Multi-color upconversion luminescence of lanthanide doped calcium molybdate

Abstract

Recently, upconversion (UC) phosphors have received considerable attention because of their potential applications to bio-technologies, as infrared light sensors, optical amplifiers, and white light emitting diodes (LEDs). Depending on the size of UC phosphors to the nano-scale, it would be extended their applications such as laser materials, nano-bio-labels, nano-lighting devices, and nano-display devices. The UC phosphors can be excellent candidate for new optical LEDs due to their controllable visible radiation of the three primary colors by modulating the doping ratio of lanthanide ions for luminescent centers. The UC phosphor can also be used as a solar catalyst in NIR quantum counters to increase solar-cell efficiency for energy storage. In this thesis, for enlargement of applications of UC luminescence, multi-color UC luminescence from lanthanide doped CaMoO4 matrix was investigated. Using various dopants of activator ions and sensitizer ion (Yb3+) for enhancement of UC luminescence, multi-color UC luminescence such as green (Er3+), blue (Tm3+) and yellow (Ho3+) colors was successfully achieved from CaMoO4 matrix. In addition, co-doping activator ions into CaMoO4 matrix, white UC luminescence was obtained. With the variations of concentrations of activator ions, controllable white UC luminescence has been successfully found in Tm3+/Ho3+/Yb3+ co-doped CaMoO4. For the bio-medical application, core-shell UC nano structures were fabricated via pulsed laser ablation (PLA) process with polypyrole. The experimental results from this thesis would be useful for the synthesis of multi-colors and nano UC phosphors. Moreover, it could be extended to numerous applications. Therefore, it is concluded that lanthanide doped CaMoO4 UC phosphors could be one of the promising candidates to meet the requirement for the biomedical application, displays and white lighting source for LEDs.