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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]

Mechanoluminescence (ML) is a phenomenon upon external mechanical stimuli and it has found diverse applications such as stress sensing, structure health diagnosis, 3‐D signature, energy harvesting etc because of its unique properties of in situ and real‐time response to the stimuli. However, ML of most of the state‐of‐art phosphors primarily appears within the spectral range from ultraviolet to visible, which does not lie in the biological transparent windows, and, therefore, limits its applications in biological field. Here, we report a strong near infrared (NIR) ML from orthorhombic Cmcm perovskite Sr3Sn2O7: Nd3+, which is peaked at ~ 900 nm and located exactly within the first optical transparent window of tissues. The ML apparates after gradual discharge of the traps deeper than 0.73 eV triggered by the external mechanical stimuli and subsequently excitation of Nd3+ to the state of 4F3/2. The rechargable ML presents well repeatable linearity to loaded force at least up to 5000 N, and it can penetrate tissues easily that are thick up to 30 mm such as pigskin and the ceramic disk of hydroxy apatite which is the main constituent of bone. These results demonstrate the potential application for in situ biomechanical sensor. Meanwhile, by recording and processing these ML signals during signing on a pellet sample, for the first time, we provide a novel signature system based on NIR ML. This could raise the security level of existed signature anti‐countering to a higher level. [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]

Light sources as the substitution for sunlight play an important role due to their practical applications in aircraft, medicine, and agriculture. Bi3+ ions show tunable emission from ultraviolet to deep red depending on local crystal field, presenting great potential in mimicking sunlight. However, these emissions are mainly limited to crystals. To stabilize Bi3+ ions inside photonic glasses with desirable emission and excellent physical properties remains challenging. Here, we managed to stabilize Bi3+ with ultrabroad and tunable emission inside glasses at air atmosphere. This emission spans the whole visible range of 350‐780 nm and matches well with the sunlight spectra. For the first time, an external quantum efficiency of 34% was obtained from Bi‐doped photonic glasses without optimizing glass composition. We find that the local oxidation atmosphere from super‐oxide ions and proper crystal field formed by AlO4 are responsible for this unique luminescence, which is revealed by the detailed comparison on the optical and structural properties of calcium aluminate glasses and Ca12Al14O33 crystals with the same composition. Moreover, glasses with distortion structure further results in multiluminescent centers of Bi3+ so as to broaden the emission band. This work provides new insights into the luminescent behaviors of Bi ions in luminescent materials, and should contribute to designing new photonic glasses in future. [ABSTRACT FROM AUTHOR]

Bismuth (Bi)‐doped glasses and fibers are of current interest as promising active media for new fiber lasers and amplifiers due to their 800‐1700 nm near‐infrared (NIR) emission. However, the optically active Bi centers in silica are easily volatilized during high‐temperature fiber drawing, which results in low Bi doping concentration and low gain NIR luminescence. Here, we explored the glass‐forming region in a model glass system of sodium tantalum silicate (Na2O‐Ta2O5‐SiO2) glass and attained suitable glass host for enhancing Bi NIR emission, right followed by detailed analysis on optical and structural characterization. Glass‐forming region roughly lies in where Ta2O5 ≤ 30 mol%, SiO2 ≥ 40 mol%, and Na2O ≤ 40 mol%. Not only is glass‐forming ability improved but also Bi NIR emission is enhanced (~60 times) by the introduction of Ta into glass network. Dissociated Na cations are restricted beside Ta, the high‐field‐strength element, so that the negative impacts of Na cations on glass formation and Bi NIR emission are weakened, which is responsible for the highly enhanced Bi NIR emission. This work helps us understand the glass‐forming of tantalum silicate glass systems and luminescent behaviors of Bi. Hopefully, it could contribute to designing the Bi‐doped laser glasses and high gain fibers with stable luminescent properties in future. [ABSTRACT FROM AUTHOR]

The development of efficient red‐emitting persistent phosphor is still an ongoing challenge. In the search of persistent materials in red range, Pr3+ is a good candidate owing to its transitions between 1D2 and 3H4 state at about 612 nm. In this paper, we investigated the red persistent properties of Pr3+‐doped perovskite oxide ABO3, (A: K, Na and B: Nb), which can be elaborated as large single crystal. KNbO3:Pr3+ appears to have weak photoluminescence and no persistent luminescence. However, the cationic substituted compounds K1−xNaxNbO3:Pr3+ (x = 0, 0.4, 0.5, 0.7 0.9, 1) exhibit intense persistent luminescence, which increases steadily with increase in Na content. We correlated persistence behavior with the position of Metal‐to‐Metal Charge Transfer (MMCT) band, which plays crucial role in tuning of the trap depth. The MMCT band position decreases with the addition of Na contents and the thermoluminescence peak shifts toward higher temperature indicating the formation of deeper traps. This is in good agreement with the enhancement of the persistent luminescence suggesting that a proper tailoring of MMCT is needed to design efficient Pr3+‐persistent phosphors with better performance. A detailed analysis on the trap depth, bandgap energy, and persistent luminescence properties is reported tuning the composition in the K1−xNaxNbO3:Pr powder. Tunable traps depths are obtained by Na/K substitution. Electron and hole traps are evidenced by thermal analysis. This gives new insights in the persistent luminescence mechanism in the Pr3+− doped perovskite compounds. [ABSTRACT FROM AUTHOR]

