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Near-infrared-II (NIR-II) luminescence, which serves as a promising spectral window for biomedical applications and spectral analysis, has numerous potential applications. In this work, the NIR-II luminescence is realized in Li4SrCa(SiO4)2:Cr4+ phosphors. Under 465 nm excitation, the emission peak of Li4SrCa(SiO4)2:3%Cr4+ is located at 1215 nm and the full width at half maximum (FWHM) is more than 230 nm, covering the ultra-long range of 950–1600 nm. The photoluminescence spectra, diffuse reflectance spectra, Raman spectra and time-resolved emission spectra confirm the NIR-II luminescence mechanism. Furthermore, a novel post-reduction strategy is proposed to realize the leap-forward enhancement of NIR-II luminescence from Cr4+. By mutually substituting Sr2+ and Ca2+, a series of Li4Sr1+zCa1−z(SiO4)2:3%Cr4+ (z = −1 to 1) samples are prepared to investigate the universality and applicable conditions of the post-reduction strategy. Benefitting from the NIR-II emission of Cr4+, it has great application potential in optical temperature measurement and spectral analysis. [ABSTRACT FROM AUTHOR]

Component modulation strategies are widely used to modulate the PL properties of fluorescent materials. Metal halide perovskites (MHPs) have many advantages for optical applications, one of which is the excellent structural tunability. In this work, a series of Cs2InCl5·H2O:xCr3+ phosphors were synthesized by a simple hydrothermal method, obtaining a broadband near-infrared (NIR) emission in the 800–1200 nm range with a peak at 910 nm under 360 nm excitation. Unlike the widely used B-site cation modulation, co doping Rb+/K+ at A sites improves the structural rigidity and thus enhances the emission intensity and luminescence thermal stability of the Cs2InCl5·H2O:Cr3+ phosphor. In particular, the emission intensity of (Cs0.7K0.3)2InCl5·H2O:0.25Cr3+ at 125 °C can retain 52% of that at room temperature. Due to its excellent performance, the (Cs0.7K0.3)2InCl5·H2O:0.25Cr3+ phosphor in combination with 380 nm ultraviolet chips shows potential applications in non-destructive testing and night vision. This strategy provides new ideas for the modulation of MHP-based fluorescent materials in the future. [ABSTRACT FROM AUTHOR]

Most near-infrared (NIR) phosphors suffer from short emission wavelength (<1000 nm) and narrow full width at half maximum (FWHM) values below 200 nm, restricting their broader applications in non-destructive tests, spectral analysis and photovoltaic fields. This study presents the successful synthesis of the wolframite-type compound InNbTiO6:Cr3+, with Cr3+ occupying a single In3+ site. Under green light irradiation, it emits an ultra-broadband NIR spectrum centered at 965 nm with a FWHM of 231 nm. Substituting In3+ with Ga3+ induces a blue shift in the emission peak from 969 nm to 934 nm, concomitant with an enhancement in the optical properties. To be specific, the NIR luminescence intensity of In0.58NbTiO6:0.02Cr3+,0.4Ga3+ is enhanced by a factor of 2.3, and its thermal stability is improved from 22.3%@400 K to 41.3%@400 K compared to In0.98NbTiO6:0.02Cr3+. The NIR pc-LED is fabricated by integrating the In0.58NbTiO6:0.02Cr3+,0.4Ga3+ phosphor with a 520 nm chip, showcasing its potential for multifunctional applications in solar cells, spectral analysis, and night vision technologies. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are the ideal light source for next-generation NIR spectroscopy, and developing novel NIR phosphors with high performance is crucial to achieve a wide range of NIR pc-LED applications. In this work, NIR luminescent material Y2Mg2Al2Si2O12 (YMAS):2%Cr3+ with good quantum efficiency (79%) and excellent thermal stability (88%@100 °C) is prepared. Under 430 nm light excitation, YMAS:2%Cr3+ emits 620–1100 nm NIR light with a full-width at half maximum (FWHM) of 153 nm. Fluorescence decay curves, photoluminescence (PL) spectra, 7 K PL spectra, the Rietveld refinement, 27Al solid-state nuclear magnetic resonance (ss-NMR) spectra and time-resolved emission spectroscopy (TRS) confirm that Cr3+ has two different luminescence centers in the YMAS lattice. Benefiting from the site elimination strategy, the double luminescence centers are proven to be derived from Cr3+ ions occupying the two sites [Al1O6] and [Al2O4]. The NIR packaging device prepared using YMAS:2%Cr3+ has outstanding NIR output power and photovoltaic conversion efficiency as high as 45.7 mW@100 mA and 16.7%@100 mA, respectively. Owing to the excellent performance of the YMAS:2%Cr3+ sample, it presents excellent practical performance in plant growth, bioimaging, non-destructive testing and night vision. [ABSTRACT FROM AUTHOR]

