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Till now, many doped persistent luminescence (PersL) phosphors have been investigated and found various applications in such as bioimaging, photocatalysis and information storage, but introducing PersL emitters into a proper host is mostly complex. In this research, a self‐activated PersL phosphor Ba2Zr2Si3O12 (BZSO) is prepared by solid state reaction. By adding NH4Cl, the self‐activated PersL intensity is evidently enhanced. The trap depths and concentrations are examined by thermoluminescence spectra. Meanwhile, Bi3+ ions are introduced into BZSO and show wide band photoluminescence (PL) from 300 to 600 nm. Moreover, the PL of Bi3+ is tunable under excitation by 265‐350 nm lights. Furthermore, as a proof‐of‐concept design, we designed a patterned quick response (QR) code based on the self‐activated PersL of BZSO, and the information of "South China University of Technology (SCUT)" can be read out by the code scanning technology. Bi3+‐doped BZSO phosphors are suggested to provide potential applications in information storage by its self‐activated PersL, and to excite researchers to study the tunable PL in Bi3+‐doped phosphor. [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]

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]

Abstract: Optical gas sensors present fundamental and industrial importance considering their broad applications. Challenges remain to obtain new photonic materials with broadband emission covering the absorption spectrum of typical combustion gases. Here, broadband near‐infrared (NIR) photoluminescence (PL) spanning the wide absorption spectrum of typical combustion products is realized through instant precipitation of stable cubic perovskite KMgF3:Ni2+ nanocrystals inside an aluminosilicate glass matrix after melt‐quenching. Excited by an 808 nm laser diode, NIR luminescence with a peak centered at ~1624 nm and a bandwidth (FWHM) greater than 315 nm is observed, originating from 3T2g(3F) → 3A2g(3F) electronic transition of octahedral coordinated Ni2+ in KMgF3 GC. Controlled precipitation of these perovskite crystals from a supercooled aluminosilicate melt enables immediate encapsulation and, hence, stabilization in an inorganic glass phase. While the precipitation temperature has only a small effect on crystallite size, it controls the redox state of the melt and the degree of dopant incorporation into the crystalline phase so that PL performance can be optimized. Spontaneous crystallization of perovskite nanocrystals inside glass may offer a new way to stabilize these novel nanocrystals. Moreover, spontaneous crystallization can be attractive in the control of activator partitioning and in the fabrication of composite fiber devices with high transparency and emission gain. In the present case, this offers a potential platform for broadly tunable gain media, for example, for combustion gas sensing. [ABSTRACT FROM AUTHOR]

We report on intense photoluminescence from materials of the (Rb,K)2Ge4O9:Mn4+ solid solution as a novel class of redemitting oxide phosphors. In these compounds, luminescence originates from a virtually ideal substitution of Mn4+ for Ge4+ on octahedral lattice sites which are well-isolated from each other within the unit cell by intermediate GeO4 species. Complete isostructural substitution of K for Rb is possible across the join. The associated slight shrinkage of the unit cell has only little effect on the apparent Mn4+ interionic distance, but enables tuning of the absorption cross section and of the band structure, hence, of the emission lifetime, of the excitation band shape, and of emission quantum yield. Partial substitution was also found to reduce thermal quenching of the Mn4+-related emission, apparently due to the lower polarizability of the K+ ion. In addition, random substitution of Rb by K enables modulation of the interaction of Mn4+ with its surrounding field at lower symmetry, leading to increasing emission bandwidth, i.e., 595 cm-1 in K1.5Rb0.5Ge4O9:Mn4+ vs 558 or 578 cm-1 in Rb2Ge4O9:Mn4+ or K2Ge4O9:Mn4+ respectively. [ABSTRACT FROM AUTHOR]

Biomedical imaging and labeling through luminescence microscopy requires materials that are active in the near‐infrared spectral range, i.e., within the transparency window of biological tissue. For this purpose, tailoring of Mn2+–Mn2+ activator aggregation is demonstrated within the ABF3 fluoride perovskites. Such tailoring promotes distinct near‐infrared photoluminescence through antiferromagnetic super‐exchange across effective dimers. The crossover dopant concentrations for the occurrence of Mn2+ interaction within the first and second coordination shells comply well with experimental observations of concentration quenching of photoluminescence from isolated Mn2+ and from Mn2+–Mn2+ effective dimers, respectively. Tailoring of this procedure is achieved via adjusting the Mn–F–Mn angle and the Mn–F distance through substitution of the A+ and/or the B2+ species in the ABF3 compound. Computational simulation and X‐ray absorption spectroscopy are employed to confirm this. The principle is applied to produce pure anti‐Stokes near‐infrared emission within the spectral range of ≈760–830 nm from codoped ABF3:Yb3+,Mn2+ upon excitation with a 976 nm laser diode, challenging the classical viewpoint where Mn2+ is used only for visible photoluminescence: in the present case, intense and tunable near‐infrared emission is generated. This approach is highly promising for future applications in biomedical imaging and labeling. [ABSTRACT FROM AUTHOR]

