Efficient red and broadband near-infrared luminescence in Mn2+/Yb3+-doped phosphate phosphor

In this work, we report a novel phosphor LSPO:Mn²⁺ that exhibits red emission at about 616 nm and pleasant broad near-infrared (NIR) emission at about 800 nm with a full width at half maximum (fwhm) of 112 nm. The structure and spectra show that the doped manganese ions occupy two kinds of Sc sites forming Mn1 and Mn2 emission centers, which are responsible for red and NIR emission, respectively. The XPS and low-temperature fluorescence spectra reveal that both red and NIR emissions come from the Mn²⁺ ions. Besides, NIR luminescence is improved by doping Yb³⁺ in LSPO:Mn²⁺, leading to the broadened NIR emission range (700-1100 nm) and enhanced luminescent thermal stability. Our results suggest that the prepared LSPO:Mn²⁺ and LSPO:Mn²⁺,Yb³⁺ phosphors offer the potential applications as red and NIR components in phosphor-converted white-light-emitting diodes (pc-WLED) and broadband NIR pc-LED. Meanwhile, this work provides a new way to design novel broadband NIR phosphors.     

Luminescent properties and LED Application of Broadband Near-Infrared Emitting NaInGe2O6: Cr3+ phosphors

A NIR-emitting Cr³⁺-activated phosphors (NaInGe₂O₆: Cr³⁺) covering whole NIR-I region (700–1200 nm) were successfully designed and prepared via solid-state reaction. XRD and Rietveld refinement verified that the octahedral In³⁺ site is the preferred site of Cr³⁺ substitution in NaInGe₂O₆ structure. The synthesized NaInGe₂O₆: Cr³⁺ phosphors exhibit two strong absorption bands at 480 and 700 nm, and show a mountain-like single-band emission at 900 nm with FWHM = 175 nm. The crystal field parameters are calculated using steady-state spectral data, in which a low Dq/B value of 1.89 is obtained and results in this broadband NIR emission. NaInGe₂O₆: Cr³⁺ exhibits good emission thermal stability, i.e. 55 % of room temperature intensity at 373 K. Besides, an efficient NIR pc-LED is fabricated and shows NIR output of 25.2 mW@120 mA. This broadband NaInGe₂O₆: Cr³⁺ NIR phosphor could be merged into pc-LED package for hand-held spectrometers, security cameras and vivo biomarkers.     

Ultrawide near-infrared SrHfO3:Cr3+ phosphor with dual emission bands

Near-infrared phosphor-converted light-emitting diodes (NIR-pc-LEDs) are superior to traditional NIR-LEDs in spectral modulation, volume, and cost, and their optoelectronic properties are dominantly controlled by the NIR phosphors, which thus boosts the search for high efficiency and broadband NIR phosphors. In this work, we attempt to realize ultra-broadband NIR phosphors by doping Cr³⁺ in self-emitting SrHfO₃ with a weak crystal field. Dual emission bands centered at 770 (host) and 1000 nm (Cr³⁺) are observed, leading to a wide spectral range of 700–1400 nm. The Cr³⁺ ions enter the HfO₆ octahedron and thus produce an NIR emission with a full width at half maximum of 190 nm and an internal quantum efficiency of 24% under 460 nm excitation. A prototype NIR-pc-LED surface light is demonstrated for machine vision by using NIR-pc-LEDs that combine the blue LED with SrHfO₃:Cr. The work paves an avenue for designing super-broadband NIR phosphors by doping Cr³⁺ or other ions into hosts with self-trapped exciton emission (e.g., halide perovskites).     

Broadband near-infrared double-perovskite phosphor Sr2ScTaO6:Cr3+, Yb3+ for NIR pc-LED applications

The broadband near-infrared (NIR) phosphor converted light emitting diode (NIR pc-LED) has garnered unprecedented attention due to its crucial role in NIR applications. However, there remains a scarcity of efficient broadband NIR luminescence materials capable of emitting NIR light with wavelengths greater than 800 nm. This study reports the synthesis, crystal structure and photoluminescence (PL) properties for double perovskite Sr₂ScTaO₆:Cr³⁺ phosphors which exhibit a broadband NIR emission in the 650–1250 nm range, peaking at∼815 nm with the full width at half maximum (FWHM) of 161 nm. The observed broadband emission arises from two distinct Cr³⁺ centers, namely Sc³⁺ and Ta⁵⁺ octahedral sites within the Sr₂ScTaO₆ structure, as demonstrated by luminescence and decay kinetic analysis. A significant enhancement of the thermal stability and a remarkable broadening of the FWHM (from 161 to 275 nm) are achieved by employing Yb³⁺ co-doping strategy. The efficient energy transfer from Cr³⁺ to Yb³⁺ was confirmed through emission and excitation spectra, as well as luminescence decay measurements. Finally, Sr₂ScTaO₆:Cr³⁺-Yb³⁺ phosphor was integrated with a 470 nm blue LED chip to fabricate a NIR pc-LED device, and its potential application in night vision was evaluated.     

