Red phosphors in MgAl2Si2O8 doping with Mn4+, Gd3+ and Lu3+ and host-sensitized luminescence properties

Mn⁴⁺ doped and Gd³⁺, Lu³⁺ co-doped MgAl₂Si₂O₈-based phosphors were first of all synthesized by solid state reaction at about 1300.0 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors which showed broad red emission bands in the range of 610–715 nm and had a different maximum intensity when activated by UV illumination was discussed. Such a red emission can be attributed to the intrinsic ²E → ⁴A₂ transitions of Mn⁴⁺.     

Mn4+-, Tb3+,4+-, and Er3+-activated red phosphors in the MgAl2Si2O8 system

Mn⁴⁺ doped and Tb^3+,4+, Er³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid-state synthesis at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had different maximum intensities when activated by UV illumination, was discussed. Such a red emission can be attributed to the intrinsic ²E → ⁴A₂ transitions of Mn⁴⁺.     

Photo and Thermo‐luminescence Properties of Mn4+, Ce4+ and Sm3+ in MgAl2Si2O8 Phosphor

Mn⁴⁺, Ce⁴⁺ and Sm³⁺ doped MgAl₂Si₂O₈‐based phosphors were synthesized at 1300 °C by solid state reaction and characterized by thermogravimetry (TG), differential thermal analysis (DTA), X‐ray powder diffraction (XRD), photoluminescence (PL), thermoluminescence (TL) and scanning electron microscopy (SEM). The phosphors showed broad red emission bands in the range of 610–715 nm and different maximum intensity when activated by UV illumination. Such a red emission can be attributed to the intrinsic ²E→⁴A₂ transitions of Mn⁴⁺.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

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.     

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⁺.     

Energy Transfer from Ce3+ to Tb3+/Dy3+/Mn2+ in Ca9Ga(PO4)7 Phosphors: Synthesis,Structure and Tunable Multicolor Luminescent Properties

A series of Ca₉Ga(PO₄)₇:Ce³⁺/Tb³⁺/Dy³⁺/Mn²⁺ phosphors with tunable color, in which Ce³⁺ acts as the sensitizer, was synthesized. Energy transfer (ET) from Ce³⁺ to Tb³⁺/Dy³⁺/Mn²⁺ was investigated in detail. Tb³⁺/Dy³⁺/Mn²⁺ single-doped Ca₉Ga(PO₄)₇ can exhibit green, yellow, and red emission, respectively. Incorporating Ce³⁺ into a Tb³⁺/Dy³⁺/Mn²⁺ single-doped Ca₉Ga(PO₄)₇ phosphor can remarkably promote the luminous efficiency of the Tb³⁺/Dy³⁺/Mn²⁺ ions. This enhancement originates from an efficient ET from Ce³⁺ to Tb³⁺/Dy³⁺/Mn²⁺. The ET was validated by luminescence spectra, decay dynamics, and schematic energy levels. Moreover, the intensity ratio of red emission of Mn²⁺ to violet emission of Ce³⁺ was analyzed based on energy-transfer and lifetime measurements. In Ce³⁺-Tb³⁺, Ce³⁺-Dy³⁺, and Ce³⁺-Mn²⁺ doped Ca₉Ga(PO₄)₇, the emitting color changed from violet to green, yellow, and red, respectively, which indicates the potential use of this new tunable phosphor in UV light-emitting diodes.     

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.     

Photoluminescence properties of rare earths (Eu3+, Tb3+, Dy3+ and Tm3+) activated NaInW2O8 wolframite host lattice

The photoluminescence (PL) studies on NaIn_1?xRE_xW₂O₈, with RE=Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ phases have shown that the relative contribution of the host lattice and of the intra-f–f emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy³⁺ and Tm³⁺ activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu³⁺, with intense red emission, the host absorption is less pronounced and the intra-f–f transitions of the Eu³⁺ ions play a major role, whereas for Tb³⁺ intra-f–f transitions are only observed, giving rise to green emission.     

