Synthesis And Characterization Of Rare Earth Doped Vanadate Micro/nano Luminescent Materials

Rare earth ions doped inorganic luminescent materials that show tunable multicolour emission and spectral modification have cast new solution for important applications in opto-electronics. Based on UVU to visible(down shift) emission, inorganic phosphors can be used in light emitting displays and photovoltaic industry as the solar spectra converter.Besides, with the help of NIR to visible(up convesion) emission, they are promising alternative in solid state lasers, three-dimensional displays and biological imaging etc.Recently much attention has been focused on two spots. One is to contorl the size and dispersion, surface morphology of nano- phosphors by adjusting experimental parameter or inventing new synthesis method. The other is to enhance emmission efficiency by introducing active ions, varying doping concentration ect. Herein, we have conducted a series of oriented and systematic experiments which concentrate on both basictheoretical research and application requirements.The following shows the main contents in this thesis:Ln3+doped YVO4 nano/microcrystals with hollow-core spherical structure have been synthesized via a facile hydrothermal route. A series of controlled experiments indicate that the ph values in the initial solution, reaction time, the organic additive citrate(Cit3-)and calcination temperature are responsible for crystal phase, surface morphology and size of final products. It is found that organic additives citrate(Cit3-) ions act as orientation agent to guide nuclei to grow along oriented direction [100] and then regulate the surface energy of nanoparticles to determinate the eventual distribution and morphology, resulting in hollow-core spherical structure. Simultaneously, the possible formation mechanisms for products with spherical architectures have been presented.Then, a systematic study on the photoluminescence of Ln3+(Ln = Eu, Er, Dy,Ce, Ho,Yb) and combination Ln3+-Yb3+( Ln = Er, Ho) ions doped in YVO4 host has beenexplored. In single doped case, samples show multicolor emission under UVU excitation.It reveals that energy can be transferred fromVO43-host to active Ln3+ions. Specially, the reduction of surface defects, adsorption and shape size of samples can promote the luminescence efficiency. This UVU to multi-visible emission conversion provides a great opportunity to apply in display field or photovoltaic device to minimize the energy loss of thermalization in c-Si solar cells.In co-doped samples, down conversion and up conversion luminescence are observed by varying the excitation wavelength. In both Er3+-Yb3+and Er3+-Yb3+couples, red emission centered at 650nm(Ho3+ 5F5?5I8; Er3+ 4F9/2?4I15/2) is significantly enhanced under NIR(980nm) excitation, while the green emission centered at 550nm(Ho3+ 5S2,5F4?5I8; Er3+ 4S3/2?4I15/2) is supressed, which is contrast to that under UV excitation.The luminescence dynamics for the up and down conversion emissions were systematically investigated at assistance of decay curve and then proposed the dynamics energy transfer mechanism. In addition, the intensity ratio of green emission to red emission can be manipulated by simply change the doping concentration. Taking advantages of the Ho3+/Er3+-Yb3+couples based up conversion, we discussed the potential application in bio-probe therapy, vivo imaging and solid-state lasers.