Multi-band photon avalanche controlling performance of BiOCl:Er3+ crystals through facile Yb3+ dopingElectronic supplementary information (ESI) available: Fig. S1-S10. See DOI: 10.1039/c5tc00224a

Photon avalanche (PA) is a seldom discovered phenomenon in upconversion (UC) materials on account of the requirement for high pumping intensities and strict construction conditions. Herein, we present the controllable PA emission behavior of violet, green, red and near infrared emission from the Er 3+ ion in Er 3+ -Yb 3+ co-doped BiOCl crystals. We show that the generation of "looping" and the cycle numbers of PA processes could be precisely controlled through the control of doped Yb 3+ concentrations. Fluorescent probe effects from doping Eu 3+ ions indicates that the manipulation of PA behaviors may arise from a strong dependence on the magnitude of the internal polarizable chemical environment of BiOCl crystals that are weakened on doping with Yb 3+ ions rather than other rare-earth dopants. Our results may offer a new insight into the mechanism for constructing PA process and promote the potential applications of PA UC phosphors in solid state lasers and optical switches. Photon avalanche (PA) emission behavior of Er 3+ ion at violet, green, red and near infrared emission bands were controlled through the Yb 3+ dopant concentration in Er 3+ -Yb 3+ co-doped BiOCl crystals.