With the increasing demand for the application of near-infrared (NIR) spectroscopy in security, agriculture, medical and other fields, people have been seeking efficient and intelligent NIR light sources. Herein, Cr3+ doped Ca3Sc2Ge3O12 (CSGG) broadband NIR phosphors are successfully synthesized. Under excitation of 480 nm, the emission peak of CSGG:Cr3+ is located at 785 nm, and the full width at half maximum (FWHM) is 106 nm. Low photoluminescence spectra (7 K and 77 K) support the broadband NIR emission coming from two Cr3+ luminescence centers occupying ScO6 and CaO8 sites, respectively. CSGG:Cr3+ exhibits excellent thermal stability (97% at 100 °C) and low internal quantum efficiency (IQE = 22%). The introduction of Ce3+ leads to the enhancement of IQE from 22% to 61% due to the following two reasons: the energy transfer from Ce3+ to Cr3+ and the lattice distortion which improves the parity forbidden transition of Cr3+. The mechanism of excellent luminescence thermal stability is revealed from the following perspectives: thermal activation energy, the Huang–Rhys factor and the thermal ionization effect. Benefiting from the excellent performance of CSGG:Cr3+,Ce3+ NIR phosphors, the combination with blue light chips demonstrates their potential applications in night vision security, biological imaging, and nondestructive testing. [ABSTRACT FROM AUTHOR]

Efficiently modulating the site occupation of activators has important implications in the design of color-tunable phosphors. In this paper, we report a series of novel Sr3Sc4O9:xEu phosphors. The activators (Eu2+) selectively occupy multiple cationic sites (Sr1–3 and Sc1–4) in the Sr3Sc4O9 matrix with the increase of doping concentration, thus achieving the modulation of emission color from deep-red to white to green. The structure-dependent luminescence mechanism is investigated in detail. The PL spectrum of the Sr3Sc4O9:0.06Eu phosphor upon blue light excitation exhibits an asymmetrically broad deep-red emission band peaking at 688 nm with a FWHM ≈ 100 nm, which clearly overlaps with the absorption curves of red-phytochrome (Pr) and far-red-phytochrome (Pfr). The photoluminescence quantum yield (PLQY) is significantly improved from 2.7% to 19.18% by adopting a double-reduction strategy. The full-visible-spectrum white emission of Sr3Sc4O9:0.01Eu is achieved when excited by UV light. A full-spectrum white LED with Ra = 86 and CCT = 5040 K was packaged with a single-component white emission Sr3Sc4O9:0.01Eu phosphor. All the results suggest the utilization potential of multifunctional Sr3Sc4O9:xEu phosphors in agricultural and full-spectrum general lighting. [ABSTRACT FROM AUTHOR]

