Tunable luminescence and energy transfer process between Tb3+ and Eu3+ in GYAG:Bi3+, Tb3+, Eu3+ phosphors

A series of Eu³⁺ ions co-doped (Gd_0.9Y_0.1)₃Al₅O₁₂:Bi³⁺, Tb³⁺ (GYAG) phosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GYAG phosphor sintered at 1500 °C confirms their garnet phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of the GYAG:Bi³⁺, Tb³⁺, Eu³⁺ phosphors consists of broad bands in the shorter wavelength region due to 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and the charge transfer band of Eu³⁺–O^2?. The present phosphors exhibit green and red colors due to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions and ⁵D₀ → ⁷F₁ transition of Eu³⁺ ions, respectively. The emission was shifted from green to red color by co-doping with Eu³⁺ ions, which indicate that the energy transfer probability from Tb³⁺ to Eu³⁺ ions are dependent strongly on the concentration of Eu³⁺ ions.     

MgAl2O4:Eu3+ nanoplates and nanoparticles as red-emitting phosphors: Shape-controlled synthesis and photoluminescent properties

We demonstrate herein a facile hydrothermal synthesis followed by post-annealing approach to selectively prepare MgAl₂O₄:Eu³⁺ nanoplates and nanoparticles. Series of scientific techniques such as XRPD, FESEM, TEM, HRTEM, and PL were adopted to characterize the as-prepared MgAl₂O₄:Eu³⁺ phosphors. First, by altering the amount of hexamethylenetetramine (abbr. HMTA) in solution, MgAl₂O₄:Eu³⁺ nanoplates occurred. Next, MgAl₂O₄:Eu³⁺ nanoparticles were prepared by adding certain amounts of sodium citrate and sodium dodecylbenzenesulfonate (abbr. SDBS). In particular, the MgAl₂O₄:Eu³⁺ nanoplates have novel porous structures. Besides, the MgAl₂O₄:Eu³⁺ phosphors exhibit excellent red-emitting properties based upon the characteristic transitions of Eu³⁺ from ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, and 4).     

Synthesis,Characterization and Luminescent Properties of La2Zr2O7:Eu3+ Nanorods

The Eu³⁺-doped La₂Zr₂O₇ phosphor with rod-like morphology was successfully synthesized by conventional solid state reaction and hydrothermal method. X-ray diffraction patterns, transmission electron microscopy, and photoluminescence spectra were employed to charac-terize its structure and morphology as well as luminescent properties. The results indicated that the red-emitting phosphor La₂Zr₂O₇:Eu³⁺ had well crystallized and belonged to the cubic structure with space group of Fd3m. The as-obtained product mainly appeared as straight nanorods with an average diameter of 47 nm and length of 50-700 nm. The pos-sible growth mechanism was also discussed. It was found that under blue excitation with a wavelength of 466 nm, the La₂Zr₂O₇:Eu³⁺ phosphor exhibited a characteristic red emission at 616 nm that was attributed to the hypersensitive ⁵DO_→⁷F2 _{electric dipole transition of Eu³⁺ ions. Meanwhile, it was more interesting to note that the emission of ⁵D}1_→⁷FJ _{(J=0, 1, 2) transitions and the splitting patterns of ⁵D}0_→⁷FJ _{(J=1, 2, 4) transitions of Eu³⁺ ions can be observed in the luminescent spectra of La2Zr2O7:Eu³⁺. It was demonstrated that Eu³⁺ preferred to occupy a low symmetry site.}     

Synthesis and characterization of Eu3+/Dy3+ codoped composite phosphors SrAl2Si2O8/SrAlSi1/2O7/2 via a one-pot nitrate-gel process

Composite phosphors SrAl₂Si₂O₈/SrAlSi_1/2O_7/2 codoped with Eu³⁺ and Dy³⁺ were synthesized via a simple one-pot nitrate-gel process. The thermal decomposition process of the precursor is investigated by thermal analysis, X-ray diffraction and infrared spectroscopy, respectively. The as-prepared Eu³⁺/Dy³⁺ codoped SrAl₂Si₂O₈/SrAlSi_1/2O_7/2 phosphors could yield blue (436 nm), bluegreen (486 nm), yellow (583 nm), and red (617 nm) lights under near-UV 380 nm excitation from a composite matrix produced by spontaneous phase separation during heat treatment of the precursor. Moreover, the effects of Dy³⁺ doping concentration on the structures, defect features, and luminescence properties of the composite phosphors were examined in detail.     