Suppression of charge imbalance via Li+-Mn4+ co-incorporated Sr2YSbO6 red phosphors for warm w-LEDs

Mn⁴⁺-activated double perovskite phosphors with composition diversity have presented excellent luminescent performances. However, the charge imbalance between Mn⁴⁺ and matrix cations would increase non-radiative recombination and reduce the structural stability. Here, novel high-efficiency stable Li⁺/Mn⁴⁺ co-incorporated Sr₂YSbO₆ red phosphors are successfully synthesized via a solid-state reaction method for warm w-LEDs, where the Li⁺ ions have the effect of charge balance for Sr₂YSbO₆:Mn⁴⁺ and reduce the non-radiative energy transfer among Mn⁴⁺ ions. It is demonstrated that the substitution of Li⁺–Mn⁴⁺ pairs for Sb⁵⁺ can enhance the bonding with low-shifted diffraction peaks and high emission intensity, and prolong the decay lifetime, compared with those of Mn⁴⁺ single-doped ones. Impressively, the thermal stability is enhanced to 89.72% from 84.61% at the original value of 303 K. Finally, a w-LED device based on the optimal phosphor Sr₂YSbO₆:0.01Mn⁴⁺/0.01Li⁺ red component exhibits a correlated color temperature of 4487 K and color rendering index of 80.2. Therefore, the incorporated Li⁺ ions serve as both charge compensator and co-activator in Mn⁴⁺-activated double perovskite phosphors with the aim of high luminescent performance and thermal stability.     

Site Occupancies,Electron–Vibration Interaction and Energy Transfer of CaMgSi2O6: Eu2+, Mn2+ Phosphors for Potential Temperature-Sensing and Anti-counterfeiting Applications

Eu²⁺-, Mn²⁺- and Eu²⁺−Mn²⁺-doped CaMgSi₂O₆ phosphors have been prepared by a high-temperature solid-state reaction. Systematic investigation of the concentration- and temperature-dependent luminescence of Mn²⁺ showed that Mn²⁺ ions occupy two distinct sites in CaMgSi₂O₆. Electron–vibration interaction (EVI) analyses of Mn²⁺ ions revealed Huang–Rhys factors of 4.73 and 2.82 as well as effective phonon energies of 313 and 383 cm⁻¹ for the two sites. Eu²⁺−Mn²⁺ energy transfer is also discussed, and its efficiency is estimated by lifetime and luminescence spectra. The different thermal quenching behaviours of Eu²⁺ and Mn²⁺, the distinct emission colours of Eu²⁺ (blue, band peak at ∼451 nm) and Mn²⁺ (yellow–red range, band peaks at ∼583 and 693 nm) endow the co-doped samples with potential applications in luminescence thermometry and temperature-/excitation wavelength-responsive dual anti-counterfeiting.     

Investigation on the upconversion luminescence of Sr3AlO4F:Yb3+, Er3+, Ho3+ phosphors

To develop new emission-tunable upconversion (UC) phosphors, the Sr₃AlO₄F:5%Yb³⁺, xEr³⁺, yHo³⁺ (0 ≤ x ≤ 1%, 0 ≤ y ≤ 1%) samples were prepared by conversional solid-state reaction method, and their luminescence properties upon 980 nm excitation were studied. Upon 980 nm excitation, Yb³⁺-Er³⁺ codoped Sr₃AlO₄F shows a predominant emission peak between 645 and 700 nm which is attributed to the ⁴F_9/2-⁴I_15/2 transition of Er³⁺, and the Er³⁺ green emissions have been almost quenched. In this case, the yellowish green emitting light is obtained. The possible reason was interpreted by the energy level diagram and the proposed UC mechanism. For Yb³⁺-Ho³⁺ codoped Sr₃AlO₄F, three emissions are observed obviously which are all derived from the Ho³⁺ ion. The corresponding chromaticity coordinates indicate a red emission has been gained. To realize the tunable emission, the typical Sr₃AlO₄F:5%Yb³⁺, 0.2%Er³⁺, 1%Ho³⁺ phosphor was developed, and its emission spectrum includes the emission peaks of both Er³⁺ and Ho³⁺. Correspondingly, the sample gives a yellow emission.     

