Orderly patterned remote phosphor crystal material and method for preparation the material and its application

Abstract

The present invention provide an orderly patterned remote phosphor crystal material and method for preparation the material and its application, which adopts short-pulse laser to make micro-structure arrays on the surface of phosphor crystal material to enhance the light extraction efficiency of the LED based on the material. The present invention overcomes the phosphor crystal material's properties of hard and dry/wet etching resistance and simplifies the processing steps, which accelerate the processing and improve the producing efficiency. The present invention is able to be performed under room temperature and environment friendly and the micro-structure is stable, which has broad application prospects in white LED field.

Claims

1. A method for preparing an orderly patterned remote phosphor crystal material, comprising steps of: 1) placing a remote phosphor crystal material ready for processing on a stage which is movable freely along 2-dimensionally horizontal directions, and focusing a short-pulse laser on a surface or above the surface of the remote phosphor crystal material ready for processing; and 2) moving a stage which carries the remote phosphor crystal material and point-by-point scanning the surface of the remote phosphor crystal material with the short-pulse laser, which forms micro-structure arrays on the surface of the remote phosphor crystal material; a shape, a size and a spacing of a single structure in the micro-structure arrays is combinedly controlled by a power of a pulsed laser, repetition frequency of the pulse laser, a spacing between a laser focal plane and the surface of the material and a moving speed of the stage; wherein the orderly patterned remote phosphor crystal material comprises: a remote phosphor crystal material body, the orderly patterned micro-structure arrays on the surface of the remote phosphor crystal material body, which are produced by laser ablation.

2. The method for making the orderly patterned remote phosphor crystal material, as recited in claim 1, wherein a pulse-width of the short-pulse laser is 20 fs-100 ns; a wavelength is 355 nm-800 nm, a repetition frequency is 10 Hz-170 kHz; a power is 0.001 W-0.5 W; a laser energy density threshold is 30 J/cm.sup.2-50 J/cm.sup.2; a moving speed of the stage is 1 mm/s-100 mm/s.

3. The method for making the orderly patterned remote phosphor crystal material, as recited in claim 1, further comprising a step of: after finishing the step 2), dipping the remote phosphor crystal material with the micro-structure arrays on the surface into a mixed acid of concentrated sulfuric acid and hydrogen peroxide, or into concentrated sulfuric acid to remove debris generated by laser ablation; wherein a volume ratio of the concentrated sulfuric acid and the hydrogen peroxide is 3:1-7:1.

4. The method for making the orderly patterned remote phosphor crystal material, as recited in claim 1, wherein the remote phosphor crystal material ready for processing is made of Y.sub.3Al.sub.5O.sub.12:Ce with a thickness of 0.1 mm-5 mm; a pulse width of the short-pulse laser is 1 ns-100 ns; a wavelength is 300 nm-400 nm; a repetition frequency is 1 kHz-30 kHz; a power is 0.01 W-0.5 W; a diameter of focused spot is 20 m; a moving speed of the stage is 1 mm/s-100 mm/s.

5. The method for making the orderly patterned remote phosphor crystal material, as recited in claim 4, wherein an absorption peak of the phosphor crystal material of Y.sub.3Al.sub.5O.sub.12:Ce is 420-460 nm; an emission peak is 510-570 nm; a doping concentration of Ce.sup.3+ in Y.sub.3Al.sub.5O.sub.12:C is 0.01-1 at %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the SEM (scanning electron microscope) of a Ce:YAG phosphor crystal material with micro-hole arrays processed by laser in the embodiments. The spacing between the micro-hole is 10 m. The diameter of every micro-hole is 7.5 m and the depth of the micro-hole is 3 m. (a) is the SEM taken at 300 times magnification, (b) is the SEM taken at 1200 times magnification, (c) is the SEM taken at 7000 times magnification.

(2) FIG. 2 illustrates the dependence of the size (diameter and depth) of micro-hole on 355 nm short-pulse laser power (a), and on moving-up distance of the light spot focal plane (b).