A template-free solvothermal synthesis and photoluminescence properties of multicolor Gd2O2S:xTb3+, yEu3+ hollow spheres

The multicolor Gd₂O₂S:xTb³⁺, yEu³⁺ hollow spheres were successfully synthesized via a template-free solvothermal route without the use of surfactant from commercially available Ln (NO₃)₃·6H₂O (Ln = Gd, Tb and Eu), absolute ethanol, ethanediamine and sublimed sulfur as the starting materials. The phase, structure, particle morphology and photoluminescence (PL) properties of the as-obtained products were investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectra. The influence of synthetic time on phase, structure and morphology was systematically investigated and discussed. The possible formation mechanism depending on synthetic time t for the Gd₂O₂S phase has been presented. These results demonstrate that the Gd₂O₂S hollow spheres could be obtained under optimal condition, namely solvothermal temperature T = 220 °C and synthetic time t = 16 h. The as-obtained Gd₂O₂S sample possesses hollow sphere structure, which has a typical size of about 2.5 μm in diameter and about 0.5 μm in shell thickness. PL spectroscopy reveals that the strongest emission peak for the Gd₂O₂S:xTb³⁺ and the Gd₂O₂S:yEu³⁺ samples is located at 545 nm and 628 nm, corresponding to ⁵D₄→⁷F₅ transitions of Tb³⁺ ions and ⁵D₀→⁷F₂ transitions of Eu³⁺ ions, respectively. The quenching concentration of Tb³⁺ ions and Eu³⁺ ions is 7%. In the case of Tb³⁺ and Eu³⁺ co-doped samples, when the concentration of Tb³⁺ or Eu³⁺ ions is 7%, the optimum concentration of Eu³⁺ or Tb³⁺ ions is determined to be 1%. Under 254 nm ultraviolet (UV) light excitation, the Gd₂O₂S:7%Tb³⁺, the Gd₂O₂S:7%Tb³⁺,1%Eu³⁺ and the Gd₂O₂S:7%Eu³⁺ samples give green, yellow and red light emissions, respectively. And the corresponding CIE coordinates vary from (0.3513, 0.5615), (0.4120, 0.4588) to (0.5868, 0.3023), which is also well consistent with their luminous photographs.     

Synthesis and luminescent properties of Eu2+ doped nitrogen-rich Ca-α-SiAlON phosphor for white light-emitting diodes

Yellow/orange-emitting nitrogen-rich Ca_0.9Si₉Al₃(O,N)₁₆: Eu²⁺ phosphors were successfully prepared by solid-state reaction synthesis. The fluorescence excitation spectra of all of the nitrogen-rich Ca_0.9Si₉Al₃(O,N)₁₆: Eu²⁺ phosphor powders displayed two broad bands centered at about 300 nm and 400–475 nm. The first peak was assigned to the absorption of the host lattice and the second to the 4f⁷ → 4f⁶5d¹ absorption of the Eu²⁺ ions, its means enhanced 4f⁷ → 4f⁶5d excitation of Eu²⁺ ion. The absorption peak intensity increased upon increasing the Eu²⁺ doping amount, but only up to a Eu²⁺ concentration ratio of 0.15. The emission spectra of the prepared Ca_0.9Si₉Al₃(O,N)₁₆: Eu²⁺ phosphors all exhibited a single broad band in the 500–700 nm region, maximum emission peak observed at 591 nm. The room temperature decay times were observed τ₁ = 1.27 μs and τ₂ = 9.90 μs.     

