Nano Wave Plates Structuring and Index Matching in Transparent Hydroxyapatite‐YAG: Ce Composite Ceramics for High Luminous Efficiency White Light‐Emitting Diodes

Abstract

Replacing traditional luminous silicone or resins with phosphor in ceramics (PiCs) as color converters has been proposed as an efficient way to improve thermal stability of high‐power white light‐emitting diodes (WLEDs). However, excessive light scattering in existing PiCs results in enormous phosphor‐converted light losses, which makes the luminosity of current PiCs color converters less efficient and means that they can only be used in devices working in reflective mode. By introducing nano wave plate structuring and Rayleigh scattering, luminous hydroxyapatite (HA)‐YAG: Ce ceramics are prepared from mesoporous HA nanorods and YAG: Ce phosphors at 850 °C, enabling for the first time WLEDs equipped with PiC color converters in transmission mode. With low‐temperature sintering and a highly transparent matrix, the quantum yield of HA‐YAG: Ce retains ≈90% of the raw phosphor, and WLEDs with the color converters exhibit a record luminous efficiency of 170 lm W−1 and a correlated color temperature below 4500 K. A facile and practical strategy of using nano structural modulation to eliminate birefringence‐induced light scattering for fabricating high‐performance ceramic converters suitable for multiple mode luminaires is demonstrated.

Construction of Inorganic Bulks through Coalescence of Particle Precursors

“…Recently, Huang et al prepared luminous hydroxyapatite-YAG:Ce ceramics at a high temperature by introducing bioceramic hydroxyapatite. High transparency for the first time is achieved in white light-emitting diodes equipped with phosphor in ceramics ( Figure 11 ) [ 7 ]. Spinel, which can transmit electromagnetic and radiation in the visible and IR portion of the spectrum, shows promising applications in advanced electromagnetic windows and transparent armor.…”

“…Abridged general view ( d , e ) of the spatial distribution of HA grains c-axis (red arrow lines) in different pressure surfaces, exhibiting a preferable arrangement with their c-axis in the planes overlay perpendicular to the pressure direction; ( f ) The linear transmittance of HA ceramic with incident light perpendicular to and parallel to pressure directions, respectively. Reproduced with permission [ 7 ]. Copyright 2020, Wiley-VCH.…”

“…An advanced technique for the construction of bulk-scaled materials is necessary to ensure their applications. Currently, the construction of these materials is commonly achieved by the compaction of their particle-precursors [ 4 , 5 , 6 , 7 ]. It is mainly because crystallization is the most common tactic for the production of most inorganic materials, resulting in nano- or micro- sized solid powders.…”

Impact of Dopants on the Electrical and Optical Properties of Hydroxyapatite

“…[58]. HAp and YAG:Ce ceramics were synthesized by Huang et al at 850°C to fabricate white light-emitting diodes with phosphor in ceramics (PiCs) color converters in transmission mode [59]. So, these green diodes are useful in reducing the consumption of toxic materials (europium, cadmium etc.)…”

Controllable synthesis of glass ceramics containing YF3:Eu3+ nanocrystals: Well‐preserved Eu and prolonged lifetime

“…How to avoid the limitations of conventional methods and controllably synthesize the YF 3 :Eu 3+ embedded GCs is a challenge need to be conquered to effectively improve luminescent properties by retaining more Eu 3+ ions in fluoride NCs. In our previous work, 25,26 highly transparent GCs have been successfully prepared by Spark Plasma Sintering (SPS), using mesoporous silica as precursor, with relatively low temperature (960°C) and short preparation time (less than 10 minutes). What's more, phosphor, a kind of temperature-sensitive material, was dispersing into the silica glass without interfacial reaction and fluorescence heat-quenching, exhibiting high quantum yields, which has been successfully applied in LED device.…”