Enhanced up-conversion luminescence and optical thermometry characteristics of Er3+/Yb3+ co-doped Sr10(PO4)6O transparent glass-ceramics

In this paper, the Yb³⁺/Er³⁺ co-doped parent glass (PG) with composition (in mol%) of 30P₂O₅-10B₂O₃-38SrO-22K₂O and transparent glass-ceramics (GCs) containing hexagonal Sr₁₀(PO₄)₆O nanocrystals (NCs) were synthesized for the first time by melt-quenching method and subsequent heating treatment in air. Under 980 nm laser prompting, the GCs samples showed intense red and green up-conversion emissions compared to those characteristics for the PG sample. The emission intensities varied with Er³⁺ concentration and heat treatment conditions. Furthermore, in Yb³⁺/Er³⁺ co-doped GCs specimens, the optical thermometry was researched by means of fluorescence intensity ratio (FIR) of ⁴S_3/2 and ²H_11/2 levels. The GC sample heated at 620°C for 5 hours possessed a high relative temperature sensitivity (S_r) of 0.769% K⁻¹ at 303 K and the maximal absolute temperature sensitivity (S_a) of 5.951 × 10⁻³ K⁻¹ at 663 K, respectively. It is expected that the as-fabricated GC materials with Sr₁₀(PO₄)₆O NCs are promising efficient up-conversion materials for optical temperature sensor.     

The effect of Li+ incorporation in Yb3+-Nd3+ co-doped CaF2 phosphors over the NIR photoluminescence emission excited under visible light

The structural and optical characteristics of Nd³⁺-Yb³⁺ doped CaF₂ phosphors with and without the addition of Li⁺ ions are described in this work. The phosphors synthetized by hydrothermal and co-precipitation methods showed near-infrared (NIR) luminescence emission associated with inter-electronic transition of the Yb³⁺ ion in the range of 900–1050 nm via energy transfer process from Nd³⁺ ions under visible light excitation. The addition of Li⁺ to these phosphors resulted in an improvement of the NIR luminescence intensity by a factor up to 5. The effect of the incorporation of Li⁺ ions into the CaF₂ crystallite structure, the reduction of luminescence quenching states, as well as the energy transfer mechanism involved are discussed.     

Site occupancy and enhanced luminescence of broadband NIR gallogermanate phosphors by energy transfer

Super broadband near-infrared (NIR) La₃Ga₅GeO₁₄(LGGO): Cr³⁺ phosphor is in urgent needs for food testing. Unfortunately, it suffers from poor luminescence intensity in applications. Herein, the enhanced NIR luminescence performance can be realized in LGGO: Pr³⁺, Cr³⁺. The preferential crystallographic site of Cr³⁺ is validated on the basis of EPR spectrum, Rietveld refinement, and the first-principles DFT calculations. It is of great importance that the as-prepared phosphors can be excited by blue light (460 nm), which is beneficial to the application of blue-pumped LEDs. The critical distance of Pr³⁺ in LGGO host has been calculated by concentration-quenching method. For co-doped sample, it is observed that Cr³⁺ luminescence intensity enhancement by a factor of 3 can be achieved by doping Pr³⁺ owing to the energy transfer from Pr³⁺ to Cr³⁺. In addition, the introduction of Pr³⁺ can also improve the Cr³⁺ luminescence intensity at elevated temperature. Furthermore, using the optimized phosphor, a blue-based NIR phosphor-converted LEDs (NIR pc- LEDs) is fabricated, the forward voltage and the intensity of LED hardly change after thermal aging for 500 hours under high temperature/ high humidity condition, indicating its great reliability for NIR pc-LEDs. Therefore, LGGO:Pr³⁺, Cr³⁺ has great potential to serve as an attractive candidate in the application of blue light-excited NIR pc-LEDs in view of its capability for blue to enhanced broadband NIR conversion.     