Structure and spectroscopic properties of (Y,Eu)(PO3)3 polyphosphate red phosphors

A series of orange-red emitting phosphor Y(PO₃)₃: xEu³⁺ (x = 0.1–1.0) was prepared by a solid-state reaction route. The phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) as well as decay lifetimes. Studies revealed the phase transfer from monoclinic to orthorhombic when Y³⁺ is totally replaced by Eu³⁺, and expansion of the unit cell occurs with increasing Eu³⁺ doped content. The PL spectra show that the phosphors Y(PO₃)₃: xEu³⁺ can be effectively excited by near ultraviolet (n-UV) light, and exhibit strong red-orange emission with no concentration quenching. The profile of PL spectra changes significantly at high Eu³⁺ content (x ≥ 0.80), which is due to the variation of preference for substitution of Eu³⁺. The luminescence due to the ⁵D₀ → ⁷F_J (J = 1, 2) transitions at 77 K exhibits its own spectral features for different crystallographic site. It is found that Eu³⁺ ions occupy the centers of octahedral polyhedron and form C_i/C₁ point group in Y(PO₃)₃.     

Synthesis and optical studies of novel Eu2+ and Ce3+ doped BaMg8Al18Si18O72 phosphors

Novel Eu²⁺ and Ce³⁺ activated BaMg₈Al₁₈Si₁₈O₇₂ phosphors was prepared by combustion method and their PL characteristics were investigated. The result shows that all samples can be excited efficiently by near UV excitation under 334 nm and 316 nm. The emission was observed for BaMg₈Al₁₈Si₁₈O₇₂:Eu²⁺ phosphor at 437 nm corresponding to d → f transition, under 334 nm broad-band excitation, whereas BaMg₈Al₁₈Si₁₈O₇₂:Ce³⁺ phosphor shows emission band at 376 nm under 316 nm excitation. Phase purity of the phosphor was checked with the help of XRD pattern. SEM analysis shows the external morphology of the combustion synthesized phosphor.     

Enhancement of the photoluminescence and long afterglow properties of Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript> phosphor by Dy<Superscript>3+</Superscript> co-doping

The Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺, Dy³⁺ long afterglow phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) techniques. The luminescence properties were investigated using thermoluminescence (TL), photoluminescence (PL), long afterglow, mechanoluminescence (ML), and ML spectra techniques. The crystal structure of sintered phosphors was an akermanite type structure, which belongs to the tetragonal crystallography. TL properties of these phosphors were investigated, and the results were also compared. Under the ultraviolet excitation, the emission spectra of both prepared phosphors were composed of a broad band peaking at 535 nm, belonging to the broad emission band. When the Ca₂MgSi₂O₇:Eu²⁺ phosphor is co-doped with Dy³⁺, the PL, afterglow and ML intensity is strongly enhanced. The decay graph indicates that both the sintered phosphors contain fast decay and slow decay process. The ML intensities of Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors were proportionally increased with the increase of impact velocity, which suggests that this phosphor can be used as sensors to detect the stress of an object.     

Finding an efficient far-red-emitting CaMg2La2W2O12:Mn4+ phosphor toward indoor plant cultivation LED lighting

The development of high-brightness far-red-emitting phosphors with emission wavelength within 650–750 nm is of great significance for indoor plant cultivation light-emitting diode (LED) lighting. Herein, we demonstrate a novel efficient far-red-emitting phosphors CaMg₂La₂W₂O₁₂:Mn⁴⁺ (abbreviated as CMLW:Mn⁴⁺) toward application in plant cultivation LEDs. Interestingly, the CMLW:Mn⁴⁺ phosphors show a broad excitation band in the 250–600 nm spectral range with two peaks at 352 and 479 nm, indicating they could be efficiently excited by near-ultraviolet and blue light. Under 352 nm excitation, the CMLW:Mn⁴⁺ phosphors exhibit an intense far-red emission band in the wavelength range of 650–800 nm peaking at 708 nm, corresponding to the ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. Mn⁴⁺ doping concentration-dependent luminescence properties are studied in detail, and the concentration quenching mechanism is also investigated. Particularly, the internal quantum efficiency of CMLW:Mn⁴⁺ phosphors reaches as high as 44%, and their PL spectra match well with the absorption spectrum of phytochrome P_FR (P_FR stands for far-red-absorbing form of phytochrome). Furthermore, a prototype LED device is fabricated by coating the as-prepared CMLW:0.8%Mn⁴⁺ phosphors on a 460 nm blue LED chip, which produces bright far-red emissions upon 20–300 mA driving currents. This work reveals that the newly discovered far-red-emitting CMLW:Mn⁴⁺ phosphors hold great potential for application in indoor plant cultivation.     

