Formation mechanism and optimized luminescence of Mn4+‐doped unequal dual‐alkaline hexafluorosilicate Li0.5Na1.5SiF6

A novel red phosphor Li_0.5Na_1.5SiF₆:Mn⁴⁺ (LNSF:Mn) based on the unequal dual‐alkaline hexafluorosilicate with superior optical performances has been synthesized via ion‐exchange between [MnF₆]^2? and [SiF₆]^2? at room temperature. The composition and the crystal structure of the as‐obtained phosphor LNSF:Mn were determined by energy‐dispersive x‐ray spectroscopy (EDS) and x‐ray diffraction (XRD), respectively. The formation mechanism of the red phosphor LNSF:Mn has been discussed in detail. The phosphor LNSF:Mn exhibits good chromaticity properties and a quantum yield (QY) of 96.1%, which are better than the identified fluorosilicate phosphors Na₂SiF₆:Mn⁴⁺ (NSF:Mn) and K₂SiF₆:Mn⁴⁺ (KSF:Mn). A broad and intense absorption in the blue and a bright emission in red‐shifted wavelengths make the phosphor LNSF:Mn a desired candidate for applications in warm white light‐emitting diodes.     

Surface modification of K2TiF6:Mn4+ phosphor with SrF2 coating to enhance water resistance

K₂TiF₆:Mn⁴⁺ is an attractive narrow-band red-emitting phosphor for warm white light-emitting diodes (LEDs). Nevertheless, the hexafluoride phosphor is liable to deliquesce in moist environments, which leads to a sharp deterioration performance of luminescence. Surface modification of K₂TiF₆:Mn⁴⁺ phosphor with SrF₂ coating has been introduced, with the aid of KHF₂ transition layer to moderate the lattice mismatch. The reaction mechanism is discussed in detail, as so as the influence of SrF₂ coating on the luminescence intensity. The SrF₂ coating is able to prevent the hydrolysis of internal [MnF₆]²⁻ group; thereby, the luminescence intensity retains over 90% of initial value after being immersed in distilled water for 2 h. The LED devices fabricated with commercial Y₃Al₅O₁₂:Ce³⁺ and as-modified K₂TiF₆:Mn⁴⁺ phosphors exhibit bright white light with tunable chromaticity coordinate, correlated color temperature, and color rendering index. It enlightens a convenient method to enhance the moisture resistance of Mn⁴⁺ doped fluoride phosphors for commercial application in the field of white LEDs.     

Optimized photoluminescence of red phosphor Na2SnF6:Mn4+ as red phosphor in the application in “warm” white LEDs

The Mn⁴⁺ activated fluostannate Na₂SnF₆ red phosphor was synthesized from starting materials metallic tin shots, NaF, and K₂MnF₆ in HF solution at room temperature by a two‐step method. The formation mechanism responsible for preparing Na₂SnF₆:Mn⁴⁺ (NSF:Mn) has been investigated. The influences of synthetic parameters: such as concentrations of HF and K₂MnF₆ in reaction system, reaction time, and temperature on crystallinity, microstructure, and luminescence intensity of NSF:Mn have been investigated based on detailed experimental results. The actual doping concentration of Mn⁴⁺ in the NSF:Mn host lattice is less than 0.12 mol%. The most of K₂MnF₆ is decomposed in HF solution especially in hydrothermal system at elevated temperatures. The color of the as‐prepared NSF:Mn samples changes from orange to white when the temperature is higher than 120°C, which indicates the lower concentration of luminescence centers in the crystals. A series of “warm” white light‐emitting diodes with color rendering index (CRI) higher than 88 and correlated color temperatures between 3146 and 5172 K were obtained by encapsulating the as‐prepared red phosphors NSF:Mn with yellow one Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) on 450 nm blue InGaN chips. The advantage of the synthetic strategy to obtain NSF:Mn can be extended to developing Mn⁴⁺‐doped red phosphors from low‐costing metals at room temperature for large‐scale industrial applications.     