Energy transfer and color-tunable emission in Ba2Y2Si4O13:Bi3+,Eu3+ phosphors

Single-composition Ba₂Y₂Si₄O₁₃:Bi³⁺,Eu³⁺ (BYSO:Bi³⁺,Eu³⁺) phosphors with color-tunable and white emission were prepared by conventional high temperature solid-state reaction method. The structural and luminescent properties of these phosphors were thoroughly investigated through X-ray diffraction, photoluminescence, and decay curves. BYSO:Bi³⁺ phosphors show two excitation peaks at 342 and 373 nm, and give two emission peaks at 414 and 503 nm, respectively, indicating that there are two sites of Bi³⁺ in BYSO. The energy transfer from Bi³⁺ to Eu³⁺ was investigated in detail. Varied hues from blue (chromaticity coordinate [0.219, 0.350]) to white (0.288, 0.350) and orange-red light (0.644, 0.341) can be generated by adjusting the content of Eu³⁺. Pure white light emission (0.311, 0.338) can be obtained under the excitation of 355 nm in BYSO:3%Bi³⁺,20%Eu³⁺ phosphor. Besides, BYSO:Bi³⁺,Eu³⁺ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 473 K is 82.6% of that at 298 K. Our results indicate that BYSO:Bi³⁺,Eu³⁺ may be applied as conversion phosphors for n-UV-based W-LEDs.     

Ce3+/Tb3+-coactived NaMgBO3 phosphors toward versatile applications in white LED,FED, and optical anti-counterfeiting

Ce³⁺/Tb³⁺ co-doped NaMgBO₃ phosphors were successfully synthesized by solid-state method. Under 381 nm excitation, the cyan emission owing to the 5d → 4f of Ce³⁺ ions and green emissions arising from the ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions of Tb³⁺ ions were seen in all the phosphors. Through theoretical analysis, one knows that the energy transfer from Ce³⁺ to Tb³⁺ ions with high efficiency of 83.74% was contributed by dipole–dipole transition. Furthermore, the internal quantum efficiency of NaMgBO₃:0.01Ce³⁺,0.03Tb³⁺ phosphor was 54.28%. Compared with that of at 303 K, the emission intensity of the developed products at 423 K still kept 73%, revealing the splendid thermal stability of the studied phosphors. Through utilizing the resultant phosphors as cyan-green components, the fabricated white-LED device exhibited an excellent correlated color temperature of 2785 K, high color-rendering index of 85.73, suitable luminance efficiency of 25.00 lm/W, and appropriate color coordinate of (0.4279, 0.3617). Aside from the superior photoluminescence, the synthesized phosphors also exhibited excellent cathode-luminescence properties which were sensitive to the current and accelerating voltage. Furthermore, the NaMgBO₃:0.01Ce³⁺,0.03Tb³⁺ phosphors with multi-mode emissions were promising candidates for optical anti-counterfeiting. All the results indicated that the Ce³⁺/Tb³⁺ co-doped NaMgBO₃ phosphors were potential multi-platforms toward white-LED, field emission displays, and optical anti-counterfeiting applications.     

Sr3Lu (VO4)3: Eu3+ red-emitting phosphors for warm white LEDs

A series of novel red emission phosphors Sr₃Lu_1-x(VO₄)₃:xEu³⁺(x = 0.007, 0.009, 0.02, 0.04, 0.06) were synthesized successfully by traditional high-temperature solid-state reaction. The results of X-ray diffraction (XRD) reveal the doped Eu³⁺ ions have replaced the lattice sites of Lu³⁺ ions. The diffuse reflectance spectra illustrate the energy gap of Sr₃Lu(VO₄)₃ host is 3.61 eV. The room-temperature steady-state fluorescence spectra show that these phosphors can be effectively pumped by the charge-transfer band (CTB) of the host in near ultraviolet (NUV) spectral region and then produce strong and pure red emission at 615 nm originated from ⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺. The Commission Internationale de L’Eclairage (CIE) coordinates of Sr₃Lu_0.96(VO₄)₃:0.04Eu³⁺ are (x = 0.65, y = 0.35), which are very close to the red standard of National Television Standards Committee NTSC (0.67, 0.33). The fabricated warm white-light-emitting diodes (LED) demonstrate high color-rendering index Ra as 93. The results imply the red-emitting Sr₃Lu(VO₄)₃:Eu³⁺ phosphors could be potentially utilized in the fields of solid-state lighting.     

