Following pioneering work, solution-processable Mn4+-activated fluoride pigments, such as A2BF6 (A = Na, K, Rb, Cs; A2 = Ba, Zn; B = Si, Ge, Ti, Zr, Sn), have attracted considerable attention as highly promising red phosphors for warm white light-emitting diodes (W-LEDs). To date, these fluoride pigments have been synthesized via traditional chemical routes with HF solution. However, in addition to the possible dangers of hypertoxic HF, the uncontrolled precipitation of fluorides and the extensive processing steps produce large morphological variations, resulting in a wide variation in the LED performance of the resulting devices, which hampers their prospects for practical applications. Here, we demonstrate a prototype W-LED with K3AlF6:Mn4+ as the red light component via an efficient and water-processable cation-exchange green route. The prototype already shows an efficient luminous efficacy (LE) beyond 190 lm/W, along with an excellent color rendering index (Ra = 84) and a lower correlated color temperature (CCT = 3665 K). We find that the Mn4+ ions at the distorted octahedral sites in K3AlF6:Mn4+ can produce a high photoluminescence thermal and color stability, and higher quantum efficiency (QE) (internal QE (IQE) of 88% and external QE (EQE) of 50.6%.) that are in turn responsible for the realization of a high LE by the warm W-LEDs. Our findings indicate that the water-processed K3AlF6 may be a highly suitable candidate for fabricating high-performance warm W-LEDs.
Yang Chen,Tan Yuhuan,Li Zheyi,Liang Shan,Guan Xi-Hua,Yang Zhong-Jian,Lian Shixun,Zhou Wenli
The reduction in photoluminescence efficiency due to crystallite downsizing is a significant issue in Mn 4+ -doped fluoride nanomaterials, crucial for their application in full-color micro-LED displays. This study presents a strategy to enhance the photoluminescence efficiency of K 3 AlF 6 :Mn 4+ nanocrystals (NCs) by incorporating Mg 2+ for charge compensation and utilizing the plasmonic effect of Au nanorods. We found that Mg 2+ incorporation effectively reduced lattice defects, increasing photoluminescence intensity by 17% and internal quantum efficiency from 22.37% to 27.56%. Fabricating Au@SiO 2 /fluoride nanocomposites, we investigated how the SiO 2 spacer layer thickness, Au@SiO 2 resonance wavelength, and relative concentration affect photoluminescence properties. Optimizing the balance between Purcell and Förster resonance energy transfer effects further increased photoluminescence intensity by 25%, internal quantum efficiency to 32.09%, and external quantum efficiency from 14.20% to 18.05%. Additionally, we assessed the potential application of these nanocomposites in micro-LED display technology by examining nanocomposite-PMMA films. This work provides insights into the development of highly efficient red-emitting nanomaterials.
Mn4+-doped fluoride red phosphors are widely used in white LED lighting and display applications due to their excellent luminescent properties. However, their synthesis relies heavily on highly toxic aqueous hydrofluoric acid, which not only causes severe environmental and soil/water pollution but also makes it difficult to control the microstructure of the products due to the rapid reaction rate. In this study, low-melting-point NH4HF2was used as the molten salt, with KMnO4and MnF2as manganese sources, to synthesize the red phosphor K3AlF6: Mn4+via the molten salt method. After the reaction, impurities such as NH4HF2were removed by washing with a dilute H2O2solution. The microstructure, photoluminescence properties, thermal quenching behavior, and application in warm white light-emitting diodes (W-LEDs) of the K3AlF6: Mn4+phosphors were investigated. The results indicate that the phosphors prepared by this method consist of a single pure phase. By adjusting the molten salt content, the morphology of the product can be transformed from nanoparticle-like to nanorod-like structures. All products exhibit the characteristic red emission of Mn4+under blue and violet light excitation, with the optimally doped sample achieving an internal quantum efficiency (IQE) of 69% under blue light excitation. The combination of the obtained K3AlF6: Mn4+with the yellow phosphor YAG enabled the fabrication of W-LEDs. These W-LEDs achieved a color rendering index (Ra) of 86.8, a luminous efficacy (LE) of 77 lm/W, and a correlated color temperature (CCT) of 3690 K, along with excellent color stability under operating conditions.
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