Zhigang Feng

Luminescent properties of Ce3+/Tb3+co-doped glass ceramics containing YPO4 nanocrystals for W-LEDs

Abstract Ce 3+ /Tb 3+ co-doped transparent glass ceramics containing YPO 4 nanocrystals were prepared using high temperature melting method, and their structural and luminous properties were investigated. XRD analysis and TEM images confirmed the existence of YPO 4 nanocrystals in glass ceramics. The transmission spectra proved that the glass ceramics specimens still maintained a high transparency. Then the excitation and emission spectra of the Ce 3+ and Tb 3+ single-doped and co-doped glass and glass ceramics were discussed, which proved that the glass ceramics had better luminescent properties. Under the near ultraviolet (331 nm) excitation, the broadband emission located at 385 nm was observed which was ascribed to 5d→ 2 F 5/2 and 2 F 7/2 transition of Ce 3+ ions. Several characteristic sharp peaks centered at 489, 543, 578 and 620 nm originated from the 5 D 4 to 7 F J ( J =6, 5, 4, 3) of Tb 3+ ions. The decay time of Tb 3+ ions at 543 nm and the relevant energy levels of Ce 3+ ions and Tb 3+ ions illustrated the transfer process from Ce 3+ ions to Tb 3+ ions. The best CIE chromaticity coordinate of the glass ceramics specimen was calculated as ( x =0.3201, y =0.3749), which was close to the NTSC standard values for white ( x =0.333, y =0.333). All the results suggested that the YPO 4 -based Ce 3+ /Tb 3+ co-doped glass ceramics could act as potential luminescent materials for white light-emitting diodes.

Luminescent properties of Eu3+-doped α-NaYF4 single crystal under NUV-excitation

Abstract This paper reports on successful synthesis of α-NaYF4 single crystal doped with Eu3+ at various concentrations by a modified Bridgman method. The crystal structure is characterized by means of X-ray diffraction. The absorption spectra, excitation spectra and emission spectra were measured to investigate the optical properties of the single crystals. An intense red emission located at 611 nm with long lifetime of 9.03 ms was observed in single crystal under the excitation of 394 nm light. It benefits from the low maximum phonon energy of α-NaYF4 single crystal matrix (390 cm−1). The CIE chromaticity coordinate of the α-NaYF4 single crystal doped Eu3+ in 4 mol% concentration was calculated (x = 0.6055, y = 0.388), which was close to the National Television Standard Committee standard values for red phosphor (x = 0.67, y = 0.33). All these spectral properties suggest that that this kind of fluoride crystal with high thermal stability and high efficiency of red emission may be used as potential red phosphors for optical devices.