Tunable Optical Properties and Enhanced Thermal Quenching of Non-Rare-Earth Double-Perovskite (Ba1–xSrx)2YSbO6:Mn4+ Red Phosphors Based on Composition Modulation

An efficient rare-earth free deep red-emitting GdGeSbO6:Mn4+ phosphor for white light-emitting diodes

Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn4+-activated deep red phosphor GdGeSbO6:x%Mn4+ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn4+ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO6:0.3%Mn4+ produces a narrow emission peak centred at 682 nm in the range of 650-800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited 2Eg → 4A2g transition of Mn4+ ions. Notably, the optimal phosphor GdGeSbO6:0.3%Mn4+ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance (I423 K/I303 K ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO6:0.3%Mn4+ phosphors with commercial phosphors on the surface of a 365 nm UV chip.

Phosphors Ba2 LaTaO6 :Mn4+ and its alkali metal charge compensation for plant growth illumination

A series of Mn4+ -doped and Mn4+ ,K+ -co-doped Ba2 LaTaO6 (BLT) double-perovskite phosphors was synthesized using a high-temperature solid-state reaction. The phase purity and luminescence properties were also studied. The optimum doping concentration of Mn4+ and K+ was obtained by investigating the photoluminescence excitation spectra and photoluminescence emission spectra. The comparison of BLT:Mn4+ phosphors with and without K+ ions shows that the photoluminescence intensity of K+ -doped phosphors was greatly enhanced. This is because there was a charge difference when Mn4+ ions were doped with Ta5+ ions in BLT. Mn4+ -K+ ion pairs were formed after doping K+ ions, which hinders the nonradiative energy transfer between Mn4+ ions. Therefore, the luminescence intensity, quantum yield, and thermal stability of phosphors were enhanced. The electroluminescence spectra of BLT:Mn4+ and BLT:Mn4+ ,K+ were measured. The spectra showed that the light emitted from the phosphors corresponded well with chlorophyll a and phytochrome PR . The results show that the BLT:Mn4+ ,K+ phosphors had good luminescence properties and application prospects and are ideal materials for plant-illuminated red phosphors.

Luminescence properties and energy-transfer behavior of Y2-x-yBixEuyMgTiO6 phosphors

In recent years, double perovskite has become a research hotspot of luminescent matrix materials due to its flexible structure, easy doping and good thermal stability. By using a high temperature solid-state technique, Bi3+ and Eu3+ co-doped Y2-x-yBixEuyMgTiO6 (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.5) phosphors were made. X-ray diffraction (XRD) analysis shows that the crystal structure of all samples is monoclinic system, P21/n; Bi3+ and Eu3+ can be doped into the position of Y3+ in the substitution system of Y2MgTiO6. Both photoluminescence spectroscopy (PL) and X-ray excitation luminescence spectroscopy (XEL) were used to investigate the link between Bi3+ and Eu3+ doping concentrations and luminescence intensity. PL shows that: When 375 nm is used as the excitation wavelength, by varying the doping concentration of Eu3+ in the Y1.995-yBi0.005EuyMgTiO6 phosphor, it is possible to create the color-tunable emission from blue to red; The introduction of an appropriate amount of Bi3+ will increase the typical Eu3+ emission; The way that the system's Bi3+ and Eu3+ exchange energy can be observed by combining the fluorescence decay curve and photoluminescence. Fitting by concentration quenching model shows that the resonant dipole-dipole transition is the mechanism of energy transfer between Bi3+→Eu3+; X-rays may successfully stimulate the phosphor, and the spectral distribution of XEL and PL is basically the same; The introduction of an appropriate amount of Bi3+ is also beneficial to improving the sensitivity of XEL; Changes in temperature affect the sample's emission intensity; In addition, the samples remain stable for an extended period while being continuously exposed to X-rays at various environmental temperatures. The a forementioned findings suggest that the phosphor has potential use value in the lighting industry, X-ray imaging and temperature sensor.

