Orange super-long persistent luminescent materials: (Sr1-xBax)3SiO5:Eu2+,Nb5+

 Mater. Chem. Front., 2021, 5, 333-340

image file: d0qm00488j-f1.tif

Persistent luminescent materials are widely used as night-vision and marking materials in various important fields. Although significant achievements have been made in blue and green persistent luminescent (PersL) materials, the research and development of PersL materials in the warm-color region (550–660 nm) are relatively lacking. Only the orange PersL phosphor Y2O2S:Eu3+,Mg2+,Ti4+ (∼610 nm) and deep red PersL phosphor (Ca1−xSrx)S:Eu2+,Tm3+ (∼650 nm) fulfill the demands of commercial applications. However, sulfide phosphors have poor chemical stability and a relatively short persistent duration time. Herein, we report a series of orange PersL materials, (Sr1−xBax)3SiO5:Eu2+,Nb5+, which exhibit a strong PersL emission band at 550–670 nm and a super-long persistent time of more than 20 h at the 0.32 mcd m−2 threshold value after UV radiation. These new orange PersL materials are compared to the commercial warm-color sulfide PersL phosphor, Y2O2S:Eu,Mg,Ti, with regards to PersL time and brightness, and it is determined that they would have great potential applications.

Broadband deep‐red‐to‐near‐infrared emission from Mn2+ in strong crystal‐field of nitride MgAlSiN3

 J Am Ceram Soc., 2020; 103: 6793– 6800. https://doi.org/10.1111/jace.17304

Broadband near‐infrared (NIR) phosphors have received increasing attention for fabricating phosphor‐converted light‐emitting diodes (pc‐LEDs) as NIR light source. Most of the reported broadband NIR phosphors originate from Cr3+ in weak crystal field environments. Herein, we report a luminescent material, MgAlSiN3:Mn2+ with CaAlSiN3‐type structure, demonstrating that broadband deep‐red‐to‐NIR emission can be achieved via doping Mn2+ into crystallographic sites with strong crystal field in inorganic solids. This phosphor is synthesized via easy‐handle solid‐state reaction, and the optimized sample, (Mg0.93Mn0.07) AlSiN3 shows an emission band with peak at ~754 nm, FWHM of 150 nm, and internal quantum efficiency of 70.1%. The photoluminescence intensity can further be enhanced by co‐doping Eu2+ as sensitizer. This work provides a new strategy for discovering new broadband NIR phosphors using Mn2+ in strong crystal field as luminescence center.

Infrared-photostimulable and long-persistent ultraviolet-emitting phosphor LiLuGeO4:Bi3+,Yb3+ for biophotonic applications

Mater. Chem. Front., 2021,5, 1468-1476.https://doi.org/10.1039/D0QM00932F

Graphical abstract: Infrared-photostimulable and long-persistent ultraviolet-emitting phosphor LiLuGeO4:Bi3+,Yb3+ for biophotonic applications

Photodynamic therapy needing ultraviolet (UV) in deep tissue is hindered due to the low biological tissue penetration ability of UV light. Here, we demonstrate a persistent ultraviolet-emitting phosphor, LiLuGeO4:Bi3+,Yb3+, which can be re-stimulated by near infrared (NIR) light. Yb3+-doping significantly enhances the trap density without changing the thermoluminescence peak positions. The phosphor can be effectively activated by a 254 nm lamp and exhibits prominent persistent luminescence peaking at 350 nm. The decay time can be recorded much longer than 15 h. This phosphor exhibits simulated in vivo photostimulated persistent luminescence after a longtime decay by using in vitro NIR light penetrating biological tissue. Combined with CaAlSiN3:Eu2+, red persistent luminescence from Eu2+ is obtained. LiLuGeO4:Bi3+,Yb3+ makes up the shortage of excellent UVA persistent phosphors. It is expected to have potential applications as an in vivo renewable excitation source to trigger photosensitizers or fluorescent probes when used for biophotonic applications.

Tolerance factor, phase stability and order–disorder of the pyrochlore structure

Inorg. Chem. Front., 2020,7, 1583-1590. https://doi.org/10.1039/D0QI00016G

Graphical abstract: Tolerance factor, phase stability and order–disorder of the pyrochlore structure

The tolerance factor is a structural indicator that connects the crystal structure and chemical composition. In this work, we establish the tolerance factor for pyrochlore A2B2O7-type compounds, using ionic radii of the compositional species. It is derived following similar procedures to those of perovskite and garnet structures. More than 180 A2B2O7 type compounds are examined to test its validity in predicting the pyrochlore phase stability. It can also be used to understand the reverse and order–disorder cationic occupations. This structural descriptor could be used together with machine learning or high-throughput screening methods for new material design and discovery.

