Narrowband Ultraviolet-B Persistent Luminescence in an Indoor-Lighting Environment through Energy Transfer from Host Excitons to Gd3+ Emitters in ScPO4.

Narrowband ultraviolet-B (NB-UVB) luminescent materials are characterized by high photon energy, narrow spectral width, and visible-blind emission, thus holding great promise for photochemistry and photomedicine. However, most NB-UVB phosphors developed so far are photoluminescent, where continuous external excitation is needed. Herein, we realize NB-UVB persistent luminescence (PersL) in an indoor-lighting environment by exploiting the interaction between self-trapped/defect-trapped excitons and Gd3+ emitters in ScPO4. The phosphor shows a self-luminescing feature with a peak maximum at 313 nm with a time duration of >24 h after ceasing X-ray irradiation, which can be clearly imaged by an UVB camera in a bright environment. Spectroscopic and theoretical approaches reveal that thermo- and photo-stimulations of energies trapped at intrinsic lattice defects followed by energy transfer to Gd3+ emitters account for the emergence of the afterglow. The present results can initiate more exploration of NB-UVB PersL phosphors for emerging applications in secret optical tagging and phototherapy.

X-ray-Excited Long-Lasting Narrowband Ultraviolet-B Persistent Luminescence from Gd3+-Doped Sr2P2O7 Phosphor.

Persistent phosphors emitting in the narrowband ultraviolet-B (NB-UVB) spectral region have aroused significant interest, owing to their special self-illuminating feature in realizing many advanced technological applications under excitation-free conditions, such as dermatological therapy and invisible optical tagging. Here, we focus our discussion on a new Gd3+-doped persistent phosphor, Sr2P2O7:Gd3+, which exhibits long-lasting NB-UVB persistent luminescence peaking at 312 nm for more than 24 h after charging by an X-ray beam. The NB-UVB light emission from the charged Sr2P2O7:Gd3+ phosphor can be clearly detected by a UVB camera in bright indoor environment. More importantly, the enhancement of NB-UVB afterglow intensity and decay time can be observed under continuous photostimulation of polychromic indoor ambient light. Furthermore, applying charged Sr2P2O7:Gd3+ phosphors as invisible optical taggants, clear and interference-free recognition of the encrypted message and location of different objects have been realized due to the lack of UVB light in bright indoor environment. The as-prepared Sr2P2O7:Gd3+ persistent phosphor is expected to offer new directional solutions for the development and application of ultraviolet luminescence technology.

Electrospinning Superassembled Mesoporous AIEgen-Organosilica Frameworks Featuring Diversified Forms and Superstability for Wearable and Washable Solid-State Fluorescence Smart Sensors.

Flexible optical sensors are widely studied and applied in many fields. However, developing highly stable and washable wearable sensors in optics is still facing significant challenges. Here, we demonstrate an AIEgen-organosilica framework (TPEPMO) hybrid nanostructure-based flexible optical sensor, which is prepared by a two-step co-condensation and electrospinning superassembly process. Organosilica precursors with aggregation-induced emission (AIE) features are covalently linked into periodic mesoporous organosilica (PMO) frameworks with high fluorescent efficiency due to the restriction of intramolecular motion. The three-dimensional space of ordered porous materials provides abundant reaction sites, allowing rapid and sensitive monitoring of analytes. TPEPMOs exhibit good properties as acidic pH fluorescent sensors with a pKa of 4.3. A flexible film is obtained by dispersing TPEPMO nanospheres in a poly(lactic-co-glycolic acid) (PLGA) and polyacrylonitrile (PAN) hybrid fibrous matrix (TPEPMO-CFs) using the electrospinning superassembly technique and is successfully served as an efficient fluorescent probe for the naked eye detection of ammonia gas and HCl vapor by emission changes. The fluorescence of TPEPMO-CFs can be reversed in the presence of volatile acidic/alkaline gas for more than five cycles, exhibiting excellent recyclability. In addition, TPEPMO-CF sensors show excellent washability and long-term photostability (fluorescence was maintained above 94% after washing 10 times). These stimuli-responsive AIEgen-organosilica frameworks featuring diversified forms and superstability for wearable and washable solid-state fluorescence exhibit great potential for smart gas sensors, wearable devices, and solid-state lighting applications.

Structure, Crystallographic Sites, and Tunable Luminescence Properties of Eu(2+) and Ce(3+)/Li(+)-Activated Ca1.65Sr0.35SiO4 Phosphors.

Eu(2+) and Ce(3+)/Li(+) singly doped and Eu(2+)/Ce(3+)/Li(+)-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the αL'-Ca2SiO4 phase with the Sr addition into Ca2SiO4, and the preferred crystallographic positions of the Eu(2+) and Ce(3+)/Li(+) ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2­x)Sr(x)SiO4 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce(3+)/Li(+) singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in the range of 250­450 nm and a blue emission peak centered at about 465 nm. When Eu(2+) ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce(3+) to Eu(2+). The involved energy-transfer process between Ce(3+) and Eu(2+) and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs).