In this work, using β-Ca3(PO4)2 as a structural model, a series of [Ca9Na3xY1−x(PO4)7 (CNYPO-I, 0 ≤ x ≤ 1/2) ← Ca3(PO4)2 → Ca9+yNa3/2−y/2Y(1−y)/2(PO4)7 (CNYPO-II, 0 ≤ y ≤ 1)] phosphors were prepared using a cationic heterovalent substitution approach. The substitution of Y3+ and Na+ for Ca2+ led to a redistribution of Eu2+ within the lattice and was accompanied by changes to the corresponding luminescence behavior. As the x and y values increased, the vacancies in the structure were gradually occupied by Na+ to form Na(4) sites that are conducive to Eu2+ occupation. When y = 1, the vacancies were completely occupied, and the Eu2+ emission peaks from Ca(1/2) and Ca(3) sites showed a significant blue shift. The underlying mechanism of that shift is discussed. The CNYPO-I (x = 0) sample displayed the best thermal stability; the effects of vacancies, thermal ionization and cross-over mechanism on thermal quenching are also discussed. As x and y increase, the thermal stability of the samples gradually decreased. Eu2+ and Mn2+ co-doped CNYPO-I (0 ≤ x ≤ 1/2) and CNYPO-II (0 ≤ y ≤ 1) phosphors achieved full coverage of the visible light region (400–800 nm). These white LEDs have relatively high color-rendering indexes (>80) and adjustable color temperatures from 2854–7000 K. This work provides an effective strategy for designing novel luminescent materials and realizing multi-site adjustment of activator ions. [ABSTRACT FROM AUTHOR]

Herein, we report a new series of Ba1+xSr1−xGa4O8:Bi3+ (x = 0–0.7) phosphors that exhibit extremely broadband emission, covering almost the entire visible region and extending to the deep-red region, when excited by ultraviolet light. BaSrGa4O8:Bi3+ exhibits two emission bands located at 470 and 570 nm originating from different emission centers. With the gradual substitution of Ba for Sr, both of the emission bands show a red-shift, from 470 to 510 nm and from 570 to 630 nm, respectively. The corresponding full width at half maximum (FWHM) increases from 192 to 283 nm, which is attributed to a superposition of multiple emission centers via crystal field regulation. As a result, the emission can be tuned from cyan to orange across the warm white light region in Ba1+xSr1−xGa4O8:Bi3+ (x = 0–0.7) systems. Simultaneously, this series of phosphors presents good thermal stability (97% intensity at 150 °C for the Ba1.5Sr0.5Ga4O8:Bi3+ sample) and the thermal quenching will decrease with the formation of a solid solution due to the increasing rigidity of the lattice structure. Interestingly, the two emission bands in the representative Ba1+xSr1−xGa4O8:Bi3+ (x = 0–0.7) sample exhibit different thermal responses to increasing temperature, thus an optical thermometer with color discrimination and good sensitivity is designed. The maximum relative sensitivity (Sr) is 1.295% K−1 in the temperature range of 7–400 K. The corresponding emission color can be tuned from blue-cyan to orange, including white light. This work presents a rational design strategy for controllable ultra-broadband emission tuning across the white light region and to further explore potential optical sensor applications. [ABSTRACT FROM AUTHOR]

In the field of white LEDs, the research and development of red phosphors have been confronting a challenge. In this paper, a novel red-emitting Ca9MnNa(PO4)7 (CMNPO) phosphor, whose emission was attributed to the 4T1(4G)–6A1(6S) transition of Mn2+ ions, was prepared by a high-temperature solid-state reaction. We utilized a chemical co-substitution strategy to optimize the luminescence properties and realize an impressive red emission in our CMNPO phosphor. The introduction of Zn2+/Mg2+ into CMNPO could break the intrinsic structural confinement of Mn2+, which improved the red emission from Mn2+ in the narrow confines. The novelty of this work lies in realizing an efficient red phosphor by doping trace amounts of Eu2+. By partially replacing Mn2+ ions with trace amounts of Eu2+, we obtained a CMNPO phosphor that emitted a dazzling red light, and the quantum yield reached up to 82%. The intensity dependence of this red emission on the trace amounts of doped Eu2+ was quantitatively analyzed. The substitution of Eu2+ ions played a dual role in improving the luminescence properties, not only disturbing the structural confinement of Mn2+ but also transferring energy to Mn2+ efficiently. By employing it as a red phosphor, we fabricated various high-performance white LEDs with low correlated color temperatures (4642–4956 K) and high-color-rendering indices (80.5–83.4). These findings show the potential promise of the CMNPO phosphor as a red phosphor in warm white LEDs and open up new avenues for the exploration of novel red-emitting phosphors. [ABSTRACT FROM AUTHOR]