Enhanced luminescence and energy transfer performance of double perovskite structure Gd2MgTiO6:Bi3+, Mn4+ phosphor for indoor plant growth LED lighting

Deep-red light emitting phosphors are widely used in LEDs for indoor plant growth because of the critical role played by red light in plant growth. The luminescence properties of deep-red phosphors are still not well understood at present. An energy transfer strategy is a common and effective method to improve luminescence properties. In principle, the energy transfer process may occur when the sensitizer's emission spectra overlap with the activator's excitation spectra. In this work, Bi³⁺ and Mn⁴⁺ were incorporated into the matrix of Gd₂MgTiO₆ as sensitisers and activators, respectively. Mn⁴⁺ ions tend to occupy the [TiO₆] octahedral site and the Bi³⁺ ions are expected to substituted in the site of Gd³⁺. The energy transfer process from Bi³⁺ to Mn⁴⁺ was realised and the photoluminescence (PL) intensity of Mn⁴⁺ increased with the doping content of Bi³⁺. Upon excitation at 375 nm, the PL intensity of Mn⁴⁺ increased to 116.4% when the doping concentration of Bi³⁺ reached 0.3%. Finally, the pc-LED devices were prepared by a Gd₂MgTiO₆:Bi³⁺, Mn⁴⁺ phosphor. The high red luminescence indicated that this phosphor has potential applications in indoor LED lighting.     

HF-free molten salt route for synthesis of highly efficient and water-resistant K2SiF6:Mn4+ for warm white LED

It has been one of the hot issues to prepare the red-emitting Mn⁴⁺-doped fluoride phosphors with highly efficient and waterproofness for warm white-light-emitting diodes (WLEDs) by the green and environmentally friendly method. Herein, we design a novel green molten salt route to synthesize K₂SiF₆:Mn⁴⁺ red powder using molten NH₄HF₂ salt instead of HF liquor as the reaction medium. The results show that KMnO₄ and MnF₂ could produce Mn⁴⁺ in NH₄HF₂ molten salt through a reduction reaction, and the resulting Mn⁴⁺-doped K₂SiF₆ exhibited a bright red emission peaked at 632 nm under blue light excitation. The luminescence intensity of the as-obtained product after immersing into water for 24 hours maintain nearly 100% of that before soaking and emission peak shape remains unchanged. The thermal stability of the sample was evaluated by temperature-dependent luminescence spectral intensity during heating and cooling. Furthermore, a warm white-light-emitting diodes (WLEDs) with an excellent color rendering index (Ra = 87.1), lower correlated color temperature (CCT = 3536K), and high luminous efficacy (116.99 lm·W⁻¹) was fabricated based on blue chip and K₂SiF₆:Mn⁴⁺ and commercial yellow phosphor (Y₃Al₅O₁₂:Ce³⁺).     

Efficient manganese luminescence induced by Ce<Superscript>3+</Superscript>-Mn<Superscript>2+</Superscript> energy transfer in rare earth fluoride and phosphate nanocrystals

Manganese materials with attractive optical properties have been proposed for applications in such areas as photonics, light-emitting diodes, and bioimaging. In this paper, we have demonstrated multicolor Mn²⁺ luminescence in the visible region by controlling Ce³⁺-Mn²⁺ energy transfer in rare earth nanocrystals [NCs]. CeF₃ and CePO₄ NCs doped with Mn²⁺ have been prepared and can be well dispersed in aqueous solutions. Under ultraviolet light excitation, both the CeF₃:Mn and CePO₄:Mn NCs exhibit Mn²⁺ luminescence, yet their output colors are green and orange, respectively. By optimizing Mn²⁺ doping concentrations, Mn²⁺ luminescence quantum efficiency and Ce³⁺-Mn²⁺ energy transfer efficiency can respectively reach 14% and 60% in the CeF₃:Mn NCs.     

