Rapid Microwave Preparation of Highly Efficient Ce³⁺-Substituted Garnet Phosphors for Solid State White Lighting

Abstract

Ce3+-substituted aluminum garnet compounds of yttrium (Y3Al5O12) and lutetium (Lu3Al5O12)both important compounds in the generation of (In,Ga)N-based solid state white lightinghave been prepared using a simple microwave heating technique involving the use of a microwave susceptor to provide the initial heat source. Carbon used as the susceptor additionally creates a reducing atmosphere around the sample that helps stabilize the desired luminescent compound. High quality, phase-pure materials are prepared within a fraction of the time and using a fraction of the energy required in a conventional ceramic preparation; the microwave technique allows for a reduction of about 95% in preparation time, making it possible to obtain phase pure, Ce3+-substituted garnet compounds in under 20 min of reaction time. It is estimated that the overall reduction in energy compared with ceramic routes as practised in the lab is close to 99%. Conventionally prepared material is compared with material prepared using microwave heating in terms of structure, morphology, and optical properties, including quantum yield and thermal quenching of luminescence. Finally, the microwave-prepared compounds have been incorporated into light-emitting diode “caps” to test their performance characteristics in a real device, in terms of their photon efficiency and color coordinates.

Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

“…It is well known that a commercial white LED using a single YAG:Ce 3 þ phosphor generally has a low CRI and high CCT, typically, R a o70 and CCT45,000 K (ref. 53), which is unsuitable for indoor lighting. By adding K 2 TiF 6 :Mn 4 þ red phosphor into the devices, warm white LEDs with R a 480 and CCTo4,000 K can be readily used for indoor lighting (LEDs 1 and 2, Table 2).…”

Stress- and Temperature-Dependent Wideband Fluorescence of a Phosphor Composite for Sensing Applications

“…More reports [38][39][40][41] suggest that deviation from cubic symmetry around the Ce 3+ ion results in an increase in the maximum emission wavelength, while yttrium aluminum garnet provides a distorted cubic local circumstance to the dopant [34]. Besides the radius of the dopant ion, environmental parameters such as temperature and stress can produce a similar distortion.…”

“…On average, for a phosphor powder-resin composite, compression should slightly diminish the difference of Ce-O distances, meaning an increasing symmetry. Lower point symmetry of Ce 3+ allows a significant modification of the separation gap between the lowest two 5d levels, namely the two 2 E levels of Ce 3+ in a garnet structure [38][39][40][41]. Both the temperature influence and the compression effect of YAG:Ce fluorescence can imply different distortions of the solid lattice.…”

Rapid microwave-assisted preparation of binary and ternary transition metal sulfide compounds

“…We report here the rapid preparation of several binary, solid solution, and ternary transition metal sulfides from the elements in 40 min by MW-assisted heating, in which activated charcoal serves as a susceptor to transfer heat to reactants [34]. FeS 2 and CoS 2 were prepared phase pure, while for their solid solution, Fe 0.5 Co 0.5 S 2 , we found a distribution of compositions present when 50 following the same MW procedure.…”

“…Microwave (MW) irradiation and MW-assisted heating have been shown to greatly reduce the time and energy required to 40 prepare inorganic materials [33]. MW preparation has been reported for ceramics, including phosphors for solid-state lighting [34,35], materials for catalysis [36] and batteries [23,37] just 5% of the conventional furnace preparation time. [40,41].…”