Stability of Phosphors for White LED Excitable by Violet Light

doi:10.15541/jim20240396

Abstract

Abstract:

Violet light excited white light emitting diodes (LEDs) have attracted widespread attention due to their advantages of tunable color temperature and visual comfort. However, high-performance phosphors suitable for violet light excitation (400-420 nm) have not yet been widely applied on a large scale. One of the key factors regarding the commercial utilizations is the stability. Unfortunately, there still lacks research on this issue. In this study, three rare-earth phosphors suitable for violet light excitation in LEDs were synthesized via a solid-state reaction method, namely K₂CaPO₄F:Eu²⁺, K_1.3Al₁₁O₁₇₊_δ:Eu²⁺ and Ca₂YHf₂Al₃O₁₂:Ce³⁺,Tb³⁺. The stability experiments were then conducted under conditions of high temperature and humidity, water immersion, and long-term violet light irradiation from LED chips. The luminescent properties, failure mechanisms, and environmental stability were analyzed. Finally, a white LED device was prepared by combining the as-synthesized three phosphors onto a 400 nm violet light chip. Results demonstrate that the as-synthesized phosphors exhibit not only optimized luminescence performance compared to phosphors prepared in former works, but also a more comprehensive evaluation of environmental stability across different conditions. The white LED device achieves a color rendering index of 93.6, a correlated color temperature of 5151 K and a color coordinate of (0.34, 0.36), showcasing excellent white light illumination performance. Furthermore, the environmental stability of the white LED device is improved compared to individual phosphors. By taking lead in investigating the environmental stability of violet light excited LED phosphors, this work provides valuable insights and guidance for advancing their applications.

Key words: environmental stability, rare earth luminescent material, white light emitting diode, violet light excitation

CLC Number:

O482

PAN Zesheng, YOU Yaping, ZHENG Ya, CHEN Haijie, WANG Lianjun, JIANG Wan. Stability of Phosphors for White LED Excitable by Violet Light[J]. Journal of Inorganic Materials, 2025, 40(3): 314-322.

Figures/Tables 15

Fig. 1 Environmental stability of K2CaPO4F:Eu2+ phosphor (a) PL spectra when kept in 85 ℃/85% RH condition for different duration time; (b) XRD patterns when kept in 85 ℃/85% RH condition for different duration time; (c) Temperature-dependent PL spectra; (d) PL spectra when radiated under 200 mW·cm-2 of violet light for different duration time. Colorful figures are available on website

Fig. 2 SEM images of K2CaPO4F:Eu2+ phosphor when kept in 85 ℃/85% RH condition for different duration time (a) 0 h; (b) 8 h; (c) 16 h; (d) 24 h

Fig. 3 Environmental stability of K1.3Al11O17+δ:Eu2+ phosphor (a) PL spectra when kept in 85 ℃/85% RH condition for different duration time; (b) XRD patterns before and after keeping in 85 ℃/85% RH condition for 14 d; (c) PL spectra before and after soaking in water for 14 d; (d) XRD patterns before and after soaking in water for 14 d; (e) Temperature-dependent PL spectra; (f) PL spectra when radiated under 200 mW·cm-2 of violet light for different duration time. Colorful figures are available on website

Fig. 4 Environmental stability of Ca2YHf2Al3O12:Ce3+,Tb3+ phosphor (a) PL spectra when kept in 85 ℃/85% RH condition for different duration time; (b) XRD patterns before and after keeping in 85 ℃/85% RH condition for 14 d; (c) PL spectra before and after soaking in water for 14 d; (d) XRD patterns before and after soaking in water for 14 d; (e) Temperature-dependent PL spectra; (f) PL spectra when radiated under 200 mW·cm-2 of violet light for different duration time. Colorful figures are available on website