Equivalent chemical substitution in double-double perovskite-type ALaLiTeO6:Mn4+ (A = Ba2+, Sr2+, Ca2+) phosphors enabling wide range crystal field strength regulation and efficient far-red emission

Mn⁴⁺-activated phosphors have shown wide prospective applications in phosphor-converted white light-emitting diodes (pc-WLEDs) and pc-LEDs used in illumination and indoor plant cultivation, respectively. Recently, double perovskites A₂B'B''O₆ with a tunable crystal structure and versatile octahedral sites have been extensively studied as good host matrixes for Mn⁴⁺-emitters to realize tunable far-red emissions. Herein, a series of double-double perovskite-type ALaLiTeO₆:Mn⁴⁺ (A = Ba, Ba_0.5Sr_0.5, Sr, Sr_0.5Ca_0.5, Ca) phosphors were synthesized and structurally characterized, and the correlations between their structure and luminescence were also studied systematically. With a decrease of the A-cation size, an increased distortion in the average structure and a structure symmetry lowering (I2/m → P2₁/_n) were observed for ALaLiTeO₆:Mn⁴⁺. In contrast, on the local scale, the degree of (Li/Te)O₆-octahedral distortion is positively correlated with the ΔIR value, which is the ionic radius difference between A²⁺ and La³⁺. The local structural changes were found to be irrelevant to the significant improvements in photoluminescence properties. In combination with careful spectroscopic analysis, we deciphered that a decreased A-cation is in fact helpful for the enhancements in crystal field strength (D_q/B = 2.12-2.82) and Mn-O covalent bonding, thereby resulting in an improved quantum efficiency, a suppressed nonradiative transition, and a redshift in photoluminescence spectra. Amongst the ALaLiTeO₆:Mn⁴⁺ phosphor series, CaLaLiTeO₆:Mn⁴⁺ exhibits the highest external quantum efficiency of 70.1% and internal quantum efficiency of 96.4% and superior thermal stability (93.3%@423 K), making CaLaLiTeO₆:Mn⁴⁺ very promising as far-red phosphors for pc-LEDs. The findings of this work will serve as a new guide for rational design of high-performance Mn⁴⁺-activated double-double perovskite-type far-red phosphors.

Fluorescence Lifetime-Based Luminescent Thermometry Material with Lifetime Varying over a Factor of 50

Recently, the growing demand for temperature detection is pushing forward the flourishing development of noncontact optical thermometry. Herein, a new red phosphor Sr₂InTa_1-xO₆:xMn⁴⁺ (SIT:xMn⁴⁺) was first constructed and systematically investigated. Based on the fairly rapid decline of the lifetime from 0.403 to 0.008 ms by increasing the temperature from 25 to 450 K, a noncontact optical thermometer can be made from phosphor SIT:0.003Mn⁴⁺ with S_r = 1.396% K^-1 at 375 K and S_a = 0.0012 K^-1 at 300 K. Because the luminescence is based on the outermost 3d orbits of Mn⁴⁺, the lifetime of SIT:xMn⁴⁺ is quite sensitive to the temperature, leading to a rapid decline of the lifetime with the increase in temperature. Moreover, multiple rounds of variable-temperature studies were performed to demonstrate the stability and reversibility of SIT:0.003Mn⁴⁺. This work suggests that Mn⁴⁺-phosphors are promising candidates for application as optical thermometric material.

Synergistic luminescent thermometer using co-doped Ca2GdSbO6:Mn4+/(Eu3+ or Sm3+) phosphors

Luminescent thermometers provide a non-contact method of probing temperature with high sensitivity and response speed at the nanoscale. Synergistic photoluminescence from different activators can realize high sensitivity for luminescent thermometers by finely selecting ions with specific crystallographic sites. Herein, the more temperature-sensitive Mn⁴⁺ and the less-sensitive Eu³⁺ (or Sm³⁺) activators are co-doped into a Ca₂GdSbO₆ matrix to form an effective thermometer, where Mn⁴⁺ and Eu³⁺ (or Sm³⁺) ions occupy the Sb⁵⁺ and Gd³⁺ sites, respectively. The co-doping of Eu³⁺ ions or Sm³⁺ ions leads to lattice expansion of Ca₂GdSbO₆ matrix and a tuned narrow emission from deep-red to orangish-red. According to the ratio of luminescence intensity, the maximal S_a and S_r values are 0.19 K^-0 (347 K) and 1.38% K^-( (420 K) for Ca₂GdSbO₆:Mn⁴⁺/Eu³⁺ probe and 0.26 K^-p (363 K) and 1.55% K^-( (430 K) for Ca₂GdSbO₆:Mn⁴⁺/Sm³⁺ probe thermometers, respectively. In addition, thermometers based on Mn⁴⁺ emission lifetimes can provide the highest relative sensitivity of 1.47% K^-s at 425 K. Thus, the highly-temperature-sensitive Ca₂GdSbO₆:Mn⁴⁺/(Eu³⁺ or Sm³⁺) phosphor is a promising candidate for practical luminescence thermometers.

