Charge Carrier Trapping Processes in RE₂O₂S (RE = La, Gd, Y, and Lu)

Abstract

Two different charge carrier trapping processes have been investigated in RE2O2S:Ln3+ (RE = La, Gd, Y, and Lu; Ln = Ce, Pr, and Tb) and RE2O2S:M (M = Ti4+ and Eu3+). Cerium, praseodymium and terbium act as recombination centers and hole trapping centers while host intrinsic defects provide the electron trap. The captured electrons released from the intrinsic defects recombine at Ce4+, Pr4+, or Tb4+ via the conduction band. On the other hand, Ti4+ and Eu3+ act as recombination centers and electron trapping centers while host intrinsic defects act as hole trapping centers. For these codopants we find evidence that recombination is by means of hole release instead of electron release. The released holes recombine with the trapped electrons on Ti3+ or Eu2+ and yield broad Ti4+ yellow-red charge transfer (CT) emission or characteristic Eu3+ 4f–4f emission. We will conclude that the afterglow in Y2O2S:Ti4+, Eu3+ is due to hole release instead of more common electron release.

Charge carrier trapping processes in lanthanide doped LaPO4, GdPO4, YPO4, and LuPO4

“…The holes liberate from Ce 4+ earlier than electrons from Sm 2+ and recombine with Sm 2+ generating Sm 3+ 4f-4f emission. The other two examples are from studies by Luo et al on Gd 1-x La x AlO 3 7 and RE 2 O 2 S. 2 The trap depth of the Tb 3+ hole trapping center in Gd 1-x La x AlO 3 can be adjusted by changing x leading to valence band energy changes. In RE 2 O 2 S:Ti 4+ a hole release process leading to Ti 4+ charge transfer emission was identified.…”

Coordination Geometry‐Dependent Multi‐Band Emission and Atypically Deep‐Trap‐Dominated NIR Persistent Luminescence from Chromium‐Doped Aluminates

“…Persistent luminescence observed in different material systems is caused by a gradual release of charged carriers from shallow trapping centers to deeper ones, whereby enough thermal energy (which is controlled by the trap depth) is available to help the captured carriers escape . Shallow traps have a tendency for a higher afterglow intensity and a shorter duration.…”

Thermoluminescence as a Research Tool to Investigate Luminescence Mechanisms

“…When studying the effect of various dopants in a host material, this method is an easy and powerful method. Examples are given by Lecointre et al [31] for YPO 4 :Pr 3+ ,Ln 3+ (Ln = Nd, Er, Ho, Dy) and Luo et al [32] for RE 2 O 2 S (RE = La, Gd, Y, and Lu).…”