Synthesis, luminescence properties, and thermal decomposition kinetics of NH4GdF4:Eu3+ with an intense negative thermal quenching effect

Abstract

Developing Eu3+-doped red emission phosphors with exceptional luminescence thermostability is crucial for advancing white light emitting diodes (WLEDs). Herein, a series of NH4GdF4:xEu3+ (NGF:Eu3+) compounds are synthesized using the co-precipitation method, with NGF:0.25Eu3+ identified as the most promising sample. The paper discusses the mechanism underlying the negative thermal quenching (NTQ) effect, indicating that NGF:0.25Eu3+ exhibits sufficient luminescence thermal stability and chemical resistance under the operational temperatures of WLEDs, making it a viable application for this purpose. Experimental results reveal the following key findings. (a) Supported by the NTQ effect, NGF:0.25Eu3+ exhibits remarkable luminous thermostability. The integrated emission intensities at 150 °C, 180 °C, and 121 °C are 210.6 %, 234.1 %, and 244.2 % respectively, of the initial intensity at 30 °C. (b) NGF:0.25Eu3+ demonstrates good chemical thermostability and sufficient luminescent thermal stability under WLED operational temperatures and commences decomposition at 200 °C, making it suitable for use in WLEDs. (c) An assembled prototype WLED combining NGF:0.25Eu3+ and YAG:Ce3+ (a yellow emitting phosphor), emits warm white light under ultraviolet excitation. Furthermore, this study delves into the thermal decomposition kinetics of NGF:0.25Eu3+ using an iterative approach, identifying a single-step reaction mechanism. Consequently, the study provides three kinetic parameters (Eα, g(α), and A) and three thermodynamic functions (ΔH#, ΔS#, and ΔG#) associated with the decomposition process.