Luminescence Characteristics Research Articles

Research on multicolor luminescence, structural and energy transfer in Dy/Eu co-doped fluoroborate glasses for W-LEDs

The composition of 50B2O3-20Al2O3-5Na2O-10Bi2O3-15CaF2-xDy-yEu (x = 0.1，0.5，1.0，1.5，2.0，3.0 mol%; y = 0, 0.1, 0.3, 0.5, 0.7, 1.0 mol%) (BACDE) glass were prepared using the traditional melt quenching process. The structure of the BACDE glass was analyzed using XRD analysis and Fourier infrared spectroscopy. The photoluminescence spectra show that concentration quenching occurs when Dy concentration is higher than 1.0mol% in fluoroborate glass. By varying the excitation circumstances and obtaining emission spectra at three distinct excitation wavelengths (364, 382, and 395 nm), the luminescence characteristics of BACDE glass were examined. The results indicate that when excited at 364 nm, the luminescence of the BACDE glass is close to the white region, a controlled color shift is achieved within a certain range. The spectral superposition and fluorescence attenuation spectra of Dy3+ emission and Eu3+ absorption demonstrate the energy transfer from Dy3+ to Eu3+, and the main transfer mechanism is the electric dipole-electric dipole interaction. The most optimal chromaticity coordinates for the BACDE glass samples were (0.3832,0.3858), (0.3672,0.3949), with a color temperature (CCT) of approximately 3992K at 364 nm excitation. By controlling the Dy/Eu content, BACDE glass can exhibit warm white, and light reddish-orange glow. Thus, Eu3+/Dy3+ co-doped BACDE glasses have potential applications in white luminescent materials and dimmable materials.

Impact of Pre-Silica-Coating on the Luminescence Properties of Silica-Coated Indium Phosphide Nanoparticles

This study examined the impact of silica-coating on the luminescence characteristics of indium phosphide (InP) nanoparticles. Silica-coated InP nanoparticles were prepared using three different techniques. The first method utilized tetraethoxysilane (TEOS) as the silica source, resulting in the encapsulation of multiple InP nanoparticles within silica spheres. This approach caused a red-shift in the luminescence peak wavelength of the InP colloidal solution post-TEOS coating, compared to the original InP colloidal solution. Conversely, the second method employed tetramethoxysilane (TMOS), resulting in the formation of irregularly shaped silica-coatings on multiple InP nanoparticles, which reduced the red-shift in the luminescence peak wavelength of the silica-coated InP colloidal solution. The third method involved pre-coating InP nanoparticles with TMOS, followed by thickening the silica shells using TEOS. This technique successfully encapsulated multiple InP nanoparticles within silica spheres, maintaining the luminescence peak wavelength of the InP colloid solution post-coating with TMOS and TEOS nearly identical to that of the original solution. This method merged the advantageous outcomes of the first two methods. Additionally, silica spheres containing InP nanoparticles synthesized using both TMOS and TEOS exhibited the highest luminescence intensity. In summary, this study introduces a novel approach in nanoparticle engineering, enhancing the functional properties of InP nanoparticles and expanding their potential applications in optoelectronic devices.

Optically stimulated luminescence properties of chicken eggshell derived hydroxyapatite for dosimetry applications

AbstractThis study investigated the optically stimulated luminescence (OSL) characteristics of hydroxyapatite (HAp) derived from chicken eggshells, a readily available bio-waste, for low-level radiation dosimetry applications which is less explored. The eggshells were employed as a calcium source in HAp synthesis. The X-ray diffraction and Fourier transform infrared spectroscopy results confirmed its purity and crystallinity. The OSL properties of the synthesized HAp demonstrated excellent reproducibility, reusability, and dose linearity up to 20 Gy, with a measurable dose range of 22 mGy. The favorable OSL characteristics, combined with the utilization of waste materials, offer significant advantages for environmental and medical radiation monitoring.

