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Technological progress has accelerated the researches into broadband near‐infrared (NIR) luminescent materials as next‐generation intelligent NIR light sources; however, poor thermal stability restricts the applications of NIR phosphors. Herein, new insights into Cr3+‐activated NIR phosphors with improved thermal stability are provided. The photoluminescence intensity originating from the 4T2→4A2 broadband emission of CaLu2Al4SiO12:Cr3+ (CLAS:Cr) with optimal electron occupation (4T2/2E) increases up to 118% at 475 K compared with that at room temperature, which is the best for Cr3+‐activated broadband NIR phosphor. Accordingly, new ideas for the design of thermally stable phosphors are proposed by optimizing the thermal population between 4T2 and 2E states and electron migration from 2E to 4T2 state. Finally, multifunctional applications of CLAS:Cr in NIR fluorescence intensity ratio thermometry, X‐ray detection, NIR phosphor‐converted light‐emitting diodes, and bio‐imaging are demonstrated. [ABSTRACT FROM AUTHOR]

In this study, a novel temperature-sensitive material, Sr3Y2Ge3O12:Bi3+,Sm3+ phosphor, was successfully synthesized by a solid-state reaction method. Under 376 nm light excitation, the as-prepared phosphor presents both blue emissions of Bi3+ and orange red emissions of Sm3+ due to energy transfer from Bi3+ to Sm3+. Owing to the significant difference in thermal quenching properties and the distinguishable emission between Bi3+ and Sm3+ ions, the temperature sensing performance of the prepared phosphor was evaluated by measuring the fluorescence intensity ratio (FIR) of Sm3+versus Bi3+. More importantly, for the first time, it was found that the absolute and relative sensitivities of Sr3Y2Ge3O12:Bi3+,Sm3+ could be tuned by changing the concentration of activators to determine the optimal temperature measurement conditions, which opened up the possibility of improving the performance of fluorescence temperature sensing materials. [ABSTRACT FROM AUTHOR]

Cr3+-Activated broadband near-infrared (NIR) luminescence materials are attracting much attention as next-generation smart NIR light sources that are widely used in night vision, bioimaging, medical treatment, and many other fields. Herein, a series of Na3GaxAl1−xF6:Cr3+ NIR phosphors with broadband emission and tunable luminescence properties were designed and prepared. The luminescence intensity, peak position and full width at half maximum (FWHM) of the materials can be controlled by adjusting the crystal field strength. Furthermore, Na3Ga0.75Al0.25F6:0.35Cr3+ exhibited high luminous efficiency and the emission intensity remained 81% at 423 K compared with the initial value at 298 K. The structural confinement and the electron–phonon coupling (EPC) effect may account for its good thermal stability. Finally, a pc-NIR-LED device with a photoelectric conversion efficiency of 6.53% at 350 mA was fabricated by combining the as-prepared NIR phosphor and a blue InGaN chip, and its applications in night vision and medical fields were further investigated. This work will promote the development of NIR phosphors with tunable luminescence properties. [ABSTRACT FROM AUTHOR]

The radius of trivalent scandium ions is much smaller than those of other rare earth ions and thus research studies targeting the substitution of the scandium site with other light-emitting rare earth ions are rarely reported. In our present work, special attention is paid to the effect of Dy3+ doping on the crystal structure, atomic site occupancy and luminescence properties of the ScCaBO4 host as Dy3+ often serves as an individual activator for single-phase white light-emitting phosphors. Herein a series of ScCaBO4:Dy3+ phosphors were prepared by solid-state reactions. The phase composition was recorded by X-ray diffraction analysis and XRD refinement reveals that a pure phase could be maintained even when the Dy3+ concentration reaches 11%. Scanning electron microscopy (SEM) was utilized to observe the morphology and EDS mapping was used to investigate elemental distribution. The luminescence performances of the phosphors were investigated using UV-vis diffuse reflectance spectra, steady-state excitation and emission spectra and also transient luminescence decays. Dy3+ luminescence can be ascribed to its 4F9/2 → 6H15/2, 6H13/2 and 6H11/2 transitions, producing blue, yellow and red emissions. The Dy3+ concentration was further optimized at 3%, at which the CIE coordinates and fluorescence lifetimes were (0.425, 0.413) and 0.546 ms, respectively. Thermal quenching studies of the ScCaBO4:0.03Dy3+ phosphor show that Dy3+ luminescence at 400 K can maintain 60.91% of its initial value measured at room temperature. All the results indicate that the ScCaBO4:Dy3+ inorganic phosphors could be a promising single component phosphor for near-UV chip based WLEDs. [ABSTRACT FROM AUTHOR]

