Evaluation of Thermally Stable Phosphor Screens for Application in Laser Diode Excited High Brightness White Light Modules

Salimian, Ali; Silver, Jack; Fern, George R.; Evans, Meirin Oan; Haghpanahan, Roohollah

doi:10.1149/2.0021601jss

Cited by 13 publications

(11 citation statements)

References 5 publications

(6 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Since the power density of LDs is several orders of magnitude larger than that of LEDs, phosphors used in laser lighting (hereafter called “laser phosphors”) are excited by much higher photon densities accompanied by heavy thermal loads . The serious luminescence saturation often occurs due to the thermal and/or optical saturation, which becomes the most critical limiting factor in the laser lighting technology.…”

Section: Introductionmentioning

confidence: 99%

Color Conversion Materials for High‐Brightness Laser‐Driven Solid‐State Lighting

Wang

Hirosaki

et al. 2018

Laser & Photonics Reviews

261

191

View full text Add to dashboard Cite

Solid‐state lighting is advancing toward higher power, higher brightness, and smaller size to cope with the market competitiveness, and laser‐driven solid‐state lighting technology is springing up owing to its super‐high brightness and compactness. These developments put forward new requirements for color conversion materials (i.e., phosphors). Here, the state‐of‐art achievements in laser phosphors are summarized, and the topics of luminescence saturation, light extraction efficiency, and light uniformity encountered in laser lighting technology are discussed. Several typical types of color converters, such as single crystal, phosphor ceramics, phosphor‐in‐glass, phosphor films, and quantum‐well light‐emitting diodes, are comparatively overviewed and discussed. The cutting‐edge applications of high‐brightness white laser light in lighting, displays, healthcare, and communications are summarized. The challenges and outlook in laser‐driven solid‐state lighting and some empirical rules for designing novel laser phosphors are highlighted.

show abstract

Section: Introductionmentioning

confidence: 99%

Color Conversion Materials for High‐Brightness Laser‐Driven Solid‐State Lighting

Wang

Hirosaki

et al. 2018

Laser & Photonics Reviews

261

191

View full text Add to dashboard Cite

show abstract

“…The nature of the phosphor material, its morphology and crystal structure need to be investigated to obtain efficient targets for the LDs. * Electrochemical Society Active Member.z E-mail: ali.salimian@brunel.ac.ukWe previously reported on our solution for the thermal management of phosphor targets which can be exposed to laser beam powers of up to 5 W. 7 In this report we looked into comparing two different commercial phosphors; both based on the yttrium aluminum garnet system but from two separate commercial suppliers. The suppliers do not declare the exact chemical compositions.…”

mentioning

confidence: 99%

“…We previously reported on our solution for the thermal management of phosphor targets which can be exposed to laser beam powers of up to 5 W. 7 In this report we looked into comparing two different commercial phosphors; both based on the yttrium aluminum garnet system but from two separate commercial suppliers. The suppliers do not declare the exact chemical compositions.…”

mentioning

confidence: 99%

Laser Diode Induced Lighting Modules

Salimian

Fern

Upadhyaya

et al. 2016

ECS J. Solid State Sci. Technol.

Self Cite

View full text Add to dashboard Cite

Laser diodes have the potential of becoming the light engines of future lighting technology since they have negligible efficiency droop factor, unlike light emitting diodes. This study demonstrates the possibility of laser diodes coupled to phosphor targets being used as a solid state lighting system with high power applications. It was revealed that white light emitting modules with efficiency of up to 217 lumens per watt based on laser diodes can currently be made and upon further development of laser diode technology and relevant phosphor materials there is room for further improvements. The report also demonstrates the ability of this technology to produce a tailored emission spectrum for a given specific requirement. Two test lamp prototypes were made using laser diodes and phosphor targets and their emission characteristics were investigated. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0101603jss] All rights reserved. Currently light emitting diodes (LEDs) coupled with phosphors are the most efficient source of solid state white light provided that they are operated at low input powers. The drop in the LED's efficiency at higher input powers is associated to a phenomenon called the efficiency droop. This phenomenon has been investigated for the past decade and is thought to be linked to the Auger effect.1-3 Despite extensive research in to the field no fundamental or definitive solution has been put forward to eliminate this effect. To achieve more lumens per power consumed, the LEDs are typically operated under higher input powers at the expense of efficiency.An alternative approach is to use Laser Diodes (LDs) in combination with the same phosphors applied in LED lighting but packaged differently to achieve high performance and efficient solid state lighting (SSL). The LDs are operated under stimulated emission and the mechanisms of efficiency droop are clamped at their lasing threshold. 4 This concludes that through application of LDs, higher efficiencies at higher input power densities can be achieved. The LDs are more efficient in this respect because they are operated by stimulated emission. At lasing threshold, all the recombination processes (The Auger, Shockley-Read-Hall mechanism & spontaneous) are clamped and additional carriers injected into the light quantum wells contribute only to stimulated emission, so it can be argued that unless a fix to the efficiency droop which is an intrinsic issue is found, the LDs will be competing with LEDs for the future of high brightness/high power SSL modules.5 Figure 1 demonstrates a comparison of the power conversion efficiency (PCE) of LDs and LEDs and what is expected in terms of performance improvement from them in future. Future LEDs will require modules which have a shift in PCE ...

