Phosphor Film Investigation

Brian Hayden, Paul Weindorf, Kong Lor – Visteon Corporation

Yasushi Ito, Nelli Soudakova – Dexerials Corporation

4.1 – Wide Color Gamut Phosphor Film Investigation for

Automotive Applications

Outline

Introduction

Phosphor Conversion Film Description

Environmental Performance

Prototype Backlight Configuration

TFT Display Panel

Test Results

Conclusions

Page 2

Introduction

Displays are being utilized more often in automotive

applications and OEMs have begun to specify increased

RGB color gamuts with higher color saturation.

Page 3

Increasing color gamuts

significantly reduce the

display luminance.

OLED and other

technologies may provide

increased gamuts, TFT

LCD displays are the

workhorse of the

automotive industry.

Automotive TFTs typically have NTSC ratios of 64-70%.

Introduction

There is therefore a need to explore alternatives for

TFT displays which may consist of the following:

Page 4

Narrower TFT color filters

Color conversion films:

– Phosphor

– Quantum Dot (QD)

RGB LEDs

RG Phosphor LEDs

Increasing the color gamut with the use of phosphor

conversion films involves moving the spectral conversion

from within the LED to the phosphor film.

Phosphor Film Description

In contrast to the Quantum Dot approach, Dexerials

uses a more traditional method of using different phosphors

to yield narrow emission spectra which results in more

saturated colors.

Page 5

Dexerials Photo-

Luminescence

Spectra

Resultant spectra

when the

phosphor

conversion film is

used with blue

LED illumination

Emission Properties of

Sulfide Phosphors

Green Red

Materials SrGa2S4:Eu CaS:Eu

Peak

Wavelength540 nm 653 nm

FWHM 47 nm 64 nm

Phosphor Film Description

The color gamut is expected to

improve with the Dexerials film

compared to a traditional white

LED backlight solution.

Although luminance falls off as

the gamut is increased, actual

relative radiance is almost the

same as a white Ce:YAG

phosphor film configuration.

Page 6

Phosphor typeLCD with YAG

phosphor film

LCD with sulfide

phosphor film

Relative

Brightness100% 75%

Relative

Radiance100% 97%


The construction of the Dexerials phosphor film

utilizes moisture barrier layers and metal film edge sealing

tape. A next generation sealing method which will reduce the

border and thickness is also being developed.

Page 7


In order to demonstrate suitability for automotive

environmental applications, extensive testing was conducted

consisting of both short term and long term evaluations.

Page 8

Short Term Operation and Storage

Luminance Results

Short Term Operation and Storage

Chromaticity Results


Long term storage (3,000 hour) showing relative

changes in luminance and chromaticity.

Page 9

Long Term Storage

Luminance Results

Long Term Storage



Long term operation (3,000 hour) showing relative

changes in luminance and chromaticity.

Page 10

Long Term Operation

Luminance Results

Long Term Operation



For the study, a prototype backlight was assembled.

In order to establish the comparison to conventional displays,

both white and blue LED illuminated versions were built.

Page 11

Light Guide &

Optical Films

Backlight LEDs


Backlight assembly film stack:

– Keiwa BS-910 (not used with conversion film)

– 3M BEF III-5T 0°

– 3M BEF III-5T 90° (when utilized for cross BEF)

– 3M DBEF-D2 400 (reflective polarization film)

Backlight LEDs:

– Configured as 4 strings of 10 LEDs (top edge only)

– Both blue and white configurations were driven at 80 mA

Page 12

Osram CB DPLS31.14 Osram KW DPLS31.SB

TFT Display Panel

The display utilized for the study was a commercially

available 10.1” TFT display.

Spectral transmission of the individual red, green and blue

TFT filters were measured and are displayed in the chart

below:

Page 13

Test Results

Color Coordinate Comparison

– White LED and phosphor conversion film with blue LED

Page 14

Test Results

Backlight Spectral Radiance & TFT Transmittance

– White LED and phosphor conversion film with blue LED

Page 15

Test Results

Color and Luminance Comparison

Page 16

TFT Filtered Luminance & Chromaticity Simulation with TFT Panel

White LED 140115AX1.0 140617AX0.8 140617AX1.0

Single BEF Cross BEF Single BEF Cross BEF Single BEF Cross BEF Single BEF Cross BEF

RED cd/m² 121.4 140.0 68.2 97.7 59.1 85.4 68.9 96.9

CIEx 0.6183 0.6198 0.6525 0.6644 0.6369 0.6511 0.6522 0.6632

CIEy 0.3467 0.3473 0.3037 0.3057 0.3094 0.3119 0.3114 0.3117

GREEN cd/m² 393.2 449.0 218.7 264.8 289.6 360.9 279.8 333.0

CIEx 0.3196 0.3207 0.2591 0.2667 0.2550 0.2612 0.2612 0.2678

CIEy 0.6266 0.6265 0.6400 0.6452 0.6552 0.6600 0.6586 0.6617

BLUE cd/m² 64.4 72.6 53.1 58.8 65.1 74.8 58.6 64.8

CIEx 0.1533 0.1532 0.1477 0.1478 0.1470 0.1469 0.1469 0.1472

CIEy 0.0831 0.0859 0.0720 0.0811 0.0836 0.0957 0.0943 0.1066

WHITE cd/m² 578.9 661.5 340.0 421.3 413.8 521.2 407.4 494.6

CIEx 0.3058 0.3100 0.2639 0.2949 0.2470 0.2721 0.2735 0.3028

CIEy 0.3304 0.3367 0.2608 0.2896 0.2930 0.3253 0.3214 0.3480

% of White LED

Luminance100.0% 100.0% 58.7% 63.7% 71.5% 78.8% 70.4% 74.8%

As expected, the improvement in color performance comes

at some expense of luminance reduction (30-40%)

depending on the white color point.

Conclusions

The phosphor conversion film, with the automotive

single BEF configuration, provides improvement in color

gamut performance over conventional white backlighting.

Page 17

An expected white point

luminance loss of ~30% with this

configured was observed.

Optimization of the overlapping

blue and green filters of the TFT

may result in improved system

performance.

Preliminary environmental testing

strongly suggests that the Dexerials film will be suitable for

automotive environmental conditions.

Page 18

www.visteon.com