WO2009063388A2 - Green emitting solid-state laser comprising a sesquioxide and/or ceramic material - Google Patents

Green emitting solid-state laser comprising a sesquioxide and/or ceramic material Download PDF

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Publication number
WO2009063388A2
WO2009063388A2 PCT/IB2008/054697 IB2008054697W WO2009063388A2 WO 2009063388 A2 WO2009063388 A2 WO 2009063388A2 IB 2008054697 W IB2008054697 W IB 2008054697W WO 2009063388 A2 WO2009063388 A2 WO 2009063388A2
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Prior art keywords
green emitting
systems
state laser
solid
ceramic material
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PCT/IB2008/054697
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French (fr)
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WO2009063388A3 (en
Inventor
Cornelis R. Ronda
Ondrej Mizerak
Ulrich Weichmann
Thomas Tj Juestel
Jaione Bengoechea Apezteguia
Joerg Meyer
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Koninklijke Philips Electronics N.V.
Philips Intellectual Property & Standards Gmbh
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Publication of WO2009063388A2 publication Critical patent/WO2009063388A2/en
Publication of WO2009063388A3 publication Critical patent/WO2009063388A3/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1608—Solid materials characterised by an active (lasing) ion rare earth erbium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/161—Solid materials characterised by an active (lasing) ion rare earth holmium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1685—Ceramics

Definitions

  • Green emitting solid-state laser comprising a sesquioxide and/or ceramic material
  • the present invention is directed to lasers, especially to green emitting solid-state lasers.
  • a green emitting solid-state laser comprising a green emitting transparent ceramic material.
  • ceramic material in the sense of the present invention means and/or includes especially a crystalline or polycrystalline compact material or green emitting transparent ceramic material with a controlled amount of pores or which is pore free.
  • polycrystalline material in the sense of the present invention means and/or includes especially a material with a volume density larger than 90 percent of the main constituent, consisting of more than 80 percent of single crystal domains, with each domain being larger than 0.5 ⁇ m in diameter and having different crystallographic orientations.
  • the single crystal domains may be connected by amorphous or glassy material or by additional crystalline constituents. However, for the application essentially phase pure, pore free and fully dense materials are preferred.
  • transparent in the sense of the present invention means especially that 80% of the incident light of a wavelength, which cannot be absorbed by the material, is transmitted through the sample for normal incidence in air (at an arbitrary angle with respect to the sample orientation). This wavelength is preferably in the range of > 400 nm and ⁇ 1000 nm.
  • green emitting in the context of this invention especially means and/or includes that the material shows an emission in the visible range (upon suitable excitation) with a peak maximum between 500 and 580 nm. It should be noted that the excitation of the green emitting transparent ceramic material is usually done by a blue laser or UV source, e.g. a blue or UV Laser light diode and this is also a preferred embodiment of the present invention.
  • green emitting solid-state laser does not exclude that this laser device may be used - e.g. with further laser sources - in a device emitting white light.
  • green emitting solid-state laser does only mean that this laser is capable of producing laser light in the green wavelength range.
  • Ceramic processing also allows for the manufacturing of more complex hosts, e.g. quaternary oxides or fluorides.
  • the activator e.g. Ce 3+ , Pr 3+ , Tb 3+ , Ho 3+ , or Er 3+ can be homogeneously distributed in a ceramic body, which is impossible in a single crystal due to the manufacturing process
  • the activator can be applied in a higher concentration, since segregation as occurring in crystal growth from a melt is not an issue.
  • the green emitting transparent ceramic material essentially has a cubic crystal lattice.
  • the term "essentially" in the context of this invention means especially that > 95 %, preferably > 97 % and most preferred > 99 % of the material has the desired structure and/or composition. If such a cubic material is used, it has been found for many applications within the present invention that due to the isotropy of the cubic structure, the use of the material within laser devices may be greatly enhanced.
  • the green emitting transparent ceramic material is essentially a material with a cubic bixbyite structure.