Preparation and photoluminescence properties of Mn-activated M2Si5N8 (M=Ca, Sr, Ba) phosphors

Mn²⁺-doped M₂Si₅N₈ (M=Ca, Sr, Ba) phosphors have been prepared by a solid-state reaction method at high temperature and their photoluminescence properties were investigated. The Mn²⁺-activated M₂Si₅N₈ phosphors exhibit narrow emission bands in the wavelength range of 500-700 nm with peak center at about 599, 606 and 567 nm for M=Ca, Sr, Ba, respectively, due to the ⁴T₁(⁴G)→⁶A₁(⁶S) transition of Mn²⁺. The long-wavelength emission of Mn²⁺ ion in the host of M₂Si₅N₈ is attributed to the effect of a strong crystal-field of Mn²⁺ in the nitrogen coordination environment. Also it is observed that there exists energy transfer between M₂Si₅N₈ host lattice and activator (Mn²⁺). The potential applications of these phosphors have been pointed out.     

Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor

Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu²⁺ in Sr₃SiO₅ was significantly modified. The yellow persistent emission intensity of Eu²⁺ was greatly enhanced by a factor of 4.5 in Sr₃SiO₅:Eu²⁺,Nd³⁺ compared with the previously reported Sr₃SiO₅:Eu²⁺, Dy³⁺. Furthermore, Sr ions were replaced with equivalent Ba to give Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu²⁺ is significantly improved by a factor of 2.7 in Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ (x=0.2) compared with Sr₃SiO₅:Eu²⁺,Dy³⁺. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu²⁺ in Sr_3?xBa_xSiO₅:Eu²⁺,RE³⁺ (RE=rare earth) is also proposed and discussed.     

Luminescence of Mn2+ in SrGa12O19, LaMgGa11O19, and BaGa12O19

Lattice parameters are given of SrGa₁₂O₁₉, BaGa₁₂O₁₉, and LaMgGa₁₁O₁₉, three new gallates with the magnetoplumbite structure. The luminescence of the compounds without and with activation by Mn²⁺ is reported. The quantum efficiencies of the Mn²⁺ phosphors are between 15% (BaGa₁₂O₁₉:Mn) and 70% ({Sr_1?xLa_x}Ga_12?xMg_xO₁₉:Mn). The emission strongly resembles that of Mn²⁺ in MgGa₂O₄. The fine structure of the Mn²⁺ emission band at 77°K is due to phonon coupling.     

Mechanistic Insight into Energy-Transfer Dynamics and Color Tunability of Na4CaSi3O9:Tb3+,Eu3+ for Warm White LEDs

In this work, a latent energy-transfer process in traditional Eu³⁺,Tb³⁺-doped phosphors is proposed and a new class of Eu³⁺,Tb³⁺-doped Na₄CaSi₃O₉ (NCSO) phosphors is presented which is enabled by luminescence decay dynamics that optimize the electron-transfer energy process. Relative to other Eu³⁺,Tb³⁺-doped phosphors, the as-synthesized Eu³⁺,Tb³⁺-doped NCSO phosphors show improved large-scale tunable emission color from green to red upon UV excitation, controlled by the Tb³⁺/Eu³⁺ doping ratio. Detailed spectroscopic measurements in the vacuum ultraviolet (VUV)/UV/Vis region were used to determine the Eu³⁺–O²⁻ charge-transfer energy, 4f–5d transition energies, and the energies of 4f excited multiplets of Eu³⁺ and Tb³⁺ with different 4f^N electronic configurations. The Tb³⁺→Eu³⁺ energy-transfer pathway in the co-doped sample was systematically investigated, by employing luminescence decay dynamics analysis to elucidate the relevant energy-transfer mechanism in combination with the appropriate model simulation. To demonstrate their application potential, a prototype white-light-emitting diode (WLED) device was successfully fabricated by using the yellow luminescence NCSO:0.03Tb³⁺, 0.05Eu³⁺ phosphor with high thermal stability and a BaMgAl₁₀O₁₇:Eu²⁺ phosphor in combination with a near-UV chip. These findings open up a new avenue to realize and develop multifunctional high-performance phosphors by manipulating the energy-transfer process for practical applications.     

