Patent ID: 8277702

Claim:
A method for preparing a near infrared absorbing agent, comprising: admixing tungsten trioxide and a reducing agent in water, wherein the tungsten trioxide has a chemical formula of WO 3 .H 2 O or WO 3 .2H 2 O and allowing a partial reduction of the tungsten trioxides in the water to proceed at a temperature of 0-100° C. and thereby yielding a reduced tungsten oxide as the near infrared absorbing agent, wherein the valence of the tungsten in the reduced tungsten oxide is from 5 to less than 6, and wherein the reducing agent is selected from the group consisting of sodium borohydride, lithium borohydride, potassium borohydride, zinc borohydride, copper borohydride, lithium aluminium hydride, ethanol or ethylene glycol.