  • the green emitting transparent ceramic material essentially comprises a sesquioxide of a trivalent metal ion as host lattice.
  • the host lattice of the green emitting transparent ceramic material is essentially made out of Y 2 O 3 , Gd 2 ⁇ 3 , LU2O3, SC2O3 and/or mixtures thereof.
  • the green emitting transparent ceramic material is doped with rare earth emitting ions, especially selected out of the group comprising Er , Ho , Ce , Tb , Pr and/or mixtures thereof.
  • the doping level of the green emitting transparent ceramic material is ⁇ O.Ol to ⁇ 10.0 atom-%, preferably > 0.02 to ⁇ 5.0 atom-%, more preferred > 0.05 to ⁇ 2.0 atom-%.
  • the emission maximum of the green emitting transparent ceramic material is > 520 nm to ⁇ 580 nm.
  • the half- width of the emission band of the material in the visible wavelength range is > 15 nm to ⁇ 160 nm.
  • the photothermal stability of the ceramic green emitting transparent material is > 80% to ⁇ 100% after exposure of the material for 1000 hrs at 200 0 C with a light power density of 10W/cm 2 and an average photon energy of 2.75 eV.
  • photothermal stability in the sense of the present invention especially means and/or includes the conservation of the laser intensity under simultaneous application of heat and high intensity excitation, i.e. a photothermal stability of 100% indicates that the material is virtually unaffected by the simultaneous irradiation and heat up.
  • the photothermal stability of the ceramic green emitting transparent material is > 82.5% to ⁇ 95%, preferably > 85% to ⁇ 97%, after exposure of the material for 1000 hrs at 200 0 C with a light power density of 10 W/cm 2 and an average photon energy of 2.75 eV.
  • the thermal conductivity of the ceramic green emitting transparent ceramic material is > 0.02 W Cm 1 K "1 to ⁇ 0.30 W cm 1 K "1
  • the ceramic green emitting transparent ceramic material has a density of > 95% and ⁇ 101% of the theoretical density.
  • the ceramic green emitting transparent ceramic material has a density of > 97% and ⁇ 100% of the theoretical density.
  • the present invention furthermore relates to a method of producing a green emitting transparent ceramic material for a green emitting solid-state laser according to the present invention comprising a sintering step.
  • the term "sintering step" in the sense of the present invention means especially densification of a precursor powder under the influence of heat, which may be combined with the application of uniaxial or isostatic pressure, without reaching the liquid state of the main constituents of the sintered material.
  • the sintering step is pressureless, preferably in ambient or slightly oxidising atmosphere.
  • sintering in pure hydrogen due to the high diffusivity or in vacuum can also be applied.
  • the thus introduced oxygen vacancies in the crystal lattice are removed by a subsequent annealing step in ambient or oxidising atmosphere.
  • the method furthermore comprises the step of pressing the ceramic composite precursor material to > 50% to ⁇ 70 %, preferably > 55% to ⁇ 65 %, of its theoretical density before sintering. It has been shown in practice that this improves the sintering steps for most green emitting transparent ceramic materials as described with the present invention.
  • the method of producing a green emitting transparent ceramic material for a green emitting solid-state laser comprises the following steps:
  • a first pressing step preferably a uniaxial pressing step using a suitable powder compacting tool with a mould in the desired shape (e.g. rod- or pellet-shape) and/ or a cold isostatic pressing step preferably at >3000 bar to ⁇ 5000 bar.
  • a suitable powder compacting tool with a mould in the desired shape (e.g. rod- or pellet-shape) and/ or a cold isostatic pressing step preferably at >3000 bar to ⁇ 5000 bar.
  • the first pressing step may be aided through the use of an organic binder, which is removed after compaction at moderate temperatures ( ⁇ 700°C) in air
  • an optional hot pressing step preferably a hot isostatic pressing step preferably at > 30 bar to ⁇ 2500 bar and preferably at a temperature of > 1300 0 C to ⁇ 1700 0 C and/or a hot uniaxial pressing step preferably at > 50 bar to ⁇ 2500 bar and preferably at a temperature of > 1300 0 C to ⁇ 2000 0 C.
