A highly efficient deep red-emitting Mn4+-powered oxyfluoride nanophosphor developed for plant growth and optical thermometric applications

This research mainly highlighted an intense deep red-emitting and Mn4+-powered oxyfluoride nanophosphor, Mg14Ge4.99O16F8:0.01Mn4+ (MGOF:Mn), which was synthesized via adopting a scalable synthesis route for commercial temperature sensing and artificial plant growth applications. The electron microscopic analysis confirmed the formation of nanosized particles without any defined shape or size distribution. The obtained nanophosphor exhibited sharp emission peaks at 659 nm and 631 nm under UV (317 nm) and blue excitation (417 nm) owing to Mn4+:2Eg → 4A2g and Mn4+:2T1g → 4A2g transitions, respectively. The emission spectrum is situated in the deep red region of the CIE color diagram where the red color purity approached 100% under both the excitations. The absorption efficiency and the internal and external quantum efficiencies of this red-emitting system were calculated to be 53%, ∼77%, and ∼41%, respectively, under blue excitation of 417 nm, which indicated its potential for indoor plant cultivation. A prototype red LED was fabricated by pasting the red-emitting MGOF:Mn4+ nanophosphor powder on a 410 nm blue LED chip. The resulting electroluminescence spectrum overlapped with those of the important organic pigments of normal plants. Importantly, the thermometric properties of the nanophosphor were evaluated in detail for FIR and lifetime-based thermometry applications. The examined nanophosphor showed an extreme absolute sensitivity of 0.00326 K-1 at 373 K with excellent reproducibility and temperature resolution. Because of the small particle size and high luminescence efficiency, the nanophosphor could be implemented in various nano-devices where non-contact optical thermometry is necessary for high performance.

Highly Sensitive Temperature Sensors Resulting from the Luminescent Behavior of Sm3+-Doped Ba2MgMoO6 High-Symmetry Double-Perovskite Molybdate Phosphors

We present double-perovskite molybdate with the formula of Ba2MgMoO6 doped with Sm3+ ions as a potential red phosphor to improve the color characteristics of white-light-emitting dioded (wLEDs). The new orange-red phosphor was synthesized using the co-precipitation (CP) method, and then its structural and spectroscopic properties were determined. Red emission at 642.6 nm dominates, which results from the electric dipole (ED) transition of the 4G5/2 → 6H9/2 type, and the materials are characterized by short luminescence decay times. BMM:Sm3+ is, to our best knowledge, the clearest example of dominant red emission of Sm3+ resulting from the location of the dopant in octahedral sites of high-symmetry cubic structure. In the sample containing 0.1% Sm3+, Sm3+ ions are located in both Mg2+ and Ba2+ sites, while at higher concentrations the Ba2+ site is less preferable for doping, as a result of which the emission becomes more uniform and single-site. The relative sensitivity calculated from FIR has a maximum of 2.7% K-1 at -30 °C and another local maximum of 1.6% K-1 at 75 °C. Such value is, to the best of our knowledge, one of the highest achieved for luminescent thermometry performed using only Sm3+ ions. To sum up, the obtained materials are good candidates as red phosphor to improve the color characteristics of wLEDs, obtaining a color-rendering index (CRI) of 91 and coordinated color temperature (CCT) of 2943 K, constituting a warm white emission. In addition to this, a promising precedent for temperature sensing using high-symmetry perovskite materials is the high sensitivity achieved, which results from the high symmetry of the BMM host.

Mn4+/Eu3+ co-doped fluoride toward a blue light-excited optical fiber thermometer

The ongoing development of ratiometric optical thermometry is mainly trapped in thermally coupled levels of rare-earth ions and inefficient ultraviolet excitation. Herein, a new-type multiple sharp line emitting, blue light-excited K2NaInF6:Mn4+, Eu3+ fluoride phosphor has been reported as a ratiometric thermometer. The f-f transition of Eu3+ paves a steady reference to a highly temperature sensitive Mn4+d-d transition and enables high relative sensitivity of 1.65% K-1 at 573 K. An optical fiber thermometry on a household oven with a relative standard deviation of 0.11% surpasses the standard of precision measurement, showing great potential in practical application. This discovery offers a highly sensitive neotype blue light-excitable ratiometric temperature sensor, that is Mn4+-doped fluoride, promoting practical applications of optical thermometry.