Tuning the luminescence properties of blue and far-red dual emitting Gd2MgTiO6: Bi3+, Cr3+ phosphor for LED plant lamp

Blue and far-red light play a key role in plant growth, so it is necessary to develop blue and far-red dual emitting phosphors. However, the match between phosphors and plant pigments is not satisfactory. In this work, we synthesized a series of blue and far-red dual emission Gd₂MgTiO₆: Bi³⁺, Cr³⁺ (GMTO: Bi³⁺, Cr³⁺) phosphors and discussed the luminescence performance. The blue emission at 430 nm is ascribed to ³P₁ → ¹S₀ transition of Bi³⁺ and the far-red emission is ascribed to ⁴T₂ → ⁴A₂ and ²E → ⁴A₂ transitions of Cr³⁺. Notably, because of the energy competition between Cr³⁺ ions and host materials, the luminescence tuning realized with the content of Cr³⁺ doping. In addition, an energy-transfer performance occurred from Bi³⁺ ions to Cr³⁺ ions and the photoluminescence intensity of Cr³⁺ can be enhanced by Bi³⁺. The pc-LEDs devices were synthesized by GMTO: Bi³⁺, Cr³⁺ phosphor, and ultraviolet (UV) chips. Finally, the emission of GMTO: Bi³⁺, Cr³⁺ phosphor matched well with the absorption spectra of plant pigments which indicated the potential applications in LED plant lamp.     

Trap distribution and photo-stimulated luminescence in LaSrAl3O7:Eu2+ long-lasting phosphors for optical data storage

Here, a green emission persistent luminescent phosphor LaSrAl₃O₇:Eu²⁺ which is chargeable by UV light, was synthesized by solid-state reaction method. Elemental mapping and fluorescence microscopy photoluminescence of the sample demonstrated the homogeneous distribution of La, Sr, Al, O, and Eu in the phosphor. Rietveld refinement shows that the as-prepared sample belongs to the tetragonal crystalline structure with space group of P42₁m. The Eu²⁺:5d-4f broad persistent luminescence with maximum emission peaking at 518 nm can be effectively obtained after irradiating in the UV light. A series of excitation temperature-dependent thermoluminescence measurements were conducted to gain some insight into the information of traps. Additionally, to verify its feasibility of optical data storage, specific information letters were encoded on the LaSrAl₃O₇:Eu²⁺ phosphor films using the laser of 405 nm, then the stored information could indeed be read out by thermal stimulation as expected. Meanwhile, NIR photo-stimulated red persistent luminescence was also obtained, which holds great potential for optical information storage. Finally, combined with the experimental and density functional theory calculation results, we proposed a tentative schematic diagram to account for the PersL and photo-stimulated persistent luminescence mechanism in LaSrAl₃O₇:Eu²⁺ phosphor.     

White light emission from novel host-sensitized single-phase Y2WO6: Ln3+ (Ln3+=Eu3+, Dy3+) phosphors

A series of Eu³⁺- or Dy³⁺-doped and Eu³⁺/Dy³⁺ co-doped Y₂WO₆ in pure phase was synthesized via high-temperature solid-state reaction. X-ray diffraction, diffuse reflection spectra, photoluminescence excitation and emission spectra, the CIE chromaticity coordinates and temperature-dependent emission spectra were exploited to investigate the phosphors. Upon UV excitation at 310 nm, efficient energy transfer from the host Y₂WO₆ to dopant ions in Eu³⁺ or Dy³⁺ single-doped samples was demonstrated and those phosphors were suitable for the UV LED excitation. The intense red emission was observed in Y₂WO₆: Eu³⁺, and blue and yellow ones were observed in Y₂WO₆: Dy³⁺. Concentration quenching in Y₂WO₆: Dy³⁺ phosphors could be attributed to the electric dipole-dipole interaction. In Eu³⁺/Dy³⁺ co-doped Y₂WO₆ phosphors energy transfer process only took place from the host to Eu³⁺/Dy³⁺ ions and warm white-light emission can be obtained by adjusting the dopant concentrations. The temperature-dependent luminescence indicated Eu³⁺/Dy³⁺ co-doped Y₂WO₆ was thermally stable. Our overall results suggested that Y₂WO₆: Ln³⁺ (Ln³⁺=Eu³⁺, Dy³⁺) as warm white-light emitting host-sensitized phosphor might be potentially applied in WLEDs.     

