An insight into the luminescent properties and Judd–Ofelt analysis of Eu3+ doped CaZn2(PO4)2 phosphors

Abstract

A batch of Eu3+ doped CaZn2(PO4)2 orange–red emitting phosphors were synthesized by the conventional high temperature solid state reaction method. The structural, morphological and spectroscopic properties of the prepared samples were investigated by experimental and theoretical studies. Powder XRD and FTIR results were used to evaluate the structural aspects of the prepared phosphors and morphology was investigated by TEM analysis. The elemental composition analysis of the representative sample was made using energy dispersive x-ray spectroscopy (EDS). The optical properties were analyzed with the aid of UV–Vis-NIR spectroscopy and photoluminescence (PL) spectroscopy. The PL excitation spectra revealed that the prepared phosphors can be efficiently excited under 393 nm that matches well with the dominant emission band of near UV- LED chip. The PL emission studies demonstrate the emission of an orange–red light with CIE coordinates (0.6075, 0.3920) with color purity 100.0% under an excitation of 393 nm. The maximum emission intensity was observed at Eu3+ concentration of 4 mol%, from which the critical distance (Rc = 1.98 nm) of quenching was calculated. The emission spectra were further used to interpret the site symmetry of Eu3+ ions. Judd–Ofelt theory was employed to predict various radiative properties such as branching ratio (βr), total transition probability (AT), radiative life time (τcalc) and stimulated emission cross section (σe). The thermal stability of the prepared phosphor was investigated using temperature dependent luminescence spectra and the emission intensity was observed to remain at 70.83% of its initial value when the temperature is raised from 310 K to 430 K. The decay kinetics analysis confirms the lifetime of the activator ions to be in the millisecond (ms) range. The better stimulated emission cross section and strong orange–red emission suggest the Eu3+ doped CaZn2(PO4)2 system as a promising candidate in the design of various optoelectronic devices such as phosphor converted LEDs (pc- LEDs) and display panels.