Orange super-long persistent luminescent materials: (Sr1−xBax)3SiO5:Eu2+,Nb5+

Mater. Chem. Front., 2021,5, 333-340. https://doi.org/10.1039/D0QM00488J

Persistent luminescent materials are widely used as night-vision and marking materials in various important fields. Although significant achievements have been made in blue and green persistent luminescent (PersL) materials, the research and development of PersL materials in the warm-color region (550–660 nm) are relatively lacking. Only the orange PersL phosphor Y2O2S:Eu3+,Mg2+,Ti4+ (∼610 nm) and deep red PersL phosphor (Ca1−xSrx)S:Eu2+,Tm3+ (∼650 nm) fulfill the demands of commercial applications. However, sulfide phosphors have poor chemical stability and a relatively short persistent duration time. Herein, we report a series of orange PersL materials, (Sr1−xBax)3SiO5:Eu2+,Nb5+, which exhibit a strong PersL emission band at 550–670 nm and a super-long persistent time of more than 20 h at the 0.32 mcd m−2 threshold value after UV radiation. These new orange PersL materials are compared to the commercial warm-color sulfide PersL phosphor, Y2O2S:Eu,Mg,Ti, with regards to PersL time and brightness, and it is determined that they would have great potential applications.

Red persistent and photostimulable phosphor SrLiAl3N4:Eu2+

J. Mater. Chem. C, 2020,8, 4956-4964. https://doi.org/10.1039/D0TC00277A

The SrLiAl3N4:Eu2+ phosphor has attracted considerable attention owing to its highly efficient narrow-band red emission. Herein, we report for the first time its red persistent luminescence (PersL) and photostimulated luminescence (PSL). After 254 nm light pre-irradiation, the SrLiAl3N4:0.1%Eu2+ phosphor shows 395 s red PersL at a 0.32 mcd m−2 threshold value and its PSL can still be detected under 980 nm light after 15 days. The thermoluminescence spectra evidence that the shallow trap (0.47 eV) plays a major role in PersL and the deep trap (0.81 eV) is responsible for PSL. The charging process for PersL and PSL is clarified by the thermoluminescence excitation (TLE) spectrum. By the aid of density functional theory (DFT) calculations, we verify that the trap levels are due to N vacancies. The electronic structure diagram (HRBE diagram) of SrLiAl3N4:Eu2+ with traps is constructed to illustrate the mechanism of PersL and PSL. The special feature that PersL and PSL both exist makes SrLiAl3N4:Eu2+ a potential candidate for applications such as anti-counterfeiting and optical information storage.

Highly efficient near-infrared phosphor LaMgGa11O19:Cr3+

Inorg. Chem. Front., 2020,7, 1467-1473. https://doi.org/10.1039/D0QI00063A

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are desirable for in vivo imaging and applications for nondestructive examination in the food industry. Accordingly, it is very important to exploit highly efficient and stable broad-band NIR phosphors. Herein we report a Cr3+-activated LaMgGa11O19 phosphor via a simple solid-state reaction, showing broad-band emission centered at 770 nm with internal/external quantum efficiency of 82.6%/42.5%. There are three six-coordinated octahedral crystallographic sites in the structure for Cr3+ occupancy, and changing the Cr3+ concentration can tune the NIR emission with tunable band centers from 715 to 800 nm. This spectral red-shift is mainly ascribed to energy transfer among multiple Cr3+ sites, which is further confirmed by decay lifetime analysis. The phosphor also shows excellent luminescence thermal stability, and the photoluminescence intensity at 410 K maintains 87% of that at room temperature. Our work provides a novel broadband NIR emission phosphor with high efficiency and excellent thermal quenching resistance for the field of NIR spectroscopy.

Tolerance Factor and Phase Stability of the Normal Spinel Structure

Cryst. Growth Des., 2020, 20, 3, 2014–2018 https://doi.org/10.1021/acs.cgd.9b01673

Tolerance factor for the normal-spinel structure is introduced as a structural descriptor to predict the phase stability. It is derived following similar principles as those of perovskite and garnet structures, i.e., the geometrical relationship between multitype polyhedra. The calculation of tolerance factor only requires the ionic radii of compositional components involved. A survey of the tolerance factor over 120 AB2X4-type compounds proves the reliability. The numerical values are distributed below 1, which originates from the compressed octahedra which support the framework of spinel. The tolerance factor will be helpful in machine learning and high-throughput screening methods for fast evaluation of phase stability and materials properties of spinel-type compounds.

Sunlight-activated yellow long persistent luminescence from Nb-doped Sr3SiO5:Eu2+ for warm-color mark applications


J. Mater. Chem. C, 2020,8, 1143-1150. https://doi.org/10.1039/C9TC05880J

Warm-color persistent luminescent materials are strongly desired for signage markings and medical imaging in comparison with green or blue counterparts. Herein we report a novel yellow long-persistent phosphor, Nb-doped Sr3SiO5:Eu2+, with a peak wavelength of ∼580 nm and persistence time of more than 14 hours at the 0.32 mcd m−2 threshold value after UV radiation. A combination of thermoluminescence (TL), thermoluminescence excitation (TLE), electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) calculations reveals that the persistent luminescence enhancement is attributed to a significant Nb-induced increase of oxygen vacancies that act as electron trapping centers with appropriate trap depths. Groups of time-dependent color-change images are realized with this material, which has potential applications as anti-counterfeit and indicator marks. This investigation also expands the application of transition metal (TM) ions to the field of persistent luminescence and would motivate further exploration of TM substitutions to design and improve silicate or aluminosilicate persistent phosphors with superior performance.