Energy transfer and color-tunable emission in Ba2Y2Si4O13:Bi3+,Eu3+ phosphors

Single-composition Ba₂Y₂Si₄O₁₃:Bi³⁺,Eu³⁺ (BYSO:Bi³⁺,Eu³⁺) phosphors with color-tunable and white emission were prepared by conventional high temperature solid-state reaction method. The structural and luminescent properties of these phosphors were thoroughly investigated through X-ray diffraction, photoluminescence, and decay curves. BYSO:Bi³⁺ phosphors show two excitation peaks at 342 and 373 nm, and give two emission peaks at 414 and 503 nm, respectively, indicating that there are two sites of Bi³⁺ in BYSO. The energy transfer from Bi³⁺ to Eu³⁺ was investigated in detail. Varied hues from blue (chromaticity coordinate [0.219, 0.350]) to white (0.288, 0.350) and orange-red light (0.644, 0.341) can be generated by adjusting the content of Eu³⁺. Pure white light emission (0.311, 0.338) can be obtained under the excitation of 355 nm in BYSO:3%Bi³⁺,20%Eu³⁺ phosphor. Besides, BYSO:Bi³⁺,Eu³⁺ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 473 K is 82.6% of that at 298 K. Our results indicate that BYSO:Bi³⁺,Eu³⁺ may be applied as conversion phosphors for n-UV-based W-LEDs.     

Energy transfer and multicolor tunable emission in single-phase Tb3+, Eu3+ co-doped Sr3La(PO4)3 phosphors

A series of green-to-red color-tunable Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors were prepared by high temperature solid-state method. The crystal structures, photoluminescence properties, fluorescence lifetimes, and energy transfer of Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ were systematically investigated in detail. The obtained phosphors show both a green emission from Tb³⁺ and a red emission from Eu³⁺ 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 Tb³⁺-Eu³⁺ energy transfer (ET). The Tb³⁺→Eu³⁺ 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 Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors might find potential applications in the field of lighting and displays.     

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu³⁺, Tb³⁺, Bi³⁺ co-doped LaPO₄ phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb³⁺ and Bi³⁺could enhance emission of Eu³⁺ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb³⁺ and Bi³⁺ is about 2.0% and 2.0%, respectively. The co-doping Tb³⁺ and Bi³⁺ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu³⁺, indicating that the energy transfer occurs from Tb³⁺ and Bi³⁺ to Eu³⁺ ions. From further investigation it can be found that co-doping Tb³⁺ and Bi³⁺ ions can also induce excitation energy reassignment between ⁵D₀–⁷F₁ and ⁵D₀–⁷F₂ in these phosphors, and result in more energy assignment to ⁵D₀–⁷F₂ emission in LaPO₄:Eu³⁺, Tb³⁺, Bi³⁺. Our research results displayed that La_0.94PO₄:Eu³⁺_0.02, Tb³⁺_0.02, Bi³⁺_0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.     

Red,green and blue-violet emission coexistence in white-light-emitting Ca3SiO4Cl2:Bi3+, Li+, Eu2+, Eu3+ phosphor

A series of emission-tunable Ca₃SiO₄Cl₂:Bi³⁺, Li⁺, Euⁿ⁺(n =2, 3) (CSC:Bi³⁺, Li⁺, Euⁿ⁺) phosphors have been synthesized via sol-gel method. The X-ray diffraction results indicate that the as-synthesized phosphors crystallize in a low temperature phase with the space group of P21/c. Energy transfer from Bi³⁺ to Eu³⁺/Eu²⁺ exists in CSC:Bi³⁺, Li⁺, Euⁿ⁺ phosphors. Under the excitation of 327 or 365 nm, the Ca_2.98−ySiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, yEuⁿ⁺(y=0.0001–0.002) phosphors show an intense green emission band around 505 nm, while under the excitation of 264 nm, three emission bands centered around 396 nm (Bi³⁺), 505 nm (Eu²⁺) and 614 nm (Eu³⁺) are observed and tunable colors from blue-violet to green or white are achieved in these phosphors by varying the content of Eu. White-light emission with the color coordinate (0.312, 0.328) is obtained in Ca_2.978SiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, 0.002Euⁿ⁺(n =2, 3). Based on these results, the as-prepared CSC:Bi³⁺, Li⁺, Eu²⁺, Eu³⁺ phosphors can act as color-tunable and single-phase white emission phosphors for potential applications in UV-excited white LEDs.     

