Electric Dipole-electric Dipole Research Articles

Tuning and high temperature fluorescence properties of LaPO4:Sm3+ nanophosphors

A series of LaPO4:x%Sm3+ nanophosphors were successfully synthesized through a one-step hydrothermal method, where the acidity of the reaction system was meticulously modulated without the addition of any organic compounds. The influence of pH values and Sm3+ doping concentration on the structure, morphology, and luminescent properties of LaPO4:x%Sm3+ was systematically investigated. The composition, structure, morphology, and luminescent properties of the products were characterized and analyzed using advanced techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM, EDS), transmission electron microscopy (TEM), and fluorescence spectrophotometry (FL). The results indicate that the acidity of the reaction system effectively influences the morphology and size of the nanophosphors, facilitating the controlled synthesis of nanorod-shaped, nano-spherical, and ellipsoidal phosphors. When the Sm3+ doping concentration is 2 %, the phosphors exhibit maximum luminescent intensity and fluorescence lifetime. The energy transfer between Sm3+ ions in LaPO4:x%Sm3+ is identified as electric dipole-electric dipole interaction, with a critical distance for energy transfer established at 1.593 nm. LaPO4:2%Sm3+ exhibits good thermal stability, characterized by a thermal quenching activation energy of 0.1660 eV. The main outcome of this research, LaPO4:2%Sm3+ phosphor, exhibits significant potential for use in optical sensors, as well as promising applications in solar cells and biological fields.

Thermally stable Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal with tunable luminescence

By using the melt crystallization process, Dy2O3/Sm2O3 co-doped glass ceramics (GCs) containing La2Sn2O7(LSO) crystal were successfully prepared. By using X-ray diffraction (XRD), the sample's phase was determined, and scanning electron microscopy (SEM), the sample's morphology was examined. The optimal heat treatment condition of glass ceramics was determined to be 650 °C/1.5 h. Under 362 nm excitation, the energy transfer of Dy3+→Sm3+ was observed in Dy2O3/Sm2O3 co-doped glass ceramic samples from the emission spectrum. Electric dipole-electric dipole interaction is identified as the mechanism of energy transfer from Dy3+ to Sm3+ according to the Dexter formula for energy transfer. The emission spectra of 0.5%Dy2O3-0.4%Sm2O3 co-doped glass ceramic samples in a range from 298 K to 458 K show that the samples have high thermal stability, and the thermal quenching activation energy at 575 nm has been estimated to be 0.265 eV. According to chromaticity coordinates and correlated color temperature, warm white light emission may be achieved by co-doping Dy2O3/Sm2O3 glass ceramics. The findings demonstrate Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal have a potential application prospect in warm white light-emitting diodes (w-LEDs).

The effect of Pr3+ concentration on the microstructure, luminescence and scintillation properties of Pr:LuAG single crystals

High-quality lutetium aluminum garnet doped with various Pr3+ concentrations ((Lu1-xPrx)3Al5O12, abbreviated to Pr:LuAG) single crystals were grown by the optical floating zone method. The concentration of Pr3+ dependence on microstructure, luminescence and scintillation properties were systematically studied. Based on the results of Rietveld refinement, the doping of Pr3+ leads to lattice distortion and lowers its symmetry. The symmetry of the LuO8 dodecahedron center is lowest at 0.010, as confirmed by the Raman spectra. When excited at 450 nm and X-rays, the primary emission peak at 614 and 300 nm, respectively, induced by Pr3+ 4f2-4f2 and 4f5d-4f2 transitions. The optimal doping concentration is 0.010. The electric dipole-electric dipole interaction between adjacent Pr3+ was responsible for the concentration quenching in the Pr:LuAG single crystals. (Lu0.990Pr0.010)3Al5O12 shows the shortest average scintillation decay time (22.55 ns) and highest light yield (23,842 ± 2300 ph./MeV) under 662 KeV 137Cs gamma-ray irradiation. In terms of overall luminescence and scintillation performance, 0.010 doping was the best for Pr3+ doped LuAG single crystals.