show abstract

“…We have previously reported on such solutions by making phosphor/ceramic composites with high thermal conductivity incorporated into various packaging solutions. 15,16 Unlike LED's, the conversion process from LDs is in reflective mode rather than transmission through the phosphor target which can be challenging when packaging constraints are considered. Our target designs were based on YAG phosphor powder materials in a ceramic composite, 15,16 however recently we have turned our attention to considering the application of single crystals of YAG:Ce (these have become readily available on the market) which possess high thermal conductivity.…”

mentioning

confidence: 99%

“…15,16 Unlike LED's, the conversion process from LDs is in reflective mode rather than transmission through the phosphor target which can be challenging when packaging constraints are considered. Our target designs were based on YAG phosphor powder materials in a ceramic composite, 15,16 however recently we have turned our attention to considering the application of single crystals of YAG:Ce (these have become readily available on the market) which possess high thermal conductivity. 14,17 The advantage of single crystal applications is that unlike synthesized phosphor powder/ ceramic composite targets, the crystals can be polished to specific roughness values, hence enabling light harvesting from various planes of the target and simplifying the challenges associated to packaging of such lighting modules.…”

mentioning

confidence: 99%

Investigating the Emission Characteristics of Single Crystal YAG When Activated by High Power Laser Beams

Salimian

Silver

Fern

et al. 2016

ECS J. Solid State Sci. Technol.

Self Cite

View full text Add to dashboard Cite

Limitations associated with light emitting diodes (LEDs) operating under high current densities due to the efficiency droop has created a need to look for alternative light sources; here we report investigations on the potential of laser diodes (LDs) for high brightness lighting solutions. High power laser diodes require phosphor targets with certain performance criteria such as high thermal conductivity, efficiency and structural geometry. Here we examine the possibility of using single crystal YAG:Ce phosphor materials as potential targets for generation of light via laser diodes. We report on the emission properties of the crystals with different sizes and examine the effect of laser beam incident angle incident on crystal target emission. Light emitting diodes (LEDs) are the current lighting technology solution gaining a wide adoption in a variety of commercial applications. They are now the dominant new lighting in office, public and domestic application, in addition they have almost completely covered the automotive head lamp market and now they are finding their way into more sophisticated instruments such as solar simulators. The best commercial LED's efficiencies are now above 60% and they are the most energy saving solution available. However there is a fundamental issue undermining their performance when they are considered for high brightness lighting applications. To generate high emission intensities, LEDs need to be driven at high current densities at which point their efficiency suffers from a phenomenon described as the efficiency droop. The efficiency droop's origin is rooted in a variety of complex processes including; Auger recombination, overflow of carriers from rich potential minima and carrier leakage out of active region.1-8 So far the highest luminous efficacies reported on LEDs are based on driving them at low current densities on the order of >11 Acm −2 . 9,10 In contrast to LEDs, Laser Diodes (LDs) can operate at very high current densities without suffering from efficiency droop. 11,12 However currently the LD's overall efficiency is well below that of LEDs and their application in lighting will require radical packaging designs and arrangement of the laser diode and phosphor target assemblies. To be able to manipulate the emission spectrum of devices based on LD induced lighting (LDIL) the type of phosphor targets and the level of impurities constituting the phosphor target material will need to be studied and adjusted. Recent research has demonstrated the necessity of these studies by investigating the structural and thermal properties of Tb, Ce doped Y 3 Al 5 O 12 (YAG) single crystals. 13,14 The results act as pointers to the research that needs to be undertaken in parallel to both develop radical designs of LDIL modules and the associated single crystals used as emitting targets. In this report we have focused on studying different crystal sizes of the same phosphor material with the same LDs. We have carried out studies on beam incident angle and relationship between the emiss...

show abstract

Evaluation of Thermally Stable Phosphor Screens for Application in Laser Diode Excited High Brightness White Light Modules

Cited by 13 publications

References 5 publications

Color Conversion Materials for High‐Brightness Laser‐Driven Solid‐State Lighting

Color Conversion Materials for High‐Brightness Laser‐Driven Solid‐State Lighting

Laser Diode Induced Lighting Modules

Investigating the Emission Characteristics of Single Crystal YAG When Activated by High Power Laser Beams

Contact Info

Product

Resources

About