A highly efficient Mn4+ activated Nb-based oxyfluoride red fluorescent material with excellent water stability: preparation and performance analysis

In this study, an efficient non-rare earth Mn4+-doped K3(NbOF5)(HF2) red fluorescent material was synthesized by using the coprecipitation method. Replacing KF with K2CO3 effectively solved the problem that KF was difficult to stir due to its strong water absorption. The sample was composed of rods. The excitation spectra consisted of two strong excitation peaks at 366 nm and 468 nm. The emission spectra consisted of a series of narrow-band emissions between 580 nm and 680 nm. Besides, the luminescence quantum efficiency (QE) reached 84.3% under the excitation of 468 nm. The fluorescent lifetime of K3(NbOF5)(HF2):Mn4+ was less than 4 ms, which can achieve fast response display in backlight display applications. The WLED was fabricated with K3(NbOF5)(HF2):Mn4+ and commercial YAG:Ce3+ and the commercial InGaN blue chip. At a 30 mA drive current, the WLED device exhibited excellent luminescence properties. The correlated color temperature (CCT) was 3853 K, the Ra was 90.1 and the luminous efficiency was 310.432 lm W-1. Therefore, K3(NbOF5)(HF2):Mn4+ has very broad prospects in WLED lighting and backlight display applications.

Efficient dual mode emission in Ce3+/Yb3+/Er3+ doped yttrium aluminium gallium garnet for led device and optical thermometry

By utilizing the effective energy transfer from Ce³⁺ to Yb³⁺, Er³⁺ and from Yb³⁺ to Er³⁺ authors have achieved dual mode emission in Y₃Al₄GaO₁₂ activated with Ce³⁺/Yb³⁺/Er³⁺ ions. Surface morphological and elemental compositions of the prepared samples have been examined using field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS) analysis, respectively. The chemical state of the dopant ions is confirmed by the X-ray photoelectron spectroscopy (XPS). On excitation with 438 nm the prepared material has shown broad visible emission band around 511 nm due to the electronic transition of Ce³⁺ ion. In addition to this sample has also shown NIR emission bands centered around 1024 nm and 1480 nm from Yb³⁺ and Er³⁺ ions, respectively. The emission band at 1024 nm could be due to the quantum cutting (QC) process. Furthermore, up-conversion (UC) emission against temperature and laser power variations is studied on 980 nm excitation wavelength. The prepared sample is used to fabricate visible and NIR LED devices by coating of sample on blue LED chip. Along with this demonstration, optical thermometry ability of the material is studied using emission intensity ratio of two emitting levels. Studies suggest that the prepared material could be useful as dual mode emitting phosphor and LED.

Luminescence of Mn4+ in a Zero-Dimensional Organic-Inorganic Hybrid Phosphor [N(CH3)4]2ZrF6 for Dual-Mode Temperature Sensing

Searching for new low-dimensional organic-inorganic hybrid phosphors is of great significance due to their unique optical properties and wide applications in the optoelectronic field. In this work, we report a Mn⁴⁺ doped zero-dimensional organic-inorganic hybrid phosphor [N(CH₃)₄]₂ZrF₆, which was synthesized by a wet chemical method. The crystal structure, thermal stability, and optical properties were systemically investigated by means of XRD, SEM, TG-DTA, FTIR, DRS, emission spectra, excitation spectra, as well as decay curves. Narrow red emission with high color purity can be observed from [N(CH₃)₄]₂ZrF₆:Mn⁴⁺ phosphor, which maintains effective emission intensity even at room temperature, indicating its potential practical application in WLEDs. In the temperature range of 13-295 K, anti-Stokes and Stokes sidebands of Mn⁴⁺ ions exhibit different temperature responses. By applying the emission intensity ratio of anti-Stokes vs. Stokes sidebands as temperature readout, an optical thermometer with a maximum absolute sensitivity of 2.13% K^-1 and relative sensitivity of 2.47% K^-1 can be obtained. Meanwhile, the lifetime Mn⁴⁺ ions can also be used for temperature sensing with a maximum relative sensitivity of 0.41% K^-1, demonstrating its potential application in optical thermometry.

