMI(λp) × τR), were determined for the sample with the highest ηQE value. The σEMI(λp) × Δλem values resulted to be 11.3 and 32.0 × 10−27 cm3 for the Nd3+: 4F3/2 → 4I9/2, 11/2 transitions, respectively. The σEMI(λp) × τR parameter values were 11.1 and 35.3 × 10−25 cm2s for Nd3+: 4F3/2 → 4I9/2,11/2 transitions, respectively. The Inokuti-Hirayama model suggested that the Nd3+ cross-relaxation process might be dominated by an electric dipole-dipole interaction, inside Nd3+-Nd3+ clusters.

Structure and luminescence properties of Eu3+ and Dy3+ implanted GaN films

X-Ray diffraction (XRD), Raman scattering , Cathodoluminescence measurements (CL) and Photoluminescence (PL) were employed to characterize the structure and optical properties of Dysprosium (Dy) and Europium (Eu) implanted GaN films grown by MOCVD. For GaN: Dy 3+ samples, Dy 3+ implantation leads to strain and radiation damage increasing with Dy 3+ implanted fluence . From the CL spectra, the characteristic transitions from the excited 4 F 9/2 level of Dy 3+ to 6 H 15/2 (485 nm), 6 H 13/2 (583 nm) and 6 H 11/2 (671 nm) were observed. For Dy 3+ and Eu 3+ co-doped GaN, considering the doping effects of Dy 3+ , we proposed that there might exist a resonance energy transfer process from Eu 3+ ions 7 F 0 → 5 D 2 to Dy 3+ ions 4 F 9/2 → 6 H 15/2 , which is dominated by the electric dipole-dipole interaction. • Eu 3+ , Dy 3+ co-implanted GaN crystalline thin films were prepared for the first time. • Energy transfer processes between Eu 3+ and Dy 3+ were proposed. • Dy implantation leads to strain and radiation damage increasing with Dy dose.

Study on the color tunability and energy transfer mechanism in Tm3+/Dy3+ co-doped LiLaSiO4 phosphors

Many color-tunable LiLaSiO4: αTm3+, βDy3+ phosphors were prepared using the traditional high-temperature solid-phase method. The phase composition, surface morphology, fluorescence spectrum, fluorescence lifetime, energy transfer mechanism, and color coordinates of the samples were analyzed using XRD, SEM, TEM and fluorescence spectrometer. The results show that LiLaSiO4: αTm3+ phosphor emits high intensity blue light at 460 nm and the concentration quenching point of Tm3+, α = 0.015 mol. In LiLaSiO4: αTm3+, βDy3+ phosphors, as the doped Dy3+ doping increases, the luminescence intensity of Tm3+ gradually decreases, the luminescence intensity of Dy3+ first increases and then decreases. The concentration quenching point of Dy3+, β = 0.015 mol. Adjustable light-emitting color can be obtained by changing the doping molar mass of Dy3+ or the wavelength of the excitation light. There is an effective energy transfer between Tm3+→Dy3+. The energy transfer mechanism is the electric dipole-electric dipole interaction, and the energy transfer efficiency reaches 90.11% when β = 0.06 mol. The quantum yield of LiLaSiO4:0.015 Tm3+,0.015Dy3+ was 39.0%. The single-matrix white light LiLaSiO4: αTm3+, βDy3+ phosphors with excellent performance is a prospective material for of white LEDs.

Garnet type Y2Mg3Ge3O12: Dy3+ / Eu3+ phosphors excited near ultraviolet: Luminescence properties and energy transfer mechanisms

A battery of Dy3+ single-doped and Dy3+/Eu3+ co-doped Y2Mg3Ge3O12 phosphors were manufactured by high-temperature solid-phase method. The XRD patterns were tested and Rietveld refined. When the samples were excited by 352 ​nm near ultraviolet light, the energy transfer efficiency can reach 83.2%, and the energy transfer mechanism is electric dipole-electric dipole interaction. The thermal stability of Y1.75Mg3Ge3O12:0.05Dy3+, 0.2Eu3+ was tested. When the temperature reached 150 ​°C, its luminous intensity droped to 92.4% of the initial temperature (30 ​°C). By changing the concentrations of Eu3+, white light with red light can be obtained. The above results indicate that these samples are expected to become candidate materials in the domain of solid-state lighting.

