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Red luminescent phosphor SrLaGa3O7:Mn4+ was prepared by the traditional high-temperature solid-state reaction. The structural characteristics, luminescence properties and the performance of this phosphor were investigated in light-emitting diode devices. Deep red emission peaking at ∼715 nm was observed under the excitation wavelength in the range of 220–550 nm, which is related to the charge transfer band of Mn4+–O2− and the 4A2g → 4T1g, 4A2g → 2T2g and 4A2g → 4T2g transitions of Mn4+. In particular, SrLaGa3(1−x) O7:3xMn4+ exhibits the strongest absorption in the near ultraviolet region (350–410 nm). This feature can well match the emission of current commercial near-ultraviolet chips, and is expected to be used in white LEDs. Moreover, we also conducted a thermal quenching experiment on the SrLaGa3O7:Mn4+ phosphor, and the obtained activation energy was 0.4 eV, indicating that the quenching temperature is (T50%) 370 K. Finally, the application of the SrLaGa3O7:Mn4+ phosphor in constructing a LED device was explored. At a driving current of 20 mA, the Commission on Illumination (CIE) coordinates of the device are (0.3281, 0.3080), with a high color rendering index (CRI) of 91.9 and a low corresponding color temperature (CCT) of 4315 K. Experimental results show that the phosphor has broad prospects in preparing white LED devices excited by near-ultraviolet light. [ABSTRACT FROM AUTHOR]

The luminescence characteristics of Bi3+ ions in solids have been extensively investigated during recent decades; however, the origin of extra spectra signals (referred to as D-bands) of Bi3+ in some compounds still remains ambiguous. In this work, a novel Bi3+-doped phosphor La3SnGa5O14:Bi3+ (LSGO:Bi3+) was successfully synthesized via the conventional solid-state reaction method. The structural characteristics, luminescence properties and concentration quenching of the LSGO:Bi3+ phosphor were investigated systematically and two emission bands centered at 360 and 540 nm were observed, respectively. The narrow band emission centered at 360 nm was attributed to the transition of 3P1 → 1S0 (A-band) of Bi3+ while the broadband emission centered at 540 nm was considered as the D-band emission. A combined experimental and theoretical approach was employed in order to confirm the origin of the D-band emission of LSGO:Bi3+. Temperature dependent photoluminescence of LSGO:Bi3+ and the fluorescence lifetime of two emission centers were studied. Moreover, the energy of metal-to-metal charge-transfer (MMCT) was also calculated. Ultimately, the D-band emission of LSGO:Bi3+ was considered to originate from the forbidden 3P0 → 1S0 electronic transition of Bi3+. This work will contribute to a better understanding of the luminescence mechanisms of Bi3+ doped phosphors and pave the way toward the future development of new effective Bi3+ activated luminescent materials. [ABSTRACT FROM AUTHOR]

In this study, a blue fluorescent material Sr3Y(BO3)3:Bi3+ was synthesized by the high temperature solid-state reaction method. The corresponding structural characteristics, concentration and temperature dependent luminescence characteristics of Sr3Y(BO3)3:Bi3+ and the LED device performances were systematically studied. At different excitation wavelengths in the range of 340–375 nm, the photoluminescence (PL) region can be adjusted from green (CIE: (0.2524, 0.4063); Peak: 511 nm) to blue (CIE: (0.1936, 0.1236); Peak: 415 nm). The best excitation peaked at ∼370 nm, which well matches with the emission of a commercial near-ultraviolet (NUV) light-emitting diode (LED) chip. The thermal quenching experiment was performed, and the activation energy was calculated as 0.23 eV. At high temperature, the Sr2.55Y(BO3)3:0.45Bi3+ phosphor presented good thermal stability (79.99% of RT emission intensity at 420 K). LED devices (chip: 370 nm) using the Sr2.55Y(BO3)3:0.45Bi3+ phosphor as a fluorescent material showed excellent electroluminescence performance. Under a driving current of 20 mA, the devices showed CIE coordinates of (0.3842, 0.3980), a correlated color temperature (CCT) of 4053 K and a high color rendering index (Ra) of 91.6. This work demonstrates that Sr3Y(BO3)3:Bi3+ is a promising NUV excited blue fluorescent material which shows advantage in white light-emitting diodes for solid-state lighting. [ABSTRACT FROM AUTHOR]