  • this production method has produced the best green emitting transparent ceramic materials as used in the present invention.
  • the present invention furthermore relates to a green emitting solid-state laser comprising a green emitting transparent material, which is essentially a metal sesquioxide.
  • green emitting in the context of this invention especially means and/or includes that the material shows an emission in the visible range (upon suitable excitation) with a peak maximum between 500 and 580 nm. It should be noted that the excitation of the green emitting transparent material is usually done by a blue laser or UV source, e.g. a blue or UV Laser light diode and this is also a preferred embodiment of the present invention.
  • sesquioxide in the context of this invention especially means that the material may comprise a metal sesquioxide as host lattice, which is doped with further suitable metal ions; actually this is a preferred embodiment of the present invention.
  • the green emitting transparent material essentially has a cubic crystal lattice.
  • the green emitting transparent material is essentially a material with a cubic bixbyite structure.
  • the host lattice of the green emitting transparent material is essentially made out of Y 2 O 3 , Gd 2 ⁇ 3 , LU 2 O 3 , SC2O3 and/or mixtures thereof.
  • the green emitting transparent material is doped with rare earth emitting ions, especially selected out of the group comprising Er 3+ , Ho 3+ , Ce 3+ , Tb 3+ , Pr 3+ and/or mixtures thereof.
  • the doping level of the green emitting transparent material is ⁇ O.Ol to ⁇ 10.0 atom-%, preferably > 0.02 to ⁇ 5.0 atom-%, more preferred > 0.05 to ⁇ 2.0 atom-%.
  • the emission maximum of the green emitting transparent material is > 520 nm to ⁇ 580 nm.
  • the half- width of the emission band of the material in the visible wavelength range is > 15 nm to ⁇ 160 nm.
  • the green emitting transparent material is a ceramic material as described above.
  • a green emitting solid-state laser according to the present invention as well as a green emitting transparent material as produced with the present method may be of use in a broad variety of systems and/or applications, amongst them one or more of the following:
  • Fig. 1 shows an emission spectrum of the material of Example I
  • Fig. 2 shows an excitation spectrum of the material of Example I
  • Fig. 3 shows a reflection spectrum of the material of Example I
  • Fig.4 shows a diagram of the integral emission intensity of several materials of the present invention with different doping levels
  • Fig. 5 shows the experimental setup of a green-emitting solid state laser using the material of Example II.
  • Fig. 6 shows a visible emission spectrum of the material of Example II.
  • Fig. 7 shows a visible emission spectrum of the material of Example II with a different incident power
  • Fig. 8 shows a visible emission spectrum of the material of Example II with a different incident power
  • Fig. 9 shows a visible emission spectrum of the material of Example II with a different incident power
  • Fig. 10 shows a visible emission spectrum of the material of Example II with a different incident power
  • Fig. 11 shows a diagram of the green emission power of the material of Example II against the pump power of the incident laser source (at 445 nm); and Fig. 12 shows a diagram of the green emission power of the material of Example II against the pump power of the incident laser source (at 488 nm)
  • Example I refers to Y2 ⁇ 3:Er (0.8 atom-% of Y) which was made the following way:
  • the precipitate (Yo,99Er o ,oi)2 was filtered, washed with distilled water and ethanol and dried in air at about 80-90°C. The dried powder was placed into a corundum crucible and heated in air at 800°C for 1 hour.
  • the powder was then re-ground and mixed with 1 mol% of Na 2 CC ⁇ .
  • the mixture was placed in corundum crucible and heated at 1500 °C for 2 hours.
  • the sample was subsequently ground, carefully washed with distilled water and ethanol and dried at 80-90°C in air.
  • Example II refers to Y2 ⁇ 3:Er (0.5 atom-% of Y), which was made in analogous fashion except that less Dierbiumtrioxide was used.