A novel single-phase Na3.6Y1.8(PO4)3:Bi3+,Eu3+ phosphor for tunable and white light emission

A new type of Bi³⁺,Eu³⁺ single- and co-doped Na_3.6Y_1.8(PO₄)₃ phosphate phosphors were manufactured using conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. The crystal structure, luminescent properties, luminescent mechanism and quantum efficiency were thoroughly explored. Results show that there are two crystallization sites for Bi³⁺ and Eu³⁺ ions. Upon the excitation of 342 and 373 nm, Bi³⁺ single-doped phosphors exhibit green and blue emission, derived from the ³P₁ to ¹S₀ transition of Bi³⁺ located in different occupancy sites. Thanks to radiative energy transfer process from Bi³⁺ to Eu³⁺, adjustable emission could be acquired by altering Eu³⁺ content in co-doped phosphors. Pure white-light emission with quantum efficiency value of 22.9% can be realized in Na_3.6Y_1.8(PO₄)₃:0.01Bi³⁺,0.1Eu³⁺ sample and the integrated intensity of white light emission at 417 K remains 85% of that at room temperature. Our results indicate that Na_3.6Y_1.8(PO₄)₃:Bi³⁺,Eu³⁺ phosphors have feasible application in high-power ultraviolet driven solid-state lighting.     

New single‐component multicolor emission Na1−xAl1+2xSi1−2xO4:xBi3+/Eu3+ phosphors via energy transfer

A series of emission‐tunable Na_1?xAl_1+2xSi_1?2xO₄:xBi³⁺/Eu³⁺ phosphors were synthesized via high temperature solid‐state reaction method. The luminescence properties, energy transfer from Bi³⁺ to Eu³⁺ ions, color tuning, thermal stability and quantum efficiency were systematically investigated. Especially, in the host, a certain amount of Si⁴⁺ were replaced by Al³⁺ in order to remedy the charge compensating defect, so that, the emission intensity had been improved. The results of Rietveld refinements, the analysis of SEM mapping and the fourier transform infrared (FT‐IR) indicated that this charge balance strategy was an effective method. Meanwhile, the energy transfer from Bi³⁺ to Eu³⁺ can be inferred and confirmed and the mechanisms were demonstrated to quadrupole–quadrupole interaction. The emission hue can be tuned from blue to pink, and finally to orange red light by properly varying the ratio of Bi³⁺ and Eu³⁺. Importantly, when the temperature was raised to 150°C, the integrated emission intensity was 71.20% of the initial value for NAS:1%Bi³⁺,2%Eu³⁺ samples indicating that these phosphors had excellent thermal stability and stable color (no emission shift). All these properties indicate that the developed phosphors may be potentially used as single‐component color‐tunable‐emitting phosphors for UV light‐emitting diodes.     

Enhancement of oxygen/pressure sensing performance of Eu3+-doped YSZ phosphors via Bi3+ sensitization

The effects of the incorporation of a Bi³⁺ sensitizer on the phosphorescence properties and oxygen partial pressure sensitivity of the Eu³⁺ doped yttria stabilized zirconia (YSZ) phosphors were studied using a lifetime-based optical measurement system. Two series of YSZ: Eu phosphors were investigated in this work: Eu_0.01Bi_xY_0.07-xZr_0.92O_1.96 substitutional series and Eu_0.01Bi_xY_0.07Zr_0.92-xO_1.96-0.5x additive series. The phosphorescence intensity of the additive-series phosphors was enhanced by 47% excited at 405 nm with a Bi³⁺ concentration of 2 mol% due to the energy transfer between Bi³⁺ and Eu³⁺. In contrast, the phosphorescence intensity of the substitutional-series phosphors decreased as the Bi³⁺ concentration increased. The phosphorescence lifetimes for both series phosphors were highly sensitive to oxygen partial pressure at elevated temperatures. With increasing Bi³⁺ concentration, the oxygen sensitivities of both series were enhanced initially, which was related to the increment of concentration dependent non-radiative decay via cross-relaxation between Bi³⁺ and Eu³⁺. With 1 mol% Bi³⁺ doping, the oxygen sensitivity was enhanced by 28% and 12% for substitutional-series and additive-series phosphors, respectively. As the Bi³⁺ concentration further increased, the oxygen sensitivities of both series declined, which was attributed to the energy transfer between Bi³⁺, the formation of Bi³⁺ aggregates as well as the increase of the Eu³⁺ site symmetry. The results of this study not only provided valuable references for phosphor thermometry, but also offered new ideas for developing high-temperature non-contact pressure sensors.     