A novel far-red phosphors Li2ZnTi3O8:Cr3+ for indoor plant cultivation:Synthesis and luminescence properties

A novel far-red phosphors Li₂ZnTi₃O₈:Cr³⁺ were successfully synthesized via the conventional solid-state method. The structural characteristics, luminescence properties and concentration quenching of the Li₂ZnTi₃O₈:Cr³⁺ phosphors were investigated systematically. Under the excitation at 360 nm and 468 nm, the Li₂ZnTi₃O₈:Cr³⁺ phosphors displays the emission spectra in the range from 600 nm to 850 nm. The far-red emission centered at 735 nm was attributed to the spin-forbidden ²E→⁴A₂ transition of Cr³⁺ ions. The research results of this paper indicate that the phosphors Li₂ZnTi₃O₈:Cr³⁺ has prospective applications in indoor plant cultivation.     

Warm white light emitting from single composition SrGa12O19:Dy3+ phosphors for AC-LED

Making illumination light sources become comfortable to the human eye is a long-term effort, which justifies the current research on warm white-light-emitting diodes (w-LEDs). In this work, a novel phosphor for w-LEDs, namely SrGa₁₂O₁₉: Dy³⁺(SGO: Dy³⁺), with a low-color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy³⁺ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off-time of a few seconds, which indicates that the SGO: Dy³⁺ phosphor has anti-flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC-LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy³⁺ phosphors with different Dy³⁺ concentrations are close with an optimal doping at 4.00 mol% Dy³⁺ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy³⁺ is a suitable candidate for illumination sources that are beneficial to human health.     

Phase evolution,structure, and up-/down-conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho,Er, Tm)

Garnet-type Li₆Ca(La_0.97Yb_0.02RE_0.01)₂Nb₂O₁₂ (RE = Ho, Er, Tm) new phosphors were successfully synthesized via solid reaction at 900°C for 5 hours, whose course of phase evolution, macroscopic/local crystal structure and up-/down-conversion (UC/DC) photoluminescence were clarified. Mechanistic study and materials characterization were attained via XRD, Rietveld refinement, DTA/TG, electron microscopy (FE-SEM/TEM), and Raman/reflectance/fluorescence spectroscopies. The phosphors were shown to exhibit UC luminescence dominated by a ~ 553 nm green band (⁵F₄/⁵S₂ → ⁵I₈ transition) for Ho³⁺, a ~ 568 nm green band (⁴S_3/2 → ⁴I_15/2 transition) for Er³⁺ and a ~ 806 nm near-infrared band (³H₄ → ³H₆ transition) for Tm³⁺ under 978 nm laser excitation, with CIE chromaticity coordinates of around (0.31, 0.68), (0.38, 0.60) and (0.17, 0.24), respectively. Analysis of the pump-power dependence of UC intensity indicated that all the emissions involve a two-photon mechanism except for the ~ 486 nm blue emission of Tm³⁺ (¹G₄ → ³H₆), which requires a three-photon process. The DC luminescence of these phosphors is featured by dominant bands at ~ 553 nm for Ho³⁺ (green, ⁵F₄/⁵S₂ → ⁵I₈ transition), ~568 nm for Er³⁺ (green, ⁴S_3/2 → ⁴I_15/2 transition) and ~ 464 nm for Tm³⁺ (blue, ¹D₂ → ³F₄ transition). The UC and DC properties were also comparatively discussed.     