Heterostructure of Hydrogen‐Bonded Organic Frameworks for White Light Emission and Information Encryption

AbstractTwo dumbbell‐shaped building blocks (TMB and TMBT), featuring methyl benzoate groups as hydrogen bond units, are selected to construct heterostructures of HOFs, aiming to achieve multiple functions including white luminescence, stimulus‐response behavior, as well as application in information encryption. TMB molecules are self‐assembled to form a flexible HOF (X‐HOF‐8) in p‐xylene, containing solvent channels and blue fluorescence. Upon removal of guests, it can transform into a nonporous crystal with gray fluorescence. In contrast, TMBT forms a guest‐free HOF (X‐HOF‐9) displaying orange fluorescence. They could form bulk heterojunction (BHJ) HOFs with energy transfer from TMB to TMBT, exhibiting composition‐dependent fluorescent color. Notably, white emission can be achieved in BHJ HOFs and can be converted to gray fluorescence upon guest removal; subsequently, white fluorescence is restored upon re‐capturing guests. Furthermore, rod‐like triblock heterojunction (THJ) HOFs can also be constructed, which exhibit regulatory behavior in response to gaining or losing guests. The unique luminescent characteristics and stimulus responsiveness of these HOFs make them an excellent platform for applications in anticounterfeit. This represents the pioneering achievement of white light emission in a BHJ HOF, as well as the groundbreaking realization of a THJ HOF with remarkable exciting response characteristics.

Comparison of YAG:Nd3+-Yb3+ nanothermometers synthesized by Pechini and solvothermal methods

Luminescence intensity ratio-based nanothermometry is a widely studied thermal sensing technique in the literature. Regarding biological purposes, it is essential to have thermal probes that are efficient in this type of environment. Thermal bioprobes demand highly crystallized nanocrystals, commonly smaller than 100 nm, with luminescence emissions in the near-infrared range that are not significantly absorbed by biological tissues. Several nanomaterials that have been studied for nanothermometry do not meet the requirements for this type of applications. Accordingly, researches are needed to develop suitable and reliable nanothermometers for thermal sensing. Therefore, our goal was to investigate the impact of Nd3+-Yb3+ co-doping on the thermometric performance of YAG matrix, a promising crystal because it presents a host structure favoring the insertion of lanthanide ions, which provide its luminescent features. In order to achieve this purpose, we first synthesized YAG:Nd3+-Yb3+ nanocrystals through a generic route - called modified Pechini method - to screen their thermal properties. Our results show that YAG:Nd3+-Yb3+ nanocrystals have the potential to work in vivo environments. The nanothermometers investigated here are excited in the first biological window (BW-I) at 805 nm with luminescence emissions within the BW-II, at 1030.5 and 1064 nm. By co-doping the YAG matrix with different Nd3+-Yb3+ concentrations, we studied the energy transfer process between the dopant ions and their impact on thermometry efficiency. By the efficient coupling of the Nd3+-Yb3+ pair, we improved the Sr value by a factor of 3 of YAG compounds up to 0.6 %.K−1. We then synthesized YAG:Nd3+-Yb3+ nanocrystals using a second type of synthesis, by solvothermal means, in order to obtain individual nanocrystals, well dispersed in aqueous solutions, and to adapt their morphology and size for biological purposes. Therefore, we compared the structural and luminescence properties and thermometry efficiencies of YAG:Nd3+-Yb3+ nanocrystals obtained through two distinct processes and showed that the nanothermometry properties are not affected by the synthesis method.

Highly and Deep Red-Luminescent Bisphenylamine-Appended Benzocarcogendiazole Fluorophores.

Benzocarcogendiazole units have been frequently utilized for optoelectronics such as organic solar cells because of their robustness, rigidity, and band-gap tunability based on their strong electron-withdrawing properties. Focusing on the luminescent characteristics, these molecules have been utilized to demonstrate highly sensitive chromisms because of the potential of charge transfer. Here, we demonstrate deep red-emissions in bis(4-tert-butylphenyl)amine-appended benzocarcogendiazole-based donor-acceptor-donor (D-A-D) fluorophores, namely 1 and 2. Because benzocarcogendiazole and bis(4-tert-butylphenyl)amine serve as strong electron acceptor and donor, respectively, strong intramolecular charge transfer (ICT) enables long wavelength of photoluminescence (PL) even in the small molecular weight. Although photoluminescence (PL) in long wavelength tends to exhibit quite low absolute PL quantum efficiency (ΦPL), the values of solutions 1 and 2 are quite high (up to 50 %). According to X-ray crystallographic characterizations and DFT calculations, these high ΦPL values are attributable to the segregated π-planes of benzocarcogendiazole units, which is induced by the bulky substituents of bis(4-tert-butylphenyl)amines.