Designing two-step tuning based on substitution of multiple cation lattices and energy transfer successfully achieved versatile colour output for single-phase phosphor-converted white LEDs in this work. Herein, we chose whitlockite-type Ca9LiY0.667(PO4)7 compound as a host which provides multiple cation sites for Eu2+ occupation. Spectral results indicate that the Ca9LiY0.667(PO4)7:Eu2+ phosphor emits a cold white emission due to its multiple emission bands at about 420, 480, and 530 nm, which correspond to emissions from the M(3), M(1)/M(2) and M(5) cation sites as ascertained by the Rietveld refinement method. In order to enhance the red emission of CLYPO:Eu2+ phosphors, they were codoped with Mn2+. Warm white emission in a single-phase host based on energy transfer was successfully obtained in the CLYPO:Eu2+,Mn2+ phosphors. The excitation band of the CLYPO:Eu2+,Mn2+ phosphors in the 360 to 450 nm range perfectly coincides with that of commercial LED chips, implying that these phosphors are desirable for white LED applications. White LEDs with a higher color rendering index (Ra = 90.2) and a lower correlated color temperature (CCT = 3614 K) were achieved by using a single-phase CLYPO:0.03Eu2+,0.10Mn2+ phosphor and a 395 nm InGaN-LED chip. [ABSTRACT FROM AUTHOR]

Controllable luminescence tuning can modify and improve the luminescence performances of phosphor materials and thus promote their application in white light emitting diodes (W-LEDs). Usually, crystal field modulation by constructing solid solutions based on diverse composition substitutions and energy transfers are effective strategies for adjusting the luminescence properties of phosphors. Herein, we report a series of novel emission-tunable Ba3−xSrxSc4O9:yBi3+,zEu3+ (x = 0–3.0, y = 0–0.15, z = 0–0.30) solid solution phosphors synthesized via a high-temperature solid-state route. The XRD patterns and Rietveld refinements were utilized to confirm the phase purity and analyze the structural variation. Cation substitution-dependent color-tunable evolution as a function of Sr content in Bi3+-doped Ba3−xSrxSc4O9 was observed and investigated in detail. The regular emission red-shift located in the blue-green region with the increase of Sr content was attributed to the combined effect of the crystal field splitting. Due to the suitable optical band gap (5.50 eV), Bi3+ ions realized a highly efficient doping in the Sr3Sc4O9 matrix. The as-prepared Sr3Sc4O9:Bi3+ samples were efficiently excited by UV light, and the photoluminescence properties presented obvious preferential-occupation selected excitation phenomenon where the emission peaks had remarkable red-shifts along with increasing the excitation wavelength. In addition, luminescence tuning from green to orange was achieved by designing the energy transfer from Bi3+ to Eu3+ ions in the as-prepared Sr2.97−zSc4O9:0.03Bi3+,zEu3+ samples and the corresponding mechanism was proposed. Moreover, the thermal stabilities of the studied phosphors were revealed. According to the distortion calculation of the Ba/Sr crystallographic occupation, the thermal stability is related to the lattice rigidity, which would become much stronger with the reduction of distortion. These results illustrate that the as-prepared Ba3−xSrxSc4O9:Bi3+,Eu3+ phosphors can be potential candidates for color-tunable phosphors applied in UV-pumped W-LEDs. [ABSTRACT FROM AUTHOR]

Currently, controllable luminescence tuning and the generation of single component white emission are viable strategies to modify and optimize the luminescence performances of phosphors, which offer appealing prospects for the w-LED lighting industry. In this paper, we designed two-dimensional (2D) tunable color coordinates on the CIE diagram in the Eu2+,Mn2+ doped (Ca,Sr)9xSc(PO4)7 system by a combination of crystal field regulation and the energy transfer method. X-ray powder diffraction (XRD) and Rietveld refinement were utilized to analyze the phase composition and structural variation of the studied phosphors. The transmission electron microscopy (TEM) and photoluminescence spectra were exploited to analyze the generation of nanosegregation. The effects of the schedule of cation substitutions and energy transfer on the photoluminescence properties were investigated in detail. The corresponding luminescence mechanisms of the red-shifted emission with Sr2+→ Ca2+ substitution and Eu2+→ Mn2+ energy transfer were deeply discussed and proposed. In addition, the temperature-dependent thermal quenching behavior and the electroluminescence (EL) performance of the fabricated w-LED devices were also investigated to characterize the prepared Ca9(1−0.03−x−y)Sr9xSc(PO4)7:0.27Eu2+,9yMn2+. Finally, a representative w-LED device composed of a 369 nm UV chip and Ca9(1−0.03−0.02−0.5)Sr4.5Sc(PO4)7:0.27Eu2+,0.18Mn2+ could present excellent EL performance with the parameters CRI = 88, CCT = 3122 K and color coordinate (0.45, 0.44), which could well meet the commercial standard of warm white light. Therefore, our results suggest that this two-step luminescence tuning method is feasible to be applied in other phosphor systems for obtaining efficient white emitting phosphors. [ABSTRACT FROM AUTHOR]