  • Fig. 4 shows a diagram of the integral emission intensity of several materials of the present invention with different doping levels. It can be clearly seen that the suitable doping level is around 1 atom% or less.
  • Example II Using the material of Example II, also the green emission was studied.
  • Example II a sample of the material of Example II was pumped by means of a (In 5 Ga)N- based compound laser diode, whose emission wavelength was about 445 nm and maximum power of 0.5 W, and by an Ar-ion laser, emitting at 488 nm, with a maximum power of 6 W.
  • a (In 5 Ga)N- based compound laser diode whose emission wavelength was about 445 nm and maximum power of 0.5 W
  • Ar-ion laser emitting at 488 nm, with a maximum power of 6 W.
  • the experimental setup used to excite the sample using the emission from a (In,Ga)N-based compound laser diode can be seen in Figure 5.
  • the light then enters a variable anamorphic prism pair 30, where it is magnified (in this experimental setup, the magnification factor was 2).
  • Figs 6 to 10 show several spectra of the visible emission of the material of Example II pumped by a 445 nm laser diode.
  • Fig. 11 shows a diagram of the green emission power of the material of Example II against the pump power of the incident laser source at 445 nm
  • Fig. 12 shows an analogous diagram with an incident laser source at 488 nm.

Abstract

The invention relates to a green emitting solid-state laser with green emitting transparent material, preferably of the material Y2O3, Gd2O3, Lu2O3, Sc2O3 and Er3+ and Ho3+ as doping ions. These materials have been found to be of excellent use for green emitting lasers.

Description

Green emitting solid-state laser comprising a sesquioxide and/or ceramic material
FIELD OF THE INVENTION
The present invention is directed to lasers, especially to green emitting solid-state lasers.
BACKGROUND OF THE INVENTION
Besides other light emitting devices, such as LEDs, in recently also laser light sources have gained much attention, in particular for projection systems.
However, the generation of white light by laser light sources - e.g. by superposition of red, green and blue emitting light sources - has been found difficult due to a lack of efficient and compact green emitting laser light sources. Whereas red and blue lasers are easily at hand, only very few suitable green emitting laser light sources are known in the art so far, each of them with known disadvantages.
There is thus an ongoing demand for alternative green emitting laser light sources, which allow the set-up of white-light emitting laser devices.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a green emitting solid-state laser.
This object is solved by a green emitting solid-state laser according to claim 1 of the present invention. Accordingly, a green emitting solid-state laser is provided comprising a green emitting transparent ceramic material. The term "ceramic material" in the sense of the present invention means and/or includes especially a crystalline or polycrystalline compact material or green emitting transparent ceramic material with a controlled amount of pores or which is pore free.
The term "polycrystalline material" in the sense of the present invention means and/or includes especially a material with a volume density larger than 90 percent of the main constituent, consisting of more than 80 percent of single crystal domains, with each domain being larger than 0.5 μm in diameter and having different crystallographic orientations. The single crystal domains may be connected by amorphous or glassy material or by additional crystalline constituents. However, for the application essentially phase pure, pore free and fully dense materials are preferred.
The term "transparent" in the sense of the present invention means especially that 80% of the incident light of a wavelength, which cannot be absorbed by the material, is transmitted through the sample for normal incidence in air (at an arbitrary angle with respect to the sample orientation). This wavelength is preferably in the range of > 400 nm and < 1000 nm.
The term "green emitting" in the context of this invention especially means and/or includes that the material shows an emission in the visible range (upon suitable excitation) with a peak maximum between 500 and 580 nm. It should be noted that the excitation of the green emitting transparent ceramic material is usually done by a blue laser or UV source, e.g. a blue or UV Laser light diode and this is also a preferred embodiment of the present invention.