Phosphorescence in Mn4+-Doped R+/R2+ Germanates (R+ = Na+ or K+, R2+ = Sr2+)

Single crystals of three new compounds, Na_0.36Sr_0.82Ge₄O₉ (1, proposed composition), Na₂SrGe₆O₁₄ (2), and K₂SrGe₈O₁₈ (3), were obtained and characterized using single-crystal X-ray diffraction. Their structures contain three-dimensional (3D) anionic frameworks built from GeO₄ and GeO₆ polyhedra. The presence of octahedral Ge⁴⁺ sites makes the new phases suitable for Mn⁴⁺ substitution to obtain red-emitting phosphors with a potential application for light conversion. Photoluminescence properties of Mn⁴⁺-substituted Na₂SrGe₆O₁₄ (2) and K₂SrGe₈O₁₈ (3) samples were studied over a range of temperatures, and red light photoluminescence associated with the electronic transitions of tetravalent manganese was observed. The Na₂SrGe₆O₁₄ (2) phase was also substituted with Pr³⁺ on the mixed Na-Sr site similar to the previously studied Na₂CaGe₆O₁₄:Pr³⁺. The red emission peak of the Pr³⁺ activator occurs at a shorter wavelength (610 nm) compared to that of Mn⁴⁺ (662-663 nm). Additionally, second harmonic generation (SHG) data were collected for the noncentrosymmetric Na₂SrGe₆O₁₄ (2) phase, indicating weak SHG activity. Diffuse reflectance spectroscopy and density of states calculations were performed to estimate the band gap values for pristine Na₂SrGe₆O₁₄ (2) and K₂SrGe₈O₁₈ (3) phases.

Photoluminescence processes in τ-phase Ba1.3Ca0.7-x-y SiO4:xDy 3+/yTb3+ phosphors for solid-state lighting

The τ-phase Ba_1.3Ca_0.7-x-y SiO₄:xDy ³⁺/yTb³⁺ phosphors co-doped with Dy ³⁺ (x = 0.03) and Tb³⁺ (y = 0.01-0.05) trivalent rare-earth ions were prepared by the gel-combustion method. The structure-property relation of the samples was examined by X-ray diffraction, scanning electron microscopy and spectrophotometer. Here, the effect of Tb³⁺'s concentration on the spectroscopic properties of Ba_1.3Ca_0.7-x-y SiO₄:xDy ³⁺/yTb³⁺ phosphors was explored by using the photoluminescence excitation, emission and decay curves. Importantly, the photonic energy transfer from (Dy ³⁺:⁴F_9/2 + Tb³⁺:⁷F₆) to (Dy ³⁺:⁶H_15/2 + Tb³⁺:⁵D₄) was observed, in which the Dy ³⁺ ions act as a light-emitting donor whereas the Tb³⁺ ions as a light-absorbing acceptor, resulting in an enhanced emission from the co-doped Ba_1.3Ca_0.7-x-y SiO₄:xDy ³⁺/yTb³⁺ (x = 0.03 and y = 0.01-0.05) phosphors. Finally, the chromaticity coordinates were determined from the measured emission spectra, locating at the green and white light regions. This observation indicates that the characteristic emission colour could be tuned from white to green by varying Tb³⁺ concentrations under ultraviolet light.

