Mechanism and Controlling Factors of Infrared-to-Visible Conversion Process in Er³⁺ and Yb³⁺-Doped Phosphors

Abstract

Luminescence and related optical properties of Er 3+ and Yb 3+ -doped YF 3 , Y 3 OC 7 and YOCl phosphors are precisely and extensively measured in the range from 4.2 K to room temperature, in order to investigate the mechanism and controlling factors of infrared-to-visible conversion. It is concluded that the red luminescence emitted from Er: 4 F 9/2 is produced by two energy transfers from Yb 3+ to Er 3+ ions, and that 4 F 9/2 is directly populated from Er: 4 I 13/2 by the second energy transfer. The cutoff phonon energy and electron-phonon coupling constant of the hosts, which dominate the probabilities of internal relaxation and phonon-assisted energy transfer, are indicated to be important controlling factors for the conversion process, in addition to the relative energy positions of Yb: 2 F 5/2 and Er: 4 I 11/2 . The hosts having larger values of these factors, such as Y 3 OCl 7 , are advantageous to the red luminescence, while those with the opposite tendency, such as YF 3 , are favorable to the green luminescence.