In pursuit of highly efficient phosphors for white LED (w-LED) lighting, chemical modification of the host lattice and the design of energy transfer in a variety of cation sites have been extensively considered. In this work, a series of novel Bi3+,Li+,Eu3+-doped BaSc2O4 phosphors with blue-to-red tunable emission were synthesized by a high-temperature solid-state reaction process. Charge compensators (Li+) and fluxes (BaF2) were jointly employed to improve the phase purity and luminescence properties of phosphors based on appropriate chemical modifications. The crystal structures were analyzed by XRD and the Rietveld refinement, and the photoluminescence properties and thermal stabilities of the studied phosphors were investigated in detail. BaSc2O4:Bi3+ could be efficiently excited by n-UV light (250–350 nm), and exhibits a bright broad blue emission band (400–520 nm) with a peak at 440 nm. Moreover, the introduction of the Li+ ion and BaF2 could efficiently enhance the emission intensity and decrease thermal quenching, which should be due to the lattice modification. Interestingly, systematic luminescence tuning from blue to red could be achieved by designing Bi3+→ Eu3+ energy transfer. The corresponding luminescence mechanism was discussed and proposed. In addition, Bi3+,Li+-doped BaSc2O4 phosphors with BaF2 demonstrate good thermal stability, with their emission intensity at 150 °C still exceeding 70% of the initial RT value. The above results indicate that the BaSc2O4:Bi3+,Li+ phosphor would be a potential blue phosphor for n-UV based w-LEDs devices. Moreover, the controllable emission adjustment from Bi3+,Eu3+-codoped BaSc2O4 phosphors could derive a series of novel phosphor materials for improving the light quality of w-LED sources. [ABSTRACT FROM AUTHOR]

Utilizing energy transfer (ET) between the sensitizer and acceptor in phosphors is a good way to obtain tunable emission color. Therefore, many researchers have devoted their interest to design phosphors with different emission colors via their energy transfer properties. It is well known that Ce3+ and Bi3+ are good sensitizers, while Mn2+, Dy3+, Eu3+ and Sm3+ can be useful activators. Further, Eu2+ and Tb3+ can be both good sensitizers and activators. Therefore, herein we summarise many recent ET systems consisting of Eu2+–Mn2+/Tb3+, Eu2+–Tb3+–Mn2+/Eu3+/Sm3+, Ce3+–Mn2+/Tb3+/Dy3+/Eu2+, Ce3+–Tb3+–Mn2+/Eu3+/Sm3+, Bi3+–Eu3+/Sm3+ and Tb3+–Eu3+/Sm3+, which show tunable emission color from ultraviolet to blue and green, blue to green, yellow, orange and pink/red, cyan to green, orange and pink/red, and green to yellow/orange and red. Based on this summary, this review will be a good reference to benefit the design and investigation of phosphors potentially applied in FEDs and LEDs with ET. [ABSTRACT FROM AUTHOR]

