Preparation and Tunable Luminescence of Eu Doped KNN Ceramics

doi:10.15541/jim20190106

Abstract

Abstract:

Rare-earth doped inorganic ferroelectrics are considered as novel photochromic materials, with potential applications for optical switch and information storage (K_0.5Na_0.5)_1-_xEu_xNbO₃(KNN:xEu) ceramics were prepared by high temperature calcination, with precursor powder obtained by hydrothermal method. Strong red emission at 615 nm was observed which corresponds to the ⁵D₀→ ⁷F₂ transition of Eu ³⁺ under excitation of 465 nm. Under UV light irradiation for 3 min, the color of the ceramics turned from milky white to dark gray. The colored samples returned to the original color when heated at 200 ℃ for 10 min, showing strong photochromic behavior. Meanwhile, the luminescence intensity of Eu ³⁺ can be tuned without obvious degradation by alternating UV light and heat stimulus. Upon UV light irradiation, large luminescence modulation ratio (ΔR_t) up to 83.9% was achieved for KNN:0.06Eu, indicating good luminescence switching behavior. A possible mechanism for non-radiative energy transfer from the luminescent center to the color center was proposed according to their luminescent behavior.

Key words: K_0.5Na_0.5NbO₃(KNN), luminescence, photochromism

CLC Number:

TQ174

WANG Meng-Hui,SHEN Hui,TIAN Tian,XIAN Qin,XU Jia-Yue,JIN Min,JIA Run-Ping. Preparation and Tunable Luminescence of Eu Doped KNN Ceramics[J]. Journal of Inorganic Materials, 2020, 35(2): 236-242.

Figures/Tables 6

Fig. 1 XRD patterns of the precursor powders synthesized at 200 ℃ for 12 h (K+/Na+=3:1) with different [OH-] concentrations (a), XRD patterns of KNN:xEu (x=0.02, 0.04, 0.06, 0.08, 0.10) powders synthesized at 200 ℃ for 12 h (K+/Na+=3:1, [OH-]=11 mol/L) (b) and zoomed XRD patterns from (b) within 30°-33° (c)

Fig. 2 SEM image of KNN:0.06Eu ceramics synthesized at 1140 ℃ for 4 h

Fig. 3 Excitaion (λem=618 nm) spectra of the KNN:0.06Eu ceramics and emission (λex=465 nm) spectra of KNN:xEu ceramics at room temperature (a) and the dynamic decay curves on Eu3+ concentrations for KNN:Eu samples under 465 excitation (b)

Fig. 4 Reflectance spectra for the KNN:0.06Eu by UV light irradiation (0 s, 30 s, 60 s, 2 and 3 min) (a), difference absorption (Δabs) spectra for the KNN:0.06Eu by UV irradiation 3 min with inset showing photographs of color changes of ceramic before and after UV irradiation (b), the Δabs vs Eu concentration (c) and reflectance intensity changes (d) of KNN:0.06Eu by alternating UV irradiation and heat treatment

Fig. 5 Changes of emission spectra (λex=465 nm) of KNN:0.06 Eu ceramics before and after UV irradiation for 3 min (a), luminescence switching ratio (ΔRt) at 615 nm as a function of Eu concentration (b) and ΔRt of KNN:0.06Eu ceramics by alternating UV light irradiation and thermal stimulus for 7 cycles (c)

Fig. 6 Luminescence modulation ratio (ΔRt) as a function of irradiation time under different irradiation wavelengths (a) and schematic diagram of luminescence modulation upon photochromic reactions for KNN:xEu ceramics (VO is oxygen vacancy, and VA is K and Na vacancy) (b)

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