Eu and Mn singly doped and codoped Na(Sr,Ba)PO phosphors were synthesized, and their luminescent properties were investigated. A broad blue emission and a broad orange emission band were observed in Na(Sr,Ba)PO:Eu, Mn phosphor. The resonant-type energy transfer from Eu to Mn was demonstrated, and the energy transfer efficiency was also calculated according to their emission spectra. Based on the principle of energy transfer, the emission intensity ration of Eu and Mn could be appropriately tuned by adjusting the contents of activators. Due to the strong absorption in the 250-400 nm range, Na(Sr,Ba)PO:Eu, Mn phosphor could be used as a potential candidate for near-UV white light-emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

Eu 2 + and Tb 3+ singly doped and co-doped NaBaPO 4 phosphors were synthesized by solid state reaction. The structure character, photoluminescence properties and the lifetime were investigated. The emission spectra of NaBaPO 4 :Eu 2+ , Tb 3+ , Na + phosphor show both broad blue emission band and sharp green emission peaks. The energy transfer mechanism from Eu 2+ to Tb 3+ in NaBaPO 4 host was discussed. The excitation spectra of NaBaPO 4 : Eu 2+ , Tb 3+ , Na + phosphor show broad excitation band in the 250–400 nm range, which was in agreement with the near-ultraviolet (n-UV) chip. The hue of the NaBaPO 4 : Eu 2+ , Tb 3+ , Na + phosphors could be appropriately tuned by adjusting the contents of activators. [ABSTRACT FROM AUTHOR]

A series of Tb3+-doped, Ce3+,Tb3+-co-doped and Ce3+,Tb3+,Mn2+-tri-doped CaScBO 4 (CSB) ceramic phosphors were prepared by solid-state reaction. X-ray diffraction (XRD) was taken to confirm the phase purity of all as-prepared phosphors powder. Steady-state and transient-state fluorescence spectra were applied to evaluate the luminescence properties of the phosphors. The results indicated that significant enhancement on Tb3+ luminescence was successfully realized by the Ce3+-induced resonance energy transfer and confirmed that the energy transfer from Ce3+ to Tb3+ was governed by an electronic dipole-dipole interaction. Compared to the CSB:Tb3+ phosphors whose optimal excitation located at 378 nm, the occurrence of Ce3+-Tb3+ energy transfer not only allowed the optimal excitation to peak at around 390 nm but also gifted the CSB:Ce3+,Tb3+ phosphors color tunability from blue, cyan to green. Then, two different designs of white light by the introduction of Mn2+ luminescence were performed. One was the combination of CSB:Ce3+,Tb3+ and CSB:Ce3+,Mn2+ phosphors, based on the co-excitation of the above two phosphors at the same wavelength. Another was the direct use of the tri-doped CSB:Ce3+,Tb3+,Mn2+ phosphors. Both designs succeeded in the generation of white light emission. The performance of these two designs in real devices were also studied. The direct use of the tri-doped CSB:Ce3+,Tb3+,Mn2+ phosphor in white light-emitting diode (WLED) device can produce white light with a color rendering index (CRI) up to 85.3 while the use of the CSB:Ce3+,Tb3+ and CSB:Ce3+,Mn2+ phosphors combination can just produce a value of 76.6 in CRI. [ABSTRACT FROM AUTHOR]

Exploration of novel red emitting phosphors containing Eu3+ ions is an everlasting topic in the field of luminescent materials due to the application requirement of warm white light-emitting diodes. In this work, the Eu3+-doped ScCaO(BO 3) phosphors were synthesized though the high temperature solid-state reaction method. The phase purity and detail information on crystal structure were obtained by X-ray diffraction (XRD) and the technology of Rietveld XRD refinement. Scanning electron microscopy (SEM) was applied to check the particle morphology and EDS mapping was taken to analyze element distributions. Optical properties of the phosphors were studied by measuring the steady-state excitation and emission spectra and also the transient luminescence decays. The emission spectra of ScCaO(BO 3):Eu3+ majorly consisted of 5D 0 -7F 1 , 7F 2 and 7F 4 transitions, covering the orange (582–605 nm), red (605–635 nm) and deep red (690–720 nm) spectral regions. The doping concentration of Eu3+ ions was optimized to 12% to maximize the optical performance of the red emitting phosphors, whose CIE coordinate and fluorescent lifetime were (0.6458, 0.3537) and 1.516 ms, respectively. The investigation of the thermal quenching behavior of the ScCaO(BO 3):0.12Eu3+ phosphor reveals that the emission intensity of Eu3+ at 400 K can maintain 68.98% of that at room temperature due to the existence of the thermal activation energy of 0.258 eV. Using such a red-emitting material, the prototype warm white LED device with the CIE coordinate of (0.3262, 0.3363), color rendering index of 86.1 and correlated color temperature of 5871 K can be obtained by combining with the blue emitting BaMgAl 10 O 17 :Eu2+ and green emitting Zn 2 SiO 4 :Mn2+ phosphors and coating all three on a near-UV LED chip. All the results demonstrate that the ScCaO(BO 3):0.12Eu3+ phosphor can sever as a potential red emitting candidate for near-UV excited warm WLEDs. • A novel red phosphor ScCaO(BO 3):Eu3+ has been synthesized. • The quantum efficiency of ScCaO(BO 3):0.12Eu3+ phosphor can reach 73.51%. • The obtained phosphors are suitable for tricolor-composited white light. [ABSTRACT FROM AUTHOR]