Insight into a novel rare-earth-free red-emitting phosphor Li3Mg2NbO6:Mn4+: Structure and luminescence properties

Red phosphor is indispensable to achieve warm white light in the white light diode (WLED) application. However, the current red phosphors suffer from high cost and harsh synthesis conditions. In this study, an oxide-based rare-earth-free red-emitting phosphor Li₃Mg₂NbO₆:Mn⁴⁺ (LMN:Mn⁴⁺) has been successfully synthesized by a simple solid-state reaction method. The relationship between crystal structure and luminescence was investigated in detail. The site occupancy of the doping Mn⁴⁺ ion in the LMN host has been discussed from the point of bond valence sum. How the coordination environment of doping Mn⁴⁺ affects the energy level of doping Mn⁴⁺ ion has been illustrated via the Tanabe-Sugano energy-level diagram. Moreover, warm white light has been obtained using LMN:Mn⁴⁺ as compensator to the YAG:Ce³⁺.     

Synthesis and photoluminescence properties of novel Ca2LaSbO6:Mn4+ double perovskite phosphor for plant growth LEDs

A novel Mn⁴⁺ activated Ca₂LaSbO₆ (CLS) far-red phosphor was synthesized by high temperature solid state reaction. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence spectra, ultraviolet-visible spectra, luminescence decay times, emission-temperature relationship and internal quantum efficiency (IQE). It is found that CLS:Mn⁴⁺ phosphor has a strong broad excitation band in the range of 200–550?nm. The samples can be excited by ultraviolet and blue light. There is a wide emission band centered at 685?nm between 600?nm and 760?nm. The optimum doping concentration of Mn⁴⁺ is approximately 0.5?mol%. In addition, all the CIE chromaticity coordinates of CLS:0.005Mn⁴⁺ located at far-red region. The concentration quenching mechanism is the dipole-dipole interaction of Mn⁴⁺ activator. Importantly, the CLS:0.005 Mn⁴⁺ sample has an IQE of up to 52.2%. Finally, a 365?nm ultraviolet light emitting diode (LED) chip combined with 0.5?mol% Mn⁴⁺ far-red phosphor was used to fabricate the LED device. All the results indicated that CLS:Mn⁴⁺ phosphors have potential applications in indoor plant cultivation.     

High luminescent thermal stability and water resistance of K2SiF6:Mn4+@CaF2 red emitting phosphor

K₂SiF₆:Mn⁴⁺ (KSF:Mn⁴⁺), as an efficient red-emitting phosphor, has a promising application in WLEDs (white light-emitting diodes). However, poor moisture resistance performance still hinders its deeper commercialization. Here, KSF:Mn⁴⁺@ CaF₂ with high water resistance and luminescent thermal stability has been prepared though H₂O₂-free hydrothermal method and surface coating process. Both KSF:Mn⁴⁺ and KSF:Mn⁴⁺@CaF₂ all have high luminescent thermal stability, due to negative thermal quenching (NTQ) effect. Mechanism of the NTQ has been discussed and suggested as thermal-light energy conversion mechanism. Compared with KSF:Mn⁴⁺, water resistance of KSF:Mn⁴⁺@CaF₂ is greatly improved by coating of CaF₂, because the outer shell of CaF₂ can effectively prevent the [MnF₆]^2- group on the surface of the phosphor from being hydrolyzed into MnO₂. The results of water resistance test shows that after immersing in water for 360 min (6 h), luminescent intensity of the uncoated product drops to 41.68% of the initial one, while that of the coated product remains to have 88.24% of its initial one. Warm white light with good luminescent performances (CCT = 3956 K and Ra = 89.3) is got from prototype WLEDs assembled by using the optimal coated sample. The results suggest that the optimal coated sample has potential application in blue-based warm WLEDs.     