It should be stressed and will be apparent to any skilled person in the art, that the term "green emitting solid-state laser" does not exclude that this laser device may be used - e.g. with further laser sources - in a device emitting white light. The term "green emitting solid-state laser" does only mean that this laser is capable of producing laser light in the green wavelength range.
Such a laser has shown for a wide range of applications within the present invention to have at least one of the following advantages:
Due to the ceramic nature of the material used, no tedious single crystal growth is necessary, which also allows the build-up of larger and more sophisticated applications. Moreover, usually ceramic processing occurs below the melting temperature, allowing the fabrication of high quality and size samples. Due to their high melting temperatures, of more than 24000C, this is of special interest in the case of the sesquioxides.
Ceramic processing also allows for the manufacturing of more complex hosts, e.g. quaternary oxides or fluorides.
The activator, e.g. Ce3+, Pr3+, Tb3+, Ho3+, or Er3+ can be homogeneously distributed in a ceramic body, which is impossible in a single crystal due to the manufacturing process
The activator can be applied in a higher concentration, since segregation as occurring in crystal growth from a melt is not an issue.
Flexibility in the design of dopant profiles in e.g. layered composite ceramic bodies, like for example, step function doping profiles or materials that have two or more dopants distributed in a defined manner.
According to a preferred embodiment of the present invention, the green emitting transparent ceramic material essentially has a cubic crystal lattice.
The term "essentially" in the context of this invention means especially that > 95 %, preferably > 97 % and most preferred > 99 % of the material has the desired structure and/or composition. If such a cubic material is used, it has been found for many applications within the present invention that due to the isotropy of the cubic structure, the use of the material within laser devices may be greatly enhanced.
Preferably, the green emitting transparent ceramic material is essentially a material with a cubic bixbyite structure.
According to a preferred embodiment of the present invention, the green emitting transparent ceramic material essentially comprises a sesquioxide of a trivalent metal ion as host lattice.
According to a preferred embodiment of the present invention, the host lattice of the green emitting transparent ceramic material is essentially made out of Y2O3, Gd2θ3, LU2O3, SC2O3 and/or mixtures thereof.
According to a preferred embodiment of the present invention, the green emitting transparent ceramic material is doped with rare earth emitting ions, especially selected out of the group comprising Er , Ho , Ce , Tb , Pr and/or mixtures thereof.
According to a preferred embodiment of the present invention, the doping level of the green emitting transparent ceramic material is ≥ O.Ol to ≤ 10.0 atom-%, preferably > 0.02 to < 5.0 atom-%, more preferred > 0.05 to < 2.0 atom-%.
According to a preferred embodiment of the present invention, the emission maximum of the green emitting transparent ceramic material is > 520 nm to < 580 nm.
According to a preferred embodiment of the present invention, the half- width of the emission band of the material in the visible wavelength range is > 15 nm to < 160 nm.
According to a preferred embodiment of the present invention, the photothermal stability of the ceramic green emitting transparent material is > 80% to < 100% after exposure of the material for 1000 hrs at 2000C with a light power density of 10W/cm2 and an average photon energy of 2.75 eV.
The term "photothermal stability" in the sense of the present invention especially means and/or includes the conservation of the laser intensity under simultaneous application of heat and high intensity excitation, i.e. a photothermal stability of 100% indicates that the material is virtually unaffected by the simultaneous irradiation and heat up.
According to a preferred embodiment of the present invention, the photothermal stability of the ceramic green emitting transparent material is > 82.5% to < 95%, preferably > 85% to < 97%, after exposure of the material for 1000 hrs at 2000C with a light power density of 10 W/cm2 and an average photon energy of 2.75 eV.
According to a preferred embodiment of the present invention, the thermal conductivity of the ceramic green emitting transparent ceramic material is > 0.02 W Cm 1K"1 to < 0.30 W cm 1K"1
According to a preferred embodiment of the present invention, the ceramic green emitting transparent ceramic material has a density of > 95% and < 101% of the theoretical density.