The cerium, manganese solely and co-doped MgAl 2 O 4 have been synthesized via traditional solid-state reaction. XRD refinement and the first-principle calculation indicate that the Mn2+ preferentially substitutes for Mg2+ while Ce3+ is more preferential for the substitution of Al site in MgAl 2 O 4 matrix. Effective energy transfer enables the photoluminescence spectra of the co-doped phosphors to show both ultraviolet (UV) emission of Ce3+ at around 359 nm and green emission of Mn2+ peaked at 516 nm. The separated emission bands of Ce3+ and Mn2+ indicate the good signal resolution. Due to relative thermally stable of Mn2+ and huge thermal quenching of Ce3+, the temperature sensing performance of the prepared phosphor was evaluated by measuring fluorescent intensity ratio (FIR) of Ce3+ to Mn2+ and lifetime of Ce3+. The maximum of the S r values is 0.59%K−1 at 448 K for FIR mode and 0.40%K−1 at 523 K for lifetime mode, respectively. Satisfactory repeatability makes it suitable for dual-mode optical thermometry. • First-principle calculation indicates Ce3+ preferentially substitutes Al3+ site. • The energy transfer mechanism from Ce3+ to Mn2+ in MgAl 2 O 4 was demonstrated. • The potential of MgAl 2 O 4 :Ce3+, Mn2+ for dual-mode thermometry was evaluated. • MgAl 2 O 4 :Ce3+, Mn2+ shows high repeatability by both FIR and lifetime technologies. [ABSTRACT FROM AUTHOR]

• A novel terbium-sensitized Eu3+-activated phosphor, Ca 2 TbSn 2 Al 3 O 12 :Eu3+, has been designed and synthesized. • The solid-state MAS NMR spectra have been used to confirm the reasonability of the XRD structural refinements. • The far red emission of Eu3+ is extremely dominant, which can well match the absorption spectra of P fr in plants. • Terbium is one of the host composition elements, and thus, highly efficient Tb3+-Eu3+ energy transfer can be realized. • An experimental evidence that proves the existence of terbium bridge energy transfer has been discussed in detail. [Display omitted] Traditional Eu3+-activated inorganic phosphors are habitually used for general lighting and display because they generally emit either intense orange (5D 0 -7F 1) or red (5D 0 -7F 2) light whose wavelength is shorter than 630 nm. However, less known nor focused is that Eu3+ at sites with specific symmetry can intensify its 5D 0 -7F 4 transition, enabling Eu3+ itself to emit deep red light (>700 nm) even stronger than the above orange and red ones. Herein, a novel Eu3+-activated phosphor, Ca 2 TbSn 2 Al 3 O 12 :Eu3+, is developed from the garnet structure. Differing from other Eu3+-activated phosphors, the 5D 0 -7F 4 transition of Eu3+ in the host is dominant and the orange, red and deep red emissions are balanced. Such special features of Eu3+ luminescence mainly meet the need of phytochromes (P FR and P R) in plants. Additionally, bridge style energy transfer from the host composition element Tb3+ to the activator Eu3+ can be observed. It is found the Tb3+-Eu3+ energy transfer here takes through the mechanism of dipole-dipole interaction and the simulation on decay curve of Eu3+ upon Tb3+ excitation, for the first time, confirms the existence of terbium bridge energy transfer. For the Ca 2 Tb 0.60 Sn 2 Al 3 O 12 :0.40Eu3+, the energy transfer efficiency is as high as 94.4% and the emission color is totally red. Thermal quenching studies reveal that the emission intensity of the phosphor at 425 K sustains 80% of its initial intensity at room temperature. By fabricating the phosphor with a 380 nm LED chip, a plant-growth LED device can be obtained. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical analysis of optical properties of two recently synthesized phosphors with the Ce3+ ions (Na3LuSi2O7 and NaSr4(BO3)3) was performed. The exchange charge model of crystal field was used to calculate the crystal field parameters and cerium 5d states splittings for each site in Na3LuSi2O7. Analysis of vibronic coupling of Ce3+ in NaSr4(BO3)3 resulted in a quantitative modeling and theoretical simulation of the experimental spectra. Electronic energy levels, vibrational frequencies and ion-lattice vibronic coupling strength are determined specifically for Ce3+ at different sites. The performed analysis allows for getting detailed description of the optical properties of trivalent cerium in the considered crystals and provides a general guide to understanding and characterizing other Ce3+ activated phosphors. [Copyright &y& Elsevier]