Deep blue,cyan, orange-red,and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi³⁺ and/or Eu³⁺ doped KBaYSi₂O₇ phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi₂O₇:Bi³⁺ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi³⁺ doping concentrations. The Bi³⁺/Eu³⁺ co-doped KBaYSi₂O₇ phosphors display intrinsic emissions of Bi³⁺ and Eu³⁺ and an energy transfer process between Bi³⁺ and Eu³⁺ can be detected. The luminescence colors of KBaYSi₂O₇:Bi³⁺,Eu³⁺ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi³⁺ and Eu³⁺. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu³⁺ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi₂O₇:Bi³⁺ or KBaYSi₂O₇:Bi³⁺,Eu³⁺ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.     

Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

It was unusual for Bi³⁺ ions to enhance the emission intensity of phosphors via nonsensitization. Here, La₂MoO₆:Eu³⁺, Bi³⁺ phosphors were successfully synthesized by a high temperature solid-state reaction method in air atmosphere. As the increase of doping concentration of Bi³⁺, the emission spectra of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors had obvious shifts, splits and the enhancement of intensities, which indicated that the characteristics of the phosphors were modified. To analyze these phenomena, the crystal structure refinements, spectral characteristic analyze and Judd-Ofelt theoretical calculation were mainly performed. Bi³⁺ ions played the role of the nonsensitizer and affected the distortion of the crystal, the sites of Eu³⁺ ions, the field splitting energy and the internal quantum yield. Moreover the nephelauxetic effects of Bi³⁺ ions and the ET process caused synergistically the life times of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors to increase and then gradually decrease. The CIE coordinates of phosphors changed within a small range. This study might be instrumental in promoting the further application of Bi³⁺ ions in rare earth luminescent materials.     

Tunable color emission in LaScO3:Bi3+,Tb3+,Eu3+ phosphor

LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ (x = 0 − 0.04, y = 0 − 0.05, z = 0 − 0.05) phosphors were prepared via high-temperature solid-state reaction. Phase identification and crystal structures of the LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors were investigated by X-ray diffraction (XRD). Crystal structure of phosphors was analyzed by Rietveld refinement and transmission electron microscopy (TEM). The luminescent performance of these trichromatic phosphors is investigated by diffuse reflection spectra and photoluminescence. The phenomenon of energy transfer from Bi³⁺ and Tb³⁺ to Eu³⁺ in LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors was investigated. By changing the ratio of x, y, and z, trichromatic can be obtained in the LaScO₃ host, including red, green, and blue emission with peak centered at 613, 544, and 428 nm, respectively. Therefore, two kinds of white light-emitting phosphors were obtained, LaScO₃:0.02Bi³⁺,0.05Tb³⁺,zEu³⁺ and LaScO₃:0.02Bi³⁺,0.03Eu³⁺,yTb³⁺. The energy transfer was characterized by decay times of the LaScO₃:xBi³⁺, yTb³⁺, zEu³⁺ phosphors. Moreover absolute internal QY and CIE chromatic coordinates are shown. The potential optical thermometry application of LaScO₃:Bi³⁺,Eu³⁺ was based on the temperature sensitivity of the fluorescence intensity ratio (FIR). The maximum S_a and S_r are 0.118 K⁻¹ (at 473.15 K) and 0.795% K⁻¹ (at 448.15 K), respectively. Hence, the LaScO₃:Bi³⁺,Eu³⁺ phosphor is a good material for optical temperature sensing.     

