Abstract
The remarkable narrow-band emission of trivalent lanthanide-doped phosphors excited by the vacuum ultraviolet (VUV) radiation lines of Xe atoms/Xe2 molecules at 147/172 nm are extensively investigated in the development of plasma display panels and Hg-free fluorescent lamps, which are frequently used in our daily lives. Numerous solid materials, particularly Tb3+-doped oxides, such as silicates, phosphates and borates, are efficient green/blue sources with color-tunable properties. The excitation wavelength and rare earth concentration are usually varied to optimize efficiency and the luminescent properties. However, some underlying mechanisms for the shift in the emission colors remain unclear. The present study shows that a UV/VUV switch systematically controls the change in the phosphor (Ba3Si6O12N2:Tb) photoluminescence from green to blue, resulting in a green emission when the system is excited with UV radiation. However, a blue color is observed when the radiation wavelength shifts to the VUV region. Thus, a configurational coordinate model is proposed for the color-reversal effect. In this model, the dominant radiative decay results in a green emission under low-energy UV excitation from the 5D4 state of the f–f inner-shell transition in the Tb system. However, under high-energy VUV excitation, the state switches into the 5D3 state, which exhibits a blue emission. This mechanism is expected to be generally applicable to Tb-doped phosphors and useful in adjusting the optical properties against well-known cross-relaxation processes by varying the ratio of the green/blue contributions.
Highlights
INTRODUCTIONInorganic-material-based phosphors have been extensively investigated for their applications in electronic illustrations, such as backlighting sources of liquid–crystal displays, plasma display panels and white light-emitting diodes (WLEDs)[1,2]
The present study shows that a UV/VUV switch systematically controls the change in the phosphor (Ba3Si6O12N2:Tb) photoluminescence from green to blue, resulting in a green emission when the system is excited with UV radiation
Inorganic-material-based phosphors have been extensively investigated for their applications in electronic illustrations, such as backlighting sources of liquid–crystal displays, plasma display panels and white light-emitting diodes (WLEDs)[1,2]
Summary
Inorganic-material-based phosphors have been extensively investigated for their applications in electronic illustrations, such as backlighting sources of liquid–crystal displays, plasma display panels and white light-emitting diodes (WLEDs)[1,2]. The most common WLED strategy is to combine blue InGaN chips and Y3Al5O12:Ce3+ (YAG:Ce) phosphor in addition to employing three light-emitting diode (LED) chips in red, green and blue, which partially converts the original blue radiation into the complementary yellow color, yielding cool white light. This cool white light, which is based on using a single phosphor, is suitable for everyday applications only if the poor color rendition index (CRI) and high-correlated color temperature are bearable[5,6]. The principal relationship between the different excitation energies and the luminescence mechanism was investigated
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