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 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. Up-converter with pure hexagonal NaYF₄:Yb^3+/Er³⁺microcrystal produces a high current output. Emission intensity data obtained by photoluminescence suggest that pure hexagonal NaYF₄:Yb^3+/Er³⁺ microcrystals are more efficient than nanocrystals when used as up-converting phosphors.