Luminescence Enhancement of Mn⁴⁺-Activated Fluorides via a Heterovalent Co-Doping Strategy for Monochromatic Multiplexing

Abstract

Mn 4+ non-equivalent doped fluorides with high color purity red emission and relatively short decay time are crucial for wide color gamut displays and emerging applications, whereas the low quantum efficiency (QE) restrains their further applications. Herein, the luminescence of Mn 4+ non-equivalent doped fluoride K 2 NaAlF 6 :Mn 4+ (KNAF:Mn 4+ ) is significantly enhanced via a heterovalent co-doping strategy, where the luminescence intensity is obviously increased by ∼85%, but the decay time is almost unchanged. The experimental characterization and density functional theory (DFT) calculations provide an understanding of the luminescence enhancement mechanism of heterovalent co-doping, which is enabled by simultaneously improving the stability of Mn 4+ and reducing the number of quenching centers (defects and impurities). Combining the shortdecay-time (τ = 4.03 ms) emission KNAF:Mn 4+ , Mg 2+ and long-decay-time (τ = 9.23 ms) emission K 2 SiF 6 :Mn 4+ , a novel monochromatic multiplexing mode in the millisecond order is presented, which can be decoded not only in high-efficiency by a digital camera but also with a high security. This work provides a new optical multiplexing for the information security applications and also inspires the design of high-efficiency Mn 4+ -activated luminescent materials.

Mn4+-Doped Fluoride Nanocrystals Enable High-Resolution Red-Emitting X-ray Imaging Screens

“…This series of emission peaks is attributed to the anti-Stokes ν 3 (t 1u ), ν 4 (t 1u ), ν 6 (t 2u ), and zero phonon line (ZPL) vibronic modes and the Stokes ν 6 (t 2u ), ν 4 (t 1u ), and ν 3 (t 1u ) vibronic modes, respectively. , Some shifts in the emission peaks can be observed between different compositions, which is related to the different crystal field strengths of Mn 4+ -doped ions, caused by differences in M–F bond strength between different compositions ,, (a dotted line is provided for guidance in Figure a). Additionally, the ZPL of K 3 AlF 6 :Mn 4+ NCs is stronger than that of other compositions, which has been previously observed in nonequivalent doped fluoride phosphors. − In fact, the intensity of the ZPL is mainly determined by the local symmetry of the Mn 4+ environment, and an increase in the ZPL line is associated with a reduction in local symmetry upon nonequivalent doping. ,, Figure c shows the photoluminescence decay curves at 630 nm emission upon excitation at 465 nm for NC colloidal solutions of different matrix compositions and a Mn 4+ concentration of about 2 at. %.…”

Mn2+-Activated Photostimulable Persistent Nanophosphors by Pr3+ Codoping for Rewritable Information Storage

“…For an ion-doped inorganic luminescent material, the local environment of the luminescent center plays a critical role in the luminescence features . To understand how doping Pr 3+ modifies the electronic structure of Mn 2+ , a series of local atomic structures and bond length variations of fully relaxed doping complexes are illustrated in Figure .…”

“…For an ion-doped inorganic luminescent material, the local environment of the luminescent center plays a critical role in the luminescence features. 47 To understand how doping Pr 3+ modifies the electronic structure of Mn 2+ , a series of local atomic structures and bond length variations of fully relaxed doping complexes are illustrated in Figure 2. In the singledoping models (M1, M2, P1, P3, and P4), except the bond length change of the substitution atom, the average bond length of the adjacent atoms has nearly no significant change.…”

Mn-Activated Fluoride Phosphors Modified by Surfactant with Outstanding Water Resistance and Luminescent Thermal Properties

“…As can be seen in Figure c, the fluorescence decay lifetime of pure KTFM is 5.74 ms, and after treatment with the surfactants CTAB and EDTA, the decay lifetime of phosphor increases significantly, reaching 6.07 ms at the highest. To further illustrate the effect of surfactant assistance on the phosphor luminescence performance, the QE of this series of samples was characterized, and the calculation formula was as follows normalA normalE = ∫ [ E false( λ false) h ν − R false( λ false) h ν ] normald λ ∫ [ E false( λ false) h ν ] normald λ normalI normalQ normalE = ∫ [ P false( λ false) h ν ] normald λ ∫ [ E false( λ false) h ν − R false( λ false) h ν ] normald λ normalE normalQ normalE = normalI normalQ normalE × normalA normalE where E (λ)/ hν , R (λ)/ h ν, and P (λ)/ h ν are the number of photons in the excitation, reflection, and emission spectra of the phosphors, respectively . The inner quantum yield (IQE) is the ratio of the number of emitted photons to the number of absorbed photons in the sample, which actually reflects the competition between luminescence-dominated radiative transition and non-radiative transition.…”

“…where E(λ)/hν, R(λ)/hν, and P(λ)/hν are the number of photons in the excitation, reflection, and emission spectra of the phosphors, respectively. 37 The inner quantum yield (IQE) is the ratio of the number of emitted photons to the number of absorbed photons in the sample, which actually reflects the competition between luminescence-dominated radiative transition and non-radiative transition. Therefore, an increase in the internal quantum yield represents an increase in the rate of radiation leap in the process of phosphor de-energization in the form of luminescence, which means that the luminescence intensity of the phosphor is positively correlated with the internal quantum yield, when the luminescence intensity increases, the internal quantum yield increases accordingly.…”