An optical humidity sensor based on Li3PO4 hollow nanospheres

Orthorhombic Li3PO4 hollow nanospheres and solid particles have been successfully prepared respectively via a simple neutralization reaction between H3PO4 and LiOH aqueous solutions, by just changing the adding sequence of H3PO4 and LiOH aqueous solutions (with PVP) in dropwise. Transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM) images display Li3PO4 hollow nanospheres with average diameters of about 400 nm and wall thickness of about 50 nm which is actually composed of nanoparticles with sizes of 20–50 nm, and Li3PO4 solid particles with lengths of 100–500 nm and widths of 100–250 nm. The photoluminescence (PL) properties of the samples reveal that the Li3PO4 hollow nanospheres show stronger PL intensity than the Li3PO4 solid particles. Furthermore, an adapted photoluminescence-type gas sensor based on Li3PO4 hollow nanospheres has been devised and its sensing property to humidity has also been investigated. This novel sensor exhibits good sensitivity, ideal linearity, quick response/recovery, and reliable repeatability in a very wide humidity range at room temperature.