Yttrium aluminum garnet fluorescent conversion films for solid-state lighting: interface reaction synthesis strategy and modulation of warm white light†

Abstract

Traditional preparation of yttrium aluminum garnet (YAG) transparent ceramics involves several steps, including powder preparation, molding process and sintering at high temperature. Herein, a new and simple method was developed to prepare YAG transparent polycrystalline films directly through a novel interface reaction between sapphire and a Y₂(OH)_x(CO₃)_y(NO₃)_(6−x−2y)·nH₂O film attached to the sapphire. The prepared YAG:5%Ce transparent polycrystalline film could be combined with a blue chip to obtain fluorescence-converted white LED, with a CCT of 6361 K and a CRI (Ra) of 73.3. Introducing 1%Pr into the YAG:5%Ce system increased the CRI (Ra) to 77.4. When these transparent polycrystalline films were combined with a blue light laser diode (LD), similar spectra were obtained under high power density (4.17 W mm⁻²) excitation. YAG:5%Ce films produced a white light CCT of 5471 K, LE of 165.1 lm W⁻¹, and Ra of 62.9, while YAG:5%Ce,1%Pr films produced a CCT of 6311 K, LE of 146.5 lm W⁻¹, and Ra increased to 69.7. This study provides a novel “powder-free” and “glue-free” synthesis strategy for preparing fluorescence-converted YAG:Ce,Pr transparent polycrystalline films, which not only overcomes the disadvantages of traditional transparent ceramic preparation methods, such as time consumption, energy consumption, and equipment dependence, but also avoids the problem of aging in traditional fluorescent conversion materials.