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⁺.     

Host-sensitized phosphorescence of Mn4+, Eu3+, and Yb3+ in MgAl2Si2O8

Mn⁴⁺ doped and Eu³⁺, Yb³⁺ 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?C715?nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the intrinsic ² E????⁴ A ₂ 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⁺.     

Synthesis and characterization of novel blue emitting Na2CaSiO4:Ce3+ phosphor

The blue phosphors Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ were synthesized by the sol–gel method and their luminescence characteristics were investigated for the first time. Structural information about prepared samples is obtained by analyzing the XRD patterns and SEM micrographs. The photoluminescence (PL) excitation spectra indicate that the Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors can be effectively excited by ultraviolet (360 nm) light. The PL emission spectra exhibit tunable blue broadband emission with the dominant wavelength of 427–447 nm under excitation of 360 nm by controlling the doping concentration of Ce³⁺. The concentration quenching effect for Ce³⁺ was found at the optimum doping concentration of 4 mol%. The Commission Internationale de l’Eclairage 1931 chromaticity coordinates of Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ are (0.1447, 0.0787), which are better color purity compared to the commercial Eu²⁺-doped BaMgAl₁₀O₁₇ phosphor. Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ composition shows intense blue emission (peak wavelength, 439 nm) with relative intensity versus commercial BaMgAl₁₀O₁₇:Eu²⁺ blue phosphor (Nichia) 65 and 158 % under 254 and 365 nm excitation, respectively. All the results indicate that Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors are potential candidate as a blue emitting phosphor for UV-converting white light-emitting diodes.     

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.     

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.     

Double Perovskite Mn4+-Doped La2CaSnO6/La2MgSnO6 Phosphor for Near-Ultraviolet Light Excited W-LEDs and Plant Growth

Non-rare earth doped oxide phosphors with far-red emission have become one of the hot spots of current research due to their low price and excellent physicochemical stability as the red component in white light-emitting diodes (W-LEDs) and plant growth. Herein, we report novel Mn⁴⁺-doped La₂CaSnO₆ and La₂MgSnO₆ phosphors by high-temperature solid-phase synthesis and analyzed their crystal structures by XRD and Rietveld refinement. Their excitation spectra consist of two distinct excitation bands with the dominant excitation range from 250 to 450 nm, indicating that they possess strong absorption of near-ultraviolet light. Their emission is located around 693 and 708 nm, respectively, and can be absorbed by the photosensitive pigments Pr and Pfr, proving their great potential for plant growth. Finally, the prepared samples were coated with 365 nm UV chips to fabricate far-red LEDs and W-LEDs with low correlation color temperature (CCT = 4958 K/5275 K) and high color rendering index (R_a = 96.4/96.6). Our results indicate that La₂CaSnO₆:Mn⁴⁺ and La₂MgSnO₆:Mn⁴⁺ red phosphors could be used as candidate materials for W-LED lighting and plant growth.     

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.     

Novel high-saturated red-emitting phosphor Sr9(Mg0.5Mn0.5)K(PO4)7: Eu2+ with great quantum efficiency enhancement by La3+ codoping for white LED application

In this work, a novel whitlockite-structure red-emitting phosphor host, Sr₉(Mg_0.5Mn_0.5)K(PO₄)₇, is designed and successfully synthesized via a solid-state reaction. Upon X-ray diffractometer Rietveld refinement, it is revealed that this compound possesses compact Eu²⁺-Mn²⁺ distance (3.6809 Å) and large intra-Mn²⁺ distance (8.9905 Å), which is beneficial to the high-efficient Eu²⁺-Mn²⁺ energy transfer. By Eu²⁺ sensitization, our new phosphor exhibits a high-saturated and bright red Mn²⁺ emission at 620 nm with high color purity of 97.9%. Great emission enhancement up to 245 times than host is achieved by La³⁺ heterovalent substitution, which can be ascribed to the La³⁺-induced further structural confinement effect. Moreover, the quantum efficiency is boosted by twofold. The as-fabricated white phosphor-converted LEDs device shows bright warm white light with correlated color temperature (CCT) of 3,487 K, color-rendering index (CRI) of 92.4, and luminous efficacy of 31.59 lm/W. This work proves the feasibility of chemical unit co-substitution strategy in emission engineering of Mn²⁺-based phosphors, which can stimulate further studies on the red-emitting phosphor materials.     

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.     

Designing ultra-highly efficient Mn2+-activated Zn2GeO4 green-emitting persistent phosphors toward versatile applications

Developing highly efficient green-emitting phosphors is very significant because human eyes are sensitive to green spectral region. Herein, Mn²⁺-activated Zn₂GeO₄ phosphors, which can emit bright green light with an ultrahigh internal quantum efficiency of 98.5%, were prepared by a solid-state reaction technology in ambient atmosphere. At 323 nm irradiation, the emission spectrum shows a narrow band centered at 534 nm, which is ascribed to the ⁴T₁ → ⁶A₁ transition of Mn²⁺, with a full width at half maxima of 49.5 nm. Through monitoring the temperature-dependent photoluminescence emission intensity and decay time of Mn²⁺, we explored the thermometric properties of the resultant compound and found maximum relative sensitivities of Zn₂GeO₄:0.02Mn²⁺ phosphor are 4.90% K^?1 and 0.74% K^?1, respectively. Furthermore, green afterglow phenomenon is observed in the designed phosphors, and its mechanism is verified by discussing the thermoluminescence. Because of the excellent luminescence behaviors, various multimode luminescent patterns for information encryption are designed, including anticounterfeiting and fingerprint identification. Furthermore, using the prepared Zn₂GeO₄:0.02Mn²⁺ as green-emitting components, a white-light-emitting diode with suitable color coordinates, high color rending index (>90), and low correlated color temperature (5,000–6,000 K) was fabricated. These results demonstrate that Mn²⁺-activated Zn₂GeO₄ phosphors are multifunctional green-emitting components for optical thermometry, anticounterfeiting, fingerprint detection, and solid-state lighting applications.     

