Exploring luminescent color tunability and efficient energy transfer mechanism of a single-phased hexagonal nanophosphor for white light emitting diodes (WLEDs) application

Abstract

Nowadays, NUV-triggered phosphor-converted white light-emitting diodes (pc-WLEDs) have gained prominence as substantial alternatives to conventional incandescent and fluorescent lamps as a source of illumination. In this study, we have successfully developed a Tm3+ codoped La2O3:Sm3+ nanophosphor and investigated its potential suitability for application in white light-emitting diodes (WLEDs). X-ray diffraction (XRD) analysis was conducted to examine the phase impurity and structural characteristics of the synthesized nanophosphor. The analysis confirmed the formation of a single-phase La2O3 nanophosphor with a hexagonal crystal structure. The FT-IR spectrum of the synthesized nanophosphor exhibited distinct peaks associated with the vibrational frequencies of La-O bonds. The peaks observed in the fingerprint region of the spectrum, indicate the presence of La-O atoms in the nanophosphor. However, the HR-TEM analysis confirmed that the prepared nanophosphor had a polycrystalline nature and the observed particle sizes lay within the nanoscale range. The incorporation of Tm3+ ions into the host matrix led to a reduction in the optical band gap, leading to enhanced emission intensity. The photoluminescence (PL) study reveals that the Tm3+ ion exhibited blue emission upon excitation at 360 nm, whereas the Sm3+ ion emits reddish-orange light when excited at 379 nm and 408 nm, respectively. However, under 325 nm excitation, the nanophosphor exhibited a white emission color that resulted from the blending of colors emitted by both Tm3+ and Sm3+ ions. This unique finding suggests that this nanophosphor has the potential to generate white light specifically under this particular excitation wavelength. The efficient energy transfer between Tm3+ and Sm3+ ions was attributed to the electric multipolar interaction between the nearest neighbor ions, leading to a quenching phenomenon. Furthermore, the photometric analysis revealed that the correlated color temperatures (CCTs) associated with the emitted white light were found to be higher than 4000 K. Thus, based on these characteristics, it can be inferred that the prepared nanophosphor has the potential to be utilized as a cool white-emitting nanophosphor for single-phased WLEDs application.