Energy-looping and photon-avalanche-like phenomena in NdxY1.00-xAl3(BO3)4 powders excited at 1064 nm

Recently, a photon-avalanche-like (PA-like) process based on trivalent neodymium ions (Nd3+) under an unconventional excitation at 1064 nm was demonstrated using stoichiometric NdAl3(BO3)4 particles. Although the Nd3+ can emit radiation at 1064 nm efficiently, they present very small absorption at this wavelength due to the absence of resonant ground-state transitions. However, phonon-assisted excitation (4I9/2 → 4F3/2 and/or 4I11/2 → 4F3/2) followed by cross-relaxation between one excited ion (4F3/2) with another at the ground state (4I9/2), and subsequent phonon emissions {4I15/2, 4I15/2 → 4I13/2, 4I13/2 → 4I11/2, 4I11/2}, provide two ions at the 4I11/2 state, from which can occur the resonant excited-state absorption to the 4F3/2 level. Reestablishing this sequence of events, the absorption of photons at 1064 nm can be greatly increased. Besides the emission around 880 nm (4F3/2 → 4I9/2), there are thermal excitations to upper-lying states, with subsequent emissions in the visible and near-infrared regions (480–2000 nm). Here, we investigate the role of the Nd3+ content on the PA characteristics in NdxY1.00-xAl3(BO3)4 particles with x ranging from 0.05 to 1.00. It is known that the replacement of Y3+ by Nd3+ into the YAl3(BO3)4 crystalline structure can introduce strong modifications of the lattice properties as well as in the photoluminescence characteristics, such as luminescence concentration quenching and broadening of spectral lines. Despite that, we observed, for low x (≤0.20), an energy-looping preceding the PA-like that ensues for x ≥ 0.40. It is associated to the proximity between the Nd3+ ions, fundamental to the electric dipole-electric dipole interaction responsible for the Nd3+ energy transfer {4F3/2, 4I9/2} → {4I15/2, 4I15/2}. We discuss the present results focusing on emerging technologies with development of ultra-sensitive thermal sensors.

Analysis of thermal chromaticity stability, energy transfer and colour tunablity of Dy3+-Eu3+ doped BBZL glasses for high-power W-LED applications

A family of highly thermal chromatic stable Dy3+-Eu3+ doped B2O3-Bi2O3-ZnO-Li2O (BBZL) glass samples was synthesised using the high-temperature melt quenching technique. The optical and thermal stability properties of the samples were analysed using their fluorescence spectra at various temperatures, fluorescence lifetime decay times and colour coordinates. The Dy3+-doped BBZL (BBZL: Dy) glass samples generated cold white light when exposed to ultraviolet (UV) light, while the Dy3+-Eu3+-doped BBZL (BBZL: DyEu) glass samples emitted neutral and warm white light, which can be attributed to the introduction of Eu3+ that substantially enhanced the colour rendering of samples. An overlap of the excitation-emission spectra of Eu3+ and Dy3+ indicated an energy transfer between Dy3+ and Eu3+. Under a 350 nm excitation, the fluorescence lifetime of BBZL: DyEu decreased from 0.5348 to 0.3642 ms. Using the Dexter theory, the energy transfer between Dy3+ and Eu3+ was demonstrated to be an electric dipole-electric dipole leap. The chromaticity shifts of BBZL: DyEu were 8.60 × 10−4 and 9.40 × 10−4 at 448 and 498 K, respectively, reflecting the high thermal stability of the sample chromaticity. The study demonstrated that Dy3+-Eu3+ doped borate glasses can be used as tunable luminescent materials in high-power white light-emitting diodes to mitigate the chromaticity shift in fluorescent materials at high temperatures.

Energy Transfer Mechanism and Quantitative Modeling of Rate from an Antenna to a Lanthanide Ion.