NIR light guided enhanced photoluminescence and temperature sensing in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor

The conversion of NIR light into visible light has been studied in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor for the first time. The crystallinity and particles size of the phosphor increase through Bi3+ doping. The absorption characteristics of Ho3+, Yb3+ and Bi3+ ions are identified by the UV-vis-NIR measurements. The Ho3+ doped phosphor produces intense green upconversion (UC) emission under 980 nm excitations. The emission intensity ~ excitation power density plots show contribution of two photons for the UC emissions. The UC intensity of green emission is weak in the Ho3+ doped phosphor, which enhances upto 128 and 228 times through co-doping of Yb3+ and Yb3+/Bi3+ ions, respectively. The relative and absolute temperature sensing sensitivities of Ho3+/Yb3+/5Bi3+ co-doped ZnGa2O4 phosphor are calculated to be 13.6 × 10-4 and 14.3 × 10-4 K-1, respectively. The variation in concentration of Bi3+ ion and power density produces excellent color tunability from green to red via yellow regions. The CCT also varies with concentration of Bi3+ ion and power density from cool to warm light. The color purity of phosphor is achieved to 98.6% through Bi3+ doping. Therefore, the Ho3+/Yb3+/Bi3+:ZnGa2O4 phosphors can be suitable for UC-based color tunable devices, green light emitting diodes and temperature sensing.

In situ growth of Z-scheme CuS/CuSCN heterojunction to passivate surface defects and enhance charge transport

Copper thiocyanate (CuSCN) has been considered as a promising hole transport material (HTMs), attributing to its inherent stability, low-cost, and suitable energy levels. To make it more attractive in practical applications, the drawbacks of CuSCN in poor charge transport and serious defect recombination are bottlenecks that need to be overcome. In this work, we propose an effective strategy of in-situ decorating CuSCN with copper sulfide quantum dots (CuS QDs), a simple one-step electrochemical deposition process, to solve these issues. Compared with the pristine CuSCN, the constructed Z-Scheme heterojunction of CuS QDs/CuSCN can significantly promote charge transport and restrict recombination. In addition, the decorated CuS QDs can not only passivate defects of CuSCN, but also provide more contacting sites to facilitate hole injection when employing as HTM. As a result, the average bulk charge lifetime was improved from 0.37 ms to 0.47 ms, and the surface recombination rate constant was suppressed. We believe that the excellent performances will pave it toward practical device applications, including solar cells, photocatalysis, photoelectrochemical sensors, and light-emitting diodes.

K2SnOF4 and K2WO3F2 – different but similar

K2SnOF4 and K2WO3F2 were synthesized via a high-pressure/high-temperature route. Single-crystal analysis showed that both substances crystallize in the orthorhombic crystal system with space group Pnma and are isostructural to each other. The main motifs of the structures are octahedral [SnO2F4]4− and [WO4F2]4− entities for K2SnOF4 and K2WO3F2, respectively. Within the structures, these units are connected to quasi-isolated infinite chains. The substances were further characterized via powder X-ray diffraction, EDX and FT-IR spectroscopy. Doping of K2SnOF4 with Mn4+ yielded a red phosphor material which was analyzed by luminescence spectroscopy. The emission maximum is located at λ max = 631 nm.

Highly sensitive optical temperature sensing based on upconversion luminescence in Gd9.33(SiO4)6O2:Yb3+-Er3+/Ho3+ phosphors

In this paper, new upconversion (UC) phosphors for Yb3+-Er3+- and Yb3+-Ho3+-doped Gd9.33(SiO4)6O2 (GSO) were designed via a solid-state reaction method. The phase purity of the samples was examined using XRD patterns. In Yb3+-Er3+ -doped GSO, the characteristic emission peaks of Er3+ appear upon 980 nm excitation, and the optimum Er3+ concentration was found to be 1 mol%. Different changes in the intensity of green and red emissions with Er3+ concentration appeared, and were interpreted by cross-relaxation between Er3+ ions. In Yb3+-Ho3+-doped GSO, three emission peaks of Ho3+ were observed, and the power-dependent UC luminescence was studied. For studying the temperature-sensing properties, different strategies were employed, including thermally coupled levels and non-thermally coupled levels. High sensitivities were obtained in the phosphors, and GSO:Yb3+,Er3+ showed the highest sensitivities. The above investigation results indicated that the developed GSO:Yb3+-Er3+/Ho3+ phosphors could have potential applications in optical thermometry.

