Achieving highly efficient far-red emission from luminescence-ignorable Ca2MgTeO6:Mn4+ to Ca2-zLnzMgTe1-yWyO6:Mn4+ (Ln = La,Y, Gd) phosphors via solid solution and impurity doping strategies

The Mn⁴⁺-doped Ca2MgTeO6 (CMTO) far-red emitting phosphors with double perovskite-type structure were successfully synthesized. Upon near-ultraviolet (n-UV, 300 nm) light excitation, the as-prepared phosphors showed far-red light at 700 nm attributed to the ²E_g→⁴A_2g transition of Mn⁴⁺ ion. The doping concentration of the CMTO:xMn⁴⁺ samples was optimized to be 0.8 mol%. The relevant mechanism of concentration quenching was demonstrated as the dipole-dipole interaction. Furthermore, solid solution and impurity doping strategies were adopted to improve the far-red emission of the luminescence-ignorable CMTO:Mn⁴⁺ phosphor. Series of Ca₂MgTe_(1−y)W_yO₆:0.8 mol%Mn⁴⁺ (y = 0–100 mol%) solid solution and Ca_2−zLn_zMgTe_0.6W_0.4O₆:Mn⁴⁺ (Ln = La, Y, and Gd, z = 10 mol%) phosphors were synthesized through the above two strategies. The luminescence intensity of the optimal Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was 13.7 times that of the CMTO:Mn⁴⁺ phosphor and 2.51 times that of red commercial phosphor K₂SiF₆:Mn⁴⁺. Notably, both CMTO:Mn⁴⁺ and Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphors exhibited remarkable thermal stability compared with most Mn⁴⁺-doped phosphors. Finally, the highly efficient Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was successfully applied in fabricating the warm white light diode (w-LED). This working along both lines strategy exhibited great potential for luminescence optimization of Mn⁴⁺-doped oxide phosphors.     

Mn ions-activated Gd3(Al,Ga)5O12 garnet solid-solution ceramics: Cation substitution for dual wavelength red-emission

Red-emitting color-convertors have attracted considerable attention for promising applications in solid-state lighting (SSL) to improve color rendition. However, the current nitride and fluoride phosphor powders have encountered several challenges, such as high cost, narrow emission bands, and insufficient stability during operation, which limit the development of high-power full-spectrum SSL. In this study, thermally robust Gd₃(Al,Ga)₅O₁₂:Mn (GAGG:Mn) solid-solution ceramics (SSCs) with dual wavelength red-emission bands were prepared via an oxygen solid-state sintering reaction. The doped Mn ions occupied octahedral Al³⁺ and Ga³⁺ sites to generate Mn⁴⁺ luminescent centers with pronounced deep-red emissions peaking at 698 nm (²E → ⁴A₂), and Mn²⁺ luminescent centers with broad red emissions at 628 nm (⁴T₁ → ⁶A₁). Because the cationic radius matching effect induced the regulation of valence state of Mn, the photoluminescence of the GAGG:Mn SSCs can be tailored by the substitution of Al³⁺ with Ga³⁺. Moreover, the Mn³⁺ also existed in the GAGG lattice host, and their concentration decreased with increasing Ga³⁺ contents owing to the mismatch of ionic radius between Mn³⁺ and Ga³⁺ ions. With the optimization of Al/Ga ratio and concentration of Mn ions, a broad emission band ranging from 550 to 800 nm (bandwidth = 250 nm) was achieved from Gd₃Al₃Ga₂O₁₂:0.3%Mn SSCs upon 465-nm excitation. Moreover, the GAGG:Mn SSC has over 17-fold enhanced thermal conductivity compared with the corresponding phosphor powder. This paper opens a door of regulating the valence state of luminescence centers with cation substitution and the application of oxide red-emitting color-convertors.     

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.     

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.     

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⁺).     

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.     