Enhanced self-activated far-red photoluminescence from Sr3LiSbO6 phosphors by Gd3+ doping for plant growth

Sr₃LiSbO₆ phosphors were prepared by high temperature solid state reaction method. The crystal phase, morphology and optical properties were characterized by X-ray powder diffraction spectroscopy, scanning electronic microscope, absorption and photoluminescence (PL) spectra. The XRD Rietveld refinement was performed to obtain the detailed crystal structure of Sr₃LiSbO₆. The electronic structure was analyzed by density functional theory (DFT) calculation. Sr₃LiSbO₆ possessed indirect band structure and the band-gap were determined to be 3.17 eV. Self-activated far-red emissions at 630-800 nm were detected under the excitation at 340 nm, which was proposed to originate from the transition between interstitial oxygen defective state to six hybrid 4d¹⁰5s⁰ states of Sb⁵⁺ according to the results of PL spectra of samples annealed at different atmospheres. The PL intensity can be significantly enhanced by 2.9 times after doping 2 mol% Gd³⁺ ions in Sr₃LiSbO₆. The internal quantum efficiency of Sr₃LiSbO₆:2 mol%Gd³⁺ was determined to be 25.2%. The influence of the Gd³⁺ doping on the self-activated PL lifetimes of Sr₃LiSbO₆ and the thermal quenching property of Sr₃LiSbO₆:2 mol%Gd³⁺ was studied.

Presence of Irregular Oxidation State of Bi4+ and Single-Element White Emission in YAl3(BO3)4: Bi

In typical single-composition white phosphors, various doping elements account for the different emission wavelengths. However, it is challenging to tune the doping ratios, and the coexistence of different activators can...

Local Structure Modulation-Induced Highly Efficient Red-Emitting Ba2Gd1-xYxNbO6:Mn4+ Phosphors for Warm WLEDs

Modulating the crystal field environment around the emitting ions is an effective strategy to improve the luminescence performance of the practical effective phosphor materials. Here, smaller Y³⁺ ions are introduced into substituting the Gd³⁺ sites in Ba₂GdNbO₆:Mn⁴⁺ phosphor to modify the optical properties, including the enhanced luminescence intensity, redshift, and longer lifetime of the Mn⁴⁺ ions. The substitution of smaller Y³⁺ ions leads to lattice contraction and then strengthens pressure on the local structure, enhances lattice rigidity, and suppresses nonradiative transition. Moreover, the prototype phosphor-converted light-emitting diode (LED) demonstrates a continuous change photoelectric performance with a correlated color temperature of 4883-7876 K and a color rendering index of 64.1-83.2, suggesting that it can be one of the most prospective fluorescent materials applied as a warm red component for white LEDss. Thus, the smaller ion partial substitution can provide a concise approach to modulate the crystal field environment around the emitting ions for excellent luminescence properties of phosphors toward the modern artificial light.

Structure and luminescence behaviour of a novel red-emitting fluoroperovskite for display backlight application

In this work, we present a brand-new narrowband red-emitting fluoroperovskite via the introduction of Mn⁴⁺ into NaZnF₃ through a facile co-precipitation method at room temperature. The physicochemical properties of the fluoroperovskite such as crystal and electronic structures, morphology, and elemental composition, as well as its spectroscopic properties such as luminescence behaviours and optical performance were characterized and investigated in detail. Evidence shows that NaZnF₃:Mn⁴⁺ exhibits a uniform particulate shape with single-phase crystallinity. By virtue of the non-equivalent substitution and the [MnF₆] octahedral distortion in the fluoride host, sharp red emissions of phonon sidebands and the zero-phonon line upon blue light excitation are identified. Benefiting from the unique spectral feature, a wide colour gamut of 104.1% NTSC is achieved by coating β-SiAlON:Eu²⁺ and NaZnF₃:Mn⁴⁺ on an InGaN chip, indicating the potential use of the Mn⁴⁺ fluoroperovskite as a colour converter for display backlight application.

Enhanced luminescence properties of Ca1+xSr2−xAl2O6:Eu3+ (0 ≤ x ≤ 1) red phosphors based on composition modulation

A series of Ca_1+xSr_2−xAl₂O₆:Eu³⁺ (0 ≤ x ≤ 1) red-emitting phosphors with adjustable optical properties and excellent quantum efficiency was developed for potential applications in warm WLEDs.

