Hydrothermal synthesis of hexagonal-phase NaYF4: Er, Yb with different shapes for application as photovoltaic up-converters

Hexagonal β-NaYF4 co-doped with Yb3+ and Er3+ is directly synthesized under mild conditions using a hydrothermal method. The variation of the ratio of Ln3+ to F− and ethylenediaminetetraacetic acid (EDTA) causes the shape of the microcrystal to change from microplate to microcolumn. The NaYF4 powder is mixed with polydimethylsiloxane (PDMS) to create an up-converter for thin film amorphous silicon solar cells so as to evaluate the effectiveness of the synthesized material as an up-converter. In order to overcome the difficulty in measuring the effectiveness of up-conversion material, a new method of using near infrared illumination to measure the short circuit current densities of solar cells both with and without up-converters is developed. An up-converter with pure hexagonal NaYF4:Yb3+/Er3+ microcrystal produces a high current output. Emission intensity data obtained by photoluminescence suggest that pure hexagonal NaYF4:Yb3+/Er3+ microcrystals are more efficient than nanocrystals when used as up-converting phosphors. (condensed matter: electronic structure, electrical, magnetic, and optical properties)