Bulk Polycrystalline Ceria Doped Al$_2$O$_3$ and YAG Ceramics for High-Power Density Laser-Driven Solid-State White Lighting: Effects of Crystallinity and Extreme Temperatures

TL;DR

This study develops Ce-doped Al2O3 ceramics with high thermal conductivity and broadband emission for use in high-brightness white lighting, exploring effects of crystallinity and extreme temperatures on their photoluminescence.

Contribution

It introduces a novel Ce:Al2O3 ceramic with enhanced properties and investigates the influence of crystallinity on Ce-dopant emission characteristics.

Findings

Ce:Al2O3 exhibits broadband emission from 400-600nm.

Crystallinity affects the photoluminescence properties of Ce-doped ceramics.

Ce:Al2O3 has potential as a phosphor layer in high-power solid-state lighting.

Abstract

Here we develop and characterize high thermal conductivity/high thermal shock resistant bulk Ce doped Al2O3 and propose it as a new phosphor converting capping layer for high-powered/high-brightness solid-state white lighting (SSWL). The bulk, dense Ce:Al2O3 ceramics have a 0.5 at.% Ce:Al concentration (significantly higher than the equilibrium solubility limit), and were produced using a simultaneous solid-state reactive Current Activated Pressure-Assisted Densification (CAPAD) approach. Ce:Al2O3 exhibits a broadband emission from 400-600nm, which encompasses the entire blue and green portions of the visible spectrum when pumped with ultra-violet (UV) light that is now commercially available in UV light emitting devices (LED) and laser diodes (LD). These broadband phosphors can be used in the commonly employed scheme of mixing with other UV converting capping layers that emit red light to produce white light. Alternatively, they can be used in a novel composite down converter approach that ensures improved thermal-mechanical properties of the converting phosphor capping layer. In this configuration Ce:Al2O3 is used with proven phosphor conversion materials such as Ce:YAG as an active encapsulant or as a capping layer to produce SSWL with an improved bandwidth in the blue portion of the visible spectrum. In order to study the effect of crystallinity on the Ce PL emission, we synthesize Ce:YAG ceramics using high-pressure CAPAD at moderate temperatures to obtain varying crystallinity (amorphous through fully -crystalline). We investigate the PL characteristics of Ce:Al2O3 and Ce:YAG from 295K to 4K, revealing unique crystal field effects from the matrix on the Ce-dopants. The unique PL properties in conjunction with the superior thermal-mechanical properties of Ce:Al2O3 can be used in high-powered/high-brightness integrated devices based on high-efficiency UV-LD that do not suffer