• A new path, cation-exchange-assisted recrystallization, was developed to synthesis of K 2 TiF 6 :Mn4+. • The absorbance of the optimal K 2 TiF 6 :Mn4+ reaches up to 74.27%. • The internal & external quantum efficiencies of K 2 TiF 6 :Mn4+ reaches up to 93.06 & 69.09%. • The white LEDs packaged using K 2 TiF 6 :Mn4+ cover color gamut of 98.61% NTSC. • The amount of phosphor usage was reduced by 37.55% with respect to commercial one. K 2 TiF 6 :Mn4+, along with K 2 SiF 6 :Mn4+ and K 2 GeF 6 :Mn4+, is a red phosphor with narrow-band emission for wide-gamut display backlight LEDs. However, its poor absorbance results in low external quantum efficiency, which is a major obstacle for commercial utilization. This paper describes our pursuit of a new path to synthesize the K 2 TiF 6 :Mn4+ phosphor through cation-exchange-assisted recrystallization achieving excellent performance. The absorbance and the internal and external quantum efficiencies of the as-prepared phosphor reached up to 74.27, 93.06, and 69.09%, respectively; the luminescence intensity at 150 °C was 97.5% of that at 25 °C. The color gamut of white LEDs packaged with optimized K 2 TiF 6 :Mn4+ covers 98.61% of the NTSC (National Television Standard Committee) color gamut and the amount of phosphor used was reduced by 37.55%, as compared with commercially available LEDs achieving similar performance. These breakthroughs strongly support the commercial implementation of K 2 TiF 6 :Mn4+ phosphors. [ABSTRACT FROM AUTHOR]

The green-emitting phosphor SrSi 2 O 2 N 2 : Eu2+, along with the cyan-emitting phosphor BaSi 2 O 2 N 2 : Eu2+, is a key component for phosphors used to package natural sunlight full-spectrum LED devices. Thereby, the synthesis of high-efficiency and thermal-stability luminous SrSi 2 O 2 N 2 : Eu2+ with an economic approach is very important for the development of LED industry. In this work, the syntheses of SrSi 2 O 2 N 2 : Eu2+ phosphors were optimized from four aspects: strontium sources, reaction atmospheres, reaction vessels, and reaction fluxes. Meanwhile, the relationship among photoluminescence performances, crystal structures, and morphologies were examined. The results show that the synthesis of SrSi 2 O 2 N 2 : Eu2+ from SrO and Sr(NO 3) 2 sources are beneficial to obtain N-rich oxynitide structure, which is helpful to improve luminescence. By employing SrCO 3 and Sr(NO 3) 2 as strontium sources, however, the SrSi 2 O 2 N 2 : Eu2+ is O-rich and the by-product Sr 2 Si 5 N 8 :Eu is introduced. The optimal conditions for the synthesis of SrSi 2 O 2 N 2 : Eu2+ is by utilizing SrO as a strontium source, in N 2 atmosphere, adopting Mo crucible, and adding NH 4 Cl as flux. The quantum yield of the optimal SrSi 2 O 2 N 2 : Eu2+ phosphor under the excitation of 380 nm reaches up to 100%. Image 1 • In addition to carbonate and orthosilicate routes, this work reports a third one to synthesize SrSi 2 O 2 N 2 :Eu2+. • Among variant strontium sources, SrO was approved as the best for synthesis of SrSi 2 O 2 N 2 :Eu2+. • The N-rich oxynitride is helpful to improve luminescence efficiency of SrSi 2 O 2 N 2 :Eu2+. • Reaction of SrO with Si 3 N 4 in N 2 atmosphere with NH 4 Cl as flux is optimal synthesis for SrSi 2 O 2 N 2 :Eu2+. • The quantum yield of SrSi 2 O 2 N 2 :Eu2+ excited with 380 nm reaches up to 100%. [ABSTRACT FROM AUTHOR]