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.     

Ultra-broadband of up to 200 nm near-infrared phosphors based on one-site occupation strategy for multipurpose applications in light-emitting diodes

Portable near-infrared (NIR) lighting source stimulates great efforts to exploit NIR phosphor-converted LEDs (pc-LEDs) that push the rapid development of broadband NIR-emitting phosphors. Although Cr³⁺-activated NIR phosphors designed by multisites occupation strategy show significant potential in emission bandwidth, poor spectral stability caused by different thermal quenching behaviors is a brake on practical application due to different local structure around Cr centers. One-site-based NIR phosphors seem to be an effective method to solve aforementioned problem. Herein, we report a type of new ultra-broadband one-site-based NIR-emitting phosphors NaSc_1-xP₂O₇:xCr³⁺ (NSP:xCr³⁺) with emission at 910 nm and full width at half maximum (FWHM) of up to ～200 nm. Their FWHM value exceeds all one-site-based Cr³⁺-activated phosphors and some multiple-sites ones. Structural analysis and low-temperature spectra demonstrate that such impressive broadband NIR emission originates from Cr³⁺ occupying at single octahedral Sc site. At 425 K, integrated emission intensity of NSP:0.04Cr³⁺ phosphor maintains 53.8% of room temperature. A NIR pc-LED prototype is fabricated by using NSP:0.04Cr³⁺ phosphor with a blue LED chip, and its multipurpose applications in non-destructive detection, night vision and analysis of foodstuff are demonstrated. These findings indicate that broadband NSP:0.04Cr³⁺ NIR phosphor enabled by one-site occupation strategy has potential prospect for multipurpose NIR pc-LEDs applications.     

The co-optimization of efficiency and emission bandwidth in GSAGG:Cr3+ NIR ceramic phosphors

The NIR phosphor-converted light-emitting diode (NIR pc-LED) is a new near-infrared light source that has been widely studied. Among various NIR phosphors, Cr³⁺ doped gadolinium aluminum gallium garnet (GAGG:Cr³⁺) ceramic phosphor has shown great potential due to its ultra-high efficiency and thermal stability. Despite its capabilities, its detection range may be limited due to a relatively narrow emission bandwidth. To make the GAGG:Cr³⁺ ceramic phosphors achieve both high efficiency and broadband emission, a series of Gd₃Al_2-x-ySc_xGa₃O₁₂:yCr³⁺ (GASGG:Cr³⁺) ceramic phosphors were prepared. Thanks to the decrease of crystal field strength with the doping of Sc³⁺, the full width at half maximum (FWHM) of GASGG:Cr³⁺ ceramic phosphors were extended from 84 nm to 117 nm, and the emission peak exhibited a red-shift of 46 nm. Meanwhile, it still retained extremely high external quantum efficiency (EQE = 47%) and excellent thermal stability (90.7%@150 °C). Then, a NIR pc-LED prototype device was fabricated by combining GASGG:Cr³⁺ ceramic phosphor with a blue LED chip. The NIR light output power and the photoelectric conversion efficiency of this device achieved 646 mW and 19.2%, respectively. Finally, the application effect in night vision and venography of this prototype device was demonstrated.     

A broadband near-infrared Sc1−x(PO3)3:XCr3+ phosphor with enhanced thermal stability and quantum yield by Yb3+ codoping

Broadband near-infrared (NIR) phosphors converted light-emitting diodes (pc-LEDs) have attracted tremendous attention for their great potential in NIR spectroscopy applications. Herein, we report on the photoluminescence (PL) properties of Cr³⁺-doped Sc(PO₃)₃, which exhibits a broadband NIR emission centered at 900 nm with a full width at half-maximum (FWHM) of 161 nm upon excitation at 480 nm. In terms of the examination of spectroscopic parameters, we find that Cr³⁺ ions occupy a weak crystal field site (Dq/B = 1.94) in the Sc(PO₃)₃ host with a stronger electron–phonon coupling (Huang-Rhys factor, S = 5.5), which results in a serious thermal quenching and a low internal quantum efficiency (IQE). Thermal stability and IQE of phosphors can be substantially enhanced by the introduction of Yb³⁺ ions. In the light of the analysis of excited-state dynamics, we demonstrate that the enhancement mechanism is ascribed to the efficient Cr³⁺→Yb³⁺ energy transfer from the thermal sensitive Cr³⁺ centers to the thermal stable Yb³⁺ emitters. An NIR pc-LED device has been finally fabricated by the combination of a blue-emitting chip and a Cr³⁺/Yb³⁺ codoped Sc(PO₃)₃ phosphor whose potential application for broadband NIR pc-LEDs is also discussed.     