Increased Eu²âº content and codoping Mn²âº induced tunable full-color emitting phosphor Ba(1.55)Ca(0.45)SiO4:Eu²âº,Mn²âº.

We demonstrated that a new intermediate composition of Ba(1.55)Ca(0.45)SiO4 between the orthosilicates Ca2SiO4 and Ba2SiO4 yields the best phosphor hosts, and interesting luminescence properties can be found from the Eu(2+) singly doped and/or Eu(2+)/Mn(2+) codoped Ba(1.55)Ca(0.45)SiO4 phosphors. The phosphors can be excited by near-ultraviolet (nUV) light at wavelengths ranging from 200 to 450 nm matching well with the nUV light-emitting diode (LED) chips. As a result of fine-tuning the activators of different Eu(2+) content and Eu(2+)/Mn(2+) couples with different ratios, tunable full-color emission under UV light excitation can be realized by combining the blue emission (460 nm) and green emission (520 nm) originating from Eu(2+) with the red emission (595 nm) from Mn(2+) in the Ba(1.55)Ca(0.45)SiO4 host lattice. Energy-transfer efficiency between Eu(2+) and Mn(2+) increases and tunable emission can be obtained with increasing Mn(2+) doping content. These results indicate that the Ba(1.55)Ca(0.45)SiO4:Eu(2+),Mn(2+) phosphor will have potential use in nUV chip pumped white LED devices.

Ultraviolet-B and Near-Infrared Dual-Band Luminescence in Bi3+/Bi2+ Codoped Persistent Phosphor for Optical Storage Application.

Discovering multifunctional luminescent materials to meet the demands of modern spectroscopy is of great significance. However, it is a standing challenge to enable multiple luminescence properties in a single material system via single metal ion doping. Here, we report the inherently Bi3+/Bi2+ codoped Ca3Ga2Ge3O12 persistent phosphor where Bi3+ is in situ reduced to Bi2+. This phosphor can act as an efficient multimodal luminescence material, which simultaneously exhibits long-lasting (>12 h) ultraviolet-B (UVB) and near-infrared (NIR) dual-band persistent luminescence after irradiation by 254 nm ultraviolet (UV) light. UVB and NIR afterglow are ascribed to the distinct Bi3+ and Bi2+ emitters, respectively, proven by comprehensive spectroscopic investigations including X-ray absorption near-edge structure spectra and X-ray photoelectron spectroscopy. Besides, this phosphor also exhibits exceptional photochromic features, accompanied by a rapid body color transformation from white to brown in response to 254 nm UV light within 60 s and excellent recovery capacity upon thermal or blue/white light stimulation. The combination of UVB persistent luminescence of Bi3+ and NIR afterglow of Bi2+ coupled with reversible white-to-brown photochromism phenomenon offers one type of promising multifunctional luminescence material, showing potential to be used for optical storage and anti-counterfeiting applications.

Broadband Short-Wave Infrared-Emitting MgGa2O4:Cr3+, Ni2+ Phosphor with Near-Unity Internal Quantum Efficiency and High Thermal Stability for Light-Emitting Diode Applications.

Blue InGaN chip-pumped short-wave infrared (SWIR) emitters have aroused tremendous attention and shown emerging applications in diverse fields such as healthcare, retail, and agriculture. However, discovering blue light-emitting diode (LED)-pumped SWIR phosphors with a central emission wavelength over 1000 nm remains a significant challenge. Herein, we demonstrate the efficient broadband SWIR luminescence of Ni2+ by simultaneously incorporating Cr3+ and Ni2+ ions into the MgGa2O4 lattice, with Cr3+ as the sensitizer and Ni2+ as the emitter. Because of the strong blue light absorption of Cr3+ and high energy transfer efficiency to Ni2+, the obtained MgGa2O4:Cr3+, Ni2+ phosphors show intense SWIR luminescence with a peak wavelength at 1260 nm and a full width at half maximum (FWHM) of 222 nm under the excitation of blue light. The optimized SWIR phosphor presents an ultra-high SWIR photoluminescence quantum efficiency of 96.5% and outstanding luminescence thermal stability (67.9%@150 °C). A SWIR light source has been fabricated through a combination of the prepared MgGa2O4:Cr3+, Ni2+ phosphor and a commercial 450 nm blue LED chip, delivering a maximum SWIR radiant power of 14.9 mW at 150 mA input current. This work not only demonstrates the feasibility of developing broadband high-power SWIR emitters using converter technology but also presents new insights into the importance of SWIR technology.

Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm.

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr3+-activated Mg2SiO4 infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr3+ emitters in two different Mg sites in the Mg2SiO4 lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg2SiO4:Cr3+ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr3+-doped phosphors.

Blue LED-pumped intense short-wave infrared luminescence based on Cr3+-Yb3+-co-doped phosphors.