A variety of Ce3+ and Tb3+-doped BaLu2Si3O10 (BLSO) phosphors were synthesized via the high-temperature solid-state reaction method. Many technologies, such as X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), solid-state NMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) measurements, were used to characterize the as-prepared samples. Lu4Si2O7N2 was generated when N3− replaced O2− in BLSO:Ce3+, which resulted in a shift of the emission band from the blue (423 nm) to the cyan (460 nm) region under UV excitation. It was speculated that energy transfer occurred in Ce3+ and Tb3+ co-doped BLSO via the spectral overlap between Ce3+ emission and Tb3+ excitation in singly-doped BLSO, demonstrated by the variation in the emission spectra and the decrease in the Ce3+ fluorescent lifetimes in Ce3+ and Tb3+ co-doped BLSO, which resulted in a color change from blue to green when the concentration ratio of Ce3+/Tb3+ in BLSO:Ce3+,Tb3+ was adjusted. The energy transfer mechanism was confirmed to be electric dipole–quadrupole interaction. Moreover, quantum yields (QYs), Commission Internationale de l'Eclairage (CIE) chromaticity coordinates and temperature-dependent PL properties have also been investigated in detail. The results show the potential of BLSO:Ce3+,Tb3+ compounds as candidates for phosphors in phosphor-converted LEDs. [ABSTRACT FROM AUTHOR]

A series of Eu2+,Mn2+-doped Na3LuSi2O7 (NLSO) phosphors have been prepared via the high-temperature solid-state reaction route. X-ray diffraction (XRD), Raman and Fourier transform infrared (FT-IR) spectra, fluorescent decay times, photoluminescence (PL) including temperature-dependent PL properties and scanning electron microscopy (SEM) were used to characterize the as-prepared samples. In Eu2+ singly-doped NLSO samples, an intense green emission is presented under UV excitation. A tunable color from green to yellowish-orange was generated when Mn2+ ions were co-doped into the NLSO:Eu2+, which is based on the energy transfer from Eu2+ to Mn2+ ions. The energy transfer from Eu2+ to Mn2+ ions can be speculated to be due to the wide spectral overlap between the Eu2+ emission and Mn2+ excitation spectra in Eu2+ or Mn2+ singly-doped NLSO samples. This is demonstrated by the similar excitation spectra of the Eu2+ and Mn2+ emission bands and the decreases in Eu2+ emission intensity and decay lifetime with the increase of Mn2+ concentration in the NLSO:Eu2+,Mn2+ samples. The energy transfer mechanism from Eu2+ to Mn2+ ions was determined to be a dipole–quadrupole interaction by the concentration quenching and spectral overlap methods. The maximum quantum yield can reach 51.5% for NLSO:0.01Eu2+,0.12Mn2+. The above results indicate that NLSO:Eu2+,Mn2+ could be a candidate as a green to yellowish-orange component for UV-excited w-LEDs. [ABSTRACT FROM AUTHOR]

A series of Bi3+,Eu3+-doped Sr2Y8(SiO4)6O2 (SYSO) phosphors were synthesized by the Pechini-type sol–gel route. XRD patterns, Rietveld refinement, FT-IR spectra, photoluminescence spectra (PL), fluorescence decay time, and quantum yields (QYs) were utilized to characterize the as-prepared samples. Intense blue-green emission due to the 3P1→1S0 transition of Bi3+ ions is produced under UV excitation in Bi3+ singly doped SYSO samples. Spectral analysis illustrates that two kinds of Bi3+ ions are generated by occupying the two kinds of sites (4f and 6h) available for Y in SYSO, denoted as Bi3+(1) and Bi3+(2), corresponding to the two main emission bands at around 413 and 493 nm, respectively. A wide spectral overlap between Bi3+ emission and Eu3+ excitation spectra results in the energy transfer from Bi3+ to Eu3+. This has been demonstrated via the excitation spectra monitored at Bi3+ and Eu3+ emission bands, and the PL emission spectra and decay time of Bi3+ in SYSO:Bi3+,Eu3+ phosphors. The energy transfer mechanism is determined to be dipole–quadrupole interaction. The critical distance of energy transfer from Bi3+ to Eu3+ ions is calculated to be 12.78 Å based on the concentration quenching method, which is in good agreement with that of the spectral overlap route (10.03–13.37 Å). Moreover, the QYs, CIE chromaticity and thermal quenching properties have also been investigated. White emission color can be realized with the CIE coordinates (0.325, 0.311) and QY 52% for SYSO:0.08Bi3+,0.48Eu3+. The above results suggest that SYSO:Bi3+,Eu3+ can be a potential single-component white-emitting phosphor for UV w-LEDs. [ABSTRACT FROM AUTHOR]