In this paper, a blue-emitting phosphor CaYGaO4:Bi3+ is reported, which has a broad emission band peaked at 435 nm covering the 375 nm to 575 nm spectral region. The CIE coordinates of CaYGaO4:Bi3+ is (0.1536, 0.0885) with color purity of 85.2%. Importantly, when Bi3+ ions are introduced into the CaYGaO4 host, the excitation peak of Bi3+ is located at 370 nm, which matches well with the efficient near-ultraviolet (NUV) light emitting diode (LED) chips. Furthermore, the emission intensity of the CaYGaO4:Bi3+ phosphor increased ∼1.47 times by adding Li2CO3 as a fluxing agent. The quantum efficiency of the prepared CaYGaO4:Bi3+,Li+ phosphor reaches 45.7% under 370 nm excitation, and the PL intensity remains 76.3% of that at room temperature at 423 K. Using the CaYGaO4:Bi3+,Li+ phosphor, coupled only with an orange phosphor (Sr,Ba)3SiO5:Eu2+ and a 370 nm NUV chip driven by 20 mA current, a NUV-based WLED, with chromaticity coordinates of (0.3610, 0.3360), correlated color temperature (CCT) = 4304 K and color rendering index (CRI) = 86.9, has been achieved. The white light emitting diodes employing CaYGaO4:Bi3+ as a blue-emitting component exhibit superior electroluminescence properties. All results demonstrate that CaYGaO4:Bi3+ is a promising blue component for application in NUV-based WLEDs. [ABSTRACT FROM AUTHOR]

A blue emitting phosphor Na2Y2B2O7:Bi3+ was synthesized by a solid state reaction method. The structure characteristics, concentration, temperature-dependent luminescence and light emitting diode (LED) device performance were systematically studied. Adjustable photoluminescence (PL) from blue to green under different excitation wavelengths from 320 to 390 nm was observed, which is attributed to the complex energy transfer between multiple Bi3+ centres. Moreover, strong absorption in the near ultraviolet region (350–400 nm) was observed in Na2Y2B2O7:Bi3+, which is desirable for LEDs excited by near ultraviolet chips. In addition, a thermal quenching experiment was carried out and the calculated activation energy was 0.28 eV, indicating that this new Na2Y2B2O7:Bi3+ phosphor has good thermal stability. Finally, we explored the application of the Na2Y2B2O7:Bi3+ phosphor by encapsulating LED devices. The device Commission of Illumination (CIE) coordinates are (0.3572, 0.3407), and a high color rendering index (CRI) of 91.1 and a low corresponding color temperature (CCT) of 4480 K under 60 mA current were recorded. These characteristics show that this phosphor can be used to prepare white LED devices excited by near ultraviolet chips. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) persistent luminescence (PersL) materials have recently evoked considerable interest in the field of biomedicine, but the choices of efficient emitters for NIR PersL phosphors are rather limited. Herein, we report a new class of Fe3+-activated NIR PersL phosphor based on the LiGaO2 host, which exhibits an intense NIR PersL at around 748 nm and possesses an ultra-long PersL time of much longer than 26 h. The optical properties of this phosphor as well as the trapping and de-trapping processes, the trap characteristics, and the underlying PersL mechanism are comprehensively studied by means of photoluminescence (PL), PersL, electron paramagnetic resonance (EPR), thermoluminescence (TL), and X-ray photoelectron spectroscopies (XPS). It was found that the NIR PersL in this material is closely related to the oxygen vacancies. Furthermore, the penetration experiments and cytotoxicity tests of the biological tissue show that this material has great potential for bioimaging applications. Our achievement in the case of nontoxic Fe3+-activated LiGaO2 phosphors lays the foundation for the future design of Cr3+-free PersL phosphors with efficient NIR PersL towards versatile bioapplications. [ABSTRACT FROM AUTHOR]