Photoluminescence optical and thermal quenching in heavily doped Gd3(Ga,Al)5O12:Ce, Mg single crystals: Dependence on the Ga3+, Ce3+, and Mg2+ concentration

Heavily doped single crystals of Gd3GaxAl5-xO12:Ce, Mg (x = 2.46–2.95) with different concentrations of Ce (0.016–0.188 at.%) and Mg (0–0.083 at.%) are investigated by the X-ray diffraction, photoluminescence, and thermoluminescence methods. Dependences of the luminescence characteristics, as well as crystal lattice parameters and distances between the Ce3+ and Mg2+ ions, on the Ga, Ce, and Mg concentration are studied. Mechanisms of the processes, resulting in the photoluminescence optical and thermal quenching and acceleration of decay kinetics, and the influence of the crystal composition on these processes are discussed. The role of close {Ce3+ - Mg2+Ga} pairs in these processes is considered. At T > 400 K, the luminescence thermal quenching is caused by the crossover process, while in the 200–350 K temperature range, by the electron transfer from the 5d1 excited state of Ce3+ to nearby defect levels (electron traps) located between the 5d1 level and the conduction band. The latter process results also in the appearance of thermally stimulated luminescence, and its efficiency depends on the Ga3+ content and concentration of intrinsic defects. The optimum concentrations of Ga3+ and Mg2+ ions in the investigated crystals are determined.

Self-reducing induced Eu2+/Eu3+ dual-emitting glasses for anti-counterfeiting and optical thermometry

Eu3+/Eu2+ co-doped glasses possess extensive application potential in diverse fields, including light-emitting diodes and sensors, due to their distinctive luminescent characteristics. To date, numerous strategies have been devised to facilitate the coexistence of Eu3+ and Eu2+ in materials. Among them, adjusting the composition of the glass matrix stands out as a straightforward and reproducible approach. Herein, a series of Eu2+/Eu3+ co-doped borosilicate aluminate glasses were successfully synthesized via a high-temperature melting method. By elevating the ratios of B2O3/MgO and Al2O3/BaO in the matrix, a remarkable self-reduction of Eu3+ in ambient air was achieved because of the structural weakness and lower optical basicity for the designed glass matrix. The reduction of Eu3+ is also related to the formation of EuZn• and VΖn′′ defects. Furthermore, by fine-tuning the melting duration and Eu content, we achieved comparable violet and red emission intensities for both Eu2+ and Eu3+ ions. Under UV irradiation with various wavelengths, anti-counterfeiting patterns fabricated from glass powder exhibited precise and pronounced color changes. Notably, the emission intensity ratio of Eu2+/Eu3+ exhibited a consistent decrease as temperature increased, enabling precise temperature determination with exceptional absolute sensitivity (1.22 % K−1) producibility, and discrimination. These findings hold significant implications for the design of Eu3+/Eu2+ co-doped inorganic multifunctional glasses.

Ultraviolet–near infrared luminescence characteristics of Nd:La2Be2O5 single crystals for near-infrared emitting scintillators

The fabrication of 0.1, 0.5, 1.0, and 5.0 % Nd:La2Be2O5 single crystals was carried out by the floating zone method, and photoluminescence (PL) and scintillation properties were measured. The PL spectra showed some emission lines which was derived from the 4f-4f transitions of Nd3+ ions. The scintillation spectra showed a broad emission band originating from some lattice defect and the emission lines due to the 4f–4f transitions of Nd3+ ions. The afterglow levels of Nd:La2Be2O5 were 192.3 (0.1 % Nd), 205.9 (0.5 % Nd), 228.2 (1.0 % Nd), and 315.4 (5.0 % Nd) ppm. The 1.0 % Nd:La2Be2O5 showed the highest intensity in the dose-rate response functions among the samples, and a lower detection limit was 0.003 Gy/h.

A pH-responsive fluorescent film with the smartphone-assistance for real-time and visual detection of food freshness

Monitoring food freshness is considerably important for food safety. In this study, a smart pH-responsive fluorescence hydroxypropyl methyl cellulose-κ-carrageenan-fluorescein isothiocyanate-NH2-CaAl2O4 (H-K-F-N) film was prepared. Taking synergetic advantage of the pH-dependent behavior of fluorescein isothiocyanate dye and the luminescence characteristics of calcium aluminate phosphor, the film exhibited a unique strong pH-responsive fluorescence with an exceptional linear relationship (correlation coefficient, R2 = 0.9993) across a wide pH rang of 2.0–12.0. Moreover, the H-K-F-N film, as a smart sensor, could be used to estimate the total volatile basic nitrogen and total viable count through fluorescence intensity based on the partial least squares regression model and support vector machine regression, respectively. Leveraging the relationship between the fluorescent image's digital signals and food freshness indicators, a smartphone-assisted system was developed. These results demonstrated that H-K-F-N film is promising for applications in intelligent food packaging and food safety monitoring.

