This article presents a novel method for synthesizing highly efficient non-rare-earth red emitting phosphors for warm white light-emitting diodes (LEDs). The method involves a cation exchange reaction, which is typically used for synthesizing nano-sized materials, but is applied here to produce microcrystals of Mn⁴⁺-activated fluoride compounds such as K₂TiF₆, K₂SiF₆, NaGdF₄, and NaYF₄. The synthesized K₂TiF₆:Mn⁴⁺ phosphor exhibits a photoluminescence quantum yield (PL QY) of 98%, which is the highest reported for such materials. This phosphor is used to fabricate a high-performance warm white LED with a low correlated colour temperature (3,556 K), high colour-rendering index (Rₐ = 81), and a luminous efficacy of 116 lm W⁻¹. These results demonstrate the potential of K₂TiF₆:Mn⁴⁺ as a commercial red phosphor for warm white LEDs and open new avenues for the development of non-rare-earth red emitting phosphors. The article discusses the challenges of synthesizing high-efficiency red phosphors for warm white LEDs, particularly the limitations of traditional rare-earth-doped (oxy)nitride phosphors. It highlights the advantages of Mn⁴⁺-activated fluoride phosphors, including their narrow absorption and emission bands, high PL QY, and low production cost. The synthesis of K₂TiF₆:Mn⁴⁺ is achieved through a cation exchange reaction, which is efficient and convenient, allowing for the production of microcrystals with high purity and uniform distribution of Mn⁴⁺ ions. The structural and optical properties of the phosphor are analyzed, revealing its unique electronic and vibronic structures, which contribute to its high PL QY and sharp emission lines. The article also investigates the temperature-dependent photoluminescence (PL) intensity of K₂TiF₆:Mn⁴⁺, revealing an unusual increase in PL intensity with temperature, which is attributed to enhanced absorption of excitation light by the sample. This finding is significant for the thermal stability of the phosphor in LED applications. The phosphor's performance is further validated by fabricating warm white LEDs with high CRI and luminous efficacy, demonstrating its potential for commercial use. The study provides a comprehensive understanding of the synthesis, optical properties, and application of Mn⁴⁺-activated fluoride phosphors, highlighting their potential as non-rare-earth alternatives to traditional red phosphors in LED technology.This article presents a novel method for synthesizing highly efficient non-rare-earth red emitting phosphors for warm white light-emitting diodes (LEDs). The method involves a cation exchange reaction, which is typically used for synthesizing nano-sized materials, but is applied here to produce microcrystals of Mn⁴⁺-activated fluoride compounds such as K₂TiF₆, K₂SiF₆, NaGdF₄, and NaYF₄. The synthesized K₂TiF₆:Mn⁴⁺ phosphor exhibits a photoluminescence quantum yield (PL QY) of 98%, which is the highest reported for such materials. This phosphor is used to fabricate a high-performance warm white LED with a low correlated colour temperature (3,556 K), high colour-rendering index (Rₐ = 81), and a luminous efficacy of 116 lm W⁻¹. These results demonstrate the potential of K₂TiF₆:Mn⁴⁺ as a commercial red phosphor for warm white LEDs and open new avenues for the development of non-rare-earth red emitting phosphors. The article discusses the challenges of synthesizing high-efficiency red phosphors for warm white LEDs, particularly the limitations of traditional rare-earth-doped (oxy)nitride phosphors. It highlights the advantages of Mn⁴⁺-activated fluoride phosphors, including their narrow absorption and emission bands, high PL QY, and low production cost. The synthesis of K₂TiF₆:Mn⁴⁺ is achieved through a cation exchange reaction, which is efficient and convenient, allowing for the production of microcrystals with high purity and uniform distribution of Mn⁴⁺ ions. The structural and optical properties of the phosphor are analyzed, revealing its unique electronic and vibronic structures, which contribute to its high PL QY and sharp emission lines. The article also investigates the temperature-dependent photoluminescence (PL) intensity of K₂TiF₆:Mn⁴⁺, revealing an unusual increase in PL intensity with temperature, which is attributed to enhanced absorption of excitation light by the sample. This finding is significant for the thermal stability of the phosphor in LED applications. The phosphor's performance is further validated by fabricating warm white LEDs with high CRI and luminous efficacy, demonstrating its potential for commercial use. The study provides a comprehensive understanding of the synthesis, optical properties, and application of Mn⁴⁺-activated fluoride phosphors, highlighting their potential as non-rare-earth alternatives to traditional red phosphors in LED technology.