Theory of Nonradiative Energy Transfer between Two Optical Ions Using Proper Adiabatic Approximation

Using the adiabatic approximation of polyatomic molecules and methods of molecular quantum electrodynamics, we have derived the Förster-Dexter theory of energy transfer between two optical ions. Although we have assumed a single configurational coordinate, the theory can be easily formulated for a multiple normal coordinate system. This approach leads smoothly to the energy transfer rates originally derived by Dexter1 for electric dipole-electric dipole interaction without any additional assumptions regarding the normalization of the wavefunctions in the energy space. Using the transfer rates thus derived, and the band shape functions, W p , a new function F(T) has been proposed to study the temperature dependence of energy transfer rates due to the overlap of the emission and absorption lineshapes of the donor and acceptor ions, respectively. This function has been studied for various scenarios of the relative alignment of the zero phonon lines of these ions in order to understand the participation of phonons in the energy transfer process. We have also compared this quantum mechanically derived F(T) function with that derived using semiclassical theory. The agreements are very good at high temperatures.

Luminescence properties and energy transfer of color-tunable LaAl2.03B4O10.54:Tm3+,Dy3+ phosphors

LaAl2.03B4O10.54:Tm3+,Dy3+ phosphors were prepared by the sol–gel method. The phase, luminescence properties, energy transfer mechanism and CIE color coordinates of the samples were analyzed by XRD, SEM and fluorescence spectrometry. The results show that the LaAl2.03B4O10.54:Tm3+ phosphor emits blue light at a monitored wavelength of 357 nm and the concentration quenching point of Tm3+ ion is 0.06 mol. In the La0.94-yAl2.03B4O10.54:0.06Tm3+,yDy3+ phosphors, the luminescence intensity of Tm3+ decreases with an increase in the Dy3+ doping concentration, while the luminescence intensity of Dy3+ increases. The color of the emitted light can be adjusted by changing the doping concentration of Dy3+ or changing the wavelength of the excited light. There is energy transfer between the Tm3+ and Dy3+ ions. When the doping concentration of Dy3+ ions is 0.1 mol, the energy transfer efficiency reaches 63.65% and the energy transfer mechanism is an electric dipole-electric dipole interaction. These results clearly indicate that La0.94-yAl2.03B4O10.54:0.06Tm3+,yDy3+ phosphors can be used as color tunable phosphors in the field of WLEDs.

Photoluminescence, optical transition properties and temperature-induced shift of charge transfer band and temperature sensing property of GdNbTiO6: Sm3+ phosphors

GdNbTiO6: Sm3+ phosphors with various Sm3+ concentrations were prepared via a high temperature solid-state reaction method. The crystal structure of the samples was characterized by means of X-ray diffraction (XRD) and the as-prepared samples were confirmed to be orthorhombic phase GdNbTiO6. Photoluminescence properties were investigated by measuring the concentration- and temperature-dependent photoluminescence spectra. Concentration-dependent luminescence quenching and luminescent thermal quenching behaviors were observed and they were respectively ascribed to the electric dipole-dipole interaction between Sm3+ ions and the cooperation of energy transfer and crossover process. The chromatic characteristics were found to be dependent on the excitation wavelength and Sm3+ concentration. In addition, temperature-induced redshift of charge transfer band of GdNbTiO6 host was found in temperature-dependent excitation spectra and the opposite variations of different excitation peaks were utilized for optical thermometry. Finally, the optical transition property was studied on the basis of the diffuse reflectance spectra and Judd-Ofelt (J-O) theory, meanwhile, its accuracy was evaluated by the result of emission spectra.