Spectroscopic investigation of La7Ta3W4O30:Sm3+ orange-red phosphor for white LEDs

The novel orange-red light emitting La₇Ta₃W₄O₃₀:xSm³⁺ (x = 0.005–0.20) phosphors were synthesized via the solid-state reaction method. The crystal structure, photoluminescence (PL) properties, optimum concentration, color purity, decay life, and thermal stability of the samples were systematically studied. Under the excitation of 404 nm, La₇Ta₃W₄O₃₀:Sm³⁺ emits intense orange-red light at 597 nm. The PL spectra of La₇Ta₃W₄O₃₀:Sm³⁺ phosphors are ascribed to the ⁴G_5/2 to ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺ ions. The concentration quenching occurs at the doping level of 1 mol%. The quenching temperature is higher than 500 K. Finally, a white LED (w-LED) with the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of (0.312, 0.296) and good color rendering index (Ra) of 86 was fabricated. As a consequence, all the results suggest that the orange-red phosphors La₇Ta₃W₄O₃₀:Sm³⁺ have potential applications in w-LEDs structures.     

High sensitivity and multicolor tunable optical thermometry in Bi3+/Eu3+ co-doped Ca2Sb2O7 phosphors

Currently, with increasing demand for non-contact fluorescence intensity ratio-based optical thermometry, a novel phosphor with high-efficiency, dual-emitting centers, and differentiable temperature sensitivity is more and more urgent to develop. In this work, an efficient dual-emitting center optical thermometry with high sensitivity and multicolor tunable in Ca₂Sb₂O₇:Bi³⁺, Eu³⁺ phosphor is firstly designed and successfully prepared. Under 330 nm excitation, the fabricated phosphor presents the featured and distinguishable emissions of Bi³⁺ and Eu³⁺ ions. The high efficiency energy transfer from Bi³⁺ to Eu³⁺ ions is proved and its corresponding mechanism belongs to dipole-dipole interaction. By modulating the ratio of Bi³⁺/Eu³⁺, the multicolor changes from blue to pink are realized. Based on the discriminative thermal quenching behavior between Bi³⁺ and Eu³⁺, the fluorescence intensity ratio of Eu³⁺ to Bi³⁺ in Ca₂Sb₂O₇ samples illustrates excellent optical thermometry performance from 298 to 523 K. The maximum absolute sensitivity (S_a) and relative sensitivity (S_r) reach as high as 0.2773 K^?1 at 523 K and 2.37% K^?1 at 448 K, respectively. Notably, the discriminated surrounding temperature can be directly confirmed by observing the emitting color from purple to orange-red with the temperature increase from 298 to 523 K. Furthermore, the as-prepared phosphor materials also demonstrate outstanding repeatability and excellent reversibility. These results exhibit that the designed Ca₂Sb₂O₇:Bi³⁺, Eu³⁺ phosphors have great promising applications in the field of non-contact optical temperature thermometry and thermochromic.     

La7O6(BO3)(PO4)2:Eu3+/Tb3+荧光材料的制备及其光致发光性能

采用优化的高温固相方法制备了稀土离子Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La₇O₆（BO₃）（PO₄）₂：Eu³⁺材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为⁵D₀→⁷F₂特征能级跃迁,Eu³⁺的最优掺杂浓度为0.08,对应的CIE坐标为（0.610 2,0.382 3）;La₇O₆（BO₃）（PO₄）₂：Tb³⁺材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb³⁺的⁵D₄→⁷F₅能级跃迁,Tb³⁺离子的最优掺杂浓度为0.15,对应的CIE坐标为（0.317 7,0.535 2）。此外,对2种材料的变温光谱分析发现Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂荧光材料均具有良好的热稳定性。     

Optical characteristics of europium and terbium doped strontium orthogermanate phosphors

