Emerging blue emitting cerium III ions doped zinc selenide thin films with high color purity for light emitting diode application

Ce³⁺:ZnSe (0 ≤ Ce³⁺ ≤ 10) thin films were deposited using chemical bath technique. All the films samples revealed polycrystalline wurtzite ZnSe with a strong (002) preferred orientation; nominal Ce³⁺ incorporation produced small shifts in peak positions and low-intensity secondary peaks in some compositions. The peak shift is attributed to incorporation of Ce³⁺ ions into the host matrix. Raman spectroscopy revealed two optical phonon peaks due to first and second order longitudinal vibrational modes. The films showed flakes-like morphology with reduced surface roughness in the doped materials as revealed by atomic force micrographs. The anticipated elements were confirmed by energy dispersive X-ray spectroscopy. Cross-sectional scanning electron micrographs showed increase in the thin films thickness with increased Ce³⁺ ion concentration. Fourier transform infrared spectroscopy revealed O-H stretching vibration modes and active bands attributed to ZnSe. The ultraviolet–visible spectroscopy results showed increased band gap with Ce³⁺ concentration and the values were dependent on the crystallite size. Blue, green and red emissions due to both the defect levels from the host and the Ce³⁺ ions were observed from the photoluminescence studies. Although it has been very difficult to observe rare earth emission from ZnSe thin films, strong blue and weak green emissions from Ce3+ ions have been successfully achieved which is a motivation for the present study. The enhanced blue emission due to Ce³⁺ ions, wide band gap, stable structure and morphology make the deposited thin films good candidates for optical applications especially in light emitting diodes.