Improvement the near-infrared luminescence properties of double perovskite phosphor La(Mg0.5Sn0.5In0.5Sc0.5)0.5O3:Cr3+ via co-doping Yb3+

In recent years, the broadband near-infrared (NIR) spectroscopy technology has been widely used in the field of nondestructive testing. However, these existing NIR phosphors showed relatively short emission wavelengths, narrower half-maximum full-width (FWHM), and narrower half-peak widths, importantly, few phosphors presented the emission from 950 nm to 1100 nm. In order to solve these problems, the Yb³⁺/Cr³⁺ ions codoped La(Mg_0.5Sn_0.5In_0.5Sc_0.5)_0.5O₃ (LMSIS) was synthesized by the solid-state method, and the emission spectrum of LMSIS:Cr³⁺ can be extended to the NIR long-wave region due to the energy transfer of Yb³⁺ and Cr³⁺, and the thermal stability of the phosphor can be improved due to the inherent temperature stability of the Yb³⁺ f-f transition. The NIR phosphor converted light emitting diodes (pc-LEDs) were fabricated by combining the LMSIS:0.003Cr³⁺, 0.0015Yb³⁺ with blue LED chip, which can be expected to be used in the field of broadband near-infrared non-destructive detection.     

Synthesis and the characterization for transition metal-ion based photonics: Broadband near-IR emission properties of nickel ion doped NaSbO3 ceramics

We report the preparation method and broadband near infrared emission characteristics of nickel ion-doped NaSbO₃ ceramics in an easy way. Selective doping of Ni²⁺ ions into proper octahedral sites is crucial to the enhancement of broadband near-infrared (NIR) emission. In this work, a broadband NIR emission with central wavelength at 1430 nm and with a full-width-at-half-maximum (FWHM) of 230 nm is reported from Ni²⁺ ion-doped perovskite NaSbO₃ lattice, which has never been reported until now, to the best of our knowledge. Nickel ion doped NaSbO₃ nanocrystals was elaborated to show the prospect that this kind of perovskite nanostructure is promising for transition metal ion (TMI) based photonics. A red shift of the emission spectra is observed comparing to the most of the former research, which is due to the Ni²⁺ ions embedded into the low crystal field. The broadband of NIR emission in the NaSbO₃: Ni²⁺ ceramics do not only cover the whole second biological NIR region, but also present a new novel structure to approach the broadband emission spectra for TMI ions.     

Energy transfer realizes efficient NIR emitting Ca2ScTaO6:Cr3+, Yb3+ perovskite-structured phosphors

Stable and efficient broadband near-infrared (NIR) emitting phosphors are vital for the next-generation NIR sources. However, it still remains challenging to construct such phosphors, particularly those with a NIR-II window. In this work, using the Cr³⁺-Yb³⁺ energy transfer (ET) strategy, the as-synthesized Ca₂ScTaO₆:Cr³⁺, Yb³⁺ phosphor retains 86.2% of the initial luminescence intensity of Yb³⁺ at 373 K with characteristic emissions of both activators ranging from 700 nm to 1200 nm. The occupation of Cr³⁺ into both Ta⁵⁺ and Sc³⁺ sites is confirmed by X-ray diffraction, time-resolved emission spectrum, and crystal structure. The efficient ET from Cr³⁺ to Yb³⁺ is revealed by the diffuse reflection spectrum, steady-state and transient fluorescence. As a result, it contributes to the excellent performance of the phosphor. Based on the optimized phosphor, a NIR light-emitting diode is fabricated and demonstrated its advantage in imaging and potential application in information encryption. The result highlights ET as a robust strategy to construct efficient NIR phosphor.     

