NOVELTY - A nanorod assembly comprises contacting rice-shaped colloidal superparticles having length-diameter ratio of 3 or more. The rice-shaped colloidal superparticles are aligned along long axis to form nanorod assembly. The colloidal superparticles comprise nanorods. The nanorod assembly has length of 50 microns or more, and diameter perpendicular to length of nanorod assembly of less than average of long axes of colloidal superparticles. Polarization ratio of nanorod assembly is equal to or more than polarization ratio of nanorods in colloidal superparticles.    USE - Nanorod assembly is used for polarizing photonic sheet for down-conversion device, (all claimed) photodetector, solar cell and thermoelectric application.    ADVANTAGE - The down-conversion device containing the nanorod assembly has high quality.    DETAILED DESCRIPTION - A nanorod assembly comprises contacting rice-shaped colloidal superparticles having length-diameter ratio of 3 or more. The rice-shaped colloidal superparticles are aligned along long axis to form nanorod assembly. The colloidal superparticles comprise nanorods aligned along long axes of rice-shaped colloidal superparticles. Average of long axes of colloidal superparticles is 3 microns or more. The nanorod assembly has length of 50 microns or more, and diameter perpendicular to length of nanorod assembly of less than average of long axes of colloidal superparticles. Polarization ratio of nanorod assembly is equal to or more than polarization ratio of nanorods in colloidal superparticles. INDEPENDENT CLAIMS are included for the following:    (1) polarizing photonic sheet, which comprises nanorod assemblies embedded within or resting upon a substrate;    (2) down-conversion device, which contains polarizing photonic sheet(s), light-emitting diode(s) and polarizer(s);    (3) rice-shaped colloidal superparticles;    (4) preparation of rice-shaped colloidal superparticles, which involves providing a solution (A) comprising solvent(s) (S1) and nanorods comprising inorganic material and ligand(s), adding additional ligand to solution (A) to form solution (B), mixing solution (B) with aqueous solution (A1) of surfactant to form solution (C), removing one portion of solvent (S1) from solution (C) to form aqueous solution (A2), and injecting aqueous solution (A2) into a water miscible solvent. The colloidal superparticles are formed in an aqueous suspension; and    (5) preparation of nanorod assembly, which involves providing a suspension comprising rice-shaped colloidal superparticles in liquid, depositing the suspension on surface of a substrate comprising at microchannel(s), infiltrating of rice-shaped colloidal superparticles into microchannels, and removing one portion of liquid from the surface. The rice-shaped colloidal superparticles are contacting each other and aligned along long axes to form nanorod assembly within microchannels of substrate.