Improved Optical Performance Analysis of YAG:Ce, NCS:Sm, and CAO:Mn Phosphors Physically Integrated with Metal-Organic Frameworks.

This research presents a thorough examination of the optical properties and performance enhancement strategies of synthesized phosphors, namely, yttrium aluminum garnet doped with cerium (YAG:Ce), sodium calcium silicate with samarium (NCS:Sm), and calcium aluminate oxide doped with manganese (CAO:Mn). The study delves into the synthesis processes of the phosphors, illumination of the crystal structures, and enhancement of luminescent characteristics. Additionally, the paper extends to the synthesis and analysis of {[Cu(μ3-dmg)(im)2]·3H2O} n (PKY159), and the coordination polymer (CP) was added the phosphors to explore a novel approach for enhanced optical performance. When the phosphor composites YAG:Ce, CAO:Mn, and NCS:Sm were made as poly(methyl methacrylate) (PMMA; for homogenization, stabilization) thin films with the coordination polymer PKY159 included, the intensity values increased by 97%, 96%, and 79%, respectively, in comparison to their pristine form. Also, all phosphors along with the PKY159 additive were examined for their decay time kinetics, thermal stabilities, CIE chromaticity coordinates, and quantum efficiencies. The YAG:Ce, NCS:Sm, and CAO:Mn mixes exhibit good thermal stability in addition to internal quantum efficiency (IQE) values that are much higher than the phosphors' additive-free form (95.6%, 66.3%, and 84.6%, respectively). This increase is correlated to an increase in steady-state measurements. These comprehensive analyses contribute valuable insights into the design and optimization of phosphor and coordination polymer blends for improved optical functionality.

Spinel‐Type Structured Phosphor Near‐Infrared‐II Emission: Intervalence Charge Transfer and Hetero‐Valent Chromium Pairs

AbstractNear‐infrared (NIR) emitting phosphors draw much attention because they show great applicability and development prospects in many fields. Herein, a series of inverse spinel‐type structured LiGa5O8 phosphors with a high concentration of Cr3+ activators is reported with a dual emission band covering NIR‐I and II regions. Except for strong ionic exchange interactions such as Cr3+−Cr3+ and Cr3+ clusters, an intervalence charge transfer (IVCT) process between aggregated Cr ion pairs is proposed as the mechanism for the ~1210 nm NIR‐II emission. Comprehensive structural and luminescence characterization points to IVCT between two Cr3+ being induced by structural distortion and further enhanced by irradiation. Construction of the configurational energy level diagram enabled elucidation of this transition within the IVCT process. Therefore, this work provides insight into the emission mechanism within the high Cr3+ concentration system, revealing a new design strategy for NIR‐II emitting phosphors to promote its response.

Green synthesis of La2O3–LaPO4 nanocomposites using Charybdis natator for DNA binding, cytotoxic, catalytic, and luminescence applications

Abstract A one-step biosynthetic pathway for the fabrication of La2O3–LaPO4 nanocomposites (NCs) was developed, employing Charybdis natator. The structure and phase changes of the NCs were confirmed, and their diverse applications were explored. The peaks at 206, 332, and 442 nm in UV-DRS studies confirmed the formation of La2O3–LaPO4 NCs. Fourier transform infrared spectral analysis revealed La–O stretching at 716 cm−1 and the presence of PO 4 3 − {\text{PO}}_{4}^{3-} bands at 532, 560, 578, and 618 cm−1. X-ray diffraction patterns showed a hexagonal phase of La2O3 with peaks at 2θ 11.04 and 28.57 and monoclinic LaPO4 phases at 2θ = 18.79 and 41.88. X-ray photoelectron spectroscopy data showed binding energy peaks at 836.04 and 852.77 eV, corresponding to 3d5/2 and 3d3/2 of the lanthanum. The average particle size from HR-TEM analysis was 28.95 nm after annealing at 800°C and SAED patterns confirmed their crystalline nature. The high affinity of the NCs towards ctDNA was established by a binding constant value of 2.08 (mg·mL−1)−1. Under UV exposure, 96% degradation efficiency for methyl orange within 120 min at pH 4 was displayed, with a rate constant of 2.72 × 10−2 min−1 affirming their photocatalytic potential. Their biocompatibility was assessed through MTT assay and luminescence characteristics were evaluated.