LED-pumped intense red luminescence based on Ba2LaTaO6: Mn4+ double perovskite phosphor

Non-rare earth Mn⁴⁺ ion-doped red oxide phosphors have great potential for applications in warm white light-emitting diodes (wLEDs) due to their low cost and stable physicochemical properties. Herein, a series of Ba₂LaTaO₆ (BLTO): Mn⁴⁺ phosphors were successfully synthesized by the high-temperature solid-state method. The theoretical values of the band gap calculated by the density functional theory are close to the experimental values obtained by the absorption spectroscopy. In addition, the phosphors have a broad excitation band in the wavelength range of 280–550 nm and emit red light at the peak wavelength of 681 nm under excitation. The concentration quenching of the BLTO: Mn⁴⁺ phosphor was caused by dipole-dipole interactions. The activation energy and the average decay lifetimes of the samples were calculated. Meanwhile, the effects of synthesis temperature and Li⁺ ion doping on the luminescence performance of the samples were also investigated. Satisfactorily, the color purity and internal quantum efficiency of the phosphor reached 98.3% and 26.8%, respectively. Further, the samples were prepared as red-light components for warm wLEDs. The correlated color temperature, color rendering index, and luminous efficiency of the representative devices driven by 60 mA current were 5190 K, 83.3, and 81.59 lm/W, respectively. This work shows that the BLTO: Mn⁴⁺ red phosphor with excellent luminescence performance can be well applied to warm wLEDs.     

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.     

Rare-earth-free Li5La3Ta2O12:Mn4+ deep-red-emitting phosphor: Synthesis and photoluminescence properties

Li₅La₃Ta₂O₁₂:Mn⁴⁺ (LLTO:Mn⁴⁺) phosphors are prepared in air via high-temperature solid-state method and investigated for their crystal structures and luminescence properties. LLTO:Mn⁴⁺ phosphor under excitation at 314 nm shows deep-red emission peaking at 714 nm due to the ²E→⁴A₂ transition of Mn⁴⁺ ion. The excitation bands in the range 220 - 570 nm are attributed to the Mn⁴⁺ - O^2- charge-transfer band and the ⁴A_2g→⁴T_1g, ²T_2g, and ⁴T_2g transitions of Mn⁴⁺, respectively. The optimal Mn⁴⁺ ion concentration is ~0.4 mol%. The concentration quenching mechanism in LLTO:Mn⁴⁺ phosphor is electric dipole-dipole interaction. The luminous mechanism and temperature quenching phenomenon are explained by the Tanabe-Sugano energy level diagram and the configurational coordinate diagram of Mn⁴⁺ in the octahedron, respectively. The experimental results indicate that LLTO:Mn⁴⁺ phosphor has a potential application prospect as candidate of deep-red component in light-emitting diode (LED) lighting.     

Enhanced luminescence properties of Li2MgTiO4: Mn4+, Ge4+ phosphor via single cation substitution for indoor plant cultivation

Red and far-red emitting phosphors have been widely used in phosphor-converted light emitting diode (pc-LED) devices to provide lighting for indoor plant growth, thus achieving desired product qualities. Among the many ways to optimize phosphors’ optical performance, cationic substitution is one of the most effective methods. In this study, red phosphors (Li₂MgTi_1-x-yO₄: xMn⁴⁺, yGe⁴⁺) were synthesized by high temperature solid state method and the optical performance of phosphors were improved with increasing Ge⁴⁺ constituents. In particular, luminescence intensity of Li₂MgTiO₄: 0.002Mn⁴⁺, 0.1Ge⁴⁺ increased by 152% under 468 nm excitation, and the thermostability of emission intensity increases from 22% (y = 0) to 43% (y = 0.1), which is about twice as much. Finally, pc-LED device was fabricated via the red phosphor Li₂MgTiO₄: 0.002Mn⁴⁺,0.1Ge⁴⁺ coated on a 470 nm ultraviolet chip. By changing the proportion of the phosphor, the electroluminescence spectra of pc-LED device could match well with the absorption regions of plant pigments. Therefore, Li₂MgTiO₄: 0.002Mn⁴⁺, 0.1Ge⁴⁺ phosphor has potential application in plant lighting. Furthermore, this work can offer some helpful references for improving luminescent efficiency by simply modulating the chemical composition.     

Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb³⁺ and Bi³⁺ co-doped ZnGa₂O₄ phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa_1.99O₄:0.01 Tb³⁺, yBi³⁺ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO₆]) at 440 nm and the characteristic emission peaks of Tb³⁺ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of ⁵D₄-⁷F_n (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi³⁺ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb³⁺ to 6 times that of Tb³⁺ singly doped ZnGa₂O₄ phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa₂O₄: Tb³⁺, Bi³⁺ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor and red emitting phosphor. The results indicate that ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.     

