Indirect evidence of Bi3+ valence change and dual role of Bi3+ in trapping electrons and holes for multimode X-ray imaging, anti-counterfeiting, and non-real-time force sensing

Discovering bismuth based smart materials that can respond to thermal, mechanical, and wide range X-ray to infrared photon excitation remains a challenge. Such materials have various uses like in advanced information encryption . In this work, valence state change between Bi 2+ , Bi 3+ , and Bi 4+ , and the dual role of Bi 3+ in trapping electrons and holes have been studied in Bi 3+ or/and Ln 3+ (Ln=Tb or Pr) doped LiScGeO 4 family of compounds by vacuum referred binding energy (VRBE) diagram construction, thermoluminescence , and spectroscopy. Electron release from Bi 2+ has been evidenced. It can be used to experimentally determine the VRBE in the Bi 2+ 2 P 1/2 ground state and to realize Bi 3+ negative quenching luminescence . Particularly, a new force induced charge carrier storage phenomenon has been discovered for non-real-time force recording. Wide range of emission tailorable afterglow , unique Bi 3+ ultraviolet-A, white, and infrared afterglow have been demonstrated by using Bi 3+ as a hole trapping and recombination center and using energy transfer processes from Bi 3+ to Tb 3+ , Pr 3+ , Dy 3+ , or Cr 3+ . Proof-of-concept advanced anti-counterfeiting, information encryption, and X-ray imaging will be demonstrated. This work not only develops smart storage phosphors , but more importantly unravels the valence change between Bi 2+ , Bi 3+ , or Bi 4+ and how it can affect the trapping and release of charge carriers with thermal, optical, or mechanical excitation. This work therefore can promote the discovery and development of Bi 3+ based smart materials for various applications.