Luminescence enhancement of Mn4+-activated double-perovskite phosphors for LEDs through a co-replacement strategy

Phosphors doped with Mn⁴⁺ ions have strong emission in the red and far-red light regions and are therefore used as red phosphors for indoor plant cultivation light-emitting diodes (LEDs) and white LEDs (w-LEDs). This paper introduces La₂Mg(Mg_1/3Ta_2/3)O₆: Mn⁴⁺ (Mg₂La₃TaO₉: Mn⁴⁺) red phosphors prepared by conventional high-temperature solid-phase method. The broad excitation band of Mg₂La₃TaO₉: Mn⁴⁺ phosphor is effectively excited by ultraviolet and blue light in the range of 250–600 nm, with the emission of 707 nm centered on far-red light. The phosphor has a high color purity of 99.07% and an internal quantum efficiency of 59.87%. To further enhance the performance of the phosphor, a cation substitution method was adopted in this paper to synthesize La₂Mg(Al_1/2Ta_1/2)O₆: Mn⁴⁺ phosphor by replacing [1/3Mg²⁺–2/3Ta⁵⁺] in La₂Mg(Mg_1/3Ta_2/3)O₆: Mn⁴⁺ with [1/2Al³⁺–1/2Ta⁵⁺]. The luminescence intensity and thermal stability of the samples were enhanced. The emission spectrum of the Mg₂La₃TaO₉: Mn⁴⁺ samples matched well with the phytochrome P_FR (phytochrome that absorbs far-red light) and is suitable for the preparation of LEDs for indoor plant cultivation. The concentration quenching effect of the samples was investigated, the main mechanism of which is the electric dipole–dipole interaction. Red LEDs and w-LEDs devices were prepared with the synthesized phosphors that produce light stably at different currents. The w-LEDs have a correlated color temperature of 5310 K and a color rendering index of 80.1. Therefore, these samples are expected to be used as red components for w-LEDs.     

Orderly‐Layered Tetravalent Manganese‐Doped Strontium Aluminate Sr4Al14O25:Mn4+: An Efficient Red Phosphor for Warm White Light Emitting Diodes

Searching for an efficient non rare earth‐based oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm and unexcitable by green light, is essential for the development of warm white light emitting diodes (WLEDs). Here, we report a promising and orderly‐layered candidate: Sr₄Al₁₄O₂₅:Mn⁴⁺ with CIE color coordinates (0.722, 0.278). It has higher luminescence efficiency particularly upon blue excitation and is much cheaper than the commercial red phosphor 3.5MgO·0.5MgF₂·GeO₂:Mn⁴⁺ (MMG:Mn⁴⁺). In sharp contrast to Eu²⁺‐doped (oxy)nitrides, the phosphor can be synthesized by a standard solid‐state reaction at 1200°C in air. The effects of flux boron content, environment, and preparation temperature, sintering dwelling time as well as Mn concentration have been systematically investigated for establishing the optimal synthesis conditions. The low temperature emission spectra reveal that there are at least three types of Mn⁴⁺ ions in Sr₄Al₁₄O₂₅:Mn⁴⁺ due to the substitution for the distorted octahedral Al³⁺ sites. The AlO₆ layers where Mn⁴⁺ prefers to reside are well separated from one another by AlO₄ tetrahedra in one dimension parallel to axis a. This scenario can efficiently isolate Mn⁴⁺ ions from local perturbations, thereby enabling the high efficiency of luminescence. The energy transfer rates and mechanism are discussed.     

Novel Mn4+ doped Ca2GdSbO6 red–emitting phosphor: A potential color converter for light-emitting diodes

As potential color converter towards white/red light–emitting diodes, novel Ca₂GdSbO₆:Mn⁴⁺ phosphors with excellent optical performances were prepared by a conventional solid–state reaction route. The as–prepared phosphors with monoclinic crystal system had abundant [SbO₆] octahedrons for Mn⁴⁺ ions to occupy and stably exist. With an excitation of 356 nm, an intense red emission peaking at 676 nm attributed to ²E_g→⁴A_2g transition of Mn⁴⁺ ions can be observed in the emission spectrum. The critical concentration of Mn⁴⁺ ions was found to be 0.6 mol% and the concentration quenching mechanism was also discussed in detail. Importantly, the Ca₂GdSbO₆:0.6%Mn⁴⁺ phosphors exhibited a high internal quantum efficiency of 38.9%.     