Luminescence and self-referenced optical temperature sensing performance in Ca2YZr2Al3O12:Bi3+,Eu3+ phosphors

Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ phosphors were elaborated by a traditional solid-state reaction method. The luminescence of Ca₂YZr₂Al₃O₁₂:Bi³⁺ samples, energy transfer from Bi³⁺ to Eu³⁺, and the temperature sensing properties of Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ samples have been systematically researched. Under the excitation of ultraviolet light, Bi³⁺ single doped phosphors give 313 and 392 nm emission bands, which origin from the substitutions of Bi³⁺ instead of Ca²⁺ and Y³⁺ sites, respectively. And the color-adjustable emission from blue to red were observed by increasing Eu³⁺ content in Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ samples. Relying on different temperature dependent variation tendency, the fluorescence intensity ratio (FIR) values present outstanding temperature sensing properties. The absolute and relative sensitivity can be up to 0.826 %K^-1 and 0.664 %K^-1, respectively. All above results suggest that Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺ phosphor is a potential alternative for optical thermometer.     

Dual-mode optical thermometry based on Bi3+/Eu3+ co-activated BaGd2O4 phosphor with high sensitivity and signal discriminability

A series of BaGd₂O₄:Bi³⁺,Eu³⁺ phosphors with dual-emitting centers were prepared by high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), fluorescence spectroscopy, lifetime decay curve and variable temperature emission spectroscopy were used to systematically study the structure, luminescence performance and temperature characteristics. Under ultraviolet (UV) excitation, the BaGd₂O₄:Bi³⁺,Eu³⁺ phosphor showed a broad-band emission in the blue region corresponding to transitions of Bi³⁺ ions and the sharp red light emission corresponding to Eu³⁺ ions. The Bi³⁺ and Eu³⁺ ion emission peaks were well-separated, which meets a prerequisite for efficient temperature signal resolution measurement. The fluorescence intensity ratio (FIR) technique was used to measure the different temperature response characteristics between Bi³⁺ blue emission and Eu³⁺ red emission. When the temperature varies from 293 K to 473 K, the relative temperature sensitivity (S_r) of BaGd₂O₄:Bi³⁺,Eu³⁺ phosphors is obtained, was determined as 1.0182%K⁻¹. In addition to calculating the relative sensitivity by FIR technology, we can also obtain the value of S_r through experiments and formulas related to the decay life, and found to be 1.0651%K⁻¹. Therefore, BaGd₂O₄: Bi³⁺,Eu³⁺ phosphor is an excellent non-contact optical temperature measurement material.     

Novel color tunable LaCaGaO4:Bi3+,Eu3+ phosphors for high color rendering warm white LEDs

A series of LaCaGaO₄:xBi³⁺,yEu³⁺ (x = 0.002–0.04, y = 0.02–0.45) phosphors with adjustable emission colors were synthesized by high-temperature solid-state reaction. The samples were identified as pure phases by X-ray diffraction and Rietveld refinement, and the crystal structures were analyzed in detail. The LaCaGaO₄:xBi³⁺ phosphor shows an intense blue emission under near-ultraviolet excitation, originating from the ³P₁ → ¹S₀ transition. The spectrum analysis reveals that the Bi³⁺ ions occupy two luminescence centers in the LaCaGaO₄ host and that energy transfer can occur. A model of the energy transfer between the Bi³⁺ and Eu³⁺ ions was also created and studied in detail. As the Eu³⁺-concentration increased, the emission color of the LaCaGaO₄:0.005Bi³⁺,yEu³⁺ phosphor changed from blue to pink to red. In addition, the fluorescence lifetime, quantum yield, thermal stability, and other properties of the phosphors were characterized and analyzed. Finally, two white light-emitting diode devices with R_a values of 96.6 and 95 and correlated color temperatures of 4578 and 3324 K were fabricated, indicating the potential of phosphors for warm white lighting applications.     

Multicolour tunable luminescence of thermal-stable Ce3+/Tb3+/Eu3+-triactivated Ca3Gd(GaO)3(BO3)4 phosphors via Ce3+ → Tb3+ → Eu3+ energy transfer for near-UV WLEDs applications

A series of single-component blue, green and red phosphors have been fabricated based on the Ca₃Gd(GaO)₃(BO₃)₄ host through doping of the Ce³⁺/Tb³⁺/Eu³⁺ ions, and their crystal structure and photoluminescence properties have been discussed in detail. A terbium bridge model via Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer has been studied. The emission colours of the phosphors can be tuned from blue (0.1661, 0.0686) to green (0.3263, 0.4791) and eventually to red (0.5284, 0.4040) under a single 344 nm UV excitation as the result of the Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer. The energy transfer mechanisms of Ce³⁺ → Tb³⁺ and Tb³⁺ → Eu³⁺ were found to be dipole-dipole interactions. Importantly, Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors had high internal quantum efficiency. Moreover, the study on the temperature-dependent emission spectra revealed that the Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors possessed good thermal stability. The above results indicate that the phosphors can be applied into white light-emitting diodes as single-component multi-colour phosphors.     

