Original Article
3D printed ceramic phosphor and the photoluminescence property under blue laser excitation

https://doi.org/10.1016/j.jeurceramsoc.2019.03.005Get rights and content

Abstract

An Al2O3/YAG: Ce3+ ceramic phosphor was fabricated for high-flux laser lighting using the digital lighting process (DLP)-based 3D printing method for the first time. The photocurable ceramic suspension for 3D printing was prepared by blending well-treated Al2O3/YAG: Ce3+ composite powders with photosensitive resin monomers and photo-initiators. The printing parameters, debinding and sintering processes were designed delicately to fabricated the dense sub-millimeter-sized cylinder ceramic with high dimensional accuracy. The ceramic showed excellent luminescence property under blue laser excitation with a threshold of 20.7 W/mm2, higher than that prepared via dry-pressing followed by vacuum sintering. The luminescence properties and the microstructures of both ceramics were further comparatively investigated to find the possible interpretations for improvement of laser flux for the 3D-printed ceramic. The present work indicated that the new developed 3D printing method was promising for preparing luminescent ceramics for high-flux laser lighting in a rapid, effective, low-cost and precision-controlled manner.

Introduction

Ceramic phosphors are emerging as preferences in special lighting technologies, especially the laser diode (LD)-based lighting with high power density, due to their excellent thermal endurance property and the thermal stability of luminescence compared with those of the resin encapsulated phosphors or the phosphor in glasses (PiGs) [[1], [2], [3], [4]]. After several years’ research and development, the garnet-structured ceramics, such as YAG, LuAG ceramics, have been standing out from the mostly studied ones, benefiting from their excellent optical as well as thermal-stability properties [5,6]. In recent, a new type of Al2O3/YAG: Ce3+ composite ceramics containing homogeneously distributed Al2O3 grains called “scattering centers” in YAG: Ce3+ ceramic matrix have drawn much attention for the remarkable enhanced light extraction efficiency and effective thermal conductivity [[7], [8], [9], [10]]. The commonly used manufacturing methods for those ceramic phosphors such as dry-pressing [11], tap-casting [12], and gel-casting [13] are proved mature and favorable to obtain ceramics with excellent luminescent performance, however, not efficient or economical enough. For instance, subjected to the forming technology, the finally obtained ceramics have to be polished to remove impurities (e.g., graphite) on double-surfaces, lapped to reach desired thickness and incised to the designed shapes or geometric configurations before they can be encapsulated onto optical modules. Moreover, the mentioned forming technologies may be confronted with inconveniences that complex instrument systems such as high-pressure or high-voltage systems, costly procedures including cold-isostatic pressing, or easily consumable molds such as graphite molds or boron nitride coated carbon molds should be partially or simultaneously imported [[14], [15], [16]]. Thus, the complex procedure would inevitably lead to an increase of production cycle and the cost. Meanwhile, leftover materials would take up much costing once final products with complicated configurations are needed. To be noticed, for LD-based lighting, a ceramic with ultra-small and thin features are generally preferred as it can be used as a quasi-point source [4]. In this circumstance, a new forming strategy should be involved to prepare ceramics with small and precise dimensions more efficiently.

Three-dimensional (3D) printing is a new emerging technology creating ceramics by adding materials to form components with complex geometries according to computer-added designs (CAD) with almost no waste of raw materials while reaching satisfactory geometric accuracy [17], which have been actively developed in preparing ceramics including structural ceramics [18], ceramic-matrix composites [19], bio-active ceramics [20,21], and other functional ceramics, e.g., SiBCN ceramics with high thermal stability and excellent oxidation resistance [22]. G. A. Dosovitskiy [23] firstly reported a ceramic scintillator with complex configuration using 3D printing method. The ceramics exhibited challenging scintillation characteristics which can be largely ascribed from the well-designed geometries. However, the dimensional accuracy which was generally recognized as the other superiority of 3D printing was not demonstrated. More importantly, to our best knowledge, almost no further attentions have been paid to prepare the luminescent ceramics for laser lighting via 3D printing method, probably due to the not easily regulated defects in ceramics during forming and sintering, but the extreme demands for ceramics to sustain the laser irradiation with high power density.

In the present work, a 3D printing strategy was adopted to prepare the Al2O3/YAG: Ce3+ ceramic phosphor based on our previous study [8]. The dimensional characteristics were precisely controlled via regulating the photocurable resins, the composition of ceramic suspensions along with the printing parameters. The luminescence property under laser irradiations and the microstructure of the ceramic phosphor were emphatically elaborated and compared with those of the ceramic prepared via the traditional dry-pressing forming method.

Section snippets

Experimental procedures

An Al2O3/Y3Al5O12: Ce3+ (Al2O3/YAG: Ce3+) composite ceramic was firstly prepared via the high-end digital lighting processing (DLP) 3D printing technology. In the composite material, 0.4 mol.% Ce3+ ions were introduced to replace the corresponding Y3+ sites and the additional Al2O3 grains with a volume fraction of 22% acted as the scattering centers to enhance light extraction [8]. The preparation process was schematically presented in Fig. 1. Firstly, the composite powders composed of Al2O3, Y2

Results and discussion

Our strategy for preparing the Al2O3/YAG: Ce3+ composite ceramic with sub-millimeter features (900 μm in diameter, 5 cm in length) via the DLP based 3D printing has been elaborately depicted (Fig. 1) and proved efficient and exquisite, especially for those functional materials with complex shapes, ultra-small sizes or hierarchical structures. The powder mixture of Al2O3/YAG: Ce3+ was firstly carefully prepared through ball-milling, grinding, sieving, and pre-sintering, in order to prevent

Conclusions

A DLP-based 3D printing approach was demonstrated in the present work to obtain ceramic phosphors with fine dimensions (φ = 900 μm) for laser lighting. The composition of the Al2O3/YAG: Ce3+ ceramic powders was based on our previous study with which high luminous efficiency was guaranteed using the conventional dry-press followed by vacuum sintering method. The mass content of the ceramic suspension for 3D printing was optimized to 77.8%, which contributed to the densification of green bodies

Acknowledgments

This work was supported by National Key R&D Program of China (No. 2018YFC0308100) and Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures (No. SKL201802).

References (32)

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