In this work, europium and terbium activated Sr₂GeO₄ phosphors were successfully developed by traditional solid state method. Powders XRD, FESEM, EDS, FTIR, DRS and PL techniques have been used to probe the as prepared phosphors. Powder XRD patterns of the phosphors are indexed. The elemental composition of phosphors was obtained from their EDS. FTIR spectra are employed to detect different vibrational groups in phosphor compositions. The DRS profiles of both pristine and Eu³⁺ (Tb³⁺) substituted samples exhibit broad and strong band in the 230–370 ​nm region. The photoluminescence studies of europium and terbium doped phosphors exhibited optimistic red emission at 617 ​nm (⁵D₀ → ⁷F₂ of Eu³⁺ ions) and intense green emission at 543 ​nm (⁵D₄ → ⁷F₅ of Tb³⁺ ions) upon ultraviolet (UV) excitations respectively. The CIE chromaticity co-ordinates are produced in deep red and green regions. Therefore, these materials may become potential alternatives for red and green phosphors in the display devices and in lamp industry.     

Luminescent properties and energy transfer process of Sm3+-Eu3+ co-doped MY2(MoO4)4 (M=Ca,Sr and Ba) red-emitting phosphors

MY₂(MoO₄)₄:Sm³⁺ and MY₂(MoO₄)₄:xSm³⁺,yEu³⁺ (M=Ca, Sr and Ba) phosphors were successfully prepared using solid-state reaction route, and their luminescent properties and energy transfer process from Sm³⁺ to Eu³⁺ were systematically investigated. The results indicate that MY₂(MoO₄)₄:Sm³⁺ phosphors can be effectively excited by 407 nm near UV light originating from the ⁶H_5/2 → ⁴F_7/2 transition of Sm³⁺, and exhibit a satisfactory red emission at 646 nm attributed to the ⁴G_5/2 → ⁶H_9/2 transition of Sm³⁺, in which the emission intensity of SrY₂(MoO₄)₄:Sm³⁺ is the strongest among the MY₂(MoO₄)₄:Sm³⁺ (M=Ca, Sr and Ba) phosphors. For Eu³⁺ co-doped MY₂(MoO₄)₄:Sm³⁺ samples, with increasing Eu³⁺ doping content, the main emission peaks of Sm³⁺ (approximately 646 nm) are decreased, but the emission peaks and intensity of Eu³⁺ are increased while the maximum intensity of luminescence at the Eu³⁺ concentration 0.9. The introduction of Eu³⁺ in the MY₂(MoO₄)₄:Sm³⁺ phosphors can remarkably generate a strong emission line at 616 nm, originating from the ⁵D₀→⁷F₂ transition of Eu³⁺ and Sm³⁺ (⁴G_5/2) → Eu³⁺ (⁵D₀) effective energy transfer process. The energy transfer mechanism from Sm³⁺ to Eu³⁺ was discussed in detail.     

Synthesis, vacuum ultraviolet and near ultraviolet-excited luminescent properties of GdCaAl3O7: RE (RE=Eu, Tb)

Vacuum ultraviolet (VUV) excitation and photoluminescent (PL) properties of Eu³⁺ and Tb³⁺ ion-doped aluminate phosphors, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ have been investigated. X-ray diffraction (XRD) patterns indicate that the phosphor GdCaAl₃O₇ forms without impurity phase at 900 °C. Field emission scanning electron microscopy (FE-SEM) images show that the particle size of the phosphor is less than 3 μm. Upon excitation with VUV irradiation, the phosphors show a strong emission at around 619 nm corresponding to the forced electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺, and at around 545 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺. The results reveal that both GdCaAl₃O₇:RE³⁺ (RE=Eu, Tb) are potential candidates as red and green phosphors, respectively, for use in plasma display panel (PDP).     

Combustion synthesis and luminescent properties of metal yttrium borates M3Y2 (BO3)4:Eu3+ (M = Ba,Sr) for PDPs applications

The polycrystalline powder samples of Eu³⁺ activated; mixed metal yttrium borate phosphors M₃Y₂(BO₃)₄ (M = Ba, Sr) with improved color purity of red emission for plasma display panels (PDPs) were prepared by solution combustion technique. The synthesis is based up on the exothermic reaction between the fuel (Urea) and oxidizer (Ammonium nitrate) .The heat generated in the reaction is utilized for auto combustion of ingredients. The formation of desired product and crystal structure was confirmed by powder XRD technique; while particle morphology was studied using FE-SEM. Samples under 254 and 147 nm excitation showed intense and pure red emission around 613 nm corresponding to the electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺, CIE chromaticity coordinates of synthesized phosphors was found to be (x = 0.67, y = 0.32) close to National Television Standard Committee (NTSC) for red color; found suitable to employ in plasma display panels (PDPs) applications.     

