Facile Synthesis of Mn4+-Activated Double Perovskite Germanate Phosphors with Near-Infrared Persistent Luminescence

Abstract

Tetravalent manganese doped phosphors are emerging as a new class of efficient near-infrared emitters for applications in a variety of areas, such as bioimaging and night-vision surveillance. Novel double perovskite-type La 2 MgGeO 6 :Mn 4+ phosphors were successfully prepared using a microwave-assisted energy-saving solid state method. This simple technique involving the use of a microwave susceptor allows for a reduction of the preparation time compared to a conventional solid state reaction. The samples were investigated using powder X-ray diffraction, scanning electron microscopy, as well as energy-dispersive X-ray spectroscopy mapping, photoluminescence excitation/emission spectroscopy, persistent luminescence decay and temperature-dependent photoluminescence analysis. Substitution between isovalent Mn 4+ and Ge 4+ can be achieved without additional charge compensators in this germanate-based phosphor, which provides strong emission in the near-infrared spectral region, assigned to the characteristic transitions of tetravalent manganese ions. Additionally, the double perovskite-type germanate phosphor exhibits excellent luminescence thermal stability. Moreover, the spectroscopic properties, excitation wavelength-dependent and temperature-dependent persistent luminescence were studied. A series of thermoluminescence measurements were presented trying to give clear information on the charging process, afterglow behavior and the nature of the traps responsible for the persistent luminescence. The present investigation expands the range of available promising near-infrared emitting persistent phosphors for medical imaging.Sr 2 MgSi 2 O 7 :Eu 2+ , Dy 3+ with blue emission and CaAl 2 O 4 :Eu 2+ , Nd 3+ having violet emission [7][8][9][10]. Development of persistent phosphors in wavelengths beyond the visible spectral region, particularly in the near-infrared (NIR), has been of great significance, ranging from night-vision surveillance to medical imaging. Biomarkers or nanoparticles with persistent luminescence in the NIR optical window can be used as ideal agents for high-sensitivity medical imaging as they allow bio-imaging without external excitation, without autofluorescence and with high signal-to-noise ratio in biological tissues [11,12]. This state-of-the-art bio-imaging technology has motivated the exploration of NIR emitting persistent phosphors with high radiance and long duration.Tetravalent manganese (Mn 4+ ) doped phosphors have been applied as a red color component for phosphor-converted white light-emitting diodes [13]. Mn 4+ ions with 3d 3 electron configuration can substitute for Al 3+ , Ga 3+ , Si 4+ , Ti 4+ , Zr 4+ , and Ge 4+ ions and be stabilized in octahedral symmetry environment of several hosts. However, in regard to NIR persistent luminescence, the number of the reported Mn 4+ doped phosphors is very limited [14][15][16][17]. Phosphors with double perovskite crystal structure have attracted increasing attention, due to their unique properties and potential applications. The double perovski...

Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors

“…Du et al [ 122 ] used the MASS method to obtain a novel Mn 4+ -doped double-perovskite germanate structure with the formula La 2 MgGeO 6 . The approach consisted of two steps, first irradiating the sample with microwaves for 40 min, and then conventional thermal treatment for 3 h. Mn 4+ phosphors are emerging as a new class of efficient NIR emitters for bioimaging and night-vision surveillance.…”

Opportunities for Persistent Luminescent Nanoparticles in Luminescence Imaging of Biological Systems and Photodynamic Therapy

“…Due to the need of controlling and optimizing two different outputs, the optical properties (i.e., high quality on excitation/emission spectra with a bright and long-lasting afterglow emission), and the particle size control (i.e., narrow size distribution and controlled morphology), synthesis of PeL materials are more challenging when compared to larger sized nanoparticles. Factors such as optimization of (co-)dopants percentage on host, annealing temperature range, heating exposure time, phase purity, amount of intrinsic defects are some of the ones to be considered [190][191][192][193][194].…”

Near‐Infrared Persistent Luminescence and Trap Reshuffling in Mn4+ Doped Alkali‐Earth Metal Tungstates

“…[31] To the best of our knowledge, only aluminates and germanates have been explored. [32,33] The search for new candidates is prerequisite and the development of Mn 4+ doped NIR persistent materials is still an ongoing challenge.…”