Rare-earth-containing perovskite nanomaterials: design, synthesis, properties and applications

As star material, perovskites have been widely used in the fields of optics, photovoltaics, electronics, magnetics, catalysis, sensing, etc. However, some inherent shortcomings, such as low efficiency (power conversion efficiency, external quantum efficiency, etc.) and poor stability (against water, oxygen, ultraviolet light, etc.), limit their practical applications. Downsizing the materials into nanostructures and incorporating rare earth (RE) ions are effective means to improve their properties and broaden their applications. This review will systematically summarize the key points in the design, synthesis, property improvements and application expansion of RE-containing (including both RE-based and RE-doped) halide and oxide perovskite nanomaterials (PNMs). The critical factors of incorporating RE elements into different perovskite structures and the rational design of functional materials will be discussed in detail. The advantages and disadvantages of different synthesis methods for PNMs will be reviewed. This paper will also summarize some practical experiences in selecting suitable RE elements and designing multi-functional materials according to the mechanisms and principles of REs promoting the properties of perovskites. At the end of this review, we will provide an outlook on the opportunities and challenges of RE-containing PNMs in various fields.

Double perovskite A2LaNbO6:Mn4+,Eu3+ (A = Ba, Ca) phosphors: potential applications in optical temperature sensing

Recently, much attention has been paid to Mn⁴⁺-doped phosphors due to their strong deep-red emissions which are in demand in white light-emitting diodes. However, a key challenge for the commercialization of Mn⁴⁺-doped phosphors is their low thermal stability caused by the thermal quenching of Mn⁴⁺ luminescence. Herein, a strategy of optical temperature sensing has been developed by specifically utilizing thermal quenching to explore the potential applications of Mn⁴⁺-doped phosphors in optical temperature sensing. In this work, we report two kinds of double perovskite type phosphors, Ba₂LaNbO₆ (BLN) and Ca₂LaNbO₆ (CLN), co-doped with Mn⁴⁺ and Eu³⁺. Through the study of temperature-dependent spectra in a large temperature range of 298-498 K, Mn⁴⁺ and Eu³⁺ yield different trends where the fluorescence intensity of Mn⁴⁺ ions decreases much more rapidly compared to that of Eu³⁺ ions as the temperature increases. Accordingly, based on the fluorescence intensity ratio (FIR) of the luminescence of Mn⁴⁺ and Eu³⁺, the optimal relative sensitivity of temperature sensing in the BLN and CLN matrices could reach 2.08% K^-1 and 1.51% K^-1, respectively. Finally, the application potential of Mn⁴⁺-doped phosphors in temperature sensing is confirmed by analyzing different temperature sensing results in the two matrices.

Enhanced deep-red emission from Mn4+/Mg2+ co-doped CaGdAlO4 phosphors for plant cultivation

Mn4+-Doped oxide phosphors are under intensive investigation owing to their low manufacture cost and attractive luminescent features for indoor plant cultivation applications. However, it is still a challenge to develop Mn4+-doped oxides with high luminescence efficiency and thermal stability. Herein, Mn4+-Mg2+ pairs are incorporated into a CaGdAlO4 host to reduce non-radiative channels formed by Mn4+-Mn4+-O2- clusters. The photoluminescence and quantum efficiency are significantly enhanced after the introduction of Mg2+ ions to the host. A prolonged Mn4+ decay time is also obtained from the Mn4+/Mg2+ co-doped samples. Intense red emission with a narrow peak at 712 nm due to the 2Eg → 4A2g transition of Mn4+ ions is observed under 335 nm excitation. LEDs fabricated by coating the synthesized phosphor on a 365 nm near-UV chip exhibit an intense deep-red emission with CIE chromaticity coordinates of (0.712, 0.285). The results indicate Mn4+/Mg2+ co-doped CaGdAlO4 phosphors may be applicable to plant cultivation fields.

Facile preparation of Eu3+-activated Ca7(VO4)4O nanoparticles: a blue light-triggered red-emitting platform for indoor solid-state lighting

Eu³⁺-Activated Ca₇(VO₄)₄O nanoparticles with excellent luminescence behavior and good colorific properties for blue chip based WLED applications.