Luminescence characteristics and energy transfer of Eu2+/Tb3+ doped single phase multi-color phosphor

The investigation on single phase multi-color phosphors is highly meaningful for near-ultraviolet chip based white light emitting diodes. In this work, a series of Eu²⁺ and Tb³⁺ singly doped and Eu²⁺/Tb³⁺ codoped Sr₅(PO₄)₃Cl phosphors were synthesized via a high-temperature solid state reaction method. The luminescence spectra and decay curves of Eu²⁺ and Tb³⁺ singly doped samples were discussed, the optimal doping concentrations were determined. Thanks to the spectra overlap between Eu²⁺ and Tb³⁺, nonradiative energy transfer from Eu²⁺ to Tb³⁺ was investigated. It is found electric dipole-dipole interaction played the main role for the energy transfer in codoped samples, the highest energy transfer efficiency was calculated to be 60.98%. Tunable emissions are observed for codoped samples by adjusting doping concentration. The thermal quenching properties were discussed and the activation energy (ΔE) was estimated in the present work.     

Photoluminescent properties and site occupation preference in Bi3+, Eu3+ doped CaY4(SiO4)3O phosphor

Bi³⁺, Eu³⁺ doped CaY₄(SiO₄)₃O phosphors were synthesized through high temperature solid state reaction. Their photoluminescent properties were investigated and site occupation preference of Bi³⁺ in cationic sites was analyzed. The structure of CaY₄(SiO₄)₃O is characterized by three non-equivalent cationic sites with different coordination and cation-oxygen distances. By means of dielectric theory of the chemical bond for complex crystals, several kinds of chemical bond parameters like fractional covalence of CaY₄(SiO₄)₃O were calculated and integrated to yield environmental factor h_e. According to quantitative equations between the transition energy of Bi³⁺ and environmental factor h_e, the excitation bands at 308 and 226 nm were assigned to ¹S₀→³P₁ transition of Bi³⁺ in Y(6h) and Y(4f) site, respectively. Another excitation band centered at 210 nm should be the overlap of Bi³⁺ A-band in Ca site and C-band in Y(6h) site. Optical band gap of pure CYSO was calculated using Kubelka–Munk method from diffuse reflectance spectra. Red emission can be realized in CaY₄(SiO₄)₃O:Bi³⁺, Eu³⁺ under UV light excitation because of efficient energy transfer from Bi³⁺ to Eu³⁺ and decay behaviors of Bi³⁺ and Eu³⁺ emission were investigated. Without optimization, the internal quantum efficiency of CYSO:2%Bi³⁺, 7%Eu³⁺ at 310 and 393 nm excitations were 31.563%, 74.252%, respectively.     

Cation and polyhedron substitution strategies: Effects on local crystal structure and on Bi3+ and Eu3+ co-doped inverse garnet phosphors’ luminescence property

Following the rapid growth of lightning technology, the development of red-emitting phosphors is effective for improving color temperature and color rendering index for w-LEDs devices. Herein, a single phased garnet phosphor with cation and polyhedron substitution modification was firstly prepared. For Mg₃Gd₂Ge₃O₁₂: Bi³⁺, Eu³⁺, the intensity has been remarkably improved by about 16% compared to the one without Bi³⁺ sensitization. The energy transfer mechanism is identified in this work. Based on cation and polyhedron substitution strategies, novel phosphors with different compositions were obtained and further modified the PL properties. With Lu³⁺ substitution, the bond lengths between Bi³⁺ ion and anion ligands are decreased and the site symmetry has been strengthened, which leads to a 21 nm blue shift when Lu³⁺ totally replaced Gd³⁺ ions. In addition, Lu³⁺ and [SiO₄] substitution strategies both effectively increased symmetric rigid structure, which leads to a significant improvement in thermal stability, indicating the samples own great potential in optical applications This work provides a new insight to synthesis red-emitting phosphors for warm white-LEDs.     