Nitride phosphors have drawn much interest because of their outstanding thermal and chemical stability and interesting photoluminescence properties. Currently, it remains a challenge to synthesize these phosphors through a convenient chemical route. Herein we propose a general and convenient strategy based on hydrothermal-ammonolysis reaction to successfully prepare zinc germanium nitride (ZnGeN2) and Mn2+ doped ZnGeN2 phosphors. The crystal structure, composition, morphology, luminescence and reflectance spectra, quantum efficiency, and the temperature-dependent photoluminescence behavior were studied respectively. The phase formation and crystal structure of ZnGeN2 were confirmed from powder X-ray diffraction and Rietveld refinement. EDX analysis confirmed the actual atomic ratios of Zn/Ge and N/Ge and suggested the presence of Ge vacancy defects in the ZnGeN2 host, which is associated with its yellow emission at 595 nm with a FWHM of 143 nm under UV light excitation. For Mn2+ doped ZnGeN2 phosphor, it exhibits an intense red emission due to the 4T1g→6A1g transition of Mn2+ ions. The unusual red emission of Mn2+ at the tetrahedral Zn2+ sites is attributed to the strong nephelauxetic effect and crystal field between Mn2+ and the tetrahedrally coordinated N3−. Moreover, the PL intensity of ZnGeN2:Mn2+ phosphors can be enhanced by Mg2+ ions partially substituting for Zn2+ ions in a certain concentration range. The optimal Mn2+ doping concentration in the ZnGeN2 host is 0.4 mol%. The critical energy transfer distance of this phosphor is calculated to be about 27.99 Å and the concentration quenching mechanism is proved to be the dipole–dipole interaction. With increasing temperature, the luminescence of ZnGeN2:Mn2+ phosphors gradually decreases and the FWHM of the emission band broadens from 54 nm to 75 nm. The corresponding activation energy Ea was reckoned to be 0.395 eV. And the nonradiative transition probability increases with the increasing temperature, finally leading to the lifetime decrease with the increase of the temperature. [ABSTRACT FROM AUTHOR]

Co-doping of Ce3+/Eu2+, Tb3+, Mn2+ ions into a single-component host is commonly used to achieve white-light phosphors through energy transfer, which present good color stability and high color rendering index (CRI) values. In this work, a series of single-component trichromatic white-light-emitting Ca9Bi(PO4)7(CBPO):Ce3+,Tb3+,Mn2+ phosphors were synthesized and investigated. The crystal structure, luminescence properties and energy transfer behavior are discussed in detail. The energy transfer process from Ce3+ to Tb3+/Mn2+ has been demonstrated to be a resonant type via the dipole–dipole–quadrupole–quadrupole interaction mechanism, respectively, which makes the emission color shift from purple-blue to green/red with the corresponding Commission Internationale de L'Eclairage (CIE) chromaticity coordinates from (0.166, 0.011) to (0.260, 0.569) and (0.582, 0.287), respectively. Additionally, the white light emission by controlling the concentration ratio of Tb3+ and Mn2+ ions has been acquired in the CBPO:0.08Ce3+,0.22Tb3+,0.11Mn2+ sample with the CIE chromaticity coordinates of (0.375, 0.310) and an absolute quantum yield of 50% upon 292 nm excitation. The maximum quantum yield is 84% for CBPO:0.08Ce3+,0.90Tb3+. The good thermal stability of the CBPO:0.08Ce3+,0.22Tb3+,0.11Mn2+ sample shows about 83.6% at 150 °C of its initial PL intensity at room temperature, which attracts more attention. The results suggest that the present phosphors can be potentially applied as candidates of single-component white-light phosphors for UV-pumped w-LEDs. [ABSTRACT FROM AUTHOR]