Mn4+-activated BaLaMgSbO6 double-perovskite phosphor: a novel high-efficiency far-red-emitting luminescent material for indoor plant growth lighting

In this paper, we reported on Mn⁴⁺-activated BaLaMgSbO₆ double-perovskite phosphors showing efficient far-red emissions for plant growth applications.

Insight into emission-tuning and luminescence thermal quenching investigations in NaLa1−xGdxCa4W2O12:Mn4+ phosphors via the ionic couple substitution of Na+ + Ln3+ (Ln = La, Gd) for 2Ca2+ in Ca6W2O12:Mn4+ for plant-cultivation LED applications

Luminescence properties of a series of NaLa_1−xGd_xCa₄W₂O₁₂ were investigated in detail.

Highly efficient red-emitting Ca2YSbO6:Eu3+ double perovskite phosphors for warm WLEDs

A double perovskite Ca₂YSbO₆:Eu³⁺ red-emitting phosphor with high concentration quenching and excellent quantum efficiency was developed to find a potential application in warm WLEDs.

Luminescent perovskites: recent advances in theory and experiments

This review summarizes previous research on luminescent perovskites, including oxides and halides, with different structural dimensionality. The relationship between the crystal structure, electronic structure and properties is discussed in detail.

Synthesis, structure, and luminescence characteristics of far-red emitting Mn4+-activated LaScO3 perovskite phosphors for plant growth

Far-red emitting phosphors LaScO₃:Mn⁴⁺ were successfully synthesized via a high-temperature solid-state reaction method. The X-ray powder diffraction confirmed that the pure-phase LaScO₃:Mn⁴⁺ phosphors had formed. Under 398 nm excitation, the LaScO₃:Mn⁴⁺ phosphors emitted far red light within the range of 650–800 nm peaking at 703 nm (14 225 cm⁻¹) due to the ²E_g → ⁴A_2g transition, which was close to the spectral absorption center of phytochrome P_FR located at around 730 nm. The optimal doping concentration and luminescence concentration quenching mechanism of LaScO₃:Mn⁴⁺ phosphors was found to be 0.001 and electric dipole–dipole interaction, respectively. And the CIE chromaticity coordinates of the LaScO₃:0.001Mn⁴⁺ phosphor were (0.7324, 0.2676). The decay lifetimes of the LaScO₃:Mn⁴⁺ phosphors gradually decreased from 0.149 to 0.126 ms when the Mn⁴⁺ doping concentration increased from 0.05 to 0.9 mol%. Crystal field analysis showed that the Mn⁴⁺ ions experienced a strong crystal field in the LaScO₃ host. The research conducted on the LaScO₃:Mn⁴⁺ phosphors illustrated their potential application in plant lighting to control or regulate plant growth.

Far-red emitting Mn⁴⁺-activated LaScO₃ perovskite phosphors were investigated for indoor plant growth lighting.

Preparation, characterization, and luminescence properties of double perovskite SrLaMgSbO6:Mn4+ far-red emitting phosphors for indoor plant growth lighting

Mn⁴⁺-activated SrLaMgSbO₆ far-red emitting phosphors with double perovskite structure were prepared by traditional solid-state reaction. The research on the crystal structure of the SrLaMgSbO₆:0.8%Mn⁴⁺ (SLMS:0.8%Mn⁴⁺) phosphors showed that the as-prepared sample was made up of two polyhedrons, [SbO₆] and [MgO₆]. Under the excitation of 333 nm, the SLMS:0.8%Mn⁴⁺ phosphors exhibited an intense far-red emission in the 625–800 nm wavelength range with CIE chromaticity coordinates of (0.733, 0.268), which could match well with the absorption spectrum of phytochrome P_FR. The optimal concentration of Mn⁴⁺ ions in the SLMS:Mn⁴⁺ phosphors was 0.8 mol%. Importantly, the as-prepared SLMS:0.8%Mn⁴⁺ phosphors had an internal quantum efficiency of 35%. The thermal stability of SLMS:0.8%Mn⁴⁺ phosphors was also investigated, and the activation energy was found to be 0.3 eV. Thus, the Mn⁴⁺-activated SLMS phosphors have great potential to serve as far-red emitting phosphors in indoor plant growth lighting.

Novel far-red emitting double perovskite SrLaMgSbO₆:Mn⁴⁺ phosphors were prepared and their photoluminescence properties were studied for applications in indoor plant growth lighting.