Tunable upconversion in Er3+-doped orthorhombic lead fluoride compound

Near infrared-visible upconversion in Er3+ doped orthorhombic PbF2 compound is investigated. It is experimentally observed that the red emission intensity increases monotonously with Er3+ concentration increase, while the green emission intensity first increases and then decreases. Based on the rate-equation, the energy transfers involved in the upconversion processes have been explored. It is shown that due to the different multipolar nature for the energy transfer processes of 2H11/2 (4S3/2)+4I15/2→4I9/2+4I13/2 and 4I11/2+4I11/2→4F7/2+4I15/2, the green and red upconversion emissions depend on Er3+ concentration in different ways. The theoretical results are in good agreement with the experimental observation. It is shown that the upconverted emission bands can be tuned by controlling Er3+ concentration in orthorhombic PbF2 compound, which has many photonic applications under NIR excitation.