Circularly polarized room-temperature phosphorescence (CPRTP) is of paramount importance for applications in information encoding, bioimaging and optoelectronic devices, however, it remains challenging to organize highly efficient CPRTP materials with controlled handedness and long afterglow. Herein, we disclose an outstanding novel finding that ultralong CPRTP with on-demand chiroptical properties is simple to realize using the earth-abundant cellulose and silica. It has been proved that cellulose nanocrystals can form a left-handed chiral nematic phase structure by entropy driving, which makes it a good chiral template. Cellulose-silica composite films with chiral nematic phase structure were prepared by co-assembly of organosilicon precursor and crystalline nanocellulose. Then the part of cellulose nanocrystals was removed by calcination at high temperature to obtain the pure silica film with anti-topological left-handed chiral nematic structure. This pure silica film likewise has the ability to selectively reflect left-handed circularly polarized light that matches the photonic band gap, resulting in the transmission of right-handed circularly polarized light at the corresponding wavelength.  Meanwhile, we show that the left-handed chiral nematic nanoporous silica films possess defect-related photoluminescence properties, and the phosphorescence produced by the ODC(II) defects of silica has a lifetime of up to seconds in this system. The ultralong CPRTP has unprecedented chiral control with the photonic bandgap effect derived from the combination of phosphorescent properties and structural chirality of a single component, i.e. silica. We present that the chiral nematic nanoporous silica films display on-demand ultralong CPRTP with high luminescence dissymmetry factors. The photonic bandgap of chiral nematic silica films can span the visible to the near infrared region, and the phosphoresence matching the photonic bandgap is converted to right-handed circularly polarized light while the phosphorescence located at the photonic bandgap edge is converted to left-handed circularly polarized light.We showcase the potential of the transparent chiral nematic nanoporous silica films capable of ultralong CPRTP and selective reflection of left-handed circularly polarized light for the development of anti-counterfeiting optical labels. Our work presents a versatile strategy and a step toward the development of ultralong CPRTP materials with on-demand chiroptical properties from readily available defect phosphorers for photonic applications, which unquestionably broadens the range of novel and emerging applications of nanocellulosic materials.

luminophore-based chiral nematic structures,defect luminescence,silica,circularly polarized room-temperature phosphorescence,cellulose nanocrystals