Color-tunable properties based on complex anion substitution in Eu2+ doped Ca8Sc2(PO4)6-y(SiO4)1+y phosphor

We synthesized and investigated the effect of Eu²⁺ ions doping in a novel phosphor-silicate Ca₈Sc₂(PO₄)₆(SiO₄) phosphor. The structure and photoluminescence properties were determined by X-ray powder diffraction Rietveld refinement, diffuse reflection spectra, emission-excitation spectra, decay curves and temperature dependence spectra. The phosphors showed an asymmetric broad-band blue emission (Eu²⁺) with peak at 470?nm. Furthermore, we presented the Ca_7.96Sc₂(PO₄)_6-y(SiO₄)_1+y:0.04Eu²⁺ phosphors by co-substituting [Eu²⁺-Si⁴⁺] for [Ca²⁺-P⁵⁺], and different behaviors of luminescence evolution in response to structural variation were verified among the series of phosphors. The results were attributed to the presence of multi Ca²⁺ sites, resulting in the mixing of blue and green emissions for Eu²⁺ ions. The complex anion substitution of [PO₄]^3- by [SiO₄]^4- induced an increased crystal field splitting of the Eu²⁺ ions, which caused a decrease in emission energy from the 5d excited state to the 4f ground state and a resultant red-shift from 470?nm to 520?nm. All the properties indicated that the Ca₈Sc₂(PO₄)₆(SiO₄):Eu²⁺ phosphors have potential application for color-tunable WLEDs.     

Synthesis,structure and magnetic property of the first 2-D organic–inorganic hybrid sandwich-type polyoxotungstate containing O-donor organic ligands

An unprecedented 2-D organic–inorganic hybrid sandwich-type polyoxotungstate containing O-donor organic ligands [DMAH]₄{[Mn(DMF)₄]₂[Mn₄(DMF)₂(α-B-HPW₉O₃₄)₂]} (1) (DMA = dimethylamine, DMF = N,N-dimethylformamide) has been solvothermally synthesized and characterized by IR, UV spectra and X-ray single-crystal diffraction. The 2-D organic–inorganic hybrid network of 1 is built by tetra-Mn^II substituted sandwich-type polyoxotungstates [Mn₄(DMF)₂(α-B-HPW₉O₃₄)₂]^8? and [Mn(DMF)₄]²⁺ cation bridges, which displays the common 2-D (4,4) topological net. It should be noted that the major difference between [Mn₄(DMF)₂(α-B-HPW₉O₃₄)₂]^8? in 1 and the reported [Mn₄(H₂O)₂(α-B-PW₉O₃₄)₂]^10? is that two DMF ligands substitute two H₂O ligands on the Mn₄O₁₆ unit located in the sandwich belt. Magnetic susceptibility measurement indicates the occurrence of antiferromagnetic coupling interaction within Mn^II ions.     

Preparation,luminescence properties,and application of temperature sensing and anti-counterfeiting of La2MgTiO6:Yb3+/Ln3+/Mn4+