Solvent directed morphologies and enhanced luminescent properties of BaWO4:Tm3+,Dy3+ for white light emitting diodes

A series of Tm³⁺ and Dy³⁺ codoped BaWO₄ phosphors with tunable shapes were controllably synthesized by a facile solvothermal method. The effects of ratio of ethylene glycol (EG) and water on the morphologies of BaWO₄ structures are systematically studied. It was discovered that the reason for these morphological changes is based on the reaction speed of the kinetic control, which relates to the strong chelating abilities of ethylene glycol. And when the solvent is pure ethylene glycol, the peanut-like BaWO₄:Dy³⁺ has the strongest emission intensity. Moreover, the emission color of the phosphors varied from blue (0.232, 0.180) to white (0.268, 0.250) by controlling Dy³⁺ ions content with a fixed Tm³⁺ concentration. The energy transfer mechanism was investigated in detail. With increasing the doped concentration of Dy³⁺ ions, the energy transfer efficiency of BaWO₄:0.005Tm³⁺,yDy³⁺ increased gradually and reached as high as 63% when the Dy³⁺ doped concentration is 0.03. The critical distance R_C calculated by the spectral overlap method is about 19.93 Å, and it is in good agreement with that obtained using the concentration quenching method (19.70 Å), indicating that the electric dipole-dipole interaction is the main energy transfer mechanism for BaWO₄:Tm³⁺,Dy³⁺ phosphors.     

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+

In this study, red phosphors Ca_1?n Mg _n TiO₃:Eu³⁺,Bi³⁺ were prepared by the sol?Cgel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu³⁺, Bi³⁺ and/or Mg²⁺. The emission intensity at 615?nm of Eu³⁺ increased at the presence of Bi³⁺ ions owing to the energy transfer from Bi³⁺ ion to Eu³⁺ ion. Moreover, with the addition of Mg²⁺, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467?nm, which match well with the emission of near-UV (395?C400?nm) and blue-LED (450?C470?nm), respectively. Under the near-UV (399?nm) or blue light (467?nm) excitation, the fluorescence quantum yield of the optimal composition Ca_0.9Mg_0.1TiO₃:0.18Eu³⁺,0.018Bi³⁺ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO₄:0.2Bi³⁺,0.05Eu³⁺ and the commercially available Y₂O₂S:Eu³⁺ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca_0.9Mg_0.1TiO₃:Eu³⁺,Bi³⁺ as a near-UV or blue-chip convertible red-emitting phosphor.     

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.     

Color Point Tuning in Lu3−x−yMnxAl5−xSixO12:yCe3+ for White LEDs

A series of the solid‐solution phosphors Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ is synthesized by solid‐state reaction. The obtained phosphors possess the garnet structure and exhibit similar excitation properties as the phosphor Lu₃Al₅O₁₂:Ce³⁺, but with an effectively improved red component in the emission spectrum. This can be attributed to the energy transfer from Ce³⁺ to Mn²⁺. Our investigation reveals that electric dipole–quadrupole interactions dominate the energy‐transfer mechanism and that the critical distance determined by the spectral overlap method is about 9.21 Å. The color‐tunable emissions of the Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ phosphor as a function of Mn₃Al₂Si₃O₁₂ content are realized by continuously shifting the chromaticity coordinates from (0.354, 0.570) to (0.462, 0.494). They indicate that the obtained material may have potential application as a blue radiation‐converting phosphor for white LEDs with high‐quality white light.