Post-doping induced morphology evolution boosts Mn2+ luminescence in the Cs2NaBiCl6:Mn2+ phosphor.

As we know, defects caused in the synthetic process of metal halide perovskite are the most difficult to overcome, and greatly limit their photoelectric performances. Herein, a post-doped strategy was utilized to achieve an interesting morphology evolution from a standard octahedron to a snowflake-like sheet during the Mn2+-doped Cs2NaBiCl6 process, which realizes the obvious photoluminescence quantum efficiency (PLQY) enhancement of the Cs2NaBiCl6:Mn2+ phosphor. This surprising evolution is ascribed to the morphology collapse and reconstruction induced by Mn2+ exchange. The obtained phosphor exhibits enhanced 31.56% PLQY, which is two-fold higher than that synthesized by the traditional co-precipitation method, with broad emission spectrum and good PL color stability at 150 °C. Combined with the Cs2SnCl6 : 1mol%Bi3+ phosphor to fabricate the phosphor-converted light-emitting diode, bright white light emission with Ra = 88, CCT = 4320 K, CIE (0.36, 0.33) and a good application potential in high-resolution PL imaging agents was obtained. This work provides a possible effective strategy to improve the PL performance for impurity-doped lead-free metal halide perovskite.

Phase Transformation of a K2GeF6 Polymorph for Phosphors Driven by a Simple Precipitation-Dissolution Equilibrium and Ion Exchange.

Tuning crystal phase transformations is very important for obtaining polymorphs for phosphors with the ideal optical properties and stability. Mn4+-doped K2GeF6 (KGF) is a typical polymorphic phosphor, but the thermodynamic and kinetic mechanism of its phase transformation is still unclear. Herein, the phase transformation of polymorphs varying from P63mc KGF and trigonal KGF to P63mc Si4+-doped KGF is realized by introducing the synergistic action of an HF solution and Si4+ ions. The full structural refinements of KGF polymorphs at room temperature and the electronic band structure calculations were performed. The results show that the Si4+-doped hexagonal KGF polymorph with good photoluminescence properties is the most stable phase according to the calculated total energy landscape and relative formation energy. The morphologic changes were monitored in situ to clearly understand the rapid phase transformation mechanism, which proves that the phase transformation is driven by a simple precipitation-dissolution equilibrium and ionic exchange.

Color-tunable photoluminescence and energy transfer of (Tb1-x Mn x )3Al2(Al1-x Si x )3O12:Ce3+ solid solutions for white light emitting diodes.

(Tb1-x Mn x )3Al2(Al1-x Si x )3O12:Ce3+ solid solution phosphors were synthesized by introducing the isostructural Mn3Al2(SiO4)3 (MAS) into Tb3Al5O12:Ce3+ (TbAG). Under 456 nm excitation, (Tb1-x Mn x )3Al2(Al1-x Si x )3O12:Ce3+ shows energy transfers (ET) in the host, which can be obtained from the red emission components to enhance color rendering. Moreover, (Tb1-x Mn x )3Al2(Al1-x Si x )3O12:Ce3+ (x = 0-0.2) exhibits substantial spectral broadening (68 → 86 nm) due to the 5d → 4f transition of Ce3+ and the 4T1 → 6A1 transition of Mn2+. The efficiency of energy transfer (η T, Ce3+ → Mn2+) gradually increases with increasing Mn2+ content, and the value reach approximately 32% at x = 0.2. Namely, the different characteristics of luminescence evolution based on the effect of structural variation by substituting the (MnSi)6+ pair for the larger (TbAl)6+ pair. Therefore, with structural evolution, the luminescence of the solid solution phosphors could be tuned from yellow to orange-red, tunable by increasing the content of MAS for the applications of white light emitting diodes (wLED).