Shi Chao-Shu

Electronic structure of ZnO and its defects

The electronic structure of ZnO and its native point defects has been calculated using full potential linear Muffin-tin orbital ( FP-LMTO) method for the first time. The results show that Zn3d electrons play an important role in the bonding of ZnO. Vacant Zn (Vzn) and interstitial O (Oi) produce the shallow acceptor levels at 0.3 eV and 0.4 eV above the top of the valence band (VB), while interstitial Zn (Zni) produces a shallow donor level at 0.5 eV bellow the bottom of the conduction band (CB). However, Vacant O (Vo) produces a deep donor level at 1.3 eV below the bottom of CB. On the basis of these results, we confirm that Zni is the main factor to induce the native n-type conductivity in ZnO

Photoluminescent Properties of ZnO Films Deposited on Si Substrates

The photoluminescence of ZnO films deposited on Si substrates by reactive dc sputtering has been studied by using a synchrotron radiation (SR) light source. The excitation spectra show a strong excitation band around 195 nm related to the 390 nm emission band. Under SR vacuum ultraviolet excitation, a new emission band peaked at 290 nm was found for the first time, besides the ultraviolet emission band (390 nm) and green band (520 nm).

Native Point Defect States in ZnO

The native point defect states in ZnO have been calculated by using a full-potential linear muffin-tin orbital method. The results show that Zn vacancy and O interstitial produce the shallow acceptor levels above the valence band. The O vacancy produces a deep donor level, while Zn interstitial produces a shallow donor level, both below the conduction band. The Zn interstitial is the main factor which induces the native n-type conductivity in ZnO.

Synthesis and Luminescence Properties of Red Phosphors:Mn2+ Doped MgSiO3 and Mg2SiO4 Prepared by Sol-Gel Method

Abstract Sol-gel method was utilized to synthesize two different series of red silicate phosphors: MgSiO3 and Mg2SiO4 powder samples doped with Mn2+, conducted the investigation of red long-lasting phosphor: MgSiO3: Eu2+, Dy3+, Mn2+. TGA curves of the gel precursor for two series depicted that the loss of residual organic groups and NO3 groups occurs below 450 °C. According to the XRD patterns, the major diffraction peaks of the MgSiO3 and Mg2SiO4 series are consistent with a proto-enstatite structure (JCPDS No. 11-0273) and a forsterite structure (JCPDS No. 85-1364) respectively. With the excitation at 415 nm, the red emission band of Mn2+ ions is peaked at 661 nm for MgSiO3: 1% (atom fraction) Mn2+ or 644 nm for Mg2SiO4:1% (atom fraction) Mn2+. Compared with Mg2SiO4: Mn2+ samples, MgSiO3: Mn2+ samples exhibit higher luminescence intensity and higher quenching concentration. In addition, the two series co-doped with Eu2+, Dy3+, Mn2+ were also prepared. Photo-luminescence and afterglow properties of the two co-doped series were analyzed, which show that MgSiO3: Eu2+, Dy3+, Mn2+ is more suitable for a red long-lasting phosphor.

Luminescence Spectra of SrAl12O19:Pr3+, Mn2+ under VUV–UV Excitation

Luminescence spectra of SrAl12O19:Pr3+,Mn2+ under VUV–UV excitation are investigated. The characteristic emissions between 4f levels and the excitation of 5d for Pr3+ are observed. The emission of Mn2+ peaks at 517 nm and the excitations due to the ground to multiplets are observed at 276, 360, 386 and 426 nm. However, the spectral overlap between the emission of Pr3+ and excitation of Mn2+ is absent, suggesting that the quantum splitting cannot be achieved via a Pr3+–Mn2+ ion pair in the host SrAl12O19.

A FP–LMTO study on the native shallow donor in ZnO

Abstract First-principle calculations are performed on ZnO:V O , ZnO:V Zn and ZnO:Zn I using a FP–LMTO (full potential linear muffin-tin orbital) method. The results prove that the Zn I is the dominant donor in ZnO, and V Zn , a shallow acceptor, while V O is a deep donor.

Temperature Dependence of the Luminescence Decay Time of a PbWO4 Scintillator

Experimental results are given for the temperature dependence of the decay time of the emission at 430 nm from PbWO4 crystal under vacuum-ultraviolet (82 nm) photon excitation in the temperature range of 80-300 K. The structures in the curve are interpreted for the first time by studying the thermoluminescence of PbWO4, which originates from the traps in the crystal.

Cascade Energy Transfer in CeF3 Crystals

The emission spectra of the CeF3 crystals in UV-visible region and their temperature dependence in the range of 6-453 K under UV, VUV excitation as well as their excitation spectra (4-25 eV) have been studied. The 350 nm emission band from perturbed Ce3+ can be excited by 295.2 and 302.4 nm emissions from the regular Ce3+. The 350 nm emission band, in turn, can excite the emission bands centered at 470 and 535 nm caused by some defects below room temperature. These results show that there is a cascade energy transfer process from regular Ce3+ to quenching centers via perturbed Ce3+ and defect centers in the CeF3. Meanwhile, thermoluminescence, giving peaks at about 240 and 300°C has been discovered, and the corresponding deep traps with depth ~ 1 eV are found to be a kind of quenching center for CeF3 luminescence at room temperature.

Enhancement mechanism of luminescence of RE3+ (Eu3+, Sm3+, Dy3+) in Y2O2S phosphor by a trace of Tb3+

The enhancement effects of cathodluminescence (CL) and photoluminescence (PL) of Eu3+, Sm3+ and Dy3+ in Y2O2S by a trace of Tb3+ have been investigated. The reasons for the enhancement are (1) decreasing of charge accumulation on sample surface by addition of Tb3+, (2) existing energy transfer from Tb3+ to RE3+. The mechanism of energy transfer are discussed and a model of energy transfer of free excitons is proposed.

VUV/UV/X-Ray Excited Luminescent Properties of Eu3+ and Pr3+ Doped BiSbO4

Absorption spectra of BiSbO4 are studied. The electronic structure calculated by the DFT shows that BiSbO4 is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu3+ and Pr3+ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu3+ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu3+ ions occupied Bi3+ sites, and there could be an energy transfer from Bi3+ ions to RE3+ ions.