Broadband near-infrared emission enhancement in K2Ga2Sn6O16:Cr3+ phosphor by electron-lattice coupling regulation

Cr³⁺-doped phosphors have recently gained attention for their application in broadband near-infrared phosphor-converted light-emitting diodes (pc-LEDs), but generally exhibit low efficiency. In this work, K₂Ga₂Sn₆O₁₆:Cr³⁺ (KGSO:Cr) phosphor was designed and synthesized. The experimental results show that the Cr³⁺-doped phosphor exhibited broadband emissivity in the range 650-1300 nm, with a full width at half maximum (FWHM) of approximately 220-230 nm excited by a wavelength of 450 nm. With the co-doping of Gd³⁺ ions, the internal quantum efficiency (IQE) of the KGSO:Cr phosphor increased from 34% to 48%. The Gd³⁺ ions acted neither as activators nor sensitizers, but to justify the crystal field environment for efficient Cr³⁺ ions broad emission. The Huang-Rhys factor decreased as the co-doping of Gd³⁺ ions increased, demonstrating that the nonradiative transitions were suppressed. An efficient strategy for enhancing the luminescence properties of Cr³⁺ ions is proposed for the first time. The Gd³⁺–co-doped KGSO:Cr phosphor is a promising candidate for broadband NIR pc-LEDs.     

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.     

pH dependent hydrothermal synthesis of Ca14Al10Zn6O35:0.15Mn4+ phosphor with enhanced photoluminescence performance and high thermal resistance for indoor plant growth lighting

Artificial light source for indoor cultivation has been vastly impeded by the lack of high far red emitting phosphors. Recently, Mn⁴⁺ activated phosphors were reported to be promising luminescent materials to solve above matter. In this study, controllable design of Ca₁₄Al₁₀Zn₆O₃₅:0.15Mn⁴⁺ (CAZO:0.15Mn⁴⁺) far red emitting phosphors was realized via pH assisted hydrothermal approach. The pure CAZO:0.15Mn⁴⁺ phosphors were obtained merely when the reaction pH was 1 or 2. Meanwhile, by adjusting the pH value of the reaction solution, far red emission CAZO:0.15Mn⁴⁺ phosphors with grains, sphere-like as well as aggregated bulk particles can be achieved at pH =?4, pH =?6 and pH =?10, respectively. Furthermore, the structures and morphologies depended photoluminescence (PL) performances of CAZO:0.15Mn⁴⁺ were checked. The best PL performance was found for the phosphor produced at pH =?6, while over acidic or alkaline conditions would lower the emission intensity. In addition, this phosphor also exhibit good thermal resistance which can maintain 78% initial intensity at 150?°C. The practical indoor tobacco cultivation demonstrated that CAZO:0.15Mn⁴⁺ obtained through this pH adjusted hydrothermal route is a promising phosphor for indoor plant growth lighting.     

Engineering cation vacancies to improve the luminescence properties of Ca14Al10Zn6O35: Mn4+ phosphors for LED plant lamp

In the recent years, Mn⁴⁺-doped phosphors for indoor plant cultivation have received extensive concern owing to the far-red emission that can match well with the absorption spectra of plant pigments. Whereas, many Mn⁴⁺-doped phosphors still face some challenges such as poor light efficiency and low thermal stability. It is an effective way to resolve these problems via cation vacancies engineering. Herein, the Ca_14−xAl₁₀Zn_6−yO₃₅: Mn⁴⁺ phosphors are successfully synthesized by combustion method. The luminescence intensity of Ca_14−xAl₁₀Zn_6−yO₃₅: Mn⁴⁺ phosphor is enhanced through engineering Ca²⁺ and Zn²⁺ vacancies according to the charge compensation mechanism. The optimal content of each Ca²⁺ and Zn²⁺ vacancy is equal to be 0.3. Furthermore, the defect formation is accompanied with lattice distortion, which plays a vital role in driving the excited phonon traps to reduce the energy loss by non-radiation transitions. Therefore, the thermal stability of Ca_14−xAl₁₀Zn_6−yO₃₅: Mn⁴⁺ phosphor is also improved via engineering cation vacancies. In addition, the Ca_14−xAl₁₀Zn_6−yO₃₅: Mn⁴⁺ phosphors can be effectively excited by blue light and it exhibits far-red emission due to the Mn⁴⁺ spin-forbidden ²E → ⁴A₂ transition. The results suggest that the Ca_14−xAl₁₀Zn_6−yO₃₅: Mn⁴⁺ phosphors can have a tremendous potential in indoor plant cultivation.     

