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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.

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.

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.

All inorganic metal halide perovskite quantum dots (QDs) exhibit excellent optical properties promising for diverse applications, while their inherent frangibility remains an enormous challenge for both scientific research and practical applications. Recently emerged oxide glasses doped with such QDs exhibit high stability against degradation and are thus highly promising for photonic applications. Here, we demonstrate the tuning of the linear and nonlinear optical properties of perovskite QD-doped glass through modulation of its network topology. By introducing a metal fluoride network modifier, we show that the precipitation of the QDs can be promoted as a result of the enhanced ion mobility during heat treatment. The QD-doped glasses show strong one-photon and two-photon upconversion photoluminescence (PL). Also, the PL intensity can be enhanced by up to 800% for the sample with an optimal local structure. In addition, the control of QD precipitation by modulating the glass network topology could allow for the observation of a cross-over from saturable absorption to reverse saturable absorption. The methodology for tuning the optical properties of QD-in-glass composites studied here might be applied for the design of photonic glasses for relevant applications.

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.

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.

One-dimensional nanomaterials usually possess unique anisotropic chemical or physical properties. For practical device applications, one of the biggest challenges is their large-scale assembly with predesigned architecture to render optimized collective properties. Based on our previous studies, here we report an extended investigation on the macroscopically aligned assembly of gold nanorods with tunable aspect ratio (AR) in transparent polymer films based on the electrospinning technique. The optical properties of the composite films were investigated using polarized extinction spectra and the Z-scan technique. Due to the collective longitudinal LSPR of the macroscopically aligned gold nanorods, the transparent composite films exhibited anisotropically enhanced optical nonlinearity. The intensity of the nonlinear optical signal of the films can be tuned by varying the polarization direction of the laser on the films. Moreover, the influence from the AR and the doping concentration of GNRs on the optical properties of the composite films was also investigated. To demonstrate an example of practical applications, the composite film was employed as a saturable absorber to construct a pulsed fiber laser. Inspiringly, the pulsed fiber laser with switchable mode-locking and Q-switching operation modes was realized successfully. The switching of the operation mode of the laser can be triggered simply through variation of the laser's polarization direction. Such a pulse-width tunable fiber laser is potentially useful in various application scenarios.

All solid-state PbS quantum dot (QD)-doped glass fibers with tunable near-infrared (NIR) emission were successfully fabricated by using the “melt-in-tube” method for the first time. The precursor fibers were first prepared without any obvious element diffusion or crystallization by drawing the fiber preform at a heating temperature at which the fiber core was already melted while the fiber cladding was softened. Then the PbS QDs were precipitated evenly in the matrix of the glass fiber core after a careful heat treatment at low temperature. From the PbS QD-doped glass fibers, intense wavelength-tunable broad NIR emission bands were observed upon excitation with an 808 nm laser. The transmission loss of the fibers can be reduced by further matching the thermal expansion of the fiber core and cladding glass. Therefore, after further optimizing the composition and optical properties of the PbS QD-doped glass fiber, it is expected to be a potential gain medium for the development of wavelength-tunable lasers and broadband fiber amplifiers. More importantly, the melt-in-tube method exhibits a feature of completely controllable crystallization in the fiber formation process, which would open a new route for fabricating novel functional QD-doped glass fibers.

Nanofibers are characterized with unique electronic, magnetic and optical properties, due to their extremely high aspect ratio and large specific surface area. Assembly of nanofibers with predesigned macro architectures is a key step toward practical applications. Herein, we demonstrate the scalable oriented assembly of nanofibers based on electrospinning, and explore their potential application in constructing optically anisotropic films. By the post soaking-and-drying approach, the nonwoven films assembled by oriented polymer nanofibers can be readily converted to flexible films with high transparency, which show optical transmission contrast exceeding 0.9 in the visible to near infrared region. The method for preparation of optically anisotropic films proposed here circumvents the sophisticated dye-doping and thermal drawing processes which are inevitable in conventional approaches. Considering the scalability potential of the electrospinning technique, the method demonstrated here is promising for industrial production of film polarizers.

A wide variety of activation ions have been used as near infrared (NIR) luminescent centres. However, when it comes to persistent luminescence, the numbers of known activators are relatively low. Here, we propose a holistic design concept for NIR long persistent phosphors, and successfully fabricate a series of novel Mn4+-doped MAlO3 (M = La, Gd) persistent phosphors with the emission maximum around 730 nm. By drilling down into the details of defect types and trap depths, an improvement of persistent time over 20 h is realized by co-doping Ge4+/Mn4+. The obtained imaging of deep tissues reveals that the new luminescent indicators will open the possibility of advanced optical imaging, with high resolution and weak light disturbance, for factual assessment of the structural and functional processes in cells, tissue and other complex systems.

A phosphor with remarkable long persistent luminescence features, Zn3Ga2Sn1O8:0.5 Cr3+, suitable for deep and reproducible tissue imaging has been rationally designed and successfully fabricated. This phosphor shows bright and long persistent luminescence over 300 h in the near-infrared region, and permits an enabling long-term, reproducible, real-time and reliable structural imaging of deep tissues. Moreover, the revived luminescence and persistent luminescence under the excitation of near-infrared incoherent light are also demonstrated to reveal an optional multiplexed detection. This new luminescent indicator will allow repeatable visualization of the structural and functional processes in cells, tissues and other complex systems. In addition, multifarious and systematic investigations are successfully carried out to unravel the nature of traps and also to verify the rationality of the material design.