Single‐Crystal Red Phosphors and Their Core–Shell Structure for Improved Water‐Resistance for Laser Diodes Applications

Abstract

A solvent‐vapor transport route produces centimeter‐sized single‐crystal red phosphors. The epitaxial growth route to yield its core–shell structure at ambient temperature was adopted. These red phosphors could be applied in all‐inorganic WLED devices. Cs2TiF6:Mn4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs2TiF6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three‐step photoluminescence intensity evolution mechanism has been proposed. By combining as‐prepared CTFM@CTF core–shell structured single crystal, YAG:Ce single crystal and blue‐chip, warm WLEDs with excellent color rendition (Ra=90, R9=94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins.

BaTiF6:Mn4+ Red Phosphor: Synthesis of Single Crystals at Room Temperature and the High Hydrolysis-Resistant Property

“…K 2 SiF 6 has slightly larger water solubility than BaTiF 6 , but the difference is limited. Several recent studies , reported that the single-crystal phosphors possess higher moisture resistance than their corresponding polycrystalline powdery form. It is thus deduced that the single-crystal nature of the BaTiF 6 :Mn 4+ with the relatively big size is also responsible for the improvement of water resistance.…”

“…Many strategies have been proposed to prevent the [MnF 6 ] 2– group from hydrolysis. We have classified them into the following six classes, (1) coating with a hydrophobic organic compound, (2) coating with an inorganic layer, (3) self-coating to form a core–shell structure, (4) reductive treating to form Mn 4+ -rare surface passivation, (5) recrystallization by hydrothermal treatment, and (6) preparation of bulk single-crystal phosphor. − For the last strategy, our study demonstrates that the Na 2 SiF 6 :Mn 4+ single crystals indeed experience a much slower hydrolysis-induced deterioration than its polycrystalline powdery form. Furthermore, we recently compared the deterioration behavior of BaSiF 6 :Mn 4+ , Na 2 SiF 6 :Mn 4+ , and (NH 4 ) 2 SiF 6 :Mn 4+ phosphors in water and further find that the deterioration rate is closely related to their specific solubility.…”

Shining Mn4+ in 0D Organometallic Fluoride Hosts towards Highly Efficient Photoluminescence

“…[ 7 ] In present, most of Mn 4+ ‐doped fluoride phosphors, in the form of A 2 B F 6 :Mn 4+ or A 3 M F 6 :Mn 4+ ( A = alkali metal cations; B = Si 4+ , Ge 4+ , Ti 4+ , Zr 4+ ; M = Al 3+ , Ga 3+ , Sc 3+ ), possess high internal QEs (IQEs, >80%). [ 4,8–10 ] However, on account of the above transition characteristic, all the phosphor absorption efficiency (AEs) remains low and hence a relatively poor external quantum efficiency (EQEs, <40%). [ 11–13 ] There are practical implications in increasing the Mn 4+ doping concentration for enhanced absorption whilst maintaining high IQE at the same time.…”

Towards improved waterproofness of Mn4+-activated fluoride phosphors

“…Note: the yellow colored part is the Cs 2 TiF 6 :Mn 4+ core and colorless part is the Cs 2 TiF 6 shell. 36 These studies demonstrate that the single crystal fluoride phosphors show superior water resistance property than the powder phosphor, and high-quality bulk ingot can be readily prepared at facile conditions due to the ionic bonding nature of fluorides. Besides, a Mn 4+ -free shell can also be grown on the Mn 4+ -doped single crystals for further shielding.…”

“…Fig. 14 Photographs of Cs 2 TiF 6 :Mn 4+ single crystal, silicone, and Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) crystal after heat treatment at 150 °C during the different aging periods 36. …”