Influence of charge compensation to the luminescence properties of Ba2ZnGe2O7:Bi3+ phosphor

In this work, two series of phosphors were prepared using high-temperature solid-state reactions: Ba2-xZnGe2O7:xBi(3+) (series I) and Ba1.994-yKyZnGe2O7:0.006Bi(3+) (series II). X-ray diffraction (XRD) analysis demonstrated that the doping of a small amount of Bi3+ and K+ did not significantly change the phase structure of the material. The fluorescence spectra of the samples were obtained using a fluorescence spectrometer. The results indicated that the luminescence colors of both series remained yellow-green despite a slight variation in the luminescence spectra with changes in composition. Excitation at 358 nm led to the phosphor exhibiting a broad emission band with its peak at 500 nm, which corresponded to the energy level transition from P-3(1) to S-1(0). When monitoring at 500 nm, the strongest excitation peak occurred at 358 nm, representing the energy level transition from 1S0 to 3P1. Furthermore, a shoulder peak at 320 nm was observed, indicating a charge transfer band between O-2(-) and Bi3+. Analysis of the spectral data for series I suggested that the optimal doping amount of Bi3+ was x=0.006. In this matrix, the substitution of Ba2+ by Bi3+ introduced an unequal substitution, leading to the generation of Ba2+ vacancies or interstitial O-2(-) within the lattice, which had a negative impact on the luminous intensity of the material. Co-doping with K+ acted as a charge compensator, effectively cancelling out the Ba2+ vacancies or interstitial O-2(-) by generating interstitial K+ or oxygen vacancies. Consequently, this process reduced lattice distortion and improved luminescent intensity. Further analysis of the spectral data for series II revealed that the fully charge-compensated phosphor sample exhibited luminescent intensity about 2.5 times higher than that of the sample without K+ doping.