(3) FIG. 3 is an illustration of applying the Ce:YAG phosphor crystal material in white LED encapsulation structure; 1 is the encapsulation substrate of LED; 2 is the blue LED chip; 3 is the electrode lead; 4 is the filling materials (silicon, epoxy or air); 5 is Ce:YAG phosphor crystal material; 6 is micro-hole arrays on the surface of Ce:YAG phosphor to crystal material processed by laser;

(4) FIG. 4 is a comparison of the overall EL (Electroluminescence) within the 4 (solid angle of the covered white LED of the Ce:YAG phosphor crystal material with micro-structure arrays and the Ce:YAG phosphor crystal material with smooth surface measured by integrating sphere, which is excited by 250 mA blue LED chip. The peak wavelength of the blue LED is 445 nm.

(5) FIG. 5 is a comparison EL of the covered white LED of the Ce:YAG phosphor crystal material with micro-structure arrays and the Ce:YAG phosphor crystal material with smooth surface while the spectral detector lies in 0 (vertical to YAG surface) which is excited by 250 mA blue LED chip.

(6) FIG. 6 is a comparison EL of the covered white LED of the Ce:YAG phosphor crystal material with micro-structure arrays and the Ce:YAG phosphor crystal material with smooth surface while the angle between spectral detector and the normal line is 80;

(7) FIG. 7 is a comparison absolute values of the luminous efficacy of the covered white LED of the Ce:YAG phosphor crystal material with micro-structure arrays and the Ce:YAG phosphor crystal material with smooth surface

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(8) Referring to FIG. 1 to FIG. 7 of the drawings, preferred embodiments of the present invention are illustrated, wherein the present invention provides a simple and highly effective method to pattern the surface of single crystal and polycrystalline transparent phosphor crystal material, which is able to reduce the total internal reflection of the light inside the phosphor crystal material to improve the light extraction efficiency of the LED chip and the phosphor crystal material and enhance the LED luminous efficacy (1 m/W). The present invention proposes that the patterned single crystal or polycrystalline material is a replacement for phosphor powder that under same excitation of LED chip higher conversion efficiency (1 m/W) will be obtained. The present invention has the advantages of good optical uniformity, high brightness, simplified encapsulation techniques, excellent thermostability, long service lifespan, simple structure and good performance which is particularly suitable for high-power white LED device.

(9) The phosphor crystal material is able to be Lu.sub.3Al.sub.5O.sub.12:Ce, Tb.sub.3Al.sub.5O.sub.12:Ce, Y.sub.3Al.sub.5O.sub.12:Ce, (LuY).sub.3Al.sub.5O.sub.12:Ce, Y.sub.3(Al,Ga).sub.5O.sub.12:Ce or Y.sub.3(Al,Si).sub.5(O,N).sub.12:Ce.

(10) The method is also suitable for other phosphor material that involves transparent single crystal, polycrystalline YAG phosphor crystal material include but not limited to yellow Ce:YAG (Y.sub.3Al.sub.5O.sub.12 mixed with Ce.sup.3+) transparent phosphor material. Furthermore the rare earth luminescent ions Tb, Pr, Eu, Nd, Tm, Dy is able to be doped or codoped in YAG material to modulate the wavelength. The doping substrates include but not limited to Y.sub.2O.sub.3, LuAG, Lu.sub.2O.sub.3, Sc.sub.2O.sub.3, MgAl.sub.2O.sub.4, CaF.sub.2, ZnS. Under the excitation of LED chip single or multiple wavelengths light is able to be emitted.