Deep-red-emitting SrLaLiTeO6: Mn4+ double perovskites: Correlation between Mn4+-O2− bonding and photoluminescence

Mn⁴⁺-activated deep red-emitting SrLaLiTeO₆ phosphors are investigated for indoor plant growth LED applications for the first time. The phosphors crystallize in monoclinic (P2₁/n) symmetry is isostructural with SrLaLiTeO₆ host. B-site substitution of Mn⁴⁺ ions is confirmed from the redshift of high energy phonon modes in both Raman and IR spectra. The phosphor exhibited a far-red emission centered at 696 nm corresponding to the ²E_g → ⁴A_2g spin-forbidden transition of the Mn⁴⁺ ions. Approximate crystal field parameters depict the weak influence of neighboring ligand fields on Mn⁴⁺ ions and the least covalence of Mn⁴⁺-ligand bonding compared to other double perovskite phosphors. Moreover, the phosphors exhibit excellent thermal stability with an activation energy of 0.23 eV. Phosphor parameters including CCT, color purity, and quantum yield are evaluated and their values meet the requirements of a red-emitting phosphor for LED applications. Furthermore, the PL emission spectrum of SrLaLiTeO₆: Mn⁴⁺ matches with the absorption spectrum of plant phytochromes denoting the prospects of this phosphor for indoor plant growth LED applications.     

The hydrothermally synthesis of K3AlF6:Cr3+ NIR phosphor and its performance optimization based on phase control

Phosphor-convert (pc) near-infrared (NIR) LED is the next-generation smart NIR light sources. Thus, NIR phosphors are quickly developed. The K₃Al_1−xF₆:xCr³⁺ (KAF:Cr³⁺) NIR phosphor shows broadband emission from 650 to 900 nm under 430 nm and can be used to fabricate NIR LEDs. In this work, KAF:Cr³⁺ phosphors were prepared by a hydrothermal method for the first time. Morphologies and NIR properties are tuned by controlling the hydrothermal processes. Different from the cubic KAF:Cr³⁺ synthesized by a coprecipitation method, KAF:Cr³⁺ synthesized by the hydrothermal method shows the tetragonal phase. The optimized KAF:3%Cr³⁺ shows an internal quantum efficiency of about 31.4%. A NIR pc-LED device was fabricated by integrating the KAF:3%Cr³⁺ phosphor with a blue LED chip (~450 nm). The output power of NIR light is about 5.5 mW driven at 150 mA.     

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.     

Efficient near-infrared pyroxene phosphor LiInGe2O6:Cr3+ for NIR spectroscopy application

Broadband near-infrared phosphors are essential to realize nondestructive analysis in food industry and biomedical areas. Efficient long-wavelength (>830 nm) phosphors are strongly desired for practical applications. Herein, we demonstrate an efficient broadband NIR phosphor LiInGe₂O₆:Cr³⁺, which exhibits a broad NIR emission peaking at ~880 nm with a full width at half maximum of 172 nm upon 460 nm excitation. The internal/external quantum efficiencies of LiInGe₂O₆:Cr³⁺ are measured to be 81.2% and 39.8%, respectively. The absorption of the phosphor matches well with commercial blue LEDs. Using the fabricated phosphor converted LED illuminating human palm, distribution of blood vessels can be clearly recognized under a NIR camera. These results indicate that LiInGe₂O₆:Cr³⁺ is a promising candidate to be used in future non-destructive biological applications.     

A novel extra-broadband visible-NIR phosphor doped with Ce3+ and Cr3+ towards multifunctional advanced applications

Phosphors that can emit broadband light from visible to near infrared (NIR) may have applications in the fields like white-light illumination and NIR vessel visualization, the investigation on single phase extra-broadband visible-NIR emitting phosphor is of great significance. Herein, an extra-broadband phosphor with tunable visible-NIR emission from 500 nm to longer than 900 nm (bandwidth >400 nm) was successfully prepared, which originates from the emission of Ce³⁺ (peaking at 573 nm), Cr³⁺ (peaking at 750 nm) and energy transfer from Ce³⁺ to Cr³⁺ in Y₃MgAl₃SiO₁₂ garnet. The influences of Ce³⁺/Cr³⁺ doping concentration and working temperature were discussed systematically by luminescence spectra and decay curves. A visible-NIR full-spectrum phosphor-converted light emitting diode (pc-LED) fabricated with a 460 nm LED chip and Y₃MgAl₃SiO₁₂:0.03Ce³⁺, 0.01Cr³⁺ can generate bright white light and broadband NIR light simultaneously. The co-doping of Ce³⁺ can perfectly compensate for the missing spectrum of Cr³⁺ in the visible region, thanks to the extra-broadband emission of Ce³⁺ in visible region and Cr³⁺ in NIR region, multifunctional advanced applications may be realized for the prepared phosphors.     