Broadband deep-red-to-near-infrared emission from Mn2+ in strong crystal-field of nitride MgAlSiN3

Broadband near-infrared (NIR) phosphors have received increasing attention for fabricating phosphor-converted light-emitting diodes (pc-LEDs) as NIR light source. Most of the reported broadband NIR phosphors originate from Cr³⁺ in weak crystal field environments. Herein, we report a luminescent material, MgAlSiN₃:Mn²⁺ with CaAlSiN₃-type structure, demonstrating that broadband deep-red-to-NIR emission can be achieved via doping Mn²⁺ into crystallographic sites with strong crystal field in inorganic solids. This phosphor is synthesized via easy-handle solid-state reaction, and the optimized sample, (Mg_0.93Mn_0.07) AlSiN₃ shows an emission band with peak at ~754 nm, FWHM of 150 nm, and internal quantum efficiency of 70.1%. The photoluminescence intensity can further be enhanced by co-doping Eu²⁺ as sensitizer. This work provides a new strategy for discovering new broadband NIR phosphors using Mn²⁺ in strong crystal field as luminescence center.     

Mn2+/Pr3+/Tb3+ single-doped Mg4Ga4Ge3O16 persistent luminescence materials for optical information storage application

Persistent luminescence (PersL) phosphors are considered as promising candidates for the next generation of information storage medium. Mg₄Ga₄Ge₃O₁₆ (MGG) is an electron trapping material which exhibits defect luminescence, and the luminescent properties are easily tuned via doping various activated ions. In this work, undoped and Mn²⁺/Pr³⁺/Tb³⁺ single-doped MGG phosphors were synthesized via high temperature solid phase reactions. X-ray diffraction and scanning electron microscope results confirm that the activated ions tend to occupy Mg²⁺ sites. Excited at 265 nm, the MGG host exhibits a defect emission band peaked at 450 nm. Red, pink and green emissions are observed in the Mn²⁺/Pr³⁺/Tb³⁺ single-doped MGG samples, which are ascribed to the Mn²⁺: ⁴T₁(G) → ⁶A₁(S), Pr³⁺: ¹D₂ → ³H₄ and Tb³⁺: ⁵D₄ → ⁷F₅ transitions, respectively. All the samples exhibit bright PersL for minutes after the cessation of excitation. The energy transfer, concentration quenching, luminescence decay and afterglow mechanisms are also discussed in detail. The phosphors exhibit efficient thermal and optical stimuli response, showing great potentials in the optical information storage.     

Deep‐red photoluminescence and long persistent luminescence in double perovstkite‐type La2MgGeO6:Mn4+

A novel non‐rare‐earth doped phosphor La₂MgGeO₆:Mn⁴⁺ (LMG:Mn⁴⁺) with near‐infrared (NIR) long persistent luminescence (LPL) was successfully synthesized by solid‐state reaction. The phosphors can be effectively excited using ultraviolet light, followed by a sharp deep‐red emission peaking at 708 nm, which is originated from ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. The luminescent performance was analyzed by photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The crystal field parameters were calculated to describe the environment of Mn⁴⁺ in LMG host. The LPL behaviors as well as the mechanisms were systematically discussed. This study suggests that the phosphors will broaden new horizons in designing and fabricating novel NIR long phosphorescent materials.     

Synthesis and phosphorescence mechanism of yellow-emissive long-afterglow phosphor BaAl2Si3O4N4: Yb2+

A series of novel Ba_1-xAl₂Si₃O₄N₄: xYb²⁺ yellow-emissive long-afterglow phosphors was successfully synthesized via a high-temperature solid-state reaction with two sintering steps. The phosphors exhibited broad band emission (full width at half maximum, FWHM = 107 nm) with a peak at 518 nm. With an increase in the Yb²⁺ doping content in Ba_1-xAl₂Si₃O₄N₄: xYb²⁺ phosphors, the luminescence intensity reached a maximum at x = 0.15. The long-afterglow phosphor can be activated effectively by 254 nm UV light, and the afterglow can persist for more than 7 h. From the thermoluminescence (TL) spectrum, there are three types of electron traps, with average evaluation depths of 0.485, 0.592, and 0.681 eV. The afterglow is caused by the capture and re-release of free electrons by the three trap energy levels. Finally, the thermal and chemical stability of the phosphor was tested, its luminescence intensity was 78.7% at 150 °C and 99.5% after 5 h soak in water compared to that at room temperature and original, respectively.