A series of Eu2+ singly doped α-Ca1.65Sr0.35SiO4:Eu2+ phosphors have been synthesized via the high-temperature solid-state reaction method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), diffuse reflectance spectroscopy and photoluminescence (PL) including temperature-dependent PL were used to characterize the as-prepared samples. The XRD patterns and Rietveld refinement of the presented sample show the pure phase of the as-prepared samples. All of the phosphors exhibit intense and broad absorption bands in the ultraviolet and near ultraviolet (n-UV) range, and produce bright green emission upon 365 nm UV radiation. The critical concentration of Eu2+ for the maximum intensity was determined to be about 1 mol% in α-Ca1.65Sr0.35SiO4:Eu2+ after optimizing the composition. The energy transfer mechanism between Eu2+ was demonstrated to be dipole–dipole interaction. Besides, the fluorescence decay curves, the temperature dependent PL and CIE value of α-Ca1.65Sr0.35SiO4:Eu2+ phosphors were investigated. It is reasonable that the decay times of samples decrease with increasing Eu2+ content. The CIE chromaticity coordinates shift from green (0.197, 0.395) to the border between the green and yellow (0.242, 0.547) region, which agree with the corresponding emission spectra. The maximum quantum yield is 69% for α-Ca1.65Sr0.345SiO4:0.005Eu2+. The thermal stability of luminescence of selected α-Ca1.65Sr0.34SiO4:0.01Eu2+ was also investigated and compared with that of the commercial green phosphor, which shows its good performance. The above results suggest that it is a good candidate for green-emitting phosphors applied in UV/n-UV pumped w-LEDs. [ABSTRACT FROM AUTHOR]

Ca8MgLu(PO4)7:Ce3+,Tb3+,Mn2+ (abbreviated as CMLP:Ce3+,Tb3+,Mn2+) phosphors were synthesized by a high-temperature solid-state method. X-ray diffraction (XRD), photoluminescence (PL) spectra, GSAS structural refinement, and absolute quantum yield and lifetimes were used to characterize the samples. Increasing the Ce3+ doping concentration in the CMLP host shifts the emission peak from 360 to 374 nm. Under UV excitation, the energy transfers (ETs) from Ce3+ to Tb3+ and from Ce3+ to Mn2+ in the CMLP host occurred mainly via a dipole–quadrupole mechanism, and the critical distances of the ion pairs (RC) were calculated by the quenching concentration method and spectral overlap method, respectively. The emission colors of the CMLP:Ce3+,Tb3+,Mn2+ samples could be adjusted from blue to green, and eventually to orange–red by the ET between Ce3+ and Tb3+/Mn2+. Moreover, a white light emission tunable over a wide range was obtained by precisely controlling the contents of Ce3+, Tb3+ and Mn2+. Temperature dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. Based on the good PL properties and varied hues of the CMLP host achieved by adjusting the doping concentration of the activators (Ce3+, Tb3+, Mn2+), CMLP might be promising as a host material for solid-state lighting and display fields. [ABSTRACT FROM AUTHOR]

Ba2(1−x)Zr2Si3O12 (BZSO):xEu2+ (x = 0.005–0.06) phosphors have been prepared by a high temperature solid state reaction. Using X-ray powder diffraction, the structural properties including the phase purity were analyzed through Rietveld analysis. The BZSO:Eu2+ phosphors exhibit a broad excitation band ranging from 200 to 450 nm, and an intense asymmetric green emission band centered at 501 nm under an excitation of 365 nm. The optimum doping concentration of Eu2+ was found for x = 0.03. The detailed energy transfer mechanism among Eu2+ in BZSO is found to be a dipole–dipole mechanism, and the critical distance (RC) for the Eu2+ ions calculated by the concentration quenching and spectral overlap methods are 20.45 and 25.83 Å, respectively. Furthermore, the unexpected blue shift (from green to cyan) in the emission and the increase in the thermal quenching barrier upon cation substitutions (Ca2+/Sr2+ for Ba2+) in the BZSO:0.03Eu2+ system have been investigated, which is due to the variation of the crystal field strength that the 5d orbital of the Eu2+ ion experiences. The underlying mechanism is ascribed to the differences between the average structure and the local coordination environments on the activator ions (Eu2+), as confirmed by the refinement results. Considering the merits of the near-UV light excitation, broad band emission, and good thermal stability, these materials have a potential application as white light emitting diode phosphors. [ABSTRACT FROM AUTHOR]