A novel Mn4+ doped oxyfluoride red phosphor for rapid-response backlights display

An oxyfluoride red phosphor Cs₂MoO₂F₄:Mn⁴⁺ was synthesized via a facile co-precipitation route with a certain molecular ratio of CsF and MoO₃. X-ray diffraction analysis and its Rietveld refinement reveal that Cs₂MoO₂F₄:Mn⁴⁺ crystallized in an orthorhombic structure with the Amam (63) space group. Upon blue light excitation, Cs₂MoO₂F₄:Mn⁴⁺ exhibits a series of sharp red emission lines around ∼634 nm and the zero-phonon line (ZPL) is visible at 619 nm. The optimal doping amount of Mn⁴⁺ in Cs₂MoO₂F₄ is 1.12%, and the decay curves show a good fit with the single exponential decay model. The fluorescence lifetime of the synthesized phosphors is relatively short and calculated as 3.18 to 2.46 ms, the Mn⁴⁺ ions in Cs₂MoO₂F₄ experience a strong crystal field strength with a Dq/B of ∼4.87, and the distinct nephelauxetic ratio β₁ is determined to be ∼1.0226. The thermal quenching mechanism of Mn⁴⁺ was also studied. Furthermore, by using the as-synthesized Cs₂MoO₂F₄:Mn⁴⁺ phosphor as a red component and β-SiALON as a green light component, a WLED was fabricated with a high luminous efficacy of 114.70 lm·W^-1 and wide color gamut of 109.1% of the National Television Standard Committee (NTSC) value. Hence, the Cs₂MoO₂F₄:Mn⁴⁺ phosphor with a short fluorescence lifetime could potentially be an efficient red compensator for application in rapid-response backlight displays.

New near-infrared emissions and energy transfer in Er3+ -doped MgAl layered double hydroxides

A series of Er³⁺ -doped magnesium aluminium layered double hydroxides (Er³⁺ -doped, MgAl-LDHs) with different Mg²⁺ /(Al³⁺ +Er³⁺ ) molar ratios were synthesized using the hydrothermal method. Compositional and structural analyses suggest that the Er³⁺ -doped MgAl-LDHs kept a hexagonal structure while the Mg²⁺ /(Al³⁺ +Er³⁺ ) molar ratio was at 1.0-4.1. The downconverted emission spectra of the Er³⁺ -doped MgAl-LDHs showed a red emission at 650 nm and strong infrared emissions at 720, 780, and 850 nm. These infrared emissions were hardly observed in previous downconverted emission spectra of Er³⁺ -doped materials. In the analysis of the Er³⁺ energy levels and in relevant published literature, the energy transfer diagram for Er³⁺ -doped in MgAl-LDHs is described, and infrared emissions at 720, 780, and 850 nm may be attributed to ⁴ F_7/2 →⁴ I_13/2 , ² H_11/2 →⁴ I_13/2 , and ⁴ S_3/2 →⁴ I_13/2 transitions of Er³⁺ , respectively. Er³⁺ -doped MgAl-LDHs could have potential application as marking and targeting agents in the processes for drug delivery in consideration of the strong near-infrared Er³⁺ emissions, as well as the special layered structure of MgAl-LDH.

