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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]

Developing novel luminescent materials with ideal properties is an endless project, urged by growing requirements of advances in energy saving, healthy lighting and environmental friendliness. Herein, a series of ScCaOBO3:Ce3+,Mn2+ phosphors with excellent luminescence properties were synthesized by the high temperature solid state method. X-ray diffraction was applied to analyse the phase composition of the obtained phosphors. The morphology and dopant distribution were observed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The Rietveld refinements and luminescence spectra indicate that Ce3+ preferentially occupies the Sc3+ site and produces a blue emission band at around 460 nm, which originates from the characteristic 5d–4f transitions, while Mn2+ preferentially occupies the Ca2+ site and emits red light due to its characteristic 4T1(4G)–6A1(6S) transitions. Upon excitation at 354 nm, both Ce3+ and Mn2+ emissions can be obtained and further investigations evidenced that the broad and intense light emission of Mn2+ located in the red spectral region is the result of energy transfer from Ce3+ to Mn2+. Theoretical calculations reveal that the energy transfer process from Ce3+ to Mn2+ is of the resonance type and is governed by electric dipole–dipole interactions. Since the ScCaOBO3:Ce3+,Mn2+ phosphors are capable of producing broadband emissions that widely cover the blue and red spectral regions, the introduction of a green light-emitting phosphor CMA:Tb3+ can conveniently generate high quality white light. Therefore, a white light-emitting diode device with extremely high color rendering indices, Ra = 93.7 and R9 = 91.9, was successfully obtained. [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]

A high color rendering index white light emitting diode (WLED) is generally produced by combining yellow and red mixed phosphors on a blue chip. Herein we report a single component phosphor based on CaY2Al4SiO12 (CYAS) to achieve warm white light emission with a high color rendering index (Ra), which can be up to 90.5. Ce3+, Mn2+ singly doped and co-doped CYAS phosphors have been synthesized by solid state reactions, respectively, for comparative investigations. The Rietveld X-ray diffraction (XRD) refinements show that the CYAS host crystallizes in a cubic structure with the Ia3¯d space group. The valence states of Ce and Mn inside the CYAS host have been confirmed by XPS and EPR. Ce3+ occupies the Ca2+/Y3+ site and generates a yellow emission band around 543 nm from its characteristic 5d–4f transition. Mn2+ occupies both the dodecahedron Ca2+/Y3+ and octahedral Al3+ sites, emitting red and deep red lights at 616 nm and 750 nm, respectively. These two emission bands are attributed to the 4T1(4G)–6A1(6S) transitions of Mn2+. Upon 460 nm light excitation, both the Ce3+ and Mn2+ characteristic emissions can be obtained, in which the emissions of Mn2+ result from the occurrence of energy transfer from Ce3+ in CYAS. All the results indicate that the prepared CYAS:Ce3+,Mn2+ could be a promising single component phosphor for blue chip WLEDs. [ABSTRACT FROM AUTHOR]

A narrow-band red-light component is critical to establish high color rendition and a wide color gamut of phosphor-converted white-light-emitting diodes (pc-WLEDs). In this sense, Mn 4+ -doped K 2 SiF 6 fluoride is the most successful material that has been commercialized. As with K 2 SiF 6 :Mn 4+ phosphors, Mn 4+ -doped tantalum heptafluoride (K 2 TaF 7 :Mn 4+ ) fulfills a similar luminescence behavior and has been brought in a promising narrow-band red phosphor. But the limited brightness and low moisture-resistant performances have inevitably blocked its practical application. Herein, we employed the density functional theory (DFT)-based ab initio estimation approach to quickly identify the proper sensitizer by systematically investigating the electronic-band coupling between the several possible sensitizers (Rb, Hf, Zr, Sn, Nb, and Mo) and the luminescent center (Mn). Combined with experimental results, Mo was demonstrated to be the optimal sensitizer, which resulted in a 60% enhancement of the emission. On the side, the moisture sensitivity has been effectively improved via grafting the hydrophobic octadecyltrimethoxysilane (ODTMS) layer on the phosphor surface. Through employing the K 2 TaF 7 :Mn 4+ ,Mo 6+ @ODTMS composite as a red component, warm WLEDs with good performance were achieved with a correlated color temperature (CCT) of 4352 K, a luminous efficacy (LE) of 90.1 lm/W, and a color rendering index (Ra) of 83.4. In addition, a wide color gamut reaching up to 102.8% of the NTSC 1953 value could be realized. Aging tests at 85 °C and 85% humidity for 120 h on this device manifested that the ODTMS-modified phosphor had much better moisture stability than that of the unmodified one. These studies provided viable tools for optimizing Mn 4+ luminescence in fluoride hosts.

In this study, a novel temperature-sensitive material, Sr 3 Y 2 Ge 3 O 12 :Bi 3+ ,Sm 3+ phosphor, was successfully synthesized by a solid-state reaction method. Under 376 nm light excitation, the as-prepared phosphor presents both blue emissions of Bi 3+ and orange red emissions of Sm 3+ due to energy transfer from Bi 3+ to Sm 3+ . Owing to the significant difference in thermal quenching properties and the distinguishable emission between Bi 3+ and Sm 3+ ions, the temperature sensing performance of the prepared phosphor was evaluated by measuring the fluorescence intensity ratio (FIR) of Sm 3+ versus Bi 3+ . More importantly, for the first time, it was found that the absolute and relative sensitivities of Sr 3 Y 2 Ge 3 O 12 :Bi 3+ ,Sm 3+ 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.

Cr 3+ -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 Na 3 Ga x Al 1- x F 6 :Cr 3+ 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, Na 3 Ga 0.75 Al 0.25 F 6 :0.35Cr 3+ 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.

Developing novel luminescent materials with ideal properties is an endless project, urged by growing requirements of advances in energy saving, healthy lighting and environmental friendliness. Herein, a series of ScCaOBO 3 :Ce 3+ ,Mn 2+ phosphors with excellent luminescence properties were synthesized by the high temperature solid state method. X-ray diffraction was applied to analyse the phase composition of the obtained phosphors. The morphology and dopant distribution were observed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The Rietveld refinements and luminescence spectra indicate that Ce 3+ preferentially occupies the Sc 3+ site and produces a blue emission band at around 460 nm, which originates from the characteristic 5d-4f transitions, while Mn 2+ preferentially occupies the Ca 2+ site and emits red light due to its characteristic 4 T 1 ( 4 G)- 6 A 1 ( 6 S) transitions. Upon excitation at 354 nm, both Ce 3+ and Mn 2+ emissions can be obtained and further investigations evidenced that the broad and intense light emission of Mn 2+ located in the red spectral region is the result of energy transfer from Ce 3+ to Mn 2+ . Theoretical calculations reveal that the energy transfer process from Ce 3+ to Mn 2+ is of the resonance type and is governed by electric dipole-dipole interactions. Since the ScCaOBO 3 :Ce 3+ ,Mn 2+ phosphors are capable of producing broadband emissions that widely cover the blue and red spectral regions, the introduction of a green light-emitting phosphor CMA:Tb 3+ can conveniently generate high quality white light. Therefore, a white light-emitting diode device with extremely high color rendering indices, R a = 93.7 and R 9 = 91.9, was successfully obtained.