A promising novel red-emitting Eu3+-activated neodymium calcium phosphate phosphor with good thermal stability and excellent color purity for WLEDs

A series of Ca9Nd(PO4)7:xEu3+ (abbreviates as CNP:xEu3+, where x varies from 0.1 to 0.5) phosphors were prepared via conventional solid-state reaction. The X-ray diffraction (XRD) data and Rietveld refinement suggested a successful preparation of CNP:xEu3+ with no sign of impurities. The structure of CNP:Eu3+ belongs to a trigonal crystal system the same as that of β-Ca3(PO4)2. Thus, Eu3+ ions should theoretically occupy the Ca sites in CNP. All CNP:xEu3+ phosphors showed red emission under excitation in the near-ultraviolet (n-UV) range. The optimal dosage with the best luminescent performance was found at x = 0.3 with critical interaction radius (Rc) of 15.57 Å. The electric dipole-dipole interaction was suggested to be the reason that leads to concentration quenching. The relative luminous intensity of CNP:0.3Eu3+ phosphor at 373 K can remain 70.4% of the initial value at room temperature (RT). The color purity of CNP:0.3Eu3+ phosphor is 92.8%, which is much higher than many other red phosphors. A white light emitting diode (WLED) fabricated with CNP:Eu3+ exhibited correlated color temperature (CCT) of 4602 K and a high Ra of 74.7. The above results illustrate that Ca9Nd(PO4)7:Eu3+ could serve as a promising red phosphor for n-UV WLEDs.

Investigating photoluminescence properties of Eu3+ doped CaWO4 nanoparticles via Bi3+ amalgamation for w-LEDs application

ABSTRACT Eu3+-doped CaWO4 nanophosphors were synthesised in series for different atomic wt% concentrations (0, 0.5, 1, 2, 5 and 10) of Bi3+ by polyol method. Their structure and morphology were characterised using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photoluminescence properties and energy transfer from Bi3+ to Eu3+ in CaWO4:Eu3+/Bi3+ nanophosphors were also investigated. The results revealed that red luminescence of CaWO4:2Eu3+/1Bi3+ nanophosphor is 5.4 times stronger than CaWO4:2Eu3+. It was observed that the forces exist between Bi3+ and Eu3+ are due to the interaction of electric dipole-dipole interactions. The chroma of CaWO4:2Eu3+/1Bi3+ nanophosphors was calculated to be 97.40%. The energy transfer process was studied by measuring the decay curves due to Bi3+ and Eu3+ dopants. Enhanced red emission, high thermal stability, stronger 5D0 → 7F2 absorption intensity, high colour purity and decay studies indicate that CaWO4:Eu3+/Bi3+ nanophosphors are potential candidates to be used in white light-emitting diode (wLEDs).

Down-shifting and down-conversion emission properties of novel CdO–P2O5 invert glasses activated with Pr3+ and Pr3+/Yb3+ for photonic applications

The down-shifting and down-conversion emission properties of novel CdO–P2O5 invert glasses activated with Pr3+ and Pr3+/Yb3+ were respectively studied. The down-shifting emission spectra of Pr6O11 singly doped glasses upon 443 nm excitation (Pr3+: 3H4 → 3P2), displayed the feature Pr3+ transitions in the visible and near-infrared (NIR) regions, reaching the optimum intensity at 0.7 and 0.3 mol% of Pr6O11, respectively. The emission tonality can be adjusted from the reddish-orange to orange-pink region, depending on the Pr6O11 content. Such fact coupled with the superposition of the blue light excitation might be attractive for white light-emitting diodes (W-LEDs) applications. The cross-relaxation processes involved between Pr3+-Pr3+ pairs seem to be mediated by an electric quadrupole-quadrupole interaction, as revealed by the Inokuti-Hirayama model. The emission spectra of the Pr6O11 and Yb2O3 doped glasses upon 443 nm excitation showed, in addition to the Pr3+ related transitions, a band at 977 nm associated with the Yb3+: 2F5/2 → 2F7/2 transition, which gradually grows at expenses of non-radiative energy transfer from Pr3+. This process might lead to a down-conversion (quantum cutting) emission with theoretical quantum efficiencies up to 144%. Analysis complemented by the Inokuti-Hirayama or Dexter model revealed that the non-radiative Pr3+ → Yb3+ energy transfer process arisen from Pr3+: 3P0 and 1D2 levels are most likely dominated by electric dipole-dipole and quadrupole-quadrupole interactions, respectively. The global emission properties suggest that the Pr3+ and Pr3+/Yb3+ activated CdO–P2O5 invert glasses might be interesting for WLEDs and crystalline silicon (c-Si) solar cell applications.

