Tunable emissions from Bi3+ doped phosphors for WLEDs
For phosphor-converted white LEDs (pc-WLEDs) based on UV chips, it is essential to search high efficient phosphors better featured with broadly tunable emission and particular no or less excitation in visible ranges.This could allow the designer of pc-WLEDs to select the desirable emission wavelength and, thereby, fabricate the device with comfortable color perception.Conventional rare earth scheme, for instance Ce3+ or Eu2+ doped phosphors ”1-6”, can be tuned in emission wavelengths, but they cannot overcome the severe intrinsic excitation in the range from blue to green.We report here that Bi3+, the valence of which is confirmed by X-ray photoelectron (XPS) spectrum, can exhibit almost no excitation in the visible range and an extremely broad emission covering the full visible spectral range with internal quantum efficiency up to 75% once substituted into the solid solution compounds (Y, Lu,Sc)VO4∶Bi.When crystal field around Bi3+ is tuned by gradual substitution of smaller lanthanide ion for larger lanthanide ion in the solid solution, the emission peak position can be modulated linearly between 566 nm and 635 nm due to the susceptibility of bismuth naked 6s electrons to local environment.In accordance with Rietveld refining results, static and transient photoluminescence (PL) spectra reveal the existence of single type of Bi3+ emission center in the sample, to which energy transfer happens from VO43-group to Bi3+ upon excitation into the charge transfer state of VO43-groups.The mechanism of concentration quenching of Bi3+ emission is testified possibly due to dipole-quadrupole rather than exchange interactions.This work shows the potential application of bismuth doped samples in UV converted pc-WLEDs.
Fengwen Kang Mingying Peng
State Key Laboratory of Luminescent Materials and Devices, and Institute of Optical Communication Materials, School of Materials Science and Technology, South China University of Technology, Guangzhou 510640, China
国内会议
杭州
英文
51-52
2014-05-15（万方平台首次上网日期，不代表论文的发表时间）