The excitation energy transfer (ET) pathway and mechanism from an organic antenna to a lanthanide ion has been the subject of discussion for many decades. In the case of europium (Eu3+), it has been suggested that the transfer originates from the ligand singlet state or a triplet state. Taking the lanthanide complex Eu(TTA)3(H2O)2 as an example, we have investigated the spectra and luminescence kinetics, mainly at room temperature and 77 K, to acquire the necessary experimental data. We put forward an experimental and theoretical approach to measure the energy transfer rates from the antenna to different Eu3+ levels using the Dexter formulation. We find that transfer from the ligand singlet state to Eu3+ may account for the ET pathway, by combined electric dipole–electric dipole (ED–ED) and ED-electric quadrupole (EQ) mechanisms. The contributions from the triplet state by these mechanisms are very small. An independent systems rate equation approach can effectively model the experimental kinetics results. The model utilizes the cooperative processes that take place on the metal ion and ligand and considers S0, S1, and T1 ligand states in addition to 7F0,1, 5D0, 5D1, and 5DJ (=5L6, 5D3, 5D2 combined) Eu3+ states. The triplet exchange ET rate is estimated to be of the order 107 s–1. The observation of a nanosecond risetime for the Eu3+ 5D1 level does not enable the assignment of the ET route or the mechanism. Furthermore, the 5D1 risetime may be contributed by several processes. Observation of its temperature dependence and also that of the ground-state population can supply useful information concerning the mechanism because the change in metal-ion internal conversion rate has a greater effect than changes in singlet or triplet nonradiative rates. A critical comparison is included for the model of Malta employed in the online software LUMPAC and JOYSpectra. The theoretical treatment of the exchange mechanism and its contribution are now being considered.

Triple luminescent center energy transfer enables color tuning in Na3Y(PO4)2:RE3+ (RE = Tb/Eu/Tm) for w-LEDs

Single-phase host white light-emitting materials have been widely favored by researchers recently because of their advantages, such as no color reabsorption, better CRI, coordinated CCT, and pure CIE chromaticity coordinates. In this paper, a single matrix phosphor of Na3Y(PO4)2: xTb3+, yEu3+, zTm3+ was prepared by the high-temperature solid-state method, and white light emission was obtained by color regulation. The synthesized phosphor crystallizes in the Pca21 orthorhombic system, and the doping of rare-earth ions will not affect the phase composition. Firstly, the fluorescence properties of Na3Y(PO4)2: Tb3+ are studied. Tb3+ has high doping quenching concentration and shows a typical narrow-band green emission peak caused by the f-f transition. The color can be adjusted from green (0.308, 0.587) to red (0.578, 0.378) by co-doping Tb3+-Eu3+, which has the potential for application in color display LED. The mechanism of energy transfer is characterized as electric dipole-electric dipole interaction. After the blue emission of Tm3+ is introduced, light waves of different colors are emitted at different excitation wavelengths. The color coordinates of (0.338, 0.342) can be achieved in the triple luminescence center by adjusting the concentration of Tm3+, which is very close to the standard white light emission. The single-phase white-light-emitting phosphor has specific application potential in the field of w-LEDs.

Luminescent properties of Eu3+-doped NaLaCaWO6 red phosphors and temperature sensing derived from the excited state of charge transfer band

In this study, a series of NaLaCaWO6: Eu3+ phosphors were synthesized by traditional high-temperature solid-phase method. The doping concentration of Eu3+ was explored when the phosphors had the best luminescence performance, and the quenching concentration of Eu3+ could reach 30%. The mechanism of concentration quenching is due to electric dipole-electric dipole interaction. The CIE coordinates of the phosphor are (0.66, 0.34), which are close to the standard red region of National Television Standard Committee (NTSC). Therefore, the samples could be potentially used as red phosphors of white light emitting diodes. The optical thermometry properties of NaLaCaWO6:30%Eu3+ phosphors in 298–523 K were studied through temperature-dependent excitation spectra. The results demonstrate negative thermal quenching at the edge of the charge transfer band (CTB) with a red shift of the center of this band as temperature arises. Derived from the excited state of CTB, an optical temperature sensing strategy is proposed, and the relative sensitivity achieves 2.23%/K−1.