High-performance and robust triboelectric nanogenerators based on optimal microstructured poly(vinyl alcohol) and poly(vinylidene fluoride) polymers for self-powered electronic applications

Triboelectric nanogenerators (TENGs) which are one of the notable renewable energy harvesting devices have been demonstrated for various types of energy harvesting, sensing, and self-powered electronic applications. However, enhancing the electrical output performance by optimizing the TENG parameters and reducing its processing cost is still major issues to be resolved for practical and industrial utilization. Herein, we demonstrated a cost-effective and high-performance TENG using polyvinylidene fluoride (PVDF) and microstructure aligned polyvinyl alcohol (MS@PVA) polymers as negatively and positively polarized triboelectric materials, respectively. The PVDF film developed by a facile and cost-effective ultra-sonication process and its high electroactive β-phase can be utilized to enhance the electric dipole-dipole interactions in the film, and also lead to an increase in its piezoelectric coefficient. Besides, the PVA film was produced by a simple solidification method and the microstructures on its surface are developed by merely corresponding inverse patterns on commercially available sandpaper. The resultant TENG with the PVDF and MS@PVA polymers exhibited maximum peak-to-peak open-circuit voltage, short-circuit current, and instantaneous output power density values of 230 V, 6 μA, and 3.1 W/m2, respectively. Ultimately, such a high electrical output generated by the TENG was employed to drive portable electronic devices such as displays and light-emitting diodes.

Study of the optical properties and cross relaxation process of Dy3+ under simultaneous UV-IR excitation in tellurite glasses

The purpose of this paper is to present a new spectroscopic experimental technique to study the contributions of the different cross-relaxation mechanisms observed in Dy3+ doped TeO2-GeO2-ZnO glasses, based on the luminescence decay curves from 4F9/2 → 6H13/2 (at 573 nm) transition of Dy3+ ions under spatial and temporal simultaneous UV (6H15/2 → 6P7/2) and IR (6H15/2 → 6F3/2,6H15/2 → 6H7/2 and 6H15/2 → 6H9/2) excitations, for which the results are reported. The spectroscopic characterization was carried out through Raman, optical absorption, luminescence decay time profiles, and energy transfer as a function of Dy3+ ions content (0.5–5%). Emission spectra measurements indicated that concentration quenching is active in the samples. The lifetime decay of emission at 573 nm (4F9/2 level) was studied under excitation at 355 nm. At lower concentration of Dy3+, the temporal behavior of the emission at 573 nm is exponential, however, it becomes non-exponential as the concentration increases. The emission decay curves at 573 nm were fitted to Inokuti-Hirayama model and an energy transfer process dominated by an electric dipole-dipole interaction was deduced. A shortened lifetime was observed as the dysprosium ion content increased, which is attributed to non-radiative energy transfer between Dy3+ ions through the cross-relaxation mechanism. The analysis of the 4F9/2 → 6H13/2 (573 nm) emission decays, obtained under simultaneous excitation at 355 nm and at different infrared excitations 6H15/2 → 6F3/2 (905 nm), 6H15/2 → 6H7/2 (1100 nm) and 6H15/2 → 6H9/2 (1285 nm), allowed the determination of the dominant process in the cross-relaxation mechanism at high and low concentrations of Dy3+. It was possible to infer that in the glass with low concentration of Dy3+ the mechanism occurs predominantly by 4F9/2 + 6H15/2 → 6F11/2 + 6F3/2 channel, and for high concentration of Dy3+, the channels 4F 9/2 + 6H15/2 → 6F11/2 + 6F3/2, F9/2 + 6H15/2 → 6F5/2 + 6F9/2 +5H7/2, and 4F9/2 + 6H15/2 → 6F3/2 + 6F11/2 + 5H9/2 have a similar contribution to the Dy3+-Dy3+ resonant energy transfer.