According to a preferred embodiment of the present invention, the ceramic green emitting transparent ceramic material has a density of > 97% and < 100% of the theoretical density. The present invention furthermore relates to a method of producing a green emitting transparent ceramic material for a green emitting solid-state laser according to the present invention comprising a sintering step.
The term "sintering step" in the sense of the present invention means especially densification of a precursor powder under the influence of heat, which may be combined with the application of uniaxial or isostatic pressure, without reaching the liquid state of the main constituents of the sintered material.
According to a preferred embodiment of the present invention, the sintering step is pressureless, preferably in ambient or slightly oxidising atmosphere. To achieve optimal densities sintering in pure hydrogen due to the high diffusivity or in vacuum can also be applied. In this case the thus introduced oxygen vacancies in the crystal lattice are removed by a subsequent annealing step in ambient or oxidising atmosphere.
According to a preferred embodiment of the present invention, the method furthermore comprises the step of pressing the ceramic composite precursor material to > 50% to < 70 %, preferably > 55% to < 65 %, of its theoretical density before sintering. It has been shown in practice that this improves the sintering steps for most green emitting transparent ceramic materials as described with the present invention.
According to a preferred embodiment of the present invention, the method of producing a green emitting transparent ceramic material for a green emitting solid-state laser according to the present invention comprises the following steps:
(a) preparation of a precursor powder for the green emitting transparent ceramic material, preferably by a solution precipitation method (b) firing of the precursor materials, preferably at a temperature of > 800 0C to < 15000C to remove volatile materials (such as CO2 in case carbonates are used)
(c) optional grinding and washing
(d) a first pressing step, preferably a uniaxial pressing step using a suitable powder compacting tool with a mould in the desired shape (e.g. rod- or pellet-shape) and/ or a cold isostatic pressing step preferably at >3000 bar to < 5000 bar.
(e) optionally the first pressing step may be aided through the use of an organic binder, which is removed after compaction at moderate temperatures (<700°C) in air
(f) a sintering step at >1400 0C to < 2200 0C in an inert, reducing or slightly oxidizing atmosphere with a pressure of > 10~7mbar to < 104 mbar.
(g) an optional hot pressing step, preferably a hot isostatic pressing step preferably at > 30 bar to < 2500 bar and preferably at a temperature of > 1300 0C to < 17000C and/or a hot uniaxial pressing step preferably at > 50 bar to < 2500 bar and preferably at a temperature of > 1300 0C to < 20000C.
(h) optionally a post annealing step at > 10000C to < 17000C in oxidising atmosphere
According to this method, for most desired material compositions this production method has produced the best green emitting transparent ceramic materials as used in the present invention.
The present invention furthermore relates to a green emitting solid-state laser comprising a green emitting transparent material, which is essentially a metal sesquioxide.
The term "green emitting" in the context of this invention especially means and/or includes that the material shows an emission in the visible range (upon suitable excitation) with a peak maximum between 500 and 580 nm. It should be noted that the excitation of the green emitting transparent material is usually done by a blue laser or UV source, e.g. a blue or UV Laser light diode and this is also a preferred embodiment of the present invention.
The term "sesquioxide" in the context of this invention especially means that the material may comprise a metal sesquioxide as host lattice, which is doped with further suitable metal ions; actually this is a preferred embodiment of the present invention.
Surprisingly it has been found that a green emitting laser with good optical features may be provided using such a sesquioxide material.
According to a preferred embodiment of the present invention, the green emitting transparent material essentially has a cubic crystal lattice.
The term "essentially" in the context of this invention means especially that > 95 %, preferably > 97 % and most preferred > 99 % of the material has the desired structure and/or composition.
If such a cubic material is used, it has been found for many applications within the present invention that due to the isotropy of the cubic structure, the use of the material within laser devices may be greatly enhanced.
Preferably, the green emitting transparent material is essentially a material with a cubic bixbyite structure.