Efficient and tunable emission of Na5Lu(WO4)4:Tb3+,Eu3+ phosphors for warm white LEDs with high color rendering index

Phosphors with high luminescence efficiency, tunable emission and high color rendering index (CRI) are vital importance for the quality of white light emitting diodes (w-LEDs) in real application. In this work, a new single phase color-tunable Na5Lu(WO4)4:Tb3+,Eu3+ phosphor with outstanding luminescent properties was designed and synthesized. Its crystal structure, electronic structure, and luminescence features were studied in detail. The band gap of the host was calculated to be at about 4.68 eV. The differential charge distribution after Tb, Eu doping through density functional theory simulation theoretically proved the electron redistribution in the W-O bond upon substitution of Tb3+/Eu3+. The energy transfer of Tb3+→Eu3+ enabled tunable emission of luminescent colors from green to orange-red due to the quadrupole-quadrupole interaction. The optimal Na5Lu(WO4)4:60%Tb3+,20%Eu3+ phosphor exhibited excellent photoluminescence quantum yield of 84.19% and good luminescent thermal stability (I423K/298K = 75.90%) with an activation energy of 0.1976 eV. Finally, a white LED device with color coordinates of (0.3371, 0.3636), color rendering index of 89.4 and correlated color temperature of 5334 K was fabricated. These findings demonstrated that Na5Lu(WO4)4:60%Tb3+,20%Eu3+ phosphor could be a potential orange-red-emitting color converter for white LEDs. This work not only assisted in the understanding of experimental observations but also provided a theoretical basis for the rational design of phosphors.

Optically Stimulated Luminescence (OSL) characteristics of four fluorite samples under green light stimulation

This study investigates the OSL properties of four natural fluorite color varieties (green, purple, blue-yellow banded and yellow) under green light stimulation. Thermoluminescence reveals two peaks, with the green sample showing the strongest glow. OSL exhibits a fast initial decay followed by a slower one, with phototransfer observed in purple and yellow. OSL intensity is linear with dose (1-30 Gy) for most samples, except yellow. Curve fitting using a first order kinetics model suggests multiple OSL components (between 3 and 5). Preheat treatment at 100°C increases the very fast components (thermal transfer). Anomalous fading shows rapid initial decay followed by a slower one.

Full-angle Light Out-coupling Enhancement of Quantum Dot Light-emitting Diodes by Mie-scattering Micro-lens Arrays

High efficiency, high brightness, and long-life quantum dot light-emitting diodes (QLEDs) are crucial for realizing integrated display and lighting applications. However, about 80% of the light is confined inside the device with substrate mode, waveguide mode, and plasma mode, which greatly weakens the brightness, efficiency and lifetime of the device. Here, a quasi-periodic concave template with large area was fabricated through the spontaneous condensation of droplets on the substrate surface. Based on the quasi-periodic template, SiO2 micro-lens arrays (SiO2-MLAs) Mie scattering composite structures were fabricated by nanoimprinted on SiO2-nanosphere thin film, which significantly improved light out-coupling at full angle with optimized quasi-Lambert luminescence characteristics. In comparison to the planar QLED with state-of-the-art, the external quantum efficiency (EQE) demonstrated a qualitative improvement (> 20%). Accordingly, the EQE, brightness (L), T50 lifetime (reduce to half brightness) of the green QLEDs with SiO2-MLAs structure have been optimized by 22%, 28%, 31%, and up to 24.21%, 381962.6 cd/m2, 111335 hours, respectively. This strategy provides valuable insights into mass-producing and utilizing SiO2-MLA Mie scattering composite structures to boost QLED performance in high-efficiency display and lighting applications.