Efficient Bi3+ to Eu3+ energy transfer and color tunable emissions in K7CaY2(B5O10)3-based phosphors.

Rare-earth borates are well known good photoluminescent materials due to the easy manipulation of activator concentration. K7CaY2(B5O10)3 belongs to a recently discovered borate family with outstanding nonlinear optical performances. A systematic study on Bi3+ and Eu3+ doped phosphors was performed to explore their potential in photoluminescence. K7Ca(Y1-xBix)2(B5O10)3 (0.01 ≤x≤ 0.06), K7Ca(Y1-yEuy)2(B5O10)3 (0.10 ≤y≤ 1) and K7Ca(Y0.99-zBi0.01Euz)2(B5O10)3 (0.05 ≤z≤ 0.90) were prepared by high temperature solid state reactions. Rietveld refinements reveal an 8% anti-site occupancy of Ca2+ and Eu3+ in K7CaEu2(B5O10)3, and two sets of Bi3+ emission and excitation spectra are also observed once Bi3+ is introduced. For instance, the two strongest 1S0→3P1 excitations at 270 nm and 281 nm correspond to two 3P1→1S0 emissions at 383 and 334 nm, respectively. The Eu3+ emission shows a maximal intensity at y = 0.50 under charge transfer excitation, while there is no concentration quenching effect under f-f excitation. The Bi3+-to-Eu3+ energy transfer is firmly supported by the steady photoluminescence spectra and the decreased lifetime of Bi3+ upon increasing the Eu3+ content in K7Ca(Y0.99-zBi0.01Euz)2(B5O10)3. This energy transfer mechanism occurs through the electric dipole-dipole interaction. Under excitation at 281 nm, the emission is tunable from deep blue (Bi3+) to pink and finally to red (Eu3+) all with high quantum yields (>80%).

Perovskite Based Photocatalyst for Wastewater Treatment: Green Approach of Environmental Sustainability

Persistent organic substances in wastewater are creating serious problems to the living world as well as to the environment, thereby creating huge detrimental impact on the ecosystem. In view of the grave situation, removal of the persistent organic substances from wastewater effluent holds a great promise to balance the ecosystem and to sustain societal impact value. In this respect, perovskite based photocatalysts have achieved remarkable attention to the scientific community due to their unique structural features and flexibility of composition. Again, surface polarization and electric dipole-dipole interaction in the perovskite material make them attractive for photocatalytic application. This review paper summarized the photocatalytic activity of perovskite materials and their modification to enhance catalytic activity for wastewater treatment. The modification in perovskite has been done to reduce bandgap energy for enhanced visible light activity, separation of charge carriers for their long lifetime, and fast photocatalytic reaction. The recent investigation of ABO₃ type perovskite, layered perovskite, and halide type of perovskite photocatalysts have been discussed detailly. The modification of corresponding perovskites by doped and formation of heterojunction is investigated carefully. The formation and identification of reactive oxygen species (ROS) and their degradation mechanism by trapping experiment and ESR technique has been summarized here. Finally, large scale with energy and environmental related research should be processed for a permanent solution of wastewater problem.