Abstract
The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350–420 nm). In this work, novel rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca2KZn2(VO4)3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO4:Eu2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K.
Highlights
A light-emitting diode (LED) is in the limelight since its invention by Nick Holonyak Jr. of General Electric Company and its application in solid-state lighting industry has gained a prominent interest
To obtain brighter white light, the CKZV phosphor was mixed with an approximate amount of a blue LiCaPO4: Eu2+ phosphor prepared via a solid-state technique to fabricate NUV-based white-light-emitting diodes (WLEDs)
The formed particles were found to be almost spherical in shape (Fig. 1(a)), which is a useful property required to apply the material for WLEDs
Summary
The EDX spectrum (Fig. 1(d)) revealed all the elements present in the sample including a small peak at the lower energy, which is related to carbon. These results revealed that the crystallographic parameters and atomic position of each ion in CKZV are altered when compared to the isostructural Ca2NaZn2V3O12 because of the smaller ionic radius of the Na+ (1.02 Å) than the K+ (1.38 Å). The internal quantum efficiency of the CKZV2 phosphor was compared with some other vanadate phosphors as shown in Table S2 (Supporting Information)
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