The doping of transition metal ions in the up-conversion (UC) luminescent material doped with Yb³⁺/Ln³⁺ is a facile way to increase their UC luminescence intensities and alter their colors. In this study, La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ (Ln³⁺ = Er³⁺, Ho³⁺, and Tm³⁺) phosphors showing excellent luminescence properties were prepared by a solid-state method. The sensitivity of the La₂MgTiO₆:Yb³⁺/Ln³⁺/Mn⁴⁺ phosphor was double that without Mn⁴⁺, because Mn⁴⁺ affects the UC emissions of Ln³⁺ via energy transfer between these ions. Moreover, Mn⁴⁺ also acts as a down-conversion activator, which can combine with UC ions to achieve multi-mode luminescence at different wavelengths. Under 980 nm excitation, these samples emit green light (from Er³⁺ and Ho³⁺) and blue light (from Tm³⁺). In contrast, under 365 nm excitation, they emit red light (from Mn⁴⁺). Further testing revealed that the La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ phosphors have potential applications in temperature sensing and anti-counterfeiting.     

Luminescence of MgAl2O4 and ZnAl2O4 spinel ceramics containing some 3d ions

The luminescence properties of ceramic phosphors based on two spinel hosts MgAl₂O₄ and ZnAl₂O₄ doped with manganese ions have been studied. It has been found that the spectral properties of these phosphors can be strongly varied by changing synthesis conditions. Both types of doped ceramic spinel can serve as efficient Mn²⁺ green-emitting phosphors having peak emissions at 525 and 510 nm, respectively. Mn-doped MgAl₂O₄ spinel can also be prepared as an efficient Mn⁴⁺ red-emitting phosphor having peak emission at ~651 nm by using specific temperatures of heat treatment in air. It has also been shown that the conversion of Mn²⁺ to Mn⁴⁺ and viсe versa, as well as the coexistence of Mn²⁺ green and Mn⁴⁺ red emissions, can be accomplished by properly chosen annealing conditions of the same initially synthesized MgAl₂O₄:Mn sample. Manganese doped MgAl₂O₄ spinel with an optimal intensity ratio of green and red emissions can be a promising single-phase bicolor phosphor suitable for the development of warm white phosphor-converted LED lamps. On the other hand, it has been determined that perfectly normal ZnAl₂O₄ spinel cannot be doped with Mn⁴⁺ ions in contrast to partially inverse MgAl₂O₄ spinel. However, ZnAl₂O₄ samples unintentionally doped with impurity Cr³⁺ ions show emission spectra in the far-red region with well pronounced R, N and vibronic lines of Cr³⁺ luminescence due to the perfect normal spinel structure of synthesized ZnAl₂O₄ ceramics. Also, by partially substituting Al³⁺ cations for Mg²⁺ in ZnAl₂O₄ there is an opportunity to obtain Mn⁴⁺ doped or Mn⁴⁺/Cr³⁺ codoped far-red emitting phosphors which can be suitable for indoor plant growth lighting sources.     

Accessing deep-red emission using chemical units cosubstituted LaTiSbO6:Mn4+ phosphor

Red light-emitting phosphors are important to the field of plant lighting. Therefore, it is necessary to further optimize phosphor materials. Herein, we synthesized a sequence of phosphor LaTiSbO₆:Mn⁴⁺ (LTS:Mn⁴⁺). Due to the ²E to ⁴A₂ transition, LTS:Mn⁴⁺ phosphors can emit red light in the range of 620–780 nm, with an emission peak at 687 nm. Chemical unit cosubstitution (substituting W⁶⁺ - Al³⁺/W⁶⁺ - Ga³⁺ for Ti⁴⁺ - Sb⁵⁺) was used as a method to enhance the luminescence properties of LTS:Mn⁴⁺. When the substitution ratio of W⁶⁺ - Ga³⁺ and W⁶⁺ - Al³⁺ reached 0.1% and 0.75%, respectively, the luminescence intensity increased to 204% and 182%. Using the LTS:Mn⁴⁺, W⁶⁺, Ga³⁺ phosphor and a 470 nm blue chip to fabricate a pc-LED device, the electroluminescence (EL) spectrum is well matched with the phytochrome absorption range. Therefore, the LTS:Mn⁴⁺ phosphor will be very promising for plant growth.     