Synthesis and photoluminescence properties of the high-brightness Eu-doped M2Gd4(MoO4)7 (M=Li, Na) red phosphors

A series of red-emitting phosphors Eu³⁺-doped M₂Gd₄(MoO₄)₇ (M=Li, Na) have been successfully synthesized at 850 °C by solid state reaction. The excitation spectra of the two phosphors reveal two strong excitation bands at 396 nm and 466 nm, respectively, which match well with the two popular emissions from near-UV and blue light-emitting diode chips. The intensity of the emission from ⁵D₀ to ⁷F₂ of M₂(Gd_1−xEu_x)₄(MoO₄)₇ phosphors with the optimal compositions of x=0.85 for Li or x=0.70 for Na is about five times higher than that of Y₂O₃:Eu³⁺. The quantum efficiencies of the entitled phosphors excited under 396 nm and 466 nm are also investigated and compared with commercial phosphors Sr₂Si₅N₈:Eu²⁺ and Y₃A₅O₁₂:Ce³⁺. The experimental results indicate that the Eu³⁺-doped M₂Gd₄(MoO₄)₇ (M=Li, Na) phosphors are promising red-emitting phosphors pumped by near-UV and blue light.     

Investigation of Luminescence Properties of Eu3+, Dy3+ and Gd3+ Doped MgAl2Si2O8 Red‐emitting Phosphors

Rare‐earth‐doped aluminosilicates of alkaline earth MgAl₂Si₂O₈: Eu³⁺, Dy³⁺ and MgAl₂Si₂O₈: Eu³⁺, Gd³⁺ were synthesized by the solid state reaction method at 1300 ^oC. The phosphors were characterized by X‐ray powder diffraction (XRD), photoluminescence (PL), thermoluminescence (TL) and scanning electron microscopy (SEM). X‐ray powder diffraction studies show that the phosphors were crystallized in the triclinic crystal system. The phosphors show characteristic broad band phosphorescence of Eu³⁺. This broad band phosphorescence has red emission bands in the range of 580–705 nm corresponding to ⁵D₀ → ⁷F_j (j:0,2,3,4) transitions of Eu³⁺.     

Optical Spectroscopy and Excited-State Dynamics of Eu3+-Doped Bismuth Borate Glasses Containing CuO

Bismuth borate glasses containing phosphors and luminescent rare-earths are of interest for applications in light-emitting devices. Herein, the influence of CuO impurities on red-emitting Eu³⁺-doped bismuth borate glasses of the 25Bi₂O₃-15BaO-10Li₂O-50B₂O₃ type was investigated by various spectroscopic methods. The glasses were prepared by the melt-quench technique and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV/Vis optical absorption (OA), and photoluminescence (PL) spectroscopy including decay kinetics assessment. The XRD data confirmed the amorphous nature of the glasses whereas FT-IR spectra indicated the basic structural features of trigonal BO₃ units and BO₄ tetrahedra. The OA analysis showed that addition of CuO up to 0.5 mol% results in significant growth of the visible Cu²⁺ absorption band around 715 nm, with slight decrease in the optical band gap energies assessed through Tauc plots. A drastic PL quenching of Eu³⁺ ions emission was evidenced concurring with the detrimental effect of Cu²⁺. The assessment of the Eu³⁺ emission decay curves revealed significant lifetime decrease of the ⁵D₀ emitting state with increasing CuO concentration. An analysis of quenching constants was finally performed comparing results from integrated PL data with the emission decay rates. It is argued that the bismuth borate glass system supports an effective Eu³⁺→Cu²⁺ energy transfer (more so than phosphates) in connection with a strong spectral overlap between Eu³⁺ emission and Cu²⁺ absorption.