A critical step in providing better phosphor solution for white light emitting diode (LED) is to utilize inexpensive silicate phosphors with strong thermal stability. Here, we demonstrate yellow silicate phosphor-embedded glass thick films with a high luminous efficacy of ∼32 lm/W at 200 mA as a nonconventional remote-phosphor approach. The simple screen-printing process of a paste consisting of (Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor and a low softening point glass creates a planar remote structure on a regular soda lime silicate glass with controllable film thickness and location (top vs bottom) of the phosphor layer. The glass matrix provides promising densification and adhesion with the substrate at the optimal low temperature of 410 °C, with the long-term stability in luminous efficacy over 500 h of operation. The proposed phosphor structure has important implications to overcome current limitations as phosphors.

techniques, [ 6,13,16 ] and new phosphor structures [ 17,18 ] for better performance of white LED structures. However, there have been limited improvements in luminous effi cacy, which still remains a serious challenge hindering commercial success.Trapped loss of light in the air-gap (due to backward photons) and total internal refl ection (TIR) arising within the remote structure are the main factors that critically limit the light extraction. [19][20][21] The reported earlier methods such as scattered photon extraction [ 22 ] and diffused refl ection cup approach [ 23 ] have mainly improved the extraction of back refl ected light. By contrast, few studies to enhance the luminous effi cacy by reducing the TIR in the phosphor part have been reported. Our approach in this study is to adopt a simple nanoscale surface roughening technique to enhance the luminous efficacy by minimizing the TIR at the air-phosphor layer and airglass substrate interface of a remote phosphor LED consisting of yellow phosphor screen-printed on a glass substrate. In the past, surface roughening or surface texturing approaches have been applied to the top n-GaN layer of blue InGaN LED chips to enhance blue light emission by minimizing TIR at the semiconductor-air interface. [24][25][26] Notwithstanding the promising results of surface roughening methods, there have been very limited reports on the deployment of surface texturing techniques for the phosphor layer. One related report is about the random texturing in the case of yttrium aluminum garnet (YAG) phosphor by means of an imprint technique which resulted in an increased luminous fl ux by ≈5.4%. [ 27 ] A patterned YAG phosphor created by pulsed spray coating on a transparent silicone encapsulant resin using a circular mask was reported without increasing the luminous effi cacy. [ 28 ] In this work, we explore a simple surface roughening technique of the glass substrate used as a base for printable remote silicate phosphor, (Ba,Sr,Ca) 2 SiO 4 :Eu 2+ , for the purpose of enhancing the luminescence performance. Compared to other YAG-based phosphors, this yellow silicate phosphor is known to possess higher luminous effi cacy and to have advantages in commercial utilization and cost-effectiveness. We recently reported the utilization of a glass substrate for printable silicate Nonconventional ways to modify phosphor structures have been reported to enhance the overall luminous effi cacy of white light-emitting diodes (LED). Here, a nanoscale texturing technique of a glass substrate with the simple printing process of yellow (Ba,Sr,Ca) 2 SiO 4 :Eu +2 silicate phosphor paste is combined to achieve enhanced white luminescence performance. It is demonstrated that the luminous effi cacy of the resulting printed phosphor layer can be enhanced by ≈16% as a result of controlling surface roughness of the substrate up to 151 nm. The substantial improvement obtained by texturing both sides of the substrate is attributed to the reduction of total internal refl ection of rays at the glass-air interfac...

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We suggest a simple way of forming a nonconventional remote phosphor layer for white light-emitting diodes. A printing technology using a paste consisting of yellow (Ba,Sr,Ca)(2)SiO(4):Eu(2+) silicate phosphor and ultraviolet (UV)-curable polymer is applied to form solid planar films on a common soda lime silicate glass substrate through UV radiation. Relative content of the phosphor was adjusted for the best dispersion of the phosphor particles in the polymer matrix with better emission and luminescence performance. As a result, the 70 wt. % phosphor-embedded film has a luminous efficacy of ∼70.1  lm/W at 200 mA.

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