Effect of Covalence and Degree of Cation Order on the Luminous Efficacy of Mn⁴⁺ Luminescence in the Double Perovskites, Ba₂<i>B</i>TaO₆ (<i>B</i> = Y, Lu, Sc)

The spectroscopic properties of the Mn4+ ion are investigated in the series of isostructural double perovskite compounds, Ba2BTaO6 (B = Y, Lu, Sc). A comparison of these properties highlights the influence of covalent bonding within the perovskite framework and the degree of order between the B3+–Ta cations on the energy and intensity of the Mn4+2E → 4A2 emission transition (R-line). These two parameters of the emission spectrum are of importance for practical application since they determine the phosphor luminous efficacy. The influence of covalent bonding within the corner shared BO6/2 and TaO6/2 perovskite framework on the energy of the R-line energy is investigated. From the spectroscopic data, we have derived information on the influence of the degree of order between the B3+ and Ta5+ cations on the intensity of the R-line. The lowest energy and the highest intensity of the R-line are found in the double perovskite, Ba2ScTaO6. The purpose of this work is to propose for first time an explanation of these effects in the considered double perovskites. The obtained results are useful guidelines for practical improvement and tuning of key parameters of phosphors to the desired values

Vacuum Referred Binding Energy Scheme, Electron–Vibrational Interaction, and Energy Transfer Dynamics in BaMg₂Si₂O₇:Ln (Ce³⁺, Eu²⁺) Phosphors

The host structure and the synchrotron radiation VUV–UV luminescence properties of samples BaMg₂Si₂O₇ (BMSO):Ln (Ce³⁺, Eu²⁺) at different doping levels and different temperatures were investigated in detail. Three important aspects are studied to elucidate the luminescence properties of samples: (1) the vacuum referred binding energy (VRBE) scheme is constructed with the electron binding in the BMSO host bands and in the Ce³⁺ and Eu²⁺ impurity levels with the aim to explain the different thermal stabilities of Ce³⁺ and Eu²⁺ emissions; (2) the electron–vibrational interaction analysis on the narrow Eu²⁺ emission indicates a weak electron–phonon interaction in the current case; (3) by using three models (Inokuti–Hirayama, Yokota–Tanimoto, and Burshteĭn models) at different conditions, the energy transfer dynamics between Ce³⁺ and Eu²⁺ was analyzed. It reveals that the energy transfer from Ce³⁺ to Eu²⁺ via electric dipole–dipole (EDD) interaction is dominant while energy migration between Ce³⁺ is negligible. Finally, the X-ray excited luminescence spectra of samples BMSO:Ce³⁺/Eu²⁺ are collected to evaluate their possible scintillator applications

Highly Stable K₂SiF₆:Mn⁴⁺@K₂SiF₆ Composite Phosphor with Narrow Red Emission for White LEDs

Poor water resistance and nongreen synthesis remain great challenges for commercial narrow red-emitting phosphor A₂MF₆:Mn⁴⁺ (A = alkali metal ion; M = Si, Ge, Ti) for solid-state lighting and display. We develop here a simple and green growth route to synthesize homogeneous red-emitting composite phosphor K₂SiF₆:Mn⁴⁺@K₂SiF₆ (KSFM@KSF) with excellent water resistance and high efficiency without the usage of toxic and volatile hydrogen fluoride solution. After immersing into water for 6 h, the as-obtained water-resistant products maintain 76% of the original emission intensity, whereas the emission intensity of non-water-resistant ones steeply drops down to 11%. A remarkable result is that after having kept at 85% humidity and at 85 °C for 504 h (21 days), the emission intensity of the as-obtained water-resistant products is at 80–90%, from its initial value, which is 2–3 times higher than 30–40% for the non-water-resistant products. The surface deactivation-enabled growth mechanism for these phosphors was proposed and investigated in detail. We found that nontoxic H₃PO₄/H₂O₂ aqueous solution promotes the releasing and decomposition of the surface [MnF₆]^2– ions and the transformation of the KSFM surface to KSF, which finally contributes to the homogeneous KSFM@KSF composite structure. This composite structure strategy was also successfully used to treat KSFM phosphor prepared by other methods. We believe that the results obtained in the present paper will open the pathway for the large-scale environmentally friendly synthesis of the excellent antimoisture narrow red-emitting A₂MF₆:Mn⁴⁺ phosphor to be used for white light-emitting diode applications

High Color Rendering Index of Rb₂GeF₆:Mn⁴⁺ for Light-Emitting Diodes

High Color Rendering Index of Rb₂GeF₆:Mn⁴⁺ for Light-Emitting Diode