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⁺.     

A New Mode of Energy Transfer between Mn2+ and Eu2+ in Nitride‐Based Phosphor SrAlSi4N7 with Tunable Light and Excellent Thermal Stability

In this work, reciprocal energy transfer between Mn²⁺ and Eu²⁺ ions in nitride SrAlSi₄N₇ has been found and investigated in detail. In contrast to Mn²⁺‐ and Eu²⁺‐activated oxide‐based phosphors, the red light centered at 608 nm is ascribed to 4f–5d transitions of Eu²⁺ ions and Mn²⁺‐activated SrAlSi₄N₇ emits a cyan light peaking at 500 nm. Additionally, the special broad excitation band of SrAlSi₄N₇:Mn²⁺ centered at 362 nm has been covered by that of Eu²⁺ ions ranging from 300 to 550 nm. The overlap of the energy level of Mn²⁺ and Eu²⁺ ions creates the conditions for reciprocal energy transfer between Eu²⁺ and Mn²⁺ ions. A series of SrAlSi₄N₇:0.002 Mn²⁺,xEu²⁺ (0≤x≤005) with tunable light emission have been synthesized and the decay curves of samples prove the reciprocal occurrence of the energy transfer between Mn²⁺ and Eu²⁺ ions. This mode of energy transfer not only prevents the loss of energy, but also improves the thermal stability, and the intensity of SrAlSi₄N₇:Mn²⁺,Eu²⁺ at 150 °C is still beyond 92 % of the initial intensity. The results provide a new mode of energy transfer, which is expected to reduce the drawbacks existing in energy transfer.     

Eu2+ & Mn2+‐Coactivated Ba3Gd(PO4)3 Orange‐Yellow‐Emitting Phosphor with Tunable Color Tone for UV‐Excited White LEDs

A novel orange‐yellow‐emitting Ba₃Gd(PO₄)₃:x Eu²⁺,y Mn²⁺ phosphor is prepared by high‐temperature solid‐state reaction. The crystal structure of Ba₃Gd(PO₄)₃:0.005 Eu²⁺,0.04 Mn²⁺ is determined by Rietveld refinement analysis on powder X‐ray diffraction data, which shows that the cations are disordered on a single crystallographic site and the oxygen atoms are distributed over two partially occupied sites. The photoluminescence excitation spectra show that the developed phosphor has an efficient broad absorption band ranging from 230 to 420 nm, perfectly matching the characteristic emission of UV‐light emitting diode (LED) chips. The emission spectra show that the obtained phosphors possess tunable color emissions from yellowish‐green through yellow and ultimately to reddish‐orange by simply adjusting the Mn²⁺ content (y) in Ba₃Gd(PO₄)₃:0.005 Eu²⁺,y Mn²⁺ host. The tunable color emissions origin from the change in intensity between the 4f–5d transitions in the Eu²⁺ ions and the ⁴T₁‐⁶A₁ transitions of the Mn²⁺ ions through the energy transfer from the Eu²⁺ to the Mn²⁺ ions. In addition, the mechanism of the energy transfer between the Eu²⁺ and Mn²⁺ ions are also studied in terms of the Inokuti–Hirayama theoretical model. The present results indicate that this novel orange‐yellow‐emitting phosphor can be used as a potential candidate for the application in white LEDs.     

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.     

Upconversion Luminescence Properties of a LiNb0.3Ta0.7O3:Er3+,Yb3+ Ceramic

A co-doped LiNb_0.3Ta_0.7O₃:Er³⁺,Yb³⁺ ceramic was prepared by a high temperature solid state procedure. Under the excitation of 980 nm laser radiation, intense 660 nm red light and 550 nm green light emissions corresponding to the ⁴F_9/2→⁴I_15/2 and ²H_11/2/⁴S_3/2→⁴I_15/2 transitions of Er³⁺ were observed. The change of Yb³⁺ concentration has a more significant influence on luminous intensity than the Er³⁺ concentration. The emission of red and green lights is attributed to a two-photon process. The upconversion luminescence mechanisms were analyzed in detail.     

SrSi2O2N2∶Eu2+荧光粉的制备及性能研究

以SrCO3,Si3N4,Eu2O3为原料,在N2气氛下,采用自还原高温固相法制备了SrSi2O2N2:Eu2+荧光粉。研究了该荧光粉的物相结构、发光性能和晶体形貌,同时对比在不同气氛下合成的荧光粉。结果表明,在N2气氛与N2/H2气氛下分别合成的SrSi2O2N2:Eu2+荧光粉物相结构和光谱特性基本一致。显示出合成了主晶相SrSi2O2N2,但还含有少量未知的中间项。Eu2+浓度的变化不影响激发状态,而发射光谱的波长在Eu2+浓度为1mol%-20mol%之间,从530 nm的绿光红移至550 nm的黄绿光区域。同时,激发光谱覆盖的范围宽,均能有效的被UV或蓝光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用。     

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.     

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。