The Effect of Heat Treatment on the Emission Color of P-Doped Ca₂SiO₄ Phosphor.

Hiromi Nakano,Nobuyuki Yokoyama,Konatsu Kamimoto,Koichiro Fukuda

doi:10.3390/ma10091000

Hiromi Nakano, Nobuyuki Yokoyama + Show 2 more

Open Access

https://doi.org/10.3390/ma10091000

Copy DOI

Abstract

In a series of (Ca2–x/2–yEuy□x/2)(Si1–xPx)O4 (x = 0.06, 0.02 ≤ y ≤0.5), various color-emitting phosphors were successfully synthesized by a solid-state reaction. These phosphors were characterized by photoluminescence (PL) spectroscopy, X-ray powder diffractometry, transmission electron microscopy, and X-ray absorption fine structure spectroscopy. We evaluated the effect of heat treatment on PL properties with various annealing temperatures at 1373–1773 K for 4 h before/after reduction treatment from Eu3+ to Eu2+. In the red-emitting (Ca1.95Eu3+0.02□0.03)(Si0.94P0.06)O4+δ phosphor, the highest PL intensity exhibited when it was annealed at 1773 K. On the other hand, in the green-emitting (Ca1.95Eu2+0.02□0.03)(Si0.94P0.06)O4 phosphor, the highest PL intensity was realized when it was annealed at 1473 K and consequently treated under a reductive atmosphere. With increasing annealing temperature, the emission peak wavelength steadily decreased. Furthermore, with increasing Eu2+ content, the emission peak wavelength increased, with the color of emitting light becoming yellowish. Thus, the PL properties of the phosphors were affected by both the structural change from β to α’L, which occurred by heat treatment, and the amount of doped Eu ions.

Highlights

Rare-earth-doped dicalcium silicate (Ca2 SiO4, C2 S) phosphors have been investigated by several researchers for application to white light-emitting diodes (LEDs) [1,2,3,4,5]
We prepared the Eu3+ -activated red-emitting phosphor with a chemical formula of (Ca1.95 Eu3+ 0.02 0.03 )(Si0.94 P0.06 )O4+δ, and focused on the effect of annealing on its Figure 1 shows the X-ray diffraction (XRD) patterns of the red-emitting phosphor annealed at various temperatures from 1373 K to 1773 K for 4 h
We clarified the effect of heat treatment on the emission color using X-ray powder diffractometry, transmission electron microscopy, and X-ray absorption fine structure spectroscopy

Summary

Introduction

Rare-earth-doped dicalcium silicate (Ca2 SiO4 , C2 S) phosphors have been investigated by several researchers for application to white light-emitting diodes (LEDs) [1,2,3,4,5]. Two types of phosphors have been reported so far: Eu3+ -doped and Eu2+ -doped C2 S phosphors The former phosphors are characterized by the emission of red light due to the transition of 5 D0 -7 F2 for the Eu3+ ion [3]. The luminescence originates from the 4f-4f dipole transitions of the Eu3+ ion, and the wavelength of the emission is almost the same among the various phosphors with different host materials. Eu2+ -doped C2 S phosphors are generally useful for a wide range of applications, because their luminescent colors, due to the f-d transition of the Eu2+ ion, are tunable by the crystal structures and/or compositions of the host materials. A crystal-site engineering technique was reported, which enabled us to customize the luminescent colors of C2 S:Eu2+ phosphors [5]

Methods

Results

Conclusion