Dopant and compositional modulation triggered long-wavelength ultra-broadband and tunable NIR emission in MgO: Cr3+ phosphor for NIR spectroscopy applications

Efficient ultra-broadband near-infrared (NIR) phosphors with long-wavelength (λ_max > 850 nm) and wide full width at half-maximum (FWHM, >200 nm) have sparked tremendous interest, demonstrating their immense potential in NIR spectroscopy technology. Nevertheless, the development of NIR spectroscopy technology suffers from the restricted capability to efficiently emit the ultra-broadband NIR light. Herein, the synergetic enhancement strategy of heterogeneous substitution and compositional modulation was applied to create a novel Cr³⁺ doped long-wavelength ultra-broadband MgO: Cr³⁺, Ga³⁺ phosphor, which exhibited a long-wavelength ultra-broadband NIR emission (λ_max = 850 nm) covering the range of 650–1300 nm on the electromagnetic spectrum with the FWHM of more than 200 nm under the excitation of 468 nm light. Furthermore, the tunable NIR emission from 818 nm to 862 nm with an optimized quantum efficiency of 30% was accomplished by the Ga³⁺ ions substitution and Cr³⁺ ions modulation. The phosphor exhibited remarkable thermal stability up to 100 °C, remaining 83% of the integrated emission intensity at room temperature. A prototype of the NIR phosphor-converted LED (pc-LED) demonstrated that the novel MgO: Cr³⁺, Ga³⁺ phosphor possessed a relatively strong NIR output power (15.05 mW at 100 mA driven current) with a photoelectric conversion efficiency of 5.53%, which is impressive compared with other Cr³⁺-doped long-wavelength ultra-broadband phosphors. This work not only proposes a novel long-wavelength ultra-broadband NIR phosphors with industrialization and great application prospect in night vision but highlights a synergetic enhancement strategy to effectively boost the performance of long-wavelength ultra-broadband NIR pc-LED light sources.     

Synthesis and Photoluminescence of a New Chlorogermanate Phosphor Ca8Mg(GeO4)4Cl2:Eu2+

A new chlorogermanate compound Ca₈Mg(GeO₄)₄Cl₂ (CMGC) was synthesized via high‐temperature solid‐state reaction for the first time. The crystal structure of CMGC had been refined and determined from the XRD profiles by Rietveld refinement method, which belong to space group Fd‐3m with the lattice constants a = b = c = 15.1760(25) Å. Photoluminescence properties of CMGC:Eu²⁺ phosphors were investigated by absorption spectra, excitation, and emission spectra. The occupy situation and energy transfer were investigated by decay lifetimes and emission spectra under different excitation wavelengths. Thermal stability was also measured. The results show that the absorption spectra of CMGC:Eu²⁺ phosphors cover from 250 to 500 nm. Under 365 and 435 nm excitation, the emission spectra of CMGC:Eu²⁺ phosphors show blue‐green (centered at 425 and 510 nm) and green (centered at 510 nm) emission, respectively, which attributed to Eu²⁺ ions occupying different crystal sites. Our results indicated that CMGC:Eu²⁺ phosphors had a potential application use for white light‐emitting diodes.     

A far-red-emitting (Gd,Y)3(Ga,Al)5O12:Mn2+ ceramic phosphor with enhanced thermal stability for plant cultivation

As for plants, far-red (FR) light with wavelength from 700 nm to 740 nm is critical for processes of photosynthesis and photomorphogenesis. Light-controlled development depends on light to control cell differentiation, structural and functional changes, and finally converge into the formation of tissues and organs. Phosphor converted FR emission under LED excitation is a cost-effective and high-efficient way to provide artificial FR light source. With the aim to develop an efficient FR phosphor that can promote the plant growth, a series of gadolinium yttrium gallium garnet (GYGAG) transparent ceramic phosphors co-doped with Mn²⁺ and Si⁴⁺ have been fabricated via chemical co-precipitation method, followed sintered in O₂ and hot isostatic pressing in this work. Under UV excitation, the phosphor exhibited two bright and broadband red emission spectra due to Mn²⁺: ⁴T₁ → ⁶A₁ spin-forbidden transition, and one of which located in the right FR region. And then, Ce³⁺ ions were co-doped as the activator to enhance the absorption at blue light region and the emission of Mn²⁺. It turns out that the emission band of GYGAG transparent ceramic phosphors matches well with the absorption band of phytochrome P_FR, which means they are promising to be applied in plant cultivation light-emitting diodes (LEDs) for modulating plant growth. Besides, the thermal stability of this material was investigated systematically, and an energy transferring model involves defects was also proposed to explain the phenomenon of abnormal temperature quenching.     

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%.