Bismuth (Bi)‐doped laser glasses with broadband emission are of current interest in the fields of sensing, bio‐imaging, and photonics. For practical applications, it must be considered how to improve the emission efficiency, in particular, for borate glasses with wide glass‐forming range, low melting point, and excellent fiberizing ability. Herein, we experimentally demonstrate that addition of GeO2 to aluminoborate glasses can effectively enhance Bi NIR emission by more than 300 times with prolonged decay time (~500 μs) and good homogeneity, which is, to our best knowledge, seldom achieved in Bi‐doped borate multi‐component glasses. The addition of second glass‐former GeO2, as revealed by detailed optical and structural analysis, leads to the facile regulation on local glass structure, forcing the conversion of aluminum species from AlO5 and AlO6 to AlO4 and consequently pushes the conversion of Bi3+ to Bi+ and Bi0 and stabilizes Bi NIR centers, which finally results in highly enhanced Bi NIR emission. We believe these results could contribute to designing Bi‐activated multi‐component laser glass and fibers with efficient NIR photoemission. [ABSTRACT FROM AUTHOR]

Nd3+‐doped phosphate laser glasses have been attracting much attention and widespread investigation due to their high solubility of rare earth (RE) ions, excellent spectroscopic properties, and large damage threshold. However, the narrow NIR emission bandwidth (less than 30 nm) of these Nd3+‐doped phosphate glasses limits their further application toward ultrahigh power field and efficient fiber laser in new region. Here, we demonstrate the broadening and enhancing of Nd3+NIR emission in laser glass of zinc aluminophosphate through tuning the glass structure and covalency of Nd‐O bond without limiting the radiative properties of Nd3+. The maximum bandwidth of 1.05 μm emission is broadened to 50 nm, which is comparable to that of Nd3+‐doped aluminate laser glasses. Simultaneously, the lifetime of 4F3/2 level is elongated nearly by two times. Structural and optical properties of prepared glasses were discussed systematically to reveal the mechanism. Detailed analysis on optical spectra and glass structure indicates that the bandwidth is affected by not only the covalency of Nd‐O but also the compactness of glass structure. Our results could enrich our understanding about the relationship between local glass structure and luminescence behaviors of active centers, and may be helpful in designing new RE‐doped laser glass systems. [ABSTRACT FROM AUTHOR]

A novel Mn4+‐doped strontium lanthanum gallate red phosphor SrLaGaO4:Mn4+ has been successfully prepared via the conventional solid‐state reaction method. Phase purity, photoluminescence excitation/emission spectra, concentration quenching, decay curves, and temperature‐dependent photoluminescence have been investigated systematically. SrLaGaO4:Mn4+ phosphor exhibits broad excitation band from 250 to 600 nm and emits intense red light centered at 716 nm arising from spin‐forbidden transition, 2E → 4A2 of Mn4+. The optimal dopant concentration of Mn4+ is determined to be 0.2 mol%. Dipole‐dipole interaction is supposed to be the mechanism of concentration quenching. The crystal‐field strength Dq, the Racah parameters B and C, and the nephelauxetic ratio β1 of SrLaGaO4:Mn4+ have been calculated according to its luminescent spectra. Our systematic investigation on this new phosphor can provide a reference for the development of red‐emitting phosphor. [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]

Tantalum silicate glasses serve as laser host materials to take advantage of their high refractive index and the ability to tailor their physical properties in the design of high‐performance photonic and photoelectric components. However, successful attainment of feature control in tantalum‐doped materials remains a longstanding problem due to the limited understanding of local structure around the tantalum ions, a problem that lies at the heart of predicting the micro‐ and macroscopic properties of these glasses. Herein, we present a novel approach for predicting the local structural environments in tantalum silicate glass based on a phase diagram approach. The phase relations and glass formation region of Li2O–Ta2O5–SiO2 ternary systems are explored to calculate the structure and additive physical properties of lithium tantalum silicate glasses. These measured and calculated results are in good quantitative agreement, indicating that the phase diagram approach can be applied broadly to Li2O–Ta2O5–SiO2 ternary glass systems. Using the phase diagram approach, the local structure of tantalum can be directly obtained. Each Ta atom is surrounded by six atoms, and its polyhedron, the TaO6 octahedron, bonds through oxygen to Li and Ta. As a network modifier, Ta5+ depolymerizes the silicate glass structure by modulating the local structure of lithium atoms in Li2O–Ta2O5–SiO2 ternary glass system. The compositional dependence of structure in lithium tantalum silicate glasses is quantitatively determined based on the structure of the nearest neighbor congruent compound through the lever rule. These findings offer a precise prediction of tantalum silicate glass properties with quantitative control over local structural environment of the disordered materials. [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]