Strategies for Designing Antithermal-Quenching Red Phosphors

Nowadays, red phosphor plays a key role in improving the lighting quality and color rendering index of phosphor-converted white light emitting diodes (w-LEDs). However, the development of thermally stable and highly efficient red phosphor is still a pivotal challenge. Herein, a new strategy to design antithermal-quenching red emission in Eu3+, Mn4+-codoped phosphors is proposed. The photoluminescence intensity of Mg3Y2(1- y )Ge3O12:yEu3+, Mn4+ (0 ≤ y ≤ 1) phosphors continuously enhances with rising temperature from 298 to 523 K based on Eu3+ → Mn4+ energy transfer. For Mg3Eu2Ge3O12:Mn4+ sample, the integrated intensity at 523 K remarkably reaches 120% of that at 298 K. Interestingly, through codoping Eu3+ and Mn4+ in Mg3Y2Ge3O12, the photoluminescence color is controllably tuned from orangish-red (610 nm) to deep-red (660 nm) light by changing Eu3+ concentration. The fabricated w-LEDs exhibit superior warm white light with low corrected color temperature (CCT = 4848 K) and high color rendering index (R a = 96.2), indicating the promising red component for w-LED applications. Based on the abnormal increase in antistokes peaks of Mn4+ with temperatures, Mg3Eu2Ge3O12:Mn4+ phosphor also presents a potential application in optical thermometry sensors. This work initiates a new insight to construct thermally stable and spectra-tunable red phosphors for various optical applications.

Yolk–shell structured Bi2SiO5:Yb3+,Ln3+ (Ln = Er, Ho, Tm) upconversion nanophosphors for optical thermometry and solid-state lighting

Bi₂SiO₅:Yb³⁺,Er³⁺ yolk–shell nanophosphors have been successfully synthesized, which are expected to find important applications in optical thermometry and solid-state lighting.

Achieving high thermal stability of different rare-earth ions in a single matrix host via the manipulation of the local structure by a solid solution

Thermal quenching seriously restricts the practical application of phosphors, particularly under high temperature and long-term working conditions. Here, we demonstrate that the as-obtained series of solid solutions of Ca2-xYxAl2Si1-xAlxO7:Tb3+ (x = 0-1, Ca2Al2SiO7 → CaYAl3O7) phosphors exhibit an adjustable optical performance, where CaYAl3O7:Tb3+ exhibits a greatly improved thermal stability with a shortened bond distance of the related polyhedron compared with Ca2Al2SiO7:Tb3+. The shrunken bond distance strengthens the pressure of the local structure and suppresses the non-radiative transition effectively, contributing to the prevention of the thermal degradation. The formed phosphor with excellent structural stability could be effectively incorporated with various lanthanide ions (Eu3+, Tb3+, Sm3+, Dy3+, and Pr3+) to address a pleochroism output.

An efficient down conversion luminescencent probe based on a NaGdF4:Eu3+/Ce3+ nanophosphor for chemical sensing of heavy metal ions (Cd2+, Pb2+ and Cr3+) in waste water

Eu³⁺ doped and Eu³⁺/Ce³⁺ co-doped NaGdF₄ nanophosphors are fabricated via a facile hydrothermal route. The codoped counterpart is demonstrated for efficient photoluminescence sensing of heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺) present in industrial effluents.

Temperature-sensing luminescent materials La9.67Si6O26.5:Yb3+–Er3+/Ho3+ based on pump-power-dependent upconversion luminescence

Rare earth ion doped upconversion (UC) luminescent materials could show potential applications in optical temperature sensing.

Electron–phonon coupling mechanisms of broadband near-infrared emissions from Cr3+ in the Ca3Sc2Si3O12 garnet

The electron–phonon coupling effect resulting in broad NIR emission in Ca₃Sc₂Si₃O₁₂:Cr³⁺ is revealed for the first time.

Intense deep-red zero phonon line emission of Mn4+ in double perovskite La4Ti3O12

