Enhancement of Long-Persistent Phosphorescence by Solid-State Reaction and Mixing of Spectrally Different Phosphors

Abstract

Rare-earth-doped oxide-based phosphors have attracted great interest as light-emitting materials for technical applications and fundamental research because of their high brightness, tunable emission wavelength, and low toxicity, as well as chemical and thermal stability. The recent development of rare-earth-doped nanostructured materials showed improved phosphorescence characteristics, including afterglow and lifetime. However, the development of highly efficient phosphors remains challenging in terms of brightness and long persistence. Herein, novel protocols were developed for improving phosphorescence characteristics based on the energy transfer effect by chemical mixing of spectrally different phosphors. This protocol is based on the simple mixing method of different phosphors, which is totally different from the conventional methods but provides much brighter persistent phosphorescence. Simple chemical mixing methods significantly improved the afterglow intensity and lifetime of green and blue phosphors regardless of mixed time when subjected to a high-temperature solid-state reaction. In particular, chemical mixing after a high-temperature solid-state reaction enhanced the phosphorescence intensity more effectively than did chemical mixing before the reaction. We achieved increased luminescence of the phosphor, which is 10 times greater than that of the control sample, from all of the chemical mixing methods, which resulted in more efficient energy transfer than previously reported studies. Chemical mixing of three spectrally different phosphors was also performed to achieve multistep energy transfer for the first time, exhibiting a much higher afterglow intensity (∼2 times) than that of single-step energy transfer. This study provides a novel and simple method for the production of bright and long-persistent phosphors and thus expands their application range.

Recent Developments in Lanthanide-Doped Alkaline Earth Aluminate Phosphors with Enhanced and Long-Persistent Luminescence

“…Applying this phenomenon, Zhang et al demonstrated the ratiometric temperature sensing of LaOBr:Ce 3+ ,Tb 3+ over a wide temperature-sensing range (293–443 K) with a sensitivity of 0.42% K −1 [ 103 ]. This approach has also been recently demonstrated in lanthanide-codoped aluminate phosphors with various colors, such as SrAl 2 O 4 :Eu 2+ ,Dy 3+ , Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ , and CaAl 2 O 4 :Eu 2+ ,Nd 3+ as green, blue, and violet phosphors, respectively [ 14 ]. Novel protocols have been developed based on the effect of energy transfer between spectrally different phosphors, and they were noted to significantly improve the afterglow intensities and lifetimes of green and blue phosphors.…”

“…For example, Eu 2+ dopant ions in SrAl 2 O 4 and Sr 4 Al 14 O 25 are known to generate different emission wavelengths owing to their different crystalline structures (orthorhombic for Sr 4 Al 14 O 25 and monoclinic for SrAl 2 O 4 ) [ 44 , 58 , 59 ]. Kim et al synthesized SrAl 2 O 4 :Eu 2+ ,Dy 3+ and Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ as green and blue phosphors, respectively, by taking advantage of the different emission wavelengths [ 14 ].…”

“…(right) Photoluminescence decay curves in log scale for the blue and violet phosphors mixed sample, showing enhanced luminescence intensity of blue phosphor by mixing with the violet phosphor. Adapted from [ 14 ] under Creative Commons Attribution (CC BY) license.…”

“…Particularly, the development of codoped SrAl 2 O 4 :Eu 2+ ,Dy 3+ (Dy: dysprosium) phosphors by Matsuzawa et al has received considerable attention for the replacement of traditional ZnS-based phosphors, owing to their improved afterglow intensities, lifetimes, and chemical stabilities compared to those of the previously synthesized phosphors [ 5 ]. The intense emission of rare-earth-based phosphor has led to extensive applications in light-emitting diode (LED) devices, thin-film electroluminescent (TFEL) devices, optoelectronic or cathodoluminescent devices, safety marks, radiation dosimetry, X-ray imaging, bioimaging, and photodynamic therapy [ 14 , 15 , 16 , 17 , 18 , 19 ]. In particular, their applications as LED devices can help in replacing argon-mercury discharge fluorescent lamps, which are extensively used for general lighting purposes.…”

Facile Synthesis of a Color-Tunable Microcrystal Phosphor for Anti-Counterfeit Applications

“…Over the past decade, inorganic luminescent materials have enabled significant developments in optoelectronic devices, including solid-state lasers, lighting, and displays. 14 Recently, host materials with the doping of lanthanide (Ln) ions and/or transition metal (TM) ions in the lattice to function as luminescent centers have gained specific attention. 15 The unique ladder-like arranged energy levels of Ln and TM ions enable the generation of photons efficiently in a set of a spectral region ranging from ultraviolet (UV) to visible and near-infrared (NIR).…”