(11) Take Y.sub.3Al.sub.5O.sub.12:Ce as an example, blue LED chip or ultraviolet LED excite the transparent YAG material to emit yellow light which is mixed with the emitting light of the blue LED chip or ultraviolet LED chip to form white light. A simple method to enhance the light extraction efficiency of the Ce:YAG phosphor crystal material for white LED is proposed that is to make micro-structure arrays on the surface of Ce:YAG phosphor crystal material directly by short-pulse laser to enhance the light extraction efficiency of the Ce:YAG phosphor crystal material for white LED. The short-pulse laser refers to the laser that reaches a certain energy density (in the present invention the energy density threshold of the laser is 30-50 J/cm.sup.2, the energy density threshold may varies for laser with different wavelength.), the pulse width is 1-100 fs to 1-100 ns, the wavelength is 355 nm to 800 nm (for example 355 nm or the UV laser with a wavelength less than 400 nm or other laser with long wavelength).

Embodiment 1

(12) The Implement Steps are as Follow:

(13) Step 1: place the Ce:YAG phosphor single crystal material with a thickness of 0.3 mm ready for processing on the stage which is able to move freely along 2-dimensionally horizontal directions. The short-pulse laser focuses on one side of the phosphor crystal material through objective;

(14) In step 1 the Ce:YAG phosphor material is double face polished. The absorption peak and the emission peak of the Ce:YAG phosphor material are 450 nm and 550 nm respectively; The doping concentration of the Ce in the Ce:YAG phosphor material is 0.03 at %; The pulse width, wavelength and repetition frequency of the short-pulse laser are 40 ns, 355 nm and 1 kHz respectively. The moving speed of the stage is 10 nm/s. The power of the short-pulse laser is 0.15 W and the laser spot focuses on the surface of the material (the diameter of the spot is 20 m).

(15) Step 2: Due to the special processing character of the laser, an ablation area is formed on the surface of the Ce:YAG phosphor crystal material around an area that takes the laser focus as the center that the peak energy of the generated pulse is especially high. The temperature on the focus rises rapidly and reaches the boiling point of the YAG material in a short time, then evaporate the material on the focus. The evaporated material is taken away by high speed and high pressure gas sprayed by the nozzle and a hole is formed on the surface. Moving the stage carried with the material under the control of computer software to form the micro-structure arrays on one side of Ce:YAG phosphor crystal material. Please refer to FIG. 1

(16) By adjusting the output power of the laser and the distance between the focal plane and the Ce:YAG phosphor crystal material, the micro-structure arrays with different diameter and depth are able to be formed. Refers to FIG. 2, with the gradually increase of the laser power the diameter of a single micro-structure is increased from 6 m to 17 m and the depth increased from 1.5 m to 5 m; With the gradually increase of the distance between the spot focal plane and material the diameter of a single micro-structure is increased from 18 m to 26 m and the depth decreased from 5 m to 1.5 m. By adjusting the repetition frequency of the laser and the moving speed of the stage the distribution period and spacing of between the micro-structure is able to be changed; By adjusting the scan trace the micro-structure arrays is able to form different patterns.

(17) Step 3: Put the processed Ce:YAG phosphor crystal material in the mixed acids (volume to volume ratio is 3:1) of concentrated sulfuric acid (mass fraction: 98%) and hydrogen peroxide (mass fraction: 30%) for half an hour. The appearance of the Ce:YAG phosphor crystal material surface change slightly before and after the purge of the mixed acid while the depth of the micro-hole increase a little bit. The main purpose for the purge is to clean the residual debris of the laser ablation on the surface (This step is not a must which is to purge the residual debris of the ablation and make the micro-hole smooth. The micro-structure is formed by the short-pulse laser). Purge the remaining acid with ionized water before blow-drying with nitrogen and get the patterned Ce:YAG phosphor crystal material. Longer purge time is needed when using the concentrated sulfuric acid. The purge process is able to be accelerated by heating.