Phosphors that emit in the deep-red spectral region are critical for plant cultivation light-emitting diodes. Herein, ultrabroadband deep-red luminescence of Mn⁴⁺ in La₄Ti₃O₁₂ was studied, which showed intense zero phonon line emission. The double-perovskite structural La₄Ti₃O₁₂ simultaneously contains two Ti⁴⁺ sites forming slightly- and highly-distorted TiO₆ octahedra, respectively. The influence of octahedral distortion on the Mn⁴⁺ emission energy in the two distinct Ti⁴⁺ sites was studied both experimentally and theoretically. The spectral measurements indicated that Mn⁴⁺ in La₄Ti₃O₁₂ showed intense zero phonon line emission (ZPL) at deep-red 710-740 nm under excitation of 400 nm charging the O^2-→ Mn⁴⁺ charge transfer transition. The splitting of the ZPL of the Mn^{4+ 2}E_g→⁴A_2g transition as well as the intensity of ZPL relative to the vibronic phonon sideband emissions were found to be greatly influenced by the degree of octahedral distortion. The crystal-field strength and Racah parameters of Mn⁴⁺ in each Ti⁴⁺ site were also estimated. The Mn^{4+ 2}E_g→⁴A_2g luminescence exhibited severe thermal quenching, which was explained by the low-lying ⁴T_2g level and charge-transfer state.

Cs2MnF6 Red Phosphor with Ultrahigh Absorption Efficiency

To improve absorption efficiency (AE) and subsequently improve external quantum efficiency (EQE) remains one of the significant challenges for Mn⁴⁺-doped red-emitting fluoride phosphors. In this study, we propose to use Mn⁴⁺ as a part of matrix to enhance the AE of fluoride phosphors. Red-emission phosphors Cs₂MnF₆, Cs₂MnF₆:Sc³⁺, and Cs₂MnF₆:Si⁴⁺ were synthesized successfully by a coprecipitation method. The Rietveld refinement of X-ray diffraction reveals that this red phosphor exhibits a cubic structure in Fm3̅m space group. Owing to Mn⁴⁺ being a part of matrix, this kind of red phosphor possesses an extremely high AE, which can be promoted to 88%. The doping of Sc³⁺ and Si⁴⁺ ions into Cs₂MnF₆ can effectively increase the luminescence intensity to 253 and 232%, respectively, relative to that of Cs₂MnF₆. The relative emission intensity of Cs₂MnF₆:5%Si⁴⁺ red phosphor preserves about 115% when temperature rises to 175 °C. By employing Cs₂MnF₆:5%Si⁴⁺ as a red-emitting component, high-performance LED-1 with Ra = 86.2, R9 = 82.1 and CCT = 3297 K, and LED-2 with an ultrawide color gamut (NTSC value of 122.3% and rec. 2020 value of 91.3%) are obtained. This work may provide a new idea to explore a new type of fluoride phosphor with high EQE for high-performance white-light-emitting diodes.

Red-emitting K3HF2WO2F4:Mn4+ for application in warm-white phosphor-converted LEDs – optical properties and magnetic resonance characterization

A novel efficient red-emitting Mn⁴⁺ phosphor of composition K₃HF₂MO₂F₄:Mn⁴⁺ (M = Mo, W).

Concentration and pump power-mediated color tunability, optical heating and temperature sensing via TCLs of red emission in an Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor

The Er³⁺/Yb³⁺/Li⁺ co-doped ZnGa₂O₄ phosphor gives intense red upconversion photoluminescence, color tunability with Er³⁺ ion concentration and incident pump power, R/G ratio, induced optical heating and temperature sensing characteristics.

Cannabis sativa-derived carbon dots co-doped with N–S: highly efficient nanosensors for temperature and vitamin B12

Cannabis sativa-derived carbon dots as efficient nanosensors for temperature and vitamin B₁₂.

Revisiting Cr3+-Doped Bi2Ga4O9 Spectroscopy: Crystal Field Effect and Optical Thermometric Behavior of Near-Infrared-Emitting Singly-Activated Phosphors