According to a preferred embodiment of the present invention, the host lattice of the green emitting transparent material is essentially made out of Y2O3, Gd2θ3, LU2O3, SC2O3 and/or mixtures thereof. According to a preferred embodiment of the present invention, the green emitting transparent material is doped with rare earth emitting ions, especially selected out of the group comprising Er3+, Ho3+, Ce3+, Tb3+, Pr3+ and/or mixtures thereof.
According to a preferred embodiment of the present invention, the doping level of the green emitting transparent material is ≥ O.Ol to ≤ 10.0 atom-%, preferably > 0.02 to < 5.0 atom-%, more preferred > 0.05 to < 2.0 atom-%.
According to a preferred embodiment of the present invention, the emission maximum of the green emitting transparent material is > 520 nm to < 580 nm.
According to a preferred embodiment of the present invention, the half- width of the emission band of the material in the visible wavelength range is > 15 nm to < 160 nm.
According to a preferred embodiment of the present invention, the green emitting transparent material is a ceramic material as described above.
A green emitting solid-state laser according to the present invention as well as a green emitting transparent material as produced with the present method may be of use in a broad variety of systems and/or applications, amongst them one or more of the following:
Office lighting systems household application systems shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, and decorative lighting systems portable systems automotive applications green house lighting systems
Interactive lighting systems
Lighting systems relying on pulsed light
The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional details, features, characteristics and advantages of the object of the invention are disclosed in the subclaims, the figures and the following description of the respective figures and examples, which - in an exemplary fashion - show several embodiments and examples of a green emitting transparent material for use in a green emitting solid-state laser according to the invention. Fig. 1 shows an emission spectrum of the material of Example I
Fig. 2 shows an excitation spectrum of the material of Example I
Fig. 3 shows a reflection spectrum of the material of Example I
Fig.4 shows a diagram of the integral emission intensity of several materials of the present invention with different doping levels
Fig. 5 shows the experimental setup of a green-emitting solid state laser using the material of Example II.
Fig. 6 shows a visible emission spectrum of the material of Example II.
Fig. 7 shows a visible emission spectrum of the material of Example II with a different incident power
Fig. 8 shows a visible emission spectrum of the material of Example II with a different incident power
Fig. 9 shows a visible emission spectrum of the material of Example II with a different incident power
Fig. 10 shows a visible emission spectrum of the material of Example II with a different incident power
Fig. 11 shows a diagram of the green emission power of the material of Example II against the pump power of the incident laser source (at 445 nm); and Fig. 12 shows a diagram of the green emission power of the material of Example II against the pump power of the incident laser source (at 488 nm)
EXAMPLES I and II
The invention will be better understood together with the Examples I and II which - in a mere illustrative fashion - are two Examples of inventive green emitting transparent materials.
Example I refers to Y2θ3:Er (0.8 atom-% of Y) which was made the following way:
Calculated amounts of Y2O3 and Er2C^ were dissolved by heating in cone. HNO3. Most of the HNO3 was evaporated, and the rest was mixed with water. The pH of solution was adjusted to 2 by addition of NaOH solution. Afterwards this solution was poured into a saturated solution of oxalic acid and co -precipitation of the rare-earth oxalate occurred.
The precipitate (Yo,99Ero,oi)2
Figure imgf000014_0001
was filtered, washed with distilled water and ethanol and dried in air at about 80-90°C. The dried powder was placed into a corundum crucible and heated in air at 800°C for 1 hour.
The powder was then re-ground and mixed with 1 mol% of Na2CC^. The mixture was placed in corundum crucible and heated at 1500 °C for 2 hours. The sample was subsequently ground, carefully washed with distilled water and ethanol and dried at 80-90°C in air.
From this material, transparent ceramics were obtained with the method described above at elevated temperature and uniaxial pressure (1700 0C and 100 Mpa). Example II refers to Y2θ3:Er (0.5 atom-% of Y), which was made in analogous fashion except that less Dierbiumtrioxide was used.
The emission, excitation and reflection spectrum of the material of Example I is seen in Figs. 1 to 3. The λPeakis 564 nm.