The trivalent green element of bismuth, when doped into different compounds, can produce multiple emissions in ultraviolet, blue, green or even yellow spectral regimes. The emission adjustability comes from the susceptibility of bismuth naked 6s electrons to the crystal field particularly surrounding Bi3+. However, this has never been observed in a single compound. In this work, we report that broadly tunable bismuth emission indeed occurs even within the same host (CaMoO4) when the local microenvironment around Bi3+ is modified by intentional introduction of alkali ions. As the radius of the selected alkali ion decreases, the emission regularly blue-shifts from 586 to 554 nm, and its intensity is enhanced greatly. For instance, the integrated intensity for the Li+ and Bi3+ codoped sample is 4.46 times stronger than the Bi3+ single-doped sample upon excitation at 300 nm. Low-temperature photoluminescence spectra surprisingly reveal that energy transfer can partially take place from the MoO42- group to Bi3+ at lower temperature when excited into the charge transfer state of the MoO42- group, however, this does not occur at higher temperature. The mechanism needs further study. Dynamic luminescence analysis between 10 and 300 K implies a population dependence of the excited states 3P0 and 3P1 on temperature that is responsible for the evolution of the Bi3+ emission lifetime with temperature. [ABSTRACT FROM AUTHOR]

Abstract: Ever since the discovery of ultra-broadband near-infrared (NIR) photoluminescence (PL) from Bi-doped silicate glass, this class of materials and corresponding devices have experienced rapid progress. This is mainly driven by the suggested use in broadband optical amplifiers and novel lasers for future telecommunication networks. Currently, it appears that the optical bandwidth which is provided by Bi-doped glasses and crystals cannot be achieved by any rare-earth (RE) based amplifier, or by the combination of multiple RE-doped devices. However, the nature of the optically active NIR emission centers remains highly debated. The present paper critically reviews the various arguments and models which have been proposed in this context over the last decade. From the overall conclusions, the major open questions are identified. [Copyright &y& Elsevier]

Here, a novel multifunctional phosphor of Li1−xGa5O8:xPr3+ is reported. The crystal structure, mechanoluminescence (ML), persistent luminescence (PersL), photoluminescence (PL) and photoluminescence excitation (PLE) are systematically studied. LiGa5O8 emits blue PersL peaked at 437 nm after irradiation by a 254 nm lamp for 10 s, and corresponding PersL can be observed for 30 min by naked eyes. In the same case, the PersL from Li0.995Ga5O8:0.005Pr3+ covers visible to near‐infrared lights (400–1000 nm) which can persist for 120 min. Thermoluminescence analysis shows Pr3+ doping not only increases the shallower trap (0.73 eV) concentration by at least 20 times but also helps the formation of deeper trap centers (0.87 eV). The differences between ML and PersL spectra reveal the selective effects of mechanical stimuli on the transitions of Pr3+ ions. In the end, the fabrication of an intelligent PersL quick response code (QR‐code) permits optical information write‐in after irradiation by a 254 nm lamp and then cryptical information of "SCUT" can be read out by thermal stimulation which shows the potential in information storage. Moreover, the biological tissues penetration experiments and cytotoxicity tests are carried out to display the potential of PersL in bioimaging. [ABSTRACT FROM AUTHOR]

We report on the photoluminescence (PL) properties of Eu-doped alkaline earth aluminoborate glasses MO-Al 2 O 3 -B 2 O 3 (M=Ca, Sr and Ba) as visually transparent warm-white phosphors for near-UV excitation. Due to the high acidity of the aluminoborate matrix, Eu 2+ can be readily stabilized to assume six- to eight-fold oxygen coordination. The energetic gap of the active 4f 6 5d 1 →4f 7 ( 8 S 7/2 ) transition then depends on the speciation of the alkaline earth network modifier, what enables compositional tailoring of the PL colour. In addition, we find a favorably broad emission bandwidth, covering ~180 nm (> 6000 cm -1 ) at half maximum, which we associate with the degree of structural disorder and the site-similarity which is imposed on the PL complex. The asymmetry ratio of Eu 3+ emission confirms highest average site-asymmetry for the material with highest emission bandwidth. The asymmetry ratio and, eventually, the degree of site-similarity and the associated emission bandwidth decrease with either Ca 2+ or Ba 2+ for Sr 2+ substitution. In consequence, finely tunable warm-white emission colour can be achieved through tailoring glass composition and – making use of dual-mode PL in the presence of multi-valent europium - through tuning the excitation wavelength. [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]

Abstract: Silicate glasses containing PbS quantum dots (QDs) with narrow size distribution were prepared through heat treatment. Transmission electron microscopy (TEM) results show that spherical PbS QDs are densely dispersed in the glassy matrix. Using ZnS–PbO to replace PbS as precursor of PbS QDs, the size distribution of PbS QDs in glasses becomes more uniform. Tunable infrared luminescence from 1100 to 2200nm has been obtained by controlling the glassy matrix and preparation parameters. Obvious optical amplification at communication windows of 1.55μm and 1.33μm is probed, and the PbS QDs doped glasses using ZnS–PbO as precursor exhibit larger optical amplification. The PbS QDs doped glasses with intense optical amplification are considered to be promising candidate as gain medium for broadband fiber amplifier and tunable fiber laser. [Copyright &y& Elsevier]