NUV light induced visible emission in Er3+-activated NaSrLa(MoO4)O3 phosphors for green LEDs and thermometer

Er³⁺-activated NaSrLa(MoO₄)O₃ phosphors were synthesized by a traditional solid-state reaction technique, which exhibited bright green emissions ascribing to the (²H_11/2, ⁴S_3/2) → ⁴I_15/2 transitions of Er³⁺ ions under 377 nm excitation. The luminescence intensity increased with increasing the Er³⁺ ion concentration and achieved its maximum value when the doping concentration was 4 mol%. Moreover, the critical distance was estimated to be 25.32 Å, and the dipole-dipole interaction played a significant role in NR energy transfer between Er³⁺ ions in NaSrLa(MoO₄)O₃ host lattices. At a forward bias current of 100 mA, the Light Emitting Diode (LED) device emitted a bright green emission with the color coordinate of (0.2547, 0.5996) that can be observed by the naked eye. Besides, based on the thermally coupled levels of ²H_11/2 and ⁴S_3/2, the temperature sensing performances of the prepared phosphors in the temperature range of 303-483 K were studied using the fluorescence intensity ratio technique. The maximum sensor sensitivity was about 0.0150 K⁻¹ when the temperature was 483 K, and the Er³⁺ ion concentration largely influenced the sensor sensitivity of studied samples. Furthermore, the prepared phosphors exhibited excellent water resistance and thermal stability behavior. These characteristics demonstrated that the Er³⁺ activated NaSrLa(MoO₄)O₃ phosphors were dual-functional materials for solid-state illumination and non-contact temperature measurement.     

Preparation and luminescence of SrAl2O4: Eu2+,Dy3+ phosphors coated with maleic anhydride

In this paper, maleic anhydride is directly coated on the surface of SrAl₂O₄: Eu²⁺, Dy³⁺ (SAO‐ED) phosphors by an interfacial coordination chemistry method. Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectra (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) methods are used to characterize the coating. The experimental result shows that a dense coating layer is consisting of maleic anhydride coordination with metal ions on the surface of the phosphors and the coating process does not destroy the crystal structure of the phosphors. It is also found that the introduction of maleic anhydride does not change the excitation and emission spectra of SAO‐ED phosphors, but decreases the luminous intensity, which is verified by the photoluminescence (PL) measurement. Afterglow delay curves show that the initial brightness of coated SAO‐ED phosphors decreases, but the afterglow decay rate of coated phosphors is slower than that of uncoated phosphors after they both are immersed into water for one month. This indicates that the coating layer protects the phosphors and the crystal structure of coated phosphors in water was not destroyed.     

Optical transition and luminescence properties of Sm3+-doped YNbO4 powder phosphors

A series of YNbO₄: Sm³⁺ powder phosphors with different doping concentrations were synthesized by a traditional high-temperature solid-state reaction method. The crystal structure of the obtained samples was characterized by means of X-ray diffraction. Concentration quenching, energy-transfer mechanism, and luminescence thermal stability of YNbO₄: Sm³⁺ samples were studied through the fluorescence spectra and decays. It was concluded that electric dipole-dipole interaction was the dominant energy-transfer mechanism between Sm³⁺ ions according to both Van Uitert's model and Dexter's model. Using the Arrhenius model, crossover process was proven to be responsible for the luminescence thermal quenching of Sm³⁺. Moreover, a novel approach for evaluating the optical transition properties of Sm³⁺ ion in YNbO₄ powders using the diffuse-diffraction spectrum and fluorescence decay was examined in the framework of Judd-Ofelt (J-O) theory. It was confirmed that the J-O parameters Ω_λ (λ = 2, 4, 6) of Sm³⁺ in YNbO₄ powder were reliable by comparing the radiation transition rate with the measured emission results.     

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

A series of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ samples match well with the standard Ca₅(PO₄)₃F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca₅(PO₄)₃F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions respectively. Eu³⁺ co‐doped Ca₅(PO₄)₃F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor.     

