KCa4(BO3)3:Ln3+ (Ln = Dy, Eu, Tb) phosphors for near UV excited white–light–emitting diodes

Allu Amarnath Reddy,Rupam Sen,José M F Ferreira,Renée Siegel,Luís Mafra,Subrata Das,Ashutosh Goel,G Vijaya Prakash

doi:10.1063/1.4794189

Allu Amarnath Reddy, Rupam Sen + Show 6 more

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https://doi.org/10.1063/1.4794189

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Abstract

A series of doped KCa4(BO3)3:Ln3+ (Ln: Dy, Eu and Tb) compositions were synthesized by solid–state reaction method and their photoluminescent properties were systematically investigated to ascertain their suitability for application in white light emitting diodes. The X–ray diffraction (XRD) and nuclear magnetic resonance (MAS–NMR) data indicates that Ln3+–ions are successfully occupied the non–centrosymmetric Ca2+ sites, in the orthorhombic crystalline phase of KCa4(BO3)3 having space group Ama2, without affecting the boron chemical environment. The present phosphor systems could be efficiently excitable at the broad UV wavelength region, from 250 to 350 nm, compatible to the most commonly available UV light–emitting diode (LED) chips. Photoluminescence studies revealed optimal near white–light emission for KCa4(BO3)3 with 5 wt.% Dy3+ doping, while warm white–light (CIE; X = 0.353, Y = 0.369) is obtained at 1wt.% Dy3+ ion concentration. The principle of energy transfer between Eu3+ and Tb3+ also demonstrates the potential white–light from KCa4(BO3)3:Eu3+,Tb3+ phosphor. Whereas, single Tb3+ and Eu3+–doped systems showed bright green (Tb3+) and red (Eu3+) emissions, respectively. Having structural flexibility along with remarkable chemical/thermal stability and suitable quantum efficiency these phosphors can be promising candidates as white–light–emitter for near UV LEDs.

Highlights

Recent years have witnessed an upsurge in the research and development of white–light emitting diodes (W–light–emitting diode (LED)) being known for general illumination sources due to their unmatchable benefits, for example: high brightness, longer lifetime, small volume, and low power consumption
In the undoped parent sample, a mono–mineral composition was obtained with crystalline KCa4(BO3)[3] (JCPDS:01–75–3604) phase as evidenced by the minimal mismatch between the experimental and the simulated X–ray diffraction (XRD) data and absence of any significant misfits in the difference plot obtained using Diffracplus TOPAS (Bruker AXS) software and the fitting has been performed using least–square methods
The XRD data of KCa4(BO3)3:Dy3+ and KCa4(BO3)3:5%Eu3+, 5%Tb3+ phosphors is in good agreement with that obtained for KCa4(BO3)[3] regardless of the dopant concentration as certified by the Rietveld refinement

Summary

Introduction

Recent years have witnessed an upsurge in the research and development of white–light emitting diodes (W–LEDs) being known for general illumination sources due to their unmatchable benefits, for example: high brightness, longer lifetime, small volume, and low power consumption. One of the most fashionable approaches to produce white light is uniting a blue InGaN based LED with a broadband yellow–emitting Y3Al5O12:Ce3+ (YAG) phosphor. This system lacks thermal stability at higher temperatures above 150 oC. The resultant white light exhibits low color rendering index (Ra) due to lack of individual blue, red and green region colors.[7,8,9] Uniform white–light with high Ra can be alternatively achieved by mixing several single color

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