A narrow-band emitting phosphor is essential for high performance liquid crystal display (LCD) backlights. However, most of the narrow-band emitting phosphors are only realized by doping Eu or Mn ions, which limits the optional range. Especially, the discovery of narrow-band blue-emitting phosphors without resorption in the visible light region is still challenging. Herein, an emerging rare-earth free and narrow-band blue-emitting phosphor, Y3Al2Ga3O12:Bi3+, with high color purity (up to 90.9%) has been discovered via selective excitation for the first time. The luminescence properties such as photoluminescence (PL), photoluminescence excitation (PLE) and lifetime spectra were systematically investigated. The sample exhibited tunable emission ranging from red to green and then to blue under variable excitation, originating from four Bi luminescence centers. Y3Al2Ga3O12:Bi3+ exhibits a narrow-band blue emission centered at 410 nm with a full width at half maximum of 39 nm and strong absorption in the range of 260–380 nm, which matches well with the commercial near-ultraviolet (NUV) chip. What's more, the sample shows remarkable thermal stability, retaining 90.71% of its room temperature emission intensity at 420 K. In this work, a rare-earth free narrow-band blue-emitting phosphor has been discovered for the first time. [ABSTRACT FROM AUTHOR]

To avoid color drift WLEDs at high temperatures, it is important to develop color stable luminescent materials. Herein, we have reported a phosphor YTaO4:Bi3+ with stable blue emission upon ultraviolet excitation even during the temperature changes between 300 and 480 K. Upon excitations into host absorptions, tunable blue emission can be observed from 400 nm to 450 nm due to the enhanced energy transfer efficiency from the host to bismuth ions as the concentration of bismuth increases. As the excitation scheme is modulated between 355 and 370 nm, white emission can be achieved in YTaO4 singly doped with Bi3+, which has rarely been reported previously. As a proof-of-concept study, prototype WLEDs have been developed with phosphor YTaO4:Bi3+ and 365 nm InGaN chips under different driving currents. Our findings make it possible to develop single-phase white light-emitting phosphors activated by single Bi3+ ions for WLEDs and can also inspire the development of WLED devices with high chromatic stability. [ABSTRACT FROM AUTHOR]

Fiber lasers operating at around 900 nm based on Nd3+ doped fibers have attracted intense attention recently for generating high performance pure blue laser sources by frequency doubling, which could be applied in the fields of laser color displays, laser driven solid lighting and high density storage. Although several approaches have been proposed to realize laser operation at this band, for example by nitrogen cooling or utilizing fibers with a special waveguide design, the intrinsic low fluorescence branching ratio of the three-level 4F3/2 → 4I9/2 transition (900 nm) is still a serious problem that limits the development of laser devices towards compactness and high efficiency. Here, we report a crystal field strength and structural engineering strategy; accordingly, not only can the branching ratio of Nd3+ be tuned towards enhancing the 4F3/2 → 4I9/2 transition, but also the near-infrared (NIR) emission intensity could be improved by six times. Furthermore, the lifetimes of the upper 4F3/2 level were also prolonged from 124 to 246 μs, simultaneously. Systemically, optical and structural analysis implies that the fine-tuning of Stark splitting, the spectroscopic quality factor (χ) and the dispersed state of Nd3+ are the main reasons for this intriguing scenario. These results will help us design optical glass fibers by an inherent local structure based strategy to realize efficient and compact 0.9 μm fiber lasers for high performance pure blue fiber lasers. [ABSTRACT FROM AUTHOR]

In this work, a series of novel non-rare-earth ion activated phosphors Ba2Y5−xB5O17:xBi3+ for white light-emitting diodes (WLEDs) was prepared via the high temperature solid state reaction route. The Ba2Y5−xB5O17:xBi3+ phosphors show a tunable emission range from blue to green upon different excitation wavelengths, arising from the intricate energy transfer among multi Bi3+ emission centers. Among them, when used as a blue-emitting phosphor, Ba2Y5B5O17:Bi3+ has efficient absorption in the range of 360–390 nm, which matches well with the near ultraviolet (NUV) light emitting diode (LED) chips. Furthermore, Ba2Y5B5O17:Bi3+ phosphor exhibits good resistance to thermal degradation with a quantum efficiency (QE) of 46% under 370 nm excitation. All results indicate that the Ba2Y5B5O17:Bi3+ phosphor has potential application in WLEDs. [ABSTRACT FROM AUTHOR]