The growing demand for spectroscopy applications in the areas of agriculture, retail and healthcare has led to extensive research on infrared light sources. The ability of phosphors to absorb blue light from commercial LED and convert the excitation energy into long-wavelength infrared luminescence is crucial for the design of cost-effective and high-performance phosphor-converted infrared LEDs. However, the lack of ideal blue-pumped short-wave infrared (SWIR) phosphors with an emission peak longer than 900 nm greatly limits the development of SWIR LEDs using light converter technology. Here we have developed a series of SWIR-emitting materials with high luminescence efficiency and excellent thermal stability by co-doping Cr3+-Yb3+ ion pairs into Lu0.2Sc0.8BO3 host materials. Benefitting from strong light absorption of Cr3+ in the blue waveband and very efficient Cr3+→Yb3+ energy transfer, the as-synthesized Lu0.2Sc0.8BO3:Cr3+,Yb3+ phosphor emits intense SWIR light in the 900-1200 nm from Yb3+ under excitation with blue light at ~460 nm. The optimized phosphor presents an internal quantum yield of 73.6% and the SWIR luminescence intensity at 100 °C can still keep 88.4% of the starting value at 25 °C. SWIR LED prototype device based on Lu0.2Sc0.8BO3:Cr3+,Yb3+ phosphor exhibits exceptional luminescence performance, delivering SWIR radiant power of 18.4 mW with 9.3% of blue-to-SWIR power conversion efficiency and 5.0% of electricity-to-SWIR light energy conversion efficiency at 120 mA driving current. Moreover, under the illumination of high-power SWIR LED, covert information identification and night vision lighting have been realized, demonstrating a very bright prospect for practical applications.

Broadband Short-Wave Infrared Light-Emitting Diodes Based on Cr3+-Doped LiScGeO4 Phosphor.

Short-wave infrared (SWIR) spectroscopy has recently emerged as an important technology across a wide range of areas, whether industrial, biomedical, or environmental. Nevertheless, it is still a long-standing challenge to develop robust SWIR light sources. The SWIR phosphor-convert light emitting diodes (LEDs) by coating blue LED chips with desirable SWIR-emitting phosphors are becoming an ideal alternative for solid-state SWIR light sources due to its compactness, low-cost, and long operating lifetime, as does the commercial white LEDs. Herein, we report a blue-pumped Cr3+-doped LiScGeO4 SWIR phosphor as a luminescent converter for phosphor-convert SWIR LEDs. This phosphor shows an intense SWIR emission band with a peak wavelength at ∼1120 nm owing to the 4T2 → 4A2 electron transition of Cr3+ when exciting with blue light. The full width at half-maximum (fwhm) of the phosphor is ∼300 nm and the absolute quantum efficiency is determined to be ∼26%. SWIR LED prototypes are constructed by combining the optimized phosphor materials with commercial blue InGaN LED chips, which can generate a commendable emission band in the SWIR region over 800-1600 nm and achieve a maximum output power of ∼4.78 mW at 60 mA with the photoconversion efficiency of 4.4%. The current exploration of Cr3+-doped SWIR-emitting phosphors will lay the foundation to engineer phosphor-convert SWIR LEDs for applications in night-vision surveillance and SWIR spectroscopy technology. These blue-light-excitable SWIR-emitting phosphors can serve as an important complement to the spectral gap of the current Cr3+-doped phosphors in the SWIR region and will pave the way toward cost-effective phosphor-converted solid-state SWIR light sources.

Narrowband ultraviolet-B persistent luminescence from (Y,Gd)3Ga5O12:Bi3+ phosphors for optical tagging application.

Luminescent materials that emit in the narrowband ultraviolet-B (NB-UVB; 310-313 nm) spectral region have attracted considerable attention due to their unique spectral features, which endow them with great potential applications in the fields of photochemistry and photomedicine. However, NB-UVB persistent luminescent materials are relatively lacking, especially materials that are excitable by natural sunlight. Here we report the NB-UVB persistent luminescence of Gd3+ in (Y,Gd)3Ga5O12:Bi3+ garnets by making use of the persistent energy transfer from Bi3+ to Gd3+. The optimal Bi3+ and Gd3+ concentrations for the maximum energy transfer efficiency are determined and persistent NB-UVB light emission with a peak wavelength at 313 nm and an afterglow time of more than 24 h is successfully achieved in the (Y,Gd)3Ga5O12:Bi3+ phosphor. More importantly, the as-synthesized NB-UVB persistent phosphors are also excitable by the widely available natural sunlight and exhibit exceptional NB-UVB persistent luminescence performance. Benefitting from the visible-blind emission feature, interference-free capability from indoor ambient light and self-sustained optical characteristic, the developed sunlight-excitable NB-UVB persistent phosphors here not only hold great promise for covert optical tagging applications, but also open new opportunities for optical data storage in a bright indoor environment.