Generating intense upconversion photoluminescence from a single-phase nanocrystal is a fundamental problem. Herein, we report engineered NaYF4 nanocrystals capable of converting NIR (980 nm) excitation into sharp and diverse emissions in the UV-Vis-NIR regions, which is desirable for triggering multiple photoactive agents for enhanced photo-theranostics. This unique emission profile is used for NIR-induced photo-theranostic applications by developing a nanoplatform with a white-emitting NaYF4 (WEN) core, with comparable blue, green and red emissions, and a mesoporous silica shell decorated with two different photosensitizers (PSs), Rose Bengal (hydrophilic) and zinc(II)phthalocyanine (hydrophobic) to utilize green and red emissions, respectively. A chemical assay demonstrates efficient generation of 1O2 under NIR excitation by the dual PS nanoplatform compared to the conventional systems. Furthermore, NIR-induced ROS generation leads to the enhanced photodynamic destruction of cancer cells (HeLa) in vitro. The white light from the nanoplatform is also utilized in cellular bioimaging. Unlike the previously reported upconversion probes, which required sophisticated imaging setups, the high intensity white light emission from this nanoplatform allows the probing of animal cells by a digital camera attached externally to an optical microscope. This is the first report on the theranostic application of a white-light-emitting photoluminescent nanomaterial. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim