Persistent luminescence nanophosphors (PLNPs) emitting in the second near-infrared window (1000–1700 nm, NIR-II) are emerging as one promising class of in vivo bio-imaging agents due to their unique advantages including non-autofluorescence and low optical scattering in tissues. Currently, it remains a great challenge to synthesize nanosized lanthanide-doped inorganic NIR-II phosphors with a good persistent luminescence performance. Herein, we present a salt microemulsion method for synthesizing Ce3+, Cr3+, Nd3+ codoped Y3(Al/Ga)5O12 nanocrystals, which generate multi-wavelength persistent luminescence in the visible (∼508 nm, 5d1 → 4f of Ce3+), the first near-infrared window (∼890 nm, 4F3/2 → 4I9/2 of Nd3+) and NIR-II (∼1063 nm, 4F3/2 → 4I11/2 of Nd3+) regions. Under illumination of a 410 nm diode (3 W) for 10 min, the observed duration time of NIR-II persistent luminescence is as long as 60 min at room temperature. Moreover, the persistent luminescence can be excited efficiently by multiple excitation sources including a blue diode, white LEDs and an X-ray generator, which is crucial for deep tissue imaging applications. By comparing the penetration depth between NIR-I and NIR-II persistent luminescence through chicken breast, we prove that NIR-II photons exhibit a deeper optical penetration length (3.9 mm) than that of the NIR-I ones (2.5 mm). In addition, the NIR signals can still be detected 3 min after ceasing the excitation source by a small animal imaging system (InGaAs detector) when the thickness of the covering chicken breast is 20 mm. These results show great promise for Y3(Al/Ga)5O12:Ce3+,Cr3+,Nd3+ nanocrystals as a PLNP for bio-imaging applications with deep penetration depth and a high signal-to-noise ratio.
Enjie He,Xiangxiao Chen,Yaqi Wu,Yinkang Cui,Tao Wang,Fangfang Li,Qingyan Han,Xuzhong Zuo,Nian Liu
This study presents the synthesis and characterization of efficient deep-red-emitting CaMg 2 La 2 W 2 O 12 :Mn 4+ , Nd 3+ (CMLW:Mn 4+ , Nd 3+ ) phosphors for application in light-emitting diodes (LEDs) designed for indoor plant cultivation. The phosphors were prepared via a high-temperature solid-state reaction and exhibited an orthorhombic structure with optimal luminescence properties at Mn 4+ (0.90 %) and Nd 3+ (0.60 %) doping concentrations. The enhanced performance of CMLW:0.90 %Mn 4+ , 0.60 %Nd 3+ over its Nd 3+ -free counterpart originates from three synergistic mechanisms: (1) Nd 3+ substitution for larger La 3+ induces lattice shrinkage, shortening the Mn 4+ -O 2- bond length and enhancing the crystal-field strength, thereby increasing the radiative transition probability of 2 E g → 4 A 2g emission at 708 nm; (2) Nd 3+ co-doping suppresses concentration quenching by increasing the critical distance between Mn 4+ ions, as evidenced by prolonged lifetime and higher optimal Mn 4+ concentration; (3) The optimal Nd 3+ concentration improves lattice rigidity while avoiding defect formation observed at higher doping levels. The resulting phosphor demonstrates intense deep-red emission matching the phytochrome P FR absorption band, excellent thermal stability (73.66 % intensity at 453 K), and a high internal quantum efficiency (IQE) of 86.80 %. A prototype LED device exhibits stable deep-red emission and a luminous efficacy of 0.10 lm/W under 365 nm excitation. These results position CMLW:Mn 4+ , Nd 3+ phosphor as a promising candidate for indoor plant cultivation LEDs.
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