X. H. Ji

Concentration-dependent near-infrared quantum cutting in GdBO3:Tb3+,Yb3+ nanophosphors

An efficient near-infrared (NIR) quantum-cutting (QC), involving the emission of two low-energy NIR photons from an absorbed visible photon via a cooperative downconversion mechanism in GdBO3:Tb3+,Yb3+ nanophosphors, has been demonstrated. Upon excitation of Tb3+ with a visible photon at 486nm, two NIR photons could be emitted by Yb3+ through cooperative energy transfer from Tb3+ to two Yb3+ ions. The dependence of Yb3+ doping concentration on the visible and NIR emissions, decay lifetime, and quantum efficiencies from the QC phosphors has been investigated. Calculations indicate that the optimal NIR quantum efficiency approaches 182% before reaching concentration quenching threshold. Application of the QC nanophosphors in silicon-based solar cells might greatly enhance its response.

Origin of room temperature ferromagnetism in ZnO:Cu films

Copper-doped ZnO (ZnO:Cu) films were prepared on silicon substrates by filtered cathodic vacuum arc technique at room temperature using a Zn target containing 5at.% of Cu. Room temperature ferromagnetism was observed in the ZnO:Cu films with saturation magnetization of 0.037μB∕Cu atom. The origin of the ferromagnetism in ZnO:Cu was mainly due to Cu ions substituted into the ZnO lattice. X-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy revealed that no ferromagnetic-related secondary phase could be detected in ZnO:Cu.

980nm laser-diode-excited intense blue upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses

Intense blue-upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses has been achieved under an excitation from a commercially available 980nm laser diode. Energy transfer processes and excited-state absorption account for the population of the G41 emitting level of the Tm3+. Although the addition of GeO2 has enhanced the glass thermal stability, the phonon mode associated with vibration of GeO2 has almost no influence on the blue-upconversion intensity and the radiative lifetime of H43 level. The dependence of the phonon energy of the host on contributions from multiphonon decay on the fluorescence has been discussed. Significant enhancement of the blue-upconversion has also been observed in gallate–bismuth–lead glasses with the incorporation of PbF2 content.Intense blue-upconversion in Tm3+∕Yb3+-codoped gallate–bismuth–lead glasses has been achieved under an excitation from a commercially available 980nm laser diode. Energy transfer processes and excited-state absorption account for the population of the G41 emitting level of the Tm3+. Although the addition of GeO2 has enhanced the glass thermal stability, the phonon mode associated with vibration of GeO2 has almost no influence on the blue-upconversion intensity and the radiative lifetime of H43 level. The dependence of the phonon energy of the host on contributions from multiphonon decay on the fluorescence has been discussed. Significant enhancement of the blue-upconversion has also been observed in gallate–bismuth–lead glasses with the incorporation of PbF2 content.

Ultraviolet photoluminescence from ferromagnetic Fe-doped AlN nanorods

Fe-doped AlN (AlN:Fe) nanorods on silicon substrates were fabricated using a catalysis-free vapor phase method. The AlN:Fe nanorods exhibited high crystalline quality and preferred c-axis orientation. The spontaneous saturated magnetization of the AlN:Fe nanorods was determined to be ∼0.64μB∕Fe at room temperature. Room temperature photoluminescence measurement of the AlN:Fe nanorods revealed two strong ultraviolet emissions at 3.69 and 6.02eV which could be attributed to Fe3+-related and band edge emissions, respectively. The Fe-doped AlN nanorods not only exhibited ferromagnetism but also significantly enhanced the band edge emission as compared to the undoped AlN nanorods.

Ferromagnetic Cu-doped AlN nanorods

Copper-doped AlN (AlN:Cu) nanorods were grown on catalyst-free Si substrates by chemical vapour deposition. The AlN:Cu nanorods exhibited the wurtzite structure with a growth direction along the c-axis. Ferromagnetic ordering of the AlN:Cu nanorods was observed at room temperature by an alternating gradient magnetometer. The spontaneous magnetization and the coercivity of the AlN:Cu nanorods are about 0.38?emu?cm?3 and 100?Oe, respectively. The results reveal that Cu is a potential nonmagnetic dopant for AlN.

Structural properties and nanoindentation of AlN films by a filtered cathodic vacuum arc at low temperature

Aluminium nitride (AlN) films have been fabricated on Si(100) substrates by an ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The structural and mechanical properties of the AlN films have been investigated using x-ray photoelectron spectroscopy, by means of an x-ray diffractometer, visible Raman spectroscopy, atomic force microscopy and nanoindentation. The AlN films exhibit a predominant a-axis orientation with hardness as high as 14.5 GPa, which may be suitable for surface acoustic wave devices.

Aligned InN nanofingers prepared by the ion-beam assisted filtered cathodic vacuum arc technique

We report the synthesis of aligned wurtzite InN nanofingers by the ion-beam assisted filtered cathodic vacuum arc technique. InN nanofingers exhibit a polycrystalline structure. Photoluminescence (PL) and field emission properties of the InN nanofingers were studied. The PL emission peak was centred at ~1.1 eV with a full width at half maximum of 105 meV. The field emission characteristic was observed from the InN nanofingers with turn-on field of 9.7 V µm−1 at a current density of 10 µA cm−2. The formation of InN nanofingers was attributed to the Volmer–Weber growth mode.

Nitrogen-ion-energy dependent optical and structural properties of AlN films obtained using a filtered cathodic vacuum arc

We report on the successful fabrication of transparent and uniform aluminium nitride (AlN) III–V semiconductor films using an ion-beam assisted filtered cathodic vacuum arc technique at room temperature. A nitrogen-ion beam with energy varying from 200 to 650 eV has been employed to assist the deposition of AlN films. Effects of the nitrogen-ion-beam energy on optical and structural properties of AlN films have been investigated using an optical spectrophotometer, visible Raman spectroscopy, x-ray diffraction, atomic force microscopy and nanomechanical test instruments. The optical and structural properties of the AlN films depend significantly on the nitrogen-ion-beam energy. The AlN films deposited under ion energies below 300 eV are all amorphous and enhanced polycrystalline AlN films are obtained for energies above 400 eV.

Magnetic properties and photoluminescence of undoped and transition metal doped A1N nanorods

The undoped and transition metal (TM) -doped AIN (AIN:Cu and AIN:Fe) nanorods on silicon substrates were fabricated using a catalysis-free vapor phase method. All the nanorods exhibited high crystalline quality and preferred c-axis orientation. Room-temperature photoluminescence (PL) measurement revealed that undoped AIN nanorods exhibited strong oxygen-related impurity emission at ~3.25 eV. However, AIN:Fe nanorods had two strong ultraviolet emissions at 3.69 and 6.02 eV which could be attributed to Fe 3+-related and band-edge emission, respectively. Both the Cu and Fe-doped AIN nanorods are ferromagnetic. The spontaneous saturated magnetization of the AIN:Cu and AIN:Fe nanorods were determined to be 0.38 and 3.5 emu/cm3 at room temperature, respectively. The Fe-doped AIN nanorods not only exhibited ferromagnetism but also significantly enhanced the band-edge emission as compared to the undoped AIN nanorods.