Persistent luminescent (PPL) materials have attracted wide attention in various fields, such as bio-imaging, optical information memory, and emergency lighting and signs. Single ion doped PPL materials with stable emission are ideal for practical applications, but a PPL material that covers the entire wavelength range, from visible to near infrared, is difficult to achieve in a single-ion doped material. Here, we present a novel PPL phosphor whose emission ranges from 440 to 850 nm, from a single Tm3+ ion doped Sr2SnO4. Persistent bluish-green light from the optimally alloyed sample (Sr1.98SnO4:0.02Tm3+) can be observed by the naked eye after 30 min, which may be due to the interactions between electron traps from Tm3+ doping and the host deeper than 0.71 eV, as indicated by thermoluminescence (TL) analysis. The fabricated intelligent PPL, using two-dimensional code technology with a write-in and read-out property, was achieved, while the performance of NIR PPL needs to be improved in the future. We anticipate that these results will stimulate research on single emitter-based PPL emission phosphors and diodes for next-generation lighting and anticounterfeiting technology. [ABSTRACT FROM AUTHOR]

Mechanoluminescence (ML) from most state-of-the-art phosphors primarily appears within the spectral range of ultraviolet to visible and does not lie in the biological transparency windows, therefore limiting its application in biological fields. In this study, we report a novel Nd3+ doped LiNbO3 phosphor, which demonstrates intense and elastic near infrared (NIR) ML under compressive forces. The ML intensity increases with force from 500 to 2500 N, and it remains stable under larger forces due to the failure of the resin. Both the starting and stopping of force loading are found to trigger ML, but the intensity is weakened over time. Meanwhile, this ML emission, peaking at 895 nm, is located within the first biological transparency window range (650–950 nm), and it has been proved to penetrate tissue thicker than 20 mm. This, therefore, extends ML into the NIR range and makes it possible to detect biomechanical behavior in situ inside living bodies. [ABSTRACT FROM AUTHOR]

The poor moisture-resistant property of the commercial narrow band red-emitting K2SiF6:Mn4+ phosphor restricts its practical application in high performance warm WLEDs. Herein, we report epitaxial growth via simple ethanol-induced deposition to enhance the luminescence and moisture resistance of K2SiF6:Mn4+. Specifically, an appropriate amount of ethanol at the end of the synthesis leads to epitaxial growth of a K2SiF6:Mn4+ shell. The resultant K2SiF6:Mn4+@K2SiF6:Mn4+ presents higher photoluminescence intensity due to a high Mn4+ critical concentration in the K2SiF6:Mn4+ epitaxial shell. Furthermore, the epitaxial growth of the K2SiF6 shell on K2SiF6:Mn4+ is designed to conquer the moisture resistance. As expected, the formed K2SiF6:Mn4+@K2SiF6 retains 82% of the initial emission intensity after being immersed in water for 4 h and 90% after being exposed to high temperature and humidity (85 °C, 85%) for 10 days. By employing K2SiF6:Mn4+@K2SiF6 as a red phosphor, a packaged white LED exhibits excellent performance with a CRI of 96.5, a CCT of 2879 K and a luminous efficacy of 119.74 lm W−1. More importantly, this fabricated WLED device retains high luminous efficacy and undergoes minor chromatic coordinate changes when aged at high temperature and humidity (85 °C, 85%). Therefore, these findings not only illustrate the effect of ethanol addition on the photoluminescence intensity of Mn4+ doped phosphors in the synthesis process, but also provide a facile strategy to improve the moisture resistance of K2SiF6:Mn4+ for warm WLEDs in the future. [ABSTRACT FROM AUTHOR]

