High Water Resistance and Luminescent Thermal Stability of LiNaSiF: Mn Red-Emitting Phosphor Induced by Codoping of Li.

Mn-doped fluoride phosphors are efficient narrowband red-emitting phosphors for white light-emitting diodes (WLEDs) and backlight displays. However, erosion by moisture is the main obstacle that limits their application. In this work, LNSF:Mn (LiNaSiMnF) with high quantum yield (QY), luminescent thermal stability, and waterproofness was synthesized using the HO-free reaction method at room temperature. Compared to NSF:Mn(NaMnSiF), the QY value, luminescence thermal stability, and water resistance of LNSF:Mn are obviously improved by codoping of Li because of the formation of charge-carrier transfer (CT) and rare-Mn layer induced by codoping of Li. The former produces the negative thermal quenching (NTQ) effect, which results in the improvement of the luminescent thermal stability. The latter can inhibit the hydrolysis of Mn on the surface of the sample, which leads to the enhancement of waterproofness. The formation mechanism of the rare-Mn layer is discussed. A prototype WLED emitting the ideal warm white light (CCT = 3173 K, = 90.4) was assembled by coating a mixture of LNSF:Mn, yellow emitting phosphor (YAG:Ce), and epoxy resin on the blue light InGaN chip, indicating that the performance of the WLED can be improved by using LNSF:Mn.