Synthesis And Luminescence Properties Of Mn⁴⁺ Ions-activated Fluorides Red Phosphors

White light-emitting diodes?LEDs?are regarded as the new generation lighting source and can be applied in various fields by fabricating a blue-chip and yellow-emitting phosphor,which have superior performances,include small volume,low energy consumption,high luminous brightness,high efficiency,long lifetime,and environmental friendliness.In order to improve their low colour rendering index and high correlated colour temperature,a new phosphor that can generate suitable red light emission should be introduced.As a novel class of non-rare-earth red emitting phosphors for high efficiency warm white LEDs,transition metal Mn⁴⁺ ions doped fluoride phosphors with narrow red emission,excellent thermal stability,and low cost have attracted tremendous interest recently.In this dissertation,we aim to develop Mn⁴⁺ ions doped fluoride phosphors,which would to hold the potential to supersede commercial rare earth doped nitride phosphors.The main research works are as follows.A series of BaTiF₆:Mn⁴⁺ samples were synthesized through a facile hydrothermal method.The products with bundle-like,microrod,and flower-like morphologies could be obtained by varying the hydrothermal reaction time.The luminescence spectra demonstrated that two intense excitation bands could be observed in the near-UV and blue region and an intense red emission was discovered upon 470 nm excitation.In addition,the influence of the Mn⁴⁺ ion emissions based on different reaction temperatures and barium sources were discussed.The thermal stability of the BaTiF₆:Mn⁴⁺ phosphor was evaluated by temperature-dependent luminescence experiments.Furthermore,BaTiF₆:Mn⁴⁺ had excellent photocatalytic performance.A series of Mn⁴⁺ ions doped BaTiF₆ phosphors were obtained through the hydrothermal route with citric acid as surfactant.After a systematic investigation,we illustrated the effect of reaction time,nominal concentration of HF solution,and reaction temperature on the luminescence performance of the phosphor.The BaTiF₆:Mn⁴⁺ phosphor generated narrow red emission,which was highly perceived by the human eyes and leads to excellent chromatic saturation of red emission spectra.Simultaneously,concentration and thermal quenching were investigated systematically,and the quenching mechanisms are elucidated in detail.Employing BaTi F₆:Mn⁴⁺ as a red phosphor,we fabricate a high-performance white LED with correlated color temperature of 3974 K,color rendering index of 90.6 and luminous efficacy of 132.54 lm/W,suggesting that the phosphor can improve the correlated color temperature and color rendering index of white LEDs.A series of Mn⁴⁺ ions activated BaTiF₆ phosphors had been prepared using CTAB as a surfactant or ethanol/ethylene glycol as solvents.The crystal structure and morphology of the resulting samples were characterized in detail using powder X-ray diffraction,scanning electron microscopy and energy-dispersive X-ray spectroscopy.It was noted that CTAB as a shape modifier played a critical role in the shape evolution of the final products.In addition,the shape and size of the samples can be manipulated by adjusting the radio of solvent in the initial solution.The photoluminescence spectra clearly demonstrated that two intense excitation bands could be observed in the near-UV and blue region and sharp red emissions were discovered under blue light illumination.Based on the improvement in correlated color temperature and color rendering index,Mn⁴⁺ activate BaTiF₆ phosphors can be used for red phosphor in warm white LEDs.