Bi-Doped photonic materials with broadband near infrared (NIR) photoemission have allowed rapid progress of new-generation fiber lasers and super-broadband optical amplifiers. Despite this, major challenges persist towards realizing super-broad and efficient Bi NIR emission covering the whole telecommunication window due to the complicated luminescence behavior, especially for glasses doped with a low Bi content. Here, via introducing nitride into glasses, we obtained super-broad and highly reinforced NIR emission in multi-component borogermanate glasses, which resulted from the generation of multiple Bi NIR-active centers. The spectral bandwidth exceeded ∼600 nm; this enabled Bi-activated glasses to cover the whole NIR region (850–1700 nm), which can hardly be realized by quantum-dot-doped glasses, rare earth-functionalized glasses or current Bi-doped multi-component photonic glasses. A detailed analysis of the spectra and tailoring of local glass structures revealed that the compact glass structure with the addition of antimony oxide and the bonding effect of nitrogen could contribute to significant increase in the Bi NIR emission intensity and decay lifetime. The newly generated Bi luminescent centers may have originated from the low-valence Bi effected by oxygen vacancies. These results will add new knowledge to the luminescence behaviors of Bi and may help solve the current limitations of Bi-doped glass and fiber materials. Moreover, the nitridation of materials may offer a way to fundamentally boost luminescence efficiency, especially for ultra-low activator content. [ABSTRACT FROM AUTHOR]

Mn4+ doped fluoride phosphors have attracted tremendous attention in the solid-state lighting field due to the outstanding feature of efficient narrow band red emission. However, poor resistance against moisture-induced luminescence quenching is a recognized obstacle for realizing their wider commercial use. Herein, we design and fabricate a highly stable red phosphor based on previously unnoticed Rb2SnF6:Mn4+, which, estimated by the single crystal X-ray diffraction data, crystallizes in the trigonal space group P3̅m1 with the lattice parameters a = b = 6.0323(12) Å, c = 4.7880(8) Å, and V = 150.89(7) Å3. The Rb2SnF6:Mn4+ as expected exhibits highly efficient red emission upon excitation by UV and blue light. Significantly, the poor water resistance is conquered by constructing a protective deactivated layer with surface reduction of Mn4+. A treatment solution with appropriate reducing ability is emphasized to obtain Rb2SnF6:Mn4+ with simultaneous high brightness and water resistance. The results show that the low concentration of H2C2O4 solution treated Rb2SnF6:Mn4+ preserves a bright red-emitting color analogous to its initial color and ＞95% of its initial emission intensity when immersing in water at room temperature (RT) and in boiling water for 3 h. Lastly, by employing H2C2O4 treated Rb2SnF6:Mn4+ as a red phosphor, a high quality WLED with a CRI of 90, CCT of 3936 K and luminous efficacy of 106.24 lm W−1 is fabricated. This work not only experimentally fabricates a new efficient and stable Rb2SnF6:Mn4+ phosphor that can be used for high performance warm WLEDs but also provides a deep insight into how to well address moisture-induced Mn4+ luminescence quenching through appropriate reduction of Mn4+, opening up new opportunities for future solid-state lighting purposes. [ABSTRACT FROM AUTHOR]

The generation of optical afterglow and comprehension of the structure–function mechanism in glasses have not been well studied to date owing to the uncertainty of internal structure and defects, let alone being able to tailor the afterglow. Herein, we fabricate a new type of Mn2+-doped calcium aluminium germanate photonic glasses that demonstrate red to near-infrared persistent luminescence from 560 to 820 nm. Provoked by the understanding of amorphous structure continuity, facile network topology was utilized as a tuning strategy, resulting in modulation of the persistent luminescence time from 30 min to longer than 24 h. The density of correlative electronic defects increases with their depth gradually deepening from 0.69, 0.78, and 0.83 eV to 0.80, 0.85, and 0.90 eV. Multiple measurements reveal that the internal structure evolves towards regular crosslinking, promoting the incorporation and stabilization of Mn2+ along with the change of defects, all of which are conducive to afterglow. The possible attribution of defects stems not only from the structural intrinsic state, but also from defects caused by the photo-oxidation of Mn2+. Coupled with their association to afterglow, the mechanism of persistence regulation is expounded in detail, and its potential applications in displays and in vivo imaging are demonstrated. This work suggests accessible references to the rational design of persistent materials with flexible persistence or even other advantageous functions. [ABSTRACT FROM AUTHOR]

