Search

In the arena of advanced anti-counterfeit research, developing a multi-level, anti-counterfeit material with tunable luminescence is a hot topic. However, current research has mainly focused on the visible light signal, despite the fact that near-infrared is also suitable for optical anti-counterfeit applications. The importance of the near-infrared signal is because it is more difficult to observe than the visible light signal. Here, a new, persistent, luminescent, near-infrared material composed of Zn 2+ x Ga 4-2 x Sn x O 8 :0.5%Cr3+ (x = 0-0.4) has been synthesized using the sol-gel method. A new anti-site-like defect [ Zn Ga ′ - Sn Ga. ] appeared after incorporating both Zn2+ and Sn4+, along with an intrinsic, anti-site defect [ Zn Ga ′ - Ga Zn. ]. Specifically, the former and latter defects contributed to the deep and shallow traps, respectively. Introducing Zn2+ and Sn4+ resulted in a significant, two-fold enhancement of the NIR emission intensity. This led to an obvious improvement in its persistent luminescence. In the absence of light irradiation, the NIR emitted light lasted for several hours. If heated, the disappeared NIR signal reappeared and lasted for 10 min. Primarily due to both the shallow and deep traps, the prepared samples exhibited dynamic NIR luminescence behavior. This behavior then contributed to the dynamic display information. Collectively, these results indicate that persistent phosphors have great potential for use in advanced, optical anti-counterfeit materials, owing to their ability to afford higher security. [ABSTRACT FROM AUTHOR]

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al 2 O 3 –YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al 2 O 3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting. [ABSTRACT FROM AUTHOR]

Long persistent luminescence materials developed to commercial standards are primarily concentrated in the blue and green regions, with only a few in the red region. Red, as one of the three basic colors, can be mixed in various proportions with blue and green to yield various colors. The development of red persistent phosphors has a broader application potential but remains a challenge. A solid-state reaction method was used to synthesize new red persistent luminescent materials of Ba 1- x Sr x Ga 2 O 4 :Sm3+ (x = 0–0.09). In BaGa 2 O 4 , both Sr2+ and Sm3+ preferentially occupy the Ba2+ site rather than the Ga3+ site. When exposed to UV light at 254 nm, the phosphors emit the characteristic red emission of Sm3+ at wavelengths ranging from 500 nm to 750 nm. After removing the UV light source, an intense red afterglow that lasted more than 1400 s was observed. The red afterglow signal reappears after a heating process. Doping Sr2+ reduces the trap depth and improves the red persistent luminescence significantly. Because the escaped electrons from traps compensate for the emission loss of Sm3+ during the heating process, the red phosphors have unimaginably luminescent thermal stability. Thus, the emission intensity at 200 °C is 1.6 times that at room temperature. The prepared red persistent phosphors show multimode luminescence, with the output signal being time and temperature sensitive, indicating that they are potential luminescent materials for anti-counterfeiting applications. Finally, a building-block strategy for advanced anti-counterfeiting applications of dynamic display information is proposed, with red persistent phosphors serving as an important component combined with upconversion phosphors of NaYF 4 :Yb3+, Tm3+, and green persistent phosphors of SrAl 2 O 4 :Eu2+, Dy3+. [ABSTRACT FROM AUTHOR]

Uniform phosphor mono-spheres have received continuously increasing attention owing to their excellent luminescence properties. Submicron/near micron-sized Lu 2 O 3 :Eu mono-spheres were successfully prepared by a facile and modified homogeneous precipitation technique from corresponding single-source precursor of Lu(OH)CO 3 :Eu⋅ n H 2 O, without the assistance of any dispersants. The sizes of the precursor spheres can be tuned in the range of 56–790 nm via controlling the primary particle nucleation and particle growth in the homogeneous precipitation. After calcination at 1000 °C, the synthesized precursor spheres (165–790 nm) were converted to Lu 2 O 3 :Eu (110–630 nm) without changing their original spherical shape and excellent dispersion. The particle size-dependent photoluminescence properties of Lu 2 O 3 :Eu mono-spheres were investigated in detail. Enhanced photoluminescence intensity, shorter lifetime, higher external quantum efficiency and almost the same CIE chromaticity coordinates were observed for a particle size of 480 nm. Moreover, temperature-dependent photoluminescence spectra indicated the obtained phosphor mono-spheres have good thermal stability. [ABSTRACT FROM AUTHOR]

The metastable garnet lattice of Yb/Er co-doped Gd 3 Al 5 O 12 (GdAG:Yb/Er) has been effectively stabilized by doping with significantly smaller Lu 3+ to form (Gd,Lu)AG:Yb/Er solid solutions. The phase-pure (Gd,Lu)AG:Yb/Er garnet particles have been successfully achieved by calcining their respective precursors synthesized via carbonate co-precipitation. Partially replacing Gd 3+ with Lu 3+ up to 50 at% ( x =0.5) not only lowers the temperature of garnet crystallization, but also raises the theoretical density of the material. The resultant [(Gd 1− x Lu x ) 0.948 Yb 0.05 Er 0.002 ]AG ( x =0.1–0.5) powders, with good dispersion and fairly uniform particle morphology, exhibit strong green (~510 to 590 nm, 2 H 11/2 , 4 S 3/2 → 4 I 15/2 transitions of Er 3+ ) and red (~635 to 700 nm, 4 F 9/2 → 4 I 15/2 transition of Er 3+ ) emissions under 978 nm laser excitation. The Lu 3+ incorporation effect on the visible emission color and intensity of Er 3+ , as well as the dependence of emission intensity on pumping power were all discussed in detail. The up-conversion phosphor of Yb/Er codoped (Gd,Lu)AG garnet developed in this work may potentially be used as a new type of luminescent material. [ABSTRACT FROM AUTHOR]