Fig. 4 shows a diagram of the integral emission intensity of several materials of the present invention with different doping levels. It can be clearly seen that the suitable doping level is around 1 atom% or less.
Using the material of Example II, also the green emission was studied.
To this end, a sample of the material of Example II was pumped by means of a (In5Ga)N- based compound laser diode, whose emission wavelength was about 445 nm and maximum power of 0.5 W, and by an Ar-ion laser, emitting at 488 nm, with a maximum power of 6 W.
The experimental setup used to excite the sample using the emission from a (In,Ga)N-based compound laser diode can be seen in Figure 5. As can be seen from Fig. 5, a first laser diode 10 emits light towards a first collimating lens 20 (in this experimental setup with f = 6mm). The light then enters a variable anamorphic prism pair 30, where it is magnified (in this experimental setup, the magnification factor was 2).
After passing a second focusing lens 40 (in this experimental setup with f = 11 mm), the light is guided to the transparent material 50 of Example II. The emitted light is then collected by an optical fibre 60 and sent to a spectrometer (not shown in Fig. 5) for further analysis. The emission coming from the Y2θ3:Er sample was collected by means of an optical fiber and sent to a spectrometer for analysis.
Figs 6 to 10 show several spectra of the visible emission of the material of Example II pumped by a 445 nm laser diode.
The incident power varied along the spectra as can be seen in Table I:
Table I:
Figure imgf000016_0001
Furthermore, Fig. 11 shows a diagram of the green emission power of the material of Example II against the pump power of the incident laser source at 445 nm, Fig. 12 shows an analogous diagram with an incident laser source at 488 nm.
Most surprisingly, the curves shown in Figure 11 and 12 show a clear linear behaviour, and no saturation at all.
The inventors believe that the small deviation from the linear behaviour in Figure 11 is probably related to the spectral shift of the laser diode emission that shifts with temperature and input diode current. Even more surprisingly, it has been found that in the spectra there are no blue/ultraviolet emission lines at all (which was also found in further experiments with the materials of Example I and II). This further demonstrates the great value of the inventive materials for green emitting laser devices.
The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.

Claims

1. Green emitting solid-state laser comprising a green emitting transparent ceramic material.
2. The green emitting solid-state laser of claim 1, whereby the green emitting transparent ceramic material is essentially of a cubic crystal structure.
3. The green emitting solid-state laser of claim 1 or 2 whereby the green emitting transparent ceramic material is essentially of a cubic bixbyite structure.
4. The green emitting solid-state laser of any of the claims 1 to 3 whereby the green emitting transparent ceramic material essentially comprises a sesquioxide of a trivalent metal ion as host lattice.
5. Green emitting solid-state laser comprising a green emitting transparent material, which is essentially a metal sesquioxide.
6. The green emitting solid-state laser of claim 5, whereby the green emitting transparent material is essentially of a cubic crystal structure.
7. The green emitting solid-state laser of any of the claims 5 to 6, whereby the green emitting transparent material is essentially of cubic bixbyite structure and preferably the host lattice of the green emitting transparent material is essentially made out of Y2O3, Gd2O3, Lu2O3, Sc2O3 and/or mixtures thereof.
8. The green emitting solid-state laser of any of the claims 1 to 6 whereby the green emitting transparent ceramic material is doped with rare earth ions, preferably emitting ions selected out of the group comprising Er3+, Ho3+, Ce3+, Tb3+ and/or mixtures thereof.
9. The green emitting solid-state laser of any of the claims 1 to 7, whereby the doping level of the green emitting transparent ceramic material is > 0.01 to < 10.0 atom-%.
10. A system comprising a green emitting solid-state laser according to any of the claims 1 to 9, the system being used in one or more of the following applications:
Office lighting systems household application systems shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, and decorative lighting systems portable systems automotive applications green house lighting systems Interactive lighting systems Lighting systems relying on pulsed light
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