Blue, green, and red emission from undoped and doped ZnGa₂O₄colloidal nanocrystals

Abstract

Undoped, Tb(3+)- and Eu(3+)-doped ZnGa(2)O(4) colloidal nanocrystals were synthesized by a nonhydrolytic hot solution chemistry. Undoped nanocrystals exhibited an intrinsic blue emission peaking at 437 nm by self-activated transition. The emissions of Tb(3+)-and Eu(3+)-doped ZnGa(2)O(4) nanocrystals consisted of their own characteristic green and red line peaks ((5)D(4)-(7)F(j) transitions), respectively. Synthetic parameters such as activator concentration and reaction time were varied to investigate their effects on luminescent properties. Tb(3+)-doped colloidal nanocrystals synthesized for a short reaction time showed an unprecedented, exclusively green luminescence with the host blue emission effectively suppressed. On the other hand, the emission of Eu(3+)-doped ones was weak with the host emission persistently present regardless of reaction time.

Comparison of luminescent properties of Y2O3:Eu3+ and LaPO4:Ce3+, Tb3+ phosphors prepared by various synthetic methods

“…In general, sol-gel, co-precipitated and combustion synthesized powders have high PL emission intensity and the spray pyrolyzed powders have the lowest emission intensity. The increase in PL emission intensity with increasing crystallite size may arise from several factors: (1) less lattice distortion as evidenced by the narrowing of the XRD peaks [41,42] and (2) more uniform activator distribution across the crystallite [43][44][45][46][47].…”

Emission properties of Zinc Gallate nanophosphors

“…All undoped ZnGa 2 O 4 generally exhibits the characteristic blue emission at 430 nm (2.88 eV) under 254 nm UV excitation that originates from charge transfer from O to Ga in the host material. 20) However, the spectrum in Fig. 5(a) 34) Synthesis by combustion with an organic-containing precursor is known to provide a large number of oxygen vacancies, resulting in emission peak at 680 nm (1.82 eV).…”

“…14) For example, doping with a transitional metal or rare-earth element, such as chromium or europium, shifts the emission from blue to red, 15)18) whereas manganese or terbium cause green emission. 19), 20) Other applications, such as white lighting, employ a yellow-emitting phosphor like YAG:Ce 3+ together with InGaN blue LED chips. 21) However, low colour rendering is the major drawback of such a system, arising from the lack of red emissions and different degradation rates of chip and phosphor.…”

First ZnGa2O4 transparent ceramics

“…[14] It can exhibit different emission colors when doped with transition metal elements. [1,[15][16][17] For example, when doped with Ni 2+ , a broadband infrared luminescence emission is observed around 1300nm, [18,19] while when doped with Cr 3+ , it gives rise to an long red afterglow. [16,20] Moreover, the long-lasting red luminescence properties of these spinel materials are shown to be much improved when germanium or tin are substituted to the nominal composition, leading to a Zn 1+x Ga 2-2x Ge x O 4 solid solution.…”