White light tunable emissions from ZnS: Eu³⁺nanophosphors over 330–465 nm excitation range for white LED applications

Abstract

ZnS: Eu 3+-CMC) nanophosphors of cubic (zinc blende) structure were synthesized using a precipitation technique with doping concentrations of Eu 3+ ions 1 mol% and 5 mol%. The crystal sizes were 2.56 nm and 2.91 nm respectively. Annealing at 300°C in a sulfur-rich atmosphere altered the crystal size to 4.35 nm and 3.65 nm respectively and the band gap from 4.2 eV to 3.76 eV and 3.81 eV respectively. The as-synthesized samples gave pure orange-red emission when excited at wavelengths of 394 nm and 465 nm. After thermal annealing of the samples, a broad emission band in the blue-green region assigned to defect related states emerged or were enhanced. Also enhanced were the emission lines of Eu 3+ ions in the orange-red region. A combination of these two transitions gave white light of different shades (recorded on the CIE 1931 chromaticity diagram) from cool white through daylight to warm white light, depending on Eu 3+ concentration and the excitation wavelengths (UV-330 to blue 465 nm), thus showing great potential of these nano-phosphors in the generation of high quality white light.

Synthesis and Characterization of ZnS nanoparticle doped Eu 3+ ions prepared by sol-gel method in silica glass matrix

“…The on-going luminescence studies of Eu 3+ ions on various host, for instance Al: Eu 3+ [21,22], CdS: Eu 3+ [23], ZrO2: Eu 3+ [24], LaAlGe2O7: Eu 3+ [25], Sn02: Eu 3+ [26], ZnO: Eu 3+ [27], TiO2: Eu 3+ [28] enhancing knowledge on Eu 3+ ions for photonic applications. However, there have been few works on Eu 3+ ions doped with ZnS nanoparticles in silica glass [29][30][31][32][33][34][35]. We know that the green emission for ZnS and orangered emission from Eu 3+ ions can give rise to white light for device applications.…”

Silica-Coated ZnS Quantum Dots for Multicolor Emission Tuning from Blue to White Light

“…The zinc-based II–VI semiconductor nanoparticles and quantum dots, normally have high bandgap values, allowing these systems to produce blue light emissions, while the nanostructures without zinc lack photon emissions below 500 nm, that is, they are limited to produce green, yellow, or red light because of their smaller bandgap values. ,,,− Using zinc-based nanostructures, because of their blue light emissions, allows the development of tunable light devices by modifying their optical properties through doping with re or green-emitting ions, such as rare earth ions or Mn 2+ , − facing the challenge of introducing heavy and bigger ions into small nanoparticle’s structure. But the alteration of optical properties of nanoparticles through thermal treatment is not explored widely; only a few works are studying the emission via heating processes on nanoparticles and quantum dots. − …”