Dual-activator luminescence of LuAG:Mn4+/Tb3+ phosphor for optical thermometry

Mn⁴⁺ and Tb³⁺ singly doped and Mn⁴⁺/Tb³⁺ codoped lutetium aluminum garnet (Lu₃Al₅O₁₂, or simply LuAG) phosphors were synthesized and investigated for the application of optical thermometry. X-ray powder diffraction and luminescence spectroscopy measurements were performed on all samples to analyze their crystal phases and optical properties. In particular, temperature-dependent luminescence of the LuAG:Mn⁴⁺/Tb³⁺ sample was measured at the temperature range of 270–420 K. The results showed that the luminescence intensity of Mn⁴⁺ has gone through a remarkable decline while the luminescence of Tb³⁺ has an only insignificant change with the rise of temperature which leads to a dramatic decrease in the fluorescence intensity ratio (FIR) between the two activator Mn⁴⁺ and Tb³⁺. Further analysis showed that the LuAG:Mn⁴⁺/Tb³⁺ sample used for temperature sensing has a high relative sensitivity with maximum value of 4.3% K⁻¹ at 333 K. Our research indicated that this LuAG:Mn⁴⁺/Tb³⁺ material is a promising candidate for FIR-type optical temperature sensing.     

A Halomanganates(II) with P,P’-Diprotonated Bis(2-Diphenylphosphinophenyl)ether: Wavelength-Excitation Dependence of the Quantum Yield and Role of the Non-Covalent Interactions

A [H₂DPEphos][MnX₄] [X = Br, Cl] tetrahalomanganates(II) with P,P’-diprotonated bis[2-(diphenylphosphino)phenyl]ether cation has been designed and investigated in photophysics and EPR terms. The complexes exhibit a green luminescence resulted from the Mn(II) d–d transitions (⁴T₁→⁶A₁) with the wavelength-excitation dependence of the quantum yield. The solid [H₂DPEphos][MnBr₄] complex exhibits a bright green phosphorescence (λ_max = 515 nm) with the high luminescence quantum yield depending on the excitation energy whereas the solid [H₂DPEphos][MnCl₄] complex exhibits a very weak phosphorescence (λ_max = 523 nm). The unexpected shorter luminescence lifetime for the [H₂DPEphos][MnCl₄] than for the [H₂DPEphos][MnBr₄] at 300 K can be a result of the higher non-radiative relaxation contribution. On the one hand, the non-covalent PH…X(Mn) interactions quench the manganese(II) luminescence. On the other hand, the PH…X(Mn) interactions are a pathway of the excitation transfer from [H₂DPEphos]²⁺ to [MnX₄]²⁻.     

Luminescence and Quantum Efficiencies of Eu3+‐Doped Vanadate Garnets

Nondoped and 5.0 mol% Eu³⁺‐doped vanadate garnets Ca₅Mg₄(VO₄)₆, NaCa₂Mg₂[VO₄]₃, KCa₂Mg₂[VO₄]₃, and NaSr₂Mg₂[VO₄]₃ were synthesized by solid‐state reactions. The formation of single‐phase compound with garnet structure is confirmed by X‐ray diffraction. The photoluminescence (PL) and PL excitation (PLE) spectra are investigated together with color coordinates. The luminescence process is discussed on the charge‐transfer transitions in [VO₄]^3? ions and the crystal structure. The PL quantum efficiencies (QE) are measured for nondoped and Eu³⁺‐doped samples. The Eu³⁺‐doped samples have higher QEs than the corresponding nondoped ones although the energy transfer occurs from [VO₄]^3? to Eu³⁺. Broad emission band due to [VO₄]^3? with intense sharp lines due to Eu³⁺, which gives white color, is observed in Eu³⁺‐doped NaCa₂Mg₂[VO₄]₃ and NaSr₂Mg₂[VO₄]₃ under excitation with UV light. These materials are suggested to be useful for lighting under the excitation with near‐UV LED.