Yin Min

Site-selective spectra and time-resolved spectra of nanocrystalline Y2O3:Eu

Nanocrystalline Y2O3:Eu of cubic crystal structure with different particle size was prepared by combustion reaction. High-resolution electron microscope images and extended X-ray absorption fine structure (EXAFS) analysis of the nanoscale samples indicate defected crystalline particles and co-existence of an amorphous phase. Novel emission bands centered at 613 and 622 nm with a lifetime of 0.4 ms emerge in nanoscale Y2O3:Eu. Site-selective spectra and time-resolved spectra show that the novel emission bands are from the amorphous phase in nanoscale samples.

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.

Upconversion of Er3+ Ions in LiKGdF5: Er3+, Dy3+ Single Crystal Produced by Infrared and Green Laser

Abstract The upconversion fluorescence of Er 3+ ions in LiKGdF 5 : Er 3+ , Dy 3+ single crystal was studied under 785, 514.5, and 980 nm laser excitation. With the laser excitation set at 785 nm, strong green (centered at 543 nm) upconversion emissions, as well as weak red (651 nm), violet (406 nm), and blue (470 nm) upconversion emissions were obtained. With 514.5 nm laser excitation, violet (406 nm) and blue (470 nm) upconversion emissions were observed. Under 980 nm laser excitation, strong green (543 nm) and weak red (651) emissions were also obtained. The laser power dependence of the upconverted emissions was investigated to understand the upconversion mechanism. The excited state absorption (ESA) and the energy transfer (ET) processes were discussed as the possible mechanisms for all upconversion emissions.

First-principles study of the local structure and crystal field of Yb2+ in sodium and potassium halides

The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model. Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+. Using the calculated local structures, we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method. The calculated crystal-field parameters were analyzed and compared with the fitted results.

Rare-earth doped optical spectral conversion materials with their applications

Based on the research work carried out in our laboratory in recent years, we focus on three categories of rare-earth doped spectral conversion materials, i.e., red phosphor for white-LED lighting, near-infrared downconversion materials and upconversion nanosized biological fluorescent labeling materials. Our work on the red phosphor for white-LED has been mainly focused on Eu3+ doped materials, and the energy transfer from sensitizers to Eu3+ ions is investigated in order to enhance the efficiency under the excitation of near-ultraviolet light. For the purpose of enhancing the efficiency of silicon-based solar cells, we have carried out the studies on near-infrared downconversion materials based on stepwise and cooperative energy transfer mechanisms and have clarified the downconversion mechanisms in NaYF4:Ho3+, Yb3+ and YVO4:Yb3+ materials. Biological fluorescent labeling is another important application of luminescent materials, which has some stringent requirements on the materials, such as the nanoparticle size, water-solubility, non-toxicity and luminescent efficiency. In our recent work, core/shell NaYF4:Yb3+, Er3+(Tm3+)/NaYF4 UCNPs have been successfully synthesized and transferred to aqueous phase by coating a cross-linked PMAO polymer. The cross-linked core/shell nanoparticles are very stable for several days, and are successfully internalized into human prostate cancer cells, which substantiates the utility of these nanoparticles in biolabeling applications. To sum up, due to significant existing and potential applications in biological and chemical sensing, new energy resources, energy saving and environmental protection, rare-earth doped spectral conversion materials have been attracting extensive attention. The future of rare-earth doped optical spectral conversion materials would be bright.

Simulation of the f—d transitions of lanthanide ions in YPO4 using quantum-chemical calculations

We constructed an effective one-electron Hamiltonian by using the 4f/5d energies and eigenvectors obtained from the first-principles calculation with the relativistic self-consistent discrete variational Slater software package (DV-Xα). From the effective Hamiltonian, we obtained the crystal-field and spin-orbit interaction parameters for the 4f and 5d electrons of lanthanide ions (Ce3+, Pr3+, Nd3+ and Eu3+) doped in YPO4, and these parameters were used to calculate the 4fN−4fN−15d transition. Comparison with experiments shows that the obtained parameters are reasonable and the excitation spectra can be well predicted.

Metalorganic Chemical Vapor Deposition of GaAs on Si Substrate Prepared by Room Temperature Chemical Cleaning Treatment

A new method for metalorganic chemical vapor deposition (MOCVD) of GaAs on Si substrates is developed. Instead of the usual high temperature surface cleaning treatment for Si substrate, the new method uses room temperature HF vapor polishing in the preparation chamber in the MOCVD system as the first step of the growth. Single crystal GaAs layers with mirror-like surfaces were obtained.