The increasing interest in the development of ratiometric optical thermal sensors has led to a wide variety of new systems with promising properties. Among them, singly-doped ratiometric thermometers were recently demonstrated to be particularly reliable. With the aim to discuss the development of an ideal optical thermal sensor, a combined experimental and theoretical insight into the spectroscopy of the Bi₂Ga₄O₉:Cr³⁺ system is reported showing the importance of an insightful analysis in a wide temperature range. Low-temperature photoluminescence analysis (from 10 K) and the temperature dependence of the lifetime investigation, together with the crystal field analysis and the modeling of the thermal quenching process, allow the estimation of key parameters such as the Debye temperature (cutoff frequency), the Huang-Rhys parameter, and the energy barrier between ²E_g and ⁴T_2g. Additionally, by considering the reliable class of singly-doped ratiometric thermometers based on a couple of excited states obeying the Boltzmann law, the important role played by the absolute sensitivity was discussed and the great potential of Cr³⁺ singly-activated systems was demonstrated. The results may provide new guidelines for the design of reliable optical thermometers with outstanding and robust performances.

A novel Cs2NbOF5:Mn4+ oxyfluoride red phosphor for light-emitting diode devices

The addition of a red-emitting phosphor to YAG:Ce3+-based white light-emitting diodes (WLEDs) greatly facilitates their applications in the field of high-color-rendering-index warm solid-state lighting. It is highly desirable to develop a red phosphor with satisfactory spectral features and low synthesis cost. In this study, a novel non-rare-earth and nonequivalent doping type of Cs2NbOF5:Mn4+ oxyfluoride red-emitting phosphor with high luminous efficiency was obtained via a facile room-temperature co-precipitation method, and its morphology and luminescent properties were investigated in detail. The Cs2NbOF5:Mn4+ phosphor with micro-rod-like morphology exhibited broad band absorption at blue light region (∼474 nm) and narrow bandwidth emissions at red region (∼633 nm). The color purity of the Cs2NbOF5:Mn4+ phosphor was calculated to be about 99%, and the internal quantum yield (QY) under 474 nm excitation was 63.4%. The concentration quenching of Mn4+ in Cs2NbOF5 matrix was mainly due to dipole-dipole interactions, and the activation energy of temperature quenching was calculated to be ∼0.2610 eV. The demonstration of a blue InGaN LED chip in combination with a blend of newly developed Cs2NbOF5:Mn4+ red phosphor and YAG:Ce3+ yellow phosphor greatly decreased the correlated color temperature (CCT) from 6255 to 3517 K while significantly improving the color rendering index (CRI) from 72.5 to 87.5. It deserves to be mentioned that the brand-new matrix to phosphor in the present study can be extended to various niobium/tantalum oxyfluoride series, which is very helpful for developing and designing new red phosphors.

A novel red phosphor of Mn4+ion-doped oxyfluoroniobate BaNbOF5for warm WLED applications

A novel red phosphor composed of Mn⁴⁺-activated oxyfluoroniobate BaNbOF₅was obtained at room temperature in air. The as-prepared phosphor showed a broad and intense absorption in the blue-light region and a bright red luminescence with a color purity of 97.7%.

Far-red-emitting double-perovskite CaLaMgSbO6:Mn4+ phosphors with high photoluminescence efficiency and thermal stability for indoor plant cultivation LEDs

A series of Mn⁴⁺-activated CaLaMgSbO₆ far-red-emitting phosphors were synthesized by a solid-state reaction route and the microstructure and optical characterizations were investigated in detail. Upon excitation at 370 and 469 nm, the samples showed intense far-red emission at about 708 nm originating from the ²E_g → ⁴A_2g transition and the optimal Mn⁴⁺ concentration was 0.7 mol%. The as-prepared phosphors also exhibited excellent internal quantum efficiency (88%) and high thermal stability. The emission intensity at room temperature dropped to 54% when the temperature rose to 423 K and the activation energy was 0.34 eV. The outstanding optical properties and the fact that the emission band of the obtained phosphors had a broad overlap with the absorption band of phytochrome P_FR demonstrated that the CaLaMgSbO₆:Mn⁴⁺ phosphors may be promising potential spectral converters for applying to indoor plant cultivation light-emitting diodes.

Far-red-emitting double-perovskite CaLaMgSbO₆:Mn⁴⁺ phosphors with high quantum efficiency and thermal stability were developed for potential applications in indoor plant cultivation LEDs.