Enhanced red emission and improved thermal quenching of CaAlSiN3:Eu2+ phosphors via boron doping

The development of high-performance phosphors is required for phosphor-converted white light-emitting diodes. However, most approaches are unable to achieve optimum emission intensity and thermal quenching simultaneously. Here, a series of CaAlSiN₃:Eu²⁺ (CASN:Eu²⁺) red-emitting phosphors doped with B were synthesized using field-assisted sintering technology. Compared with CASN:Eu²⁺, the B-doped phosphor exhibited high external quantum efficiency (EQE) and good thermal quenching performance. With boron doping, the EQE of CaAlSiN₃:Eu²⁺ shows an obvious growth, increasing from 48.83% to 70.68%. Meanwhile, thermal quenching performance has also been greatly improved, which is strongly associated with the band structure of Eu²⁺ and the crystal structure of CASN. The location of B in the crystal lattice was studied and the mechanism of improving thermal quenching via B doping was discussed in detail. Finally, a white LED fabricated by the combination of a GaN blue chip (450 nm) with the as-synthesized red phosphors and Y₃(Al, Ga)₅O₁₂:Ce³⁺ green phosphors (531 nm), shows a high color rendering index (Ra =91.6). This study offers a novel method to improve luminescence properties of CASN:Eu²⁺ red-emitting phosphors, which may broaden their application in solid-state lighting devices.     

High-accuracy dual-mode optical thermometry based on up-conversion luminescence in Er3+/Ho3+-Yb3+ doped LaNbO4 phosphors

Due to the non-contact and high sensitivity, optical thermometry based on rare earth doped phosphors has been paid much attention to. Herein, dual-mode optical thermometers are designed using up-conversion luminescence of Er³⁺/Ho³⁺-Yb³⁺ doped LaNbO₄ phosphors, which were synthesized for the first time by high-temperature solid-state reaction method. The LaNbO₄:1Er³⁺:10Yb³⁺ and LaNbO₄:1Ho³⁺:10Yb³⁺ phosphors exhibit reliable and excellent thermometric performance by combining fluorescence intensity ratio and decay lifetime for self-calibration. Specifically, the maximal relative sensitivities based on fluorescence lifetime were 0.27 %K⁻¹ and 0.33 %K⁻¹ for LaNbO₄:1Er³⁺:10Yb³⁺ and LaNbO₄:1Ho³⁺:10Yb³⁺ phosphors, respectively. The maximal relative sensitivity is 1.12 %K⁻¹ when using intensity ratio between thermal coupling energy levels in LaNbO₄:1Er³⁺:10Yb³⁺ as a detecting signal. Furthermore, the maximal relative sensitivity reaches as high as 0.98 %K⁻¹ when taking advantage of special non-thermal coupling energy levels in LaNbO₄:1Ho³⁺:10Yb³⁺. These results indicate that Er³⁺/Ho³⁺-Yb³⁺ doped LaNbO₄ phosphors possess great potential in self-calibrated optical thermometric techniques.     

Crystal structure and luminescence mechanism of novel Fe3+-doped Mg0.752Al2.165O4 deep red-emitting phosphors

Nonstoichiometric alumina-rich spinel provides diverse and changeable local environments for transition-metal dopants. In this contribution, novel Mg_0.752Al_2.165−xO₄:xFe³⁺ deep red-emitting phosphors were designed and prepared by the solid-state reaction method. The red emission presents an unexpected shift from 735 to 770 nm by comparing with Fe³⁺-doped MgAl₂O₄. The excitation spectrum of Mg_0.752Al_2.165−xO₄:xFe³⁺ is broadened in the UV region with a new strong peak at 320 nm. The crystal structure refinement and NMR spectra fitting reveal that the cation vacancies and disorder increase with excess Al³⁺ entering the spinel crystal lattice. According to the results of EPR, NMR, and PL/PLE measurements, it was proposed that the Fe³⁺ ions locate at the distorted octahedral coordination. The changes of the local structure of Fe³⁺ ions promote the doublet state's involvement in the d−d transition. It was proposed that the new excitation peak at 320 nm in Mg_0.752Al_2.165−xO₄:xFe³⁺ is associated with the transitions from the ground state ⁶A_1g(⁶S) to the ⁴A_2g(⁴F)/T_1g(⁴P) and doublet states. The transition between the lower energy excited state of ²T_2g(²I) and ⁶A_1g(⁶S) mainly contributes to the deep red emission and the red-shifting effect.