Tunable white light and energy transfer of Dy3+ and Eu3+ doped Y2Mo4O15 phosphors

A series of Dy³⁺ or/and Eu³⁺ doped Y₂Mo₄O₁₅ 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 Y₂Mo₄O₁₅: Dy³⁺, Eu³⁺ has the monoclinic structure with the space group of p21/C(14). Under the excitation of ultraviolet (UV) or near-UV light, the Dy³⁺ and Eu³⁺ ions activated Y₂Mo₄O₁₅ phosphors exhibit their characteristic emissions in the blue, yellow and red regions. The emitting light color of the Y₂Mo₄O₁₅: 0.08Dy³⁺, yEu³⁺ phosphors can be adjusted by varying the concentration ratio of Dy³⁺ to Eu³⁺ ions and a white light is achieved when the doping concentration of Eu³⁺ is 5%. In addition, the energy transfer from Dy³⁺ to Eu³⁺ is also confirmed based on the luminescence spectra and decay curves.     

Preparation and luminescent modulation of KGaSiO4:Eu3+ phosphors using for multiple anti-counterfeiting

Anti-counterfeiting technology is of great significance to information security. To obtain high-quality anti-counterfeiting materials, the developments of inorganic materials are crucial. In this paper, a series KGaSiO₄:xEu³⁺ phosphors with persistent luminescence, photoluminescence, and thermochromic have been successfully prepared and the application of quadruple anti-counterfeiting is realized. The X-ray diffraction and Rietveld refinement indicate that the phosphors are pure phase. With Eu³⁺ ions doping, the structure change, site occupancies, and color-tunable phenomenon are carefully investigated. Different from another Eu³⁺ doping phosphor, the emission of KGaSiO₄:0.2% Eu³⁺ phosphor changes with the excitation light in the region of 240 nm–306 nm. The emission color can be modulated with the surrounding temperature. Surprisingly, this phosphor can emit green afterglow light, which is attributed to the different luminescent properties of the matrix and doping of Eu³⁺ ions. The series of phosphors exhibit abundant luminescent properties. Based on their wavelength dependence, concentration quenching, long afterglow, and thermochromic properties, the KGaSiO₄:xEu³⁺ phosphors can be effective materials for quadruple-modal anti-counterfeiting devices.     

Influence of Bi3+ as a sensitizer and SiO2 shell coating as a protecting layer towards the enhancement of red emission in LnVO4: Bi3+, Eu3+ @ SiO2 (Ln=Gd,Y and Gd/Y) powder phosphors for optical display devices

Enhanced red luminescence in LnVO₄: Bi³⁺, Eu³⁺ @ SiO₂ phosphors has been improved mainly in three stages by investigating the effects of: (i) host composition (Gd, Y and Gd/Y), (ii) co-doping Bi³⁺ as a sensitizer and finally (iii) SiO₂ shell coating. XRD data revealed that the produced phosphors possess crystalline, pure phase with tetragonal structure. Silica coating on phosphor particles have been characterized by SEM/EDAX, TEM, PL and with the presence Si–O–Si, Si–O vibrational modes from the FT-IR spectra. Absorption band edges due to VO₄^3?, shifted to higher wavelength with Bi-concentration, owing to the presence of Bi–O bond in addition to V–O. The emission intensities of ⁵D₀→⁷F₂ transition are stronger than ⁵D₀→⁷F₁; indicating the lower inversion symmetry near Eu³⁺, ions. Red emission intensity due to the efficient energy transfer from VO₄^3? to Eu³⁺ via Bi³⁺ ions in Y_0.949VO₄: Bi³⁺_0.001, Eu³⁺_0.05 phosphor was improved significantly, i.e. 1.6 times compared to Y_0.95VO₄: Eu³⁺_0.05. This was further enhanced 2.25 times by SiO₂ shell coating. Thus, Y_0.949VO₄: Bi³⁺_0.001, Eu³⁺_0.05 @ SiO₂ are suggested to be a promising red phosphor for application in display devices or lighting.