Recently, as a key red component in the development of warm white light-emitting diodes (WLEDs), Mn4+-doped fluorides with narrow red emission have sparked rapidly growing interest because they improve color rendition and enhance the visual energy efficiency. Herein, a red nanophosphor, K2NaGaF6:Mn4+, with a diameter of 150–250 nm has been synthesized using a simple co-precipitation method. Rietveld refinement reveals that it crystallizes in the space group Fm3̅m with the cell parameter a = 8.25320(4) Å. The exchange charge model (ECM) has been used to calculate the energy levels of Mn4+ ions in K2NaGaF6, which match well with the experimental spectra. The as-synthesized phosphor exhibits a narrow red emission at around 630 nm (spin-forbidden 2Eg→4A2 transition of Mn4+ ions) when excited at 365 nm (4A2g→4T1g) and 467 nm (4A2g→4T2g), with a quantum efficiency (QE) of 61% and good resistance to thermal quenching. Based on the structure, the formation mechanism of ZPL has been discussed. In addition, the concentration-dependent decay curves of Mn4+ in K2NaGaF6 were fitted using the Inokuti–Hirayama model, suggesting that the dipole–dipole interactions determine the concentration quenching. Finally, encouraged by the good performance, a warm LED with a CRI of 89.4 and CCT of 3779 K was fabricated by employing the title nanophosphor as the red component. Our findings suggest that K2NaGaF6:Mn4+ can be a viable candidate for the red phosphor used in warm WLEDs. [ABSTRACT FROM AUTHOR]

Recently, rare earth (RE) ion doped single-phased phosphors, which can emit tunable colors upon single wavelength excitation, have received a great deal of attention, but most of them involve multiple dopants as luminescence centers. This work reports on single-phased LuVO4:Eu3+ phosphors with tunable emission colors upon a single wavelength excitation while using Eu3+ as a single dopant ion. The tunable emission is realized through precisely manipulating the energy transfer efficiency from VO43− to Eu3+ by controlling the Eu3+ doping content, which allows modulating the photoemission intensity ratio between VO43− and Eu3+ upon excitation at 265 nm and therefore color tuning from blue (0.2204, 0.2194) to red (0.6703, 0.2986). Time-resolved photoluminescence (PL) spectroscopy measurements reveal that the energy transfer process occurs 4 μs after the excitation and becomes dominant 10 μs later with the disappearance of the VO43− emission. The temperature-dependent PL spectra show that the energy transfer can be accelerated as the temperature increases, and it leads to abnormal enhancement of the Eu3+ emission at the earlier state. A similar scenario is not observed upon exciting the phosphors at the intrinsic absorption of Eu3+, which implies that the reversible energy transfer from Eu3+ to VO43− is impossible. Our results demonstrate a feasible strategy for tuning the emission color of single-phased phosphors through controlling the energy transfer process from the host to the dopant, and it opens up new possibilities for designing tunable luminescent materials for future optoelectronics applications. [ABSTRACT FROM AUTHOR]

We have investigated the mechanism of tunable luminescence in a bismuth doped ScVO4 matrix by using the first-principles calculations. It is found that some intrinsic defects generally exist in the matrix due to their low formation energies, while they have no remarkable effect in the optical band gap of the compound. The calculated formation energy of substitutional Bi at the Sc site is 2.0–3.3 eV lower than that of replacing V by Bi in various chemical environments. Yet, once there is an oxygen defect (vacancy) around a Bi atom, it is energetically preferable to form a defect complex, BiSc + VacO. Based on the calculated formation energy and the imaginary part of the dielectric function, the defect complex transfers between the neutral charge state and the 1+ charge state, which is ascribed to be responsible for the red bismuth photoemission observed in experiment. With the defect complex, tunable bismuth photoemission could be achieved by selectively controlling the content of hydrogen. Our calculations have shown that there is a passivation effect resulting from the re-padding of the oxygen defect by the hydrogen atom. This confirms the experimental observation of tunable bismuth luminescence due to the defect complex, leading to a potential facile design of other defect-controllable, micro- and nano-sized luminescent materials ranging from the visible to the near- and far-infrared spectrum. [ABSTRACT FROM AUTHOR]