Europium-Doped Silicate Phosphors with ALD Aluminum Oxide Coating

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Solution Overview

Problem

Alkaline-earth metal ortho-silicate and oxy-ortho-silicate phosphors used in LEDs are sensitive to moisture and temperature, leading to instability in emission intensity and color shift over time, particularly in high humidity and temperature conditions, which is undesirable for white LEDs.

Innovation Solution

Europium-doped alkaline-earth metal ortho-silicate and oxy-ortho-silicate phosphors coated with aluminum oxide using the atomic layer deposition (ALD) process, which provides a conformal and uniform coating that enhances stability and maintains the emission color point.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If silicate phosphors are used for conversion in pc-LEDs, then emission wavelength range from 430 to 650 nm is accessible with high efficiency, but the phosphors show poor stability in lighting devices operated at high temperature and high humidity due to moisture sensitivity and hydrolysis

Engineering Contradiction:

Improveconversion efficiencyVSAvoidstability at high temperature and humidity

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

A silane coupling agent is applied as an intermediary layer on the phosphor particle surface. This coupling agent contains both inorganic-binding groups (react with phosphor surface) and organic-binding groups (provide hydrophobic protection), acting as a mediator that connects the phosphor core to the protective coating, thereby improving moisture resistance while maintaining conversion efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

A thin film coating comprising the silane coupling agent and crosslinked siloxane groups is formed on the phosphor surface. This flexible thin film shell provides hydrophobic protection against moisture penetration while allowing the phosphor to maintain its optical properties and conversion efficiency, solving the contradiction between efficiency and reliability

Inventive Principle:

Principle #30Flexible shells and thin films

2Reliability

If phosphors are coated to protect against moisture and improve stability, then reliability is improved, but the coating process may cause particles to agglomerate forming larger aggregates with defects that reveal coating breakdown areas

Engineering Contradiction:

Improvemoisture resistanceVSAvoidcoating uniformity and particle separation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The silane coupling agent performs multiple functions automatically: it binds to the phosphor surface, forms a protective hydrophobic layer, and creates crosslinked siloxane structures. This self-service approach eliminates the need for multiple separate coating steps, preventing agglomeration while ensuring uniform coverage and defect-free coating

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The coating process utilizes controlled hydrolysis and condensation reactions of silane groups under specific pH and temperature conditions. By controlling these parameters, the coating forms uniformly without causing particle aggregation, maintaining manufacturing precision while achieving reliable moisture protection

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If wet-chemical or sol-gel coating methods are used, then coating can be applied to phosphor surfaces, but these methods require relatively large amounts of raw materials and cause individual particles to agglomerate readily

Engineering Contradiction:

Improvecoating applicabilityVSAvoidraw material consumption

Core Design Contradiction:

Ease of manufactureVSLoss of substance

Solution Approach 1:

The patent replaces wet-chemical and sol-gel methods with a vapor-phase deposition process. This substitution eliminates the need for large amounts of liquid reagents and reduces raw material consumption while preventing particle agglomeration, as the coating is deposited from vapor phase without requiring particle suspension in liquid media

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The ALD-coated phosphors exhibit improved resistance to moisture and maintain stable emission intensity and color over time, preventing the unwanted color shift and intensity loss commonly seen in uncoated materials.

Implementation Method 1

coated with a coating of aluminum oxide which has been deposited by an atomic layer deposition (ALD) process

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Implementation Method 2

Europium-doped alkaline-earth metal ortho-silicate and oxy-ortho-silicate phosphors... which can be excited in the blue and/or UV region of the spectrum

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Data Source

PatentEP3063250B1Silicate phosphors

Publication Date: 2018.08.01 MERCK PATENT GMBH

Figure 1a~1b
Figure 1c
Figure 2a~2b

AI summary

The invention relates to europium-doped silicate phosphors comprising a coating of aluminum oxide, to a process for the preparation of these compounds, and to the use thereof as conversion phosphors or in lamps.