Ternary composite fluorescent films with tunable color and long lifetime based on efficient TS-FRET

Multi-color long-wavelength organic afterglow materials are of great significance in anti-counterfeiting, but their preparation is still challenging. In this paper, a series of room temperature phosphorescence (RTP) films were constructed with polyvinyl alcohol (PVA) as rigid matrix and 9,10-diaminophenanthrene (DAphe) as guest molecule. Surprisingly, by adjusting the doping content of DAphe, their RTP emission peak width could be adjusted accordingly, and the lifetime was up to 3.25 s. Their dopant content dependent and excitation wavelength dependent luminescence characteristics and theoretical calculation results indicated that the observed broad emission peaks of RTP might be attributed to multiple luminescence centers generated by the aggregation of guest molecules. Interestingly, by doping several suitable fluorescent dyes screened as energy acceptors, multi-color, long-lasting afterglow composite films from blue to red were obtained, achieving 0.42 s delayed fluorescence at 661 nm with a fluorescence quantum yield of 32.22 %. In addition, these adjustable afterglow materials had good molding processability, so several cryptographic patterns were achieved to demonstrate their good application prospects in advanced anti-counterfeiting technologies.

Crystal growth, luminescence, and radiation response characteristics of undoped and Nd-doped langasite-type Ca3TaGa3Si2O14

Undoped and various concentrations of Nd-doped Ca3TaGa3Si2O14 (CTGS) single crystals were fabricated via the floating zone technique. The luminescence and radiation response characteristics were investigated. A broad intrinsic luminescence was observed at 300–600 nm. Sharp luminescence appeared at 900, 1060, and 1300 nm in Nd-doped samples and they originated from 4f–4f transitions of Nd3+. Photoluminescence quantum yields were calculated to be 44.7, 94.1, 87.4, and 75.5% in 0.1, 0.5, 1, and 2% Nd-doped samples, respectively when monitored at near-infrared (NIR) ranges. Linear responses between dose-rate and scintillation outputs in NIR regions were confirmed in Nd-doped samples. The 0.5% Nd-doped CTGS achieved a detection limit of 1 mGy/h.

Photoluminescence and thermally stimulated luminescence properties of Sr3Y(PO4)3 single crystals doped with Dy

Sr3Y(PO4)3 (SYPO) is recognized as a highly promising material for dosimetry applications, owing to its dosimetric properties. In this work, we synthesized the SYPO single crystals doped with 0.1, 0.5, 1, and 5% Dy using the floating zone furnace to evaluate the photoluminescence and thermally stimulated luminescence (TSL) characteristics. All the SYPO single crystals doped with Dy exhibited emission peaks at 480, 580, 670, and 760 nm in PL and TSL spectra. These emission peaks were typical for the 4f–4f transitions of Dy3+ ions. The SYPO single crystal doped with 0.1% Dy displayed a glow peak in the TSL glow curve at 70 °C. The SYPO single crystals doped with 0.5, 1, and 5% Dy showed two glow peaks at approximately 70 and 110 °C. The SYPO single crystal doped with 0.5% Dy exhibited the highest TSL intensity with a lower detection limit of 0.1 mGy. The SYPO single crystal doped with 0.5% Dy showed a spatial resolution of 50.0 μm after X-ray irradiation of 1Gy.

Optical characterization of GaN:Eu microcrystals grown by the ammonothermal method

Eu-doped gallium nitride (GaN:Eu) microcrystals with a wurtzite crystal structure were synthesized using the ammonothermal method. The Eu concentration of GaN:Eu microcrystals estimated by glow discharge mass spectrometry (GDMS) was 5.8 × 1020 atoms/cm3. The morphology of GaN:Eu microcrystals was characterized by scanning electron microscopy (SEM). The exposed crystal faces of GaN:Eu microcrystals were identified as {10−10}, {10−11}, (000−1), and (0001), respectively. The photoluminescence excitation (PLE), photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra of GaN:Eu microcrystals revealed two luminescent sites of Eu3+ ions, designated as Eu0 and Eu1. The Eu0 was excited in the range of 300 nm to 420 nm, resulting in the observation of four characteristic luminescence peaks at 599 nm (5D0-7F1), 620 nm (5D0-7F2), 632 nm (5D1-7F4), and 663 nm (5D0-7F3). The Eu1 was associated with O2- ions and emitted light at specific excitation wavelengths. The main luminescence peak of the Eu1 was located at 614 nm, accompanied with characteristic peaks at 578 nm, 591 nm, and 698 nm. In view of the distinct luminescence properties of the Eu0 and the Eu1, the energy transfer processes of two luminescence sites were proposed.