Photoluminescence properties and energy transfer of ZnNb2O6: Eu3+, Sm3+ orange-red phosphors for WLEDs

Eu3+, Sm3+ co-doped ZnNb2O6 orange-red phosphors were synthesized through the solid-state reaction method for the first time. The microstructure, photoluminescence properties, decay time, energy transfer mechanism, thermal stability and CIE chromaticity coordinates of Zn1-x-yNb2O6: xSm3+, yEu3+ phosphors were studied systematically. The XRD patterns and refinement results demonstrate that the rare earth ions have been effectively doped into ZnNb2O6 host lattices. Under the excited of 406 nm, the main emission peak intensity of Sm3+ decreased and Eu3+ increased with increasing of Eu3+ ion concentration in the Zn0.99-yNb2O6: 0.01Sm3+, yEu3+ phosphors, which due to the energy transfer from Sm3+ to Eu3+. Through the decay time measurements, energy transfer mechanism was proved to the electric dipole-electric dipole effect in the resonance transfer mode, and the transfer efficiency of ZnNb2O6: 0.25Eu3+, 0.01Sm3+ phosphor is calculated as 85.39%. Through the analysis of thermal stability properties of the co-doped sample, the thermal activation energy of thermal quenching is calculated to be 0.235 eV. The CIE chromaticity coordinates for co-doped sample are located at the orange-red region, the correlated color temperature and color purity are calculated to be 1927 K and 95.87%, respectively. In addition, a WLED device can be obtained by combing the co-doped sample with commercial blue (BaMgAl10O17: Eu2+) and green ((Sr, Ba)2SiO4: Eu2+) phosphors on a 395 nm N-UV LED chip. These results indicate that ZnNb2O6: Eu3+, Sm3+ phosphor is a promising candidate for WLEDs.

Optical properties, energy transfer and thermal stability of spherical nano-phosphor YPO4:Eu3+:Sm3+

A series of phosphors of Sm3+ and Eu3+ single-doped or co-doped YPO4 matrix are synthesized by the hydrothermal method. X-ray diffractometer (XRD), scanning electron microscope (SEM), fluorescence spectrophotometer (FL), ultraviolet–visible near infrared spectrometer (UV) and Fourier transform-infrared (FI-IR) spectrophotometer are used to analyze and characterize composition, structure, morphology, luminescent properties, fluorescence lifetime and fluorescence thermal stability of the sample. The analysis results show that the phosphor has a tetragonal crystal structure, and the morphology is the nano-sphere with the diameter of 60–100 nm. Under excitation of 395 nm and 404 nm near-ultraviolet light, YPO4:Sm3+:Eu3+ emits intense red and orange red light. In the phosphor YPO4:Sm3+:Eu3+, Sm3+ and Eu3+ undergo a process of mutual energy transfer; the critical distance of energy transfer is 1.109–2.392 nm; the energy transfer mechanism is electric dipole-electric dipole interaction; the energy transfer efficiency can reach over 65%. For the optimum product YPO4:2%Sm3+:8%Eu3+, the color coordinates are X = 0.6137, Y = 0.3813; and the fluorescence lifetime is 0.219 ms. The phosphor has good thermal stability, and the thermal quenching activation energy is 0.2053 eV. The tailored yttrium orthophosphate nanoparticles significantly displayed potentiality in the field of optical displays, and also demonstrated the applicability in the biological field.

