Preparation And Properties Of YAG:Ce³⁺ Embedded Glass Ceramic Based On Bismuth Borate Glass For WLED

White light emitting diodes(WLEDs)have been widely used in the fields of general lighting,indicators,display and automobile headlights.However,their applications in the subdivision fields of high performance and high power were restricted due to low color rendering index,high correlated color temperature and bad thermal stability.It is considered as an effective way to resolve those defects using Y3Al5O12:Ce3+ glass ceramic(YAG-GC)with RE3+-doped glass precursor.Therefore,the present work aims to deal with the problems of current of YAG-GCs including the lack of red-light,shortage of the YAG erosion mechanism by precursor glasses,and the restricted applications owing to high cost or limited usage of glass raw materials.A series of low cost and environmental friendliness bismuth borate precursor glasses including,Eu3+-doped red light-emitting glasses and YAG-GCs with these precursor glasses were explored.The properties and structure of Eu3+-doped bismuth borate glasses were studied.The erosion mechanism of YAG phosphor in the YAG-GCs with binary bismuth borate precursor glasses and the erosion behaviors of YAG phosphor in the YAG-GCs with ternary and quaternary bismuth borate precursor glasses were investigated.The optical properties of the YAG-GCs,encapsulated WLEDs with blue chips and these YAG-GCs were analyzed and their photoelectrical performances were measured.The main results include:(1)Intense blue-light excitation and red-light emission are found in the Eu3+-doped zinc bismuth borate and alkaline earth bismuth borate glasses.The emission intensities gradually increase from magnesium bismuth borate to barium bismuth borate glass.4 mol% is the optimized doping concentration of Eu3+ in zinc bismuth borate glasses.The emission intensities have no obvious variation with the decrease of n B/Bi in Eu3+ doped calcium bismuth borate glasses(ECBBG),but increase with increasing the Ca2+ concentration,and 3 mol% is the optimized concentration of Eu3+.The compactness of glass structure and the local symmetry both decrease with decreasing the nB/Bi,increase with increasing the Ca2+ concentration.The rate of the compactness of glass structure goes up first and then down and 2mol% Eu3+ is the conversion point of ECBBG.[BO3],[Bi O3],[Bi O6] and [BO4] are the main units in the structures of Eu3+ doped bismuth borate glasses.(2)The YAG crystals are almost completely eroded by precursor glasses,and the luminescence of YAG-GCs are severely weakened in the preparation of YAG-GCs with binary B2O3-Bi2O3 glass matrices.The decrease of melting temperature and the reduction of(BO3)3-anion are effective means to suppress the YAG crystal erosion,and the intermediate phase of Bi4B2O9 may be responsible for transforming YAG phase into YAB(YAl3(BO3)4)in the YAGGC with the glass matrix at high n Bi/B.(3)The YAB phase disappears at 5 mol% doping content of Ca2+ in the YAG-GC with ternary B2O3-Bi2O3-Ca O precursor glass.The erosion degree of YAG crystal and the emission intensity of YAG-GC increase with the increase of Ca2+ concentration,and 15 mol% is the optimized concentration.(4)The erosion degrees of YAG crystals all exhibit relatively low in the quaternary B2O3-Bi2O3-Ca O-Eu2O3 glass matrix,and the degree increase with increasing the melting temperature.The time of the YAG crystals erosion is about at 9.6~15.8 min from the beginning of melt operation at 700 oC.The erosion products may contain four phases including YAB,and these phases do not melt into glass matrix.The valence state of Bi3+ maintains,and the energy transfer between Ce3+ and Eu3+ is not found in the YAG-GCs with quaternary matrix.The emission intensities of those YAG-GCs increase with decreasing the melting temperature and increasing the YAG doping concentration.Higher quantum efficiency and better thermal stability are obtained in the YAG-GC sample,and the best performance of WLEDs are 105.3 lm/W of luminous efficiency,3940 K of correlated color temperature and 70.1 of color rendering index.To summarize,the as-prepared low cost,environmental friendliness and superior optical performances YAG-GCs are promising candidate materials for high power,warm WLEDs,and the study also offer theoretical reference to glass and crystal composite materials.