White-light emission from yttrium iron garnet (YIG)

Single-phase phosphors that emit broadband white-light are needed for white-light-emitting diodes (wLEDs) to reach their full potential. However, it is challenging to achieve broad white-light emission from single-phase materials. Consequently, polycrystalline inorganic bulk compounds that emit white-light sans doping are rare. We report on broadband white-light emission from a well-known garnet compound, i.e., yttrium iron garnet (YIG), without activator-ion doping. Upon near-UV excitation at 370 nm, polycrystalline bulk YIG emits broadband white-light with (1931) Commission Internationale de L’Eclairage (CIE) coordinates as (0.28, 0.35) and correlated color temperature (CCT) as 8029 K. Variable excitation wavelengths ranging from 280 to 600 nm enable color-tunable emission as cyan-white-blue-green-yellow-orange-red, including near-white-light emission for a broad range of excitation from 325 to 390 nm. Moreover, a short lifetime (sub-nanosecond) is obtained, which is desirable for LED and other applications. We demonstrated the propriety of YIG as a single-phase converting phosphor for illumination by fabricating prototype wLEDs using commercial InGaN UV-LED chips (λ = 380 nm) for excitation. The CIE coordinates and CCT of prototype wLEDs were obtained as (0.34, 0.37) and 5284 K, respectively. We believe that the reported findings signify the great potential of YIG as a single-phase white-light-emitting phosphor for broadband emission, which offers a new perspective and a viable approach for the development of wLEDs

Combinatorial evaluation of phase formation and magnetic properties of FeMnCoCrAl high entropy alloy thin film library

We report on the influence of the Al content (from 3.5 to 54 at.%) on phase formation and magnetic properties in FeMnCoCrAl high entropy alloy thin film libraries. Al additions to FeMnCoCr crystallizing in the alpha-Mn structure cause the formation of the body centered cubic (BCC) structure. This is consistent with density functional theory predictions as Al additions give rise to a larger stability for the BCC phase compared to the face centered cubic phase (FCC) which can be rationalized by the formation of a pseudogap at the Fermi level indicating the stabilization of the BCC phase over the FCC phase. Al additions to paramagnetic FeMnCoCr induce ferromagnetism. The largest saturation magnetization was measured for the film containing 8 at.% of Al. As the concentration of non-ferromagnetic Al is increased beyond 8 at.%, the number density of the ferromagnetic species is decreased causing a concomitant decrease in magnetization. This trend is consistent with ab initio predictions of the Al concentration induced changes in the magnetic moment. Based on the experimental and theoretical results presented here the effect of the Al concentration on the phase formation and the magnetic properties of FeMnCoCrAl thin film library can be rationalized