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)

Tunable Luminescence of Ce3+/Eu2+ Activated in Single-Phase Li2BaSiO4 Phosphor via Energy Transfer

A series of Ce3+,Eu2+ co-doped Li2BaSiO4 cyan-green phosphors were synthesized by a high temperature solid phase method. The crystal structure, morphology, luminescent properties and temperature characteristics of the corresponding samples were systematically studied. The main peaks of the emission spectra of Li2BaSiO4:Ce3+,Eu2+ were shifted from 400 nm to 500 nm by adjusting the Ce3+,Eu2+ co-doping concentration. And a series of phosphors with continuous changes from blue to cyan green were obtained, which effectively compensated for the gap between the white LED at 470–510 nm region. The energy transfer efficiency and mechanism of Ce3+,Eu2+ in Li2BaSiO4 were studied by fluorescence lifetime. The highest energy transfer efficiency was 46.01%, and the energy transfer mechanism was determined to be electric dipole-electric dipole transition. Finally, fabricating a white LED device which coated blue, green-yellow, red and as-prepared cyan phosphors on the surface of ultraviolet chip (350 nm), and the device exhibited excellent luminescence characteristics (Ra = 95.2, CCT = 3105 K). The results show that the Li2BaSiO4:Ce3+,Eu2+ phosphor developed can be regard as single-component tunable color luminescent materials under the excitation of near ultraviolet light.

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.

Luminescence properties and energy transfer of Tm3+–Eu3+ double-doped LiLaSiO4 phosphors

A series of LiLaSiO4:yTm3+, zEu3+ phosphors were prepared by high-temperature solid-phase reaction. The microstructure, luminescence performance and quantum yield of the phosphors are characterized by XRD, SEM and fluorescence spectrometer. When the monitoring wavelength is 360 nm, LiLaSiO4:yTm3+ phosphors showed a sharp emission peak at 460 nm, corresponding to the 7F0 → 5D2 energy level transition, and the concentration quenching point of Tm3+ ions was y = 0.015. LiLaSiO4:yTm3+, zEu3+ phosphors have emission peaks of Tm3+ ions at 460 nm and Eu3+ ions at 618 nm, respectively. As the molar mass fraction of Eu3+ ions doped increase, the luminous intensity of Tm3+ ions gradually decrease, and the luminous intensity of Eu3+ ions increase first and then decrease, and the concentration quenching point of Eu3+ ions was z = 0.08. The energy transfers of Tm3+ → Eu3+ ions through electric dipole-electric dipole interactions are demonstrated by the luminous intensity variation law and fluorescence lifetime. By changing the doping ratio of Eu3+ and Tb3+ ions, the full-color control of the phosphor luminescent color from blue to red can be achieved.

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, energy transfer properties of Dy3+/Eu3+ coactivated neutral and warm white emissions GSBG glasses

Dy3+/Eu3+ co-doped GeO2-SiO2-BaO-Ga2O3(GSBG) glass was prepared by the traditional high temperature melting method. The structure and the optical performance of the sample were characterized through X-Ray Diffraction, absorption spectra, photoluminescence spectra, the fluorescence decay time and CIE chromaticity coordinates. The density of the samples was measured. The band gap and the distance between the rare earth ions were calculated theoretically. The energy transfer between Dy3+-Eu3+ was analyzed by Dexter energy transfer formula and I–H model. The results showed that the gap width of Dy3+/Eu3+ doped GSBG glass decreased from 4.6617 eV to 4.1472 eV and the decay time of fluorescence also decreases continuously with the increase of Eu3+ concentrations. The characteristic emission bands of Dy3+ at 483 nm and 574 nm are weakened, while those of Eu3+ at 590 nm and 614 nm are significantly enhanced, indicating that there is energy transfer between Dy3+-Eu3+ and the energy transfer is electric dipole-electric dipole transfer. It is worth noting that the prepared glass emits bright white light under ultraviolet excitation. In particular, sample DE0.5 emits neutral or warm white light under 365 nm excitation. The correlated color temperature is 4763 K; the color coordinate is x = 0.3487, y = 0.3271 and the color purity is low to10.88%, close to the standard white light.

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.