Fig. 5 Environmental stability of white LED (a) EL spectrum of white LED device; (b) EL spectra of white LED device when kept in 85 ℃/85% RH condition for different duration time; (c) Temperature-dependent EL spectra of white LED device; (d) EL spectra of white LED device when radiated under 200 mW·cm-2 of violet light for different duration time. Colorful figures are available on website

Fig. S1 Optical performance of K2CaPO4F:Eu2+ phosphor (a) PLE/PL spectra; (b) PLQY spectra

Fig. S2 Optical performance of K1.3Al11O17+δ:Eu2+ phosphor (a) PLE/PL spectra; (b) PLQY spectra

Fig. S3 SEM images of K1.3Al11O17+δ:Eu2+ phosphor before (a) and after (b) soaking in water for 14 d

Fig. S4 Thermoluminescence spectrum of K1.3Al11O17+δ:Eu2+ phosphor

Fig. S5 Optical performance of Ca2YHf2Al3O12:Ce3+,Tb3+ phosphor (a) PLE/PL spectra; (b) PLQY spectra

Fig. S6 SEM images of Ca2YHf2Al3O12:Ce3+,Tb3+ phosphor before (a) and after (b) soaking in water for 14 d

Fig. S7 Dependence of ln[(I0/IT)-1] on 1/kT for Ca2YHf2Al3O12:Ce3+,Tb3+ phosphor

Fig. S8 CIE chromaticity diagram of white LED device

Fig. S9 Environmental stability data of white LED (a) EL spectra of the white LED device under different input current; (b) Relative intensity and rendering index (Ra) of white LED device when kept in 85 ℃/85% RH condition with different duration time; (c) Relative intensity and Ra of white LED device under different temperature; (d) Relative intensity and Ra of white LED device when radiated under 200 mW·cm-2 of violet light with different duration time

Table S1 Comparison of phosphors in optical performance and environmental stability

Component	PLQY	Thermal stability (150 ℃)	High temperature and high humidity stability (85 ℃/85% RH)	Water resistance	Light irradiation stability (200 mW·cm^-2)	Ref.
K₂Ca(PO₄)F:Eu²⁺	75% (407 nm)	85%	-	-	-	[20]
K₂Ca(PO₄)F:Eu²⁺	94.5% (390 nm)	82%	-	-	-	[S1]
Rb_0.5K_1.5Ca(PO₄)F:Eu²⁺	87% (395 nm)	85.5%	-	-	-	[S2]
Na₂Ca_0.995PO₄F:Eu²⁺	84% (400 nm)	~70%	-	-	-	[S3]
K₂Ca(PO₄)F:Eu²⁺	95.33% (380 nm)	82.2%	34.7%, 14 d	-	87.9%, 14 d	This Work
K_1.6Al₁₁O₁₇₊_δ:Eu²⁺	92% (400 nm)	>100%	-	-	-	[21]
K_0.84Sr_0.06Al₁₁O₁₇₊_δ:Eu²⁺	92.4% (360 nm)	>100%	-	-	-	[44]
K_0.6Ba_0.1Eu_0.1Al₁₁O₁₇:Eu²⁺	91.2% (345 nm)	~100%	-	-	-	[S4]
K_1.3Al₁₁O₁₇₊_δ:Eu²⁺	74.29% (400 nm)	81.8%	92.2%, 14 d	~100%,14 d	57.6%, 14 d	This Work
Ca₂YHf₂Al₃O₁₂:Ce³⁺,Tb³⁺	78.5% (408 nm)	43.3%	-	-	-	[22]
Ca₂YHf₂Al₃O₁₂:Ce³⁺	68.5% (400 nm)	76.6%	-	-	-	[S5]
Ca₂GdHf₂Al₃O₁₂:Ce³⁺,Tb³⁺	82.7% (408 nm)	48%	-	-	-	[S6]
Ca₂YHf₂Al₃O₁₂:Ce³⁺,Tb³⁺	95.72% (410 nm)	59.8%	84.6%, 14 d	~100%,14 d	95.5%, 14 d	This Work

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