(18) The process to make white LED using the patterned Ce:YAG phosphor crystal material comprises the following steps:

(19) Step 1: Sets the blue LED chip 2 (the peak wavelength of the emission light is 440-460 nm) on the center of the encapsulation substrate and connect the electrode lead 3;

(20) Step 2: Attaches the patterned Ce:YAG phosphor crystal material with micro-structure arrays onto the LED encapsulation substrate. The side with micro-structure arrays is facing up (the side without micro-structure arrays faces the LED chip) and get the remote phosphor converter structure white LED as illustrated in FIG. 3. Referred to FIG. 4, the present invention is able to significantly enhance the light extraction efficiency of the white LED (FIG. 3) and enhance the conversion ratio of blue photon to yellow photon. Referred to FIG. 5 and FIG. 6, the patterned Ce:YAG phosphor crystal material with micro-structure arrays mainly enhance the light emission intensity of the front (vertical to YAG surface) and on the side (angled with the normal line with big degrees) the emission intensity is increased slightly. The patterned phosphor crystal material altered the direction of light emission and increase the LED front/side light emission ratio. Referred to FIG. 7, the absolute value of the luminous efficacy of the covered white LED of the Ce:YAG phosphor crystal material with micro-structure arrays and the Ce:YAG phosphor crystal material with smooth surface increased about 15%.

(21) Chart 1 is a comparison of the optical prosperities of a smooth surface phosphor crystal material and patterned phosphor crystal material under the current 350 mA measured by integrating sphere. Generally speaking the total luminous flux of the patterned phosphor crystal material processed with the present invention is enhanced and the blue-yellow light conversion ratio increased significantly.

(22) TABLE-US-00001 CHART 1 Smooth Ce:YAG Patterned Ce:YAG phosphor crystal phosphor crystal Patterned/ material material smooth Luminous flux(lm) 98.74 109.7 1.11 Luminous efficacy 91.65 105.42 1.15 lm/W CIEx 0.3406 0.3716 1.09 CIEy 0.3881 0.4661 1.20

Embodiment 2

(23) Step 1: place the Ce:YAG phosphor single crystal material with a thickness of 0.3 mm ready for processing on the stage which is able to move freely along 2-dimensionally horizontal directions. The short-pulse laser focuses on one side of the phosphor crystal material through objective lens;

(24) In step 1 the Ce:YAG phosphor material is double face polished. The absorption peak and the emission peak of the Ce:YAG phosphor material are 450 nm and 550 nm respectively; The doping concentration of the Ce in the Ce:YAG phosphor material is 0.03 at %; The pulse width, wavelength and repetition frequency of the short-pulse laser are 50 fs, 800 nm and 1 kHz respectively. The moving speed of the stage is 10 nm/s. The power of the short-pulse laser is 0.05 W and the laser spot focuses on the surface of the material (the diameter of the spot is 20 m).

(25) Step 2: Due to the special processing character of the laser, an ablation area is formed on the surface of the Ce:YAG phosphor crystal material around an area that takes the laser focus as the center that the peak energy of the generated pulse is especially high. The temperature on the focus rises rapidly and reaches the boiling point of the YAG material in a short time, which evaporate the material on the focus. The evaporated material is taken away by high speed high pressure gas sprayed by the nozzle and a hole is formed on the surface. The diameter of the single micro-structure is 5 m and the depth is 2 m. The surface of the hole is coarse and not smooth.

(26) One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. The micro-structure processed by laser is able to be arranged periodically which includes but not limited to micro-pits, micro-grooves, micro-lens, micro-holes. The micro-structure is also able to be arranged in aperiodicity.

(27) While processing the micro-structure on one side of the phosphor crystal material, the side with micro-structure is facing the LED chip or the side without micro-structure is facing the LED chip in the LED encapsulation. The difference is that when the side with micro-structure is facing the LED chip the ratio of emitting light from the chip being reflected back by the phosphor crystal material is reduce and the light extraction efficiency of the phosphor crystal material is increased at the same time; when the side without micro-structure is facing the LED chip only the light extraction efficiency of the phosphor crystal material is increased; Processing micro-structure on both sides of the phosphor crystal material is a good choice, the micro-structure facing the LED chip is able to reduce the ratio of emitting light from the chip being reflected back and micro-structure on both sides is able to enhance the light extraction efficiency significantly.