hereinafter , light - emitting apparatuses embodying the present invention will be described with reference to the drawings . in the embodiments described hereinafter , used as a primary light source is a iii - v group nitride semiconductor laser ( hereinafter also referred to simply as a “ laser ”) or a light - emitting diode ( led ). in one light - emitting apparatus embodying the invention , as shown in fig3 a and 3b , a laser 30 is used as a primary light source in combination with a phosphor 31 . it is also possible to form a phosphorescent portion by dispersing fine - particle crystals of a iii - v group compound semiconductor in resin . in that case , between the laser 30 and the phosphor 31 , there is inserted a wavelength filter 32 that absorbs or reflects light of wavelengths shorter than 395 nm . moreover , in front of the phosphor 31 ( on the exit side thereof ), there is disposed a wavelength filter 33 that absorbs or reflects only the excitation laser light ( the primary light emitted from the laser 30 ). the laser 30 emits laser light of wavelengths in the range from 380 nm to 500 nm . in a case where the phosphorescent portion is composed of fine - particle crystals and resin , it is preferable that the laser have wavelengths in the range from 395 nm to 500 nm . the phosphor 31 , when excited with the laser light emitted from the laser 30 , emits phosphorescence in the visible light region . as shown in fig3 a and 3b , the laser 30 and the phosphor 31 may be arranged in close contact with each other , or may be arranged apart from each other . the phosphor 31 is arranged so as to face the laser 30 so that the former can receive the laser light emitted from the latter . as shown in fig3 a , the laser light may be shone on glass or resin , such as acrylic resin , in which fine - particle crystals of a iii - v group compound semiconductor are dispersed , or may be shone on a surface to which a phosphor is applied or on which a coating thereof is formed . the phosphor may even be given a shape like a sphere or optical fiber so as to achieve good optical coupling with the laser light . as shown in fig4 , an optical system such as a lens 44 may be disposed between a primary light source 40 and a phosphor 41 . as shown in fig5 , a primary light source may be coupled with the core of an optical fiber 51 in which fine - particle crystals of a iii - v group compound semiconductor are dispersed . as shown in fig6 , the phosphorescence from a phosphor 61 may be condensed with a concave surface mirror 65 . as shown in fig7 , a light - emitting apparatus may be so structured that a laser used as a primary light source 70 is coupled with a light guide plate 72 and a scattering plate 73 so that primary light is extracted perpendicularly to the light guide plate 72 , and that a phosphor 71 is disposed at where the extracted primary light is directed so that secondary light is obtained as surface - emission phosphorescence . the laser may be of any type so long as it emits laser light of wavelengths in the range from 380 to 500 nm . in a case where the phosphorescent portion is composed of fine - particle crystals and resin , it is preferable that the laser have wavelengths in the range from 395 to 500 nm , because irradiating the resin with light of wavelengths shorter than 395 nm causes deterioration of the resin . for this reason , it is preferable to dispose , between the laser and the phosphor , a wavelength filter or the like that absorbs or reflects spontaneous emission light of wavelengths shorter than 395 nm included in the light emitted from the laser . examples of the laser include a surface - emission - type device , a stripe - shaped device , and a laser array having devices of either type arranged in an array . part of the laser light may be transmitted through the phosphor so as to be used along with the phosphorescence . however , in a case where a light - emitting apparatus embodying the invention is used for illumination purposes , letting laser light out to the outside world is undesirable because of its adverse effects on the human body . thus , in such a case , it is preferable to make the phosphor absorb all the laser light , or to use a wavelength filter or the like to keep the laser light from getting out to the outside world . preferable examples of the phosphor include one sintered , one applied to a plate - shaped member of a transparent material such as quartz , one dispersed in a glass - like substance such as glass or acrylic resin and then hardened , cut , and formed into a spherical , cylindrical , or fiber - like shape . in a case where , as shown in fig3 a , a laser 30 and a phosphor 31 are arranged apart from each other , the phosphor is a single member or component . in this case , the phosphor 31 is , for example , a transparent member to which a phosphorescent substance is applied or on which a coating thereof is formed , or a glass member having a phosphorescent substance dispersed therein , and this phosphor 31 is used in combination with a laser device . fig8 shows an example of the laser 30 used in the light - emitting apparatus shown in fig3 a . the gan - based semiconductor laser 30 shown in this figure has a ridge structure , and has a cavity formed with an active layer 84 cleaved at both ends so as to resonate and emit laser light parallel to the active layer 84 . thus , the laser light oscillates in the direction perpendicular to the plane of the figure , and then exits from the laser 30 to strike the phosphor 31 , causing it to emit phosphorescence to the outside world . the laser 30 shown in fig8 has , on top of a crystal substrate ( for example , a gan crystal substrate ) 80 , an n - gan contact layer 81 , an n - algan clad layer 82 , an n - gan guide layer 83 , an ingan active layer 84 , a p - algan evaporation prevention layer 85 , a p - gan guide layer 86 , a p - algan clad layer 87 , and a p - gan contact layer 88 laid on one another . on the top and bottom of these layers are formed a p - type electrode 89 and an n - type electrode 800 , respectively , and a sio 2 layer 801 insulates the p - type electrode 89 from the p - algan clad layer 87 except in the ridge portion . as the primary light source , it is also possible to use a surface - emission laser or an led . as the crystal substrate of the device used as the primary light source , it is possible to use any conventionally known substrate other than gan so long as it permits growth of a gan - based crystal thereon . examples of such a crystal substrate include sapphire , sic , si , and quartz . light emission may be achieved with any structure so long as it is suitable for a laser to emit light and oscillate and for an led to emit light . examples of suitable structures include a double hetero - junction structure , a structure including a sqw ( single quantum well ), one including a mqw ( multiple quantum well ), and one including a quantum dot . with an led , examples of suitable structures further include a simple pn - junction formed between two layers as a homo - or hetero - junction . a light - emitting apparatus structured as shown in fig3 a was fabricated . in this example , a stripe laser structured as shown in fig8 , i . e ., one having a ridge structure , was fabricated as the primary light source . in the following description , the values given in cm − 3 are carrier densities . as shown in fig8 , on top of a gan substrate 80 , an n - gan contact layer 81 ( 3 μm thick , 1 × 10 18 cm − 3 ), an n - al 0 . 1 ga 0 . 9 n clad layer 82 ( 1 μm thick , 1 × 10 18 cm − 3 ), gan guide layer 83 ( 0 . 1 μm thick , 1 × 10 18 cm − 3 ), an in 0 . 15 ga 0 . 85 n / in 0 . 05 ga 0 . 95 n 3mqw active layer 84 , a p - al 0 . 15 ga 0 . 85 n evaporation prevention layer 85 ( 0 . 02 μm thick , 1 × 10 18 cm − 3 ), a p - gan guide layer 86 ( 0 . 1 μm thick , 1 × 10 18 cm − 3 ), a p - al 0 . 1 ga 0 . 9 n clad layer 87 ( 0 . 6 μm thick , 1 × 10 18 cm − 3 ), and a p - gan contact layer 88 ( 0 . 1 μm thick , 1 × 10 18 cm − 3 ) were laid on one another . next , by rie , this multilayer structure was partially etched from the top surface thereof so that the p - algan clad layer 87 was exposed except for a portion thereof then , on top , a sio 2 ( 0 . 3 μm ) layer 801 was laid , and , further on top , a p - type electrode 89 ( pd / mo / au ) was formed . moreover , on the bottom surface of the multilayer structure , an n - type electrode 800 ( ti / al ) was formed . the oscillation wavelength of the apparatus was 405 nm . inn nano - crystals having volumes of 8 nm 3 to 1 000 nm 3 ( 2 nm to 10 nm along each side ) were synthesized through chemical synthesis , and then , by a sol - gel process , acrylic resin having the inn nano - crystals dispersed therein was formed into a film ( 3 μm thick ). the reason that the volume varied from 8 nm 3 to 1 000 nm 3 ( 2 nm to 10 nm along each side ) was that the volume that produced the same phosphorescence wavelength varied according to the conditions of synthesis . when the laser of the above light - emitting apparatus was energized to cause laser oscillation , phosphorescence of a wavelength 635 nm was obtained with energy conversion efficiency of 80 [ lm / w ]. assuming that the length of time over which the energy conversion efficiency fell half its initial value was the lifetime , the lifetime was about 10 000 hours . for comparison , the above light - emitting apparatus was operated with the wavelength filter 32 shown in fig3 a removed . in this case , the lifetime , over which the energy conversion efficiency fell half its initial value , was 1 000 hours . a light - emitting apparatus structured as shown in fig3 b was fabricated . as the primary light source , the same laser as used in example 1 was used . inn nano - crystals having volumes of 3 . 375 nm 3 to 64 nm 3 ( 1 . 5 nm to 4 nm along each side ) were grown by laser ablation , and then , on top of the inn , gan was grown by laser ablation in a similar manner to produce inn / gan nano - crystals having a quantum well structure as shown in fig2 . then , acrylic resin having these nano - crystals dispersed therein was formed into a cylindrical shape . the reason that the volume varied from 3 . 375 nm 3 to 64 nm 3 ( 1 . 5 nm to 4 nm along each side ) was that the volume that produced the same phosphorescence wavelength varied according to the conditions of growth . when the laser of the above light - emitting apparatus was energized to cause laser oscillation , phosphorescence of a wavelength 520 nm was obtained with energy conversion efficiency of 120 [ lm / w ]. for comparison , a laser that oscillated at a different wavelength was produced and used as the excitation light source , and the correlation between the wavelength of the excitation light source and the lifetime , over which the energy conversion efficiency fell to half its initial value , was evaluated . used as the wavelength filter 32 was one that absorbed or reflected spontaneous emission light of wavelengths shorter than the oscillation wavelength . fig9 shows the relationship between the wavelength and the life time , over which the energy conversion efficiency fell to half its initial value . with glass resin , the lifetime decreased as the wavelength shortened below 380 nm ; with acrylic resin , the lifetime decreased as the wavelength shortened below 395 nm . this decrease in the lifetime was due to , with glass resin , the deterioration of the laser used as the excitation light source and , with acrylic resin , the deterioration of the acrylic resin . a light - emitting apparatus structured as shown in fig4 was fabricated . in this example , an led structured as shown in fig1 was fabricated . in the following description , the values given in cm − 3 are carrier densities . as shown in fig1 , on top of a sapphire substrate 90 , a buffer layer ( not shown ) was grown , and then an n - gan contact layer 91 ( 3 μm thick , 1 × 10 18 cm − 3 ), an in 0 . 12 ga 0 . 87 n / gan 5 mqw active layer 92 , a p - al 0 . 15 ga 0 . 85 n evaporation prevention layer 93 ( 0 . 02 μm thick , 1 × 10 18 cm − 3 ), a p - gan contact layer 94 ( 0 . 2 μm thick , 1 × 10 18 cm − 3 ), an laid on one another . next , by rie , this multilayer structure was partially etched from the top surface thereof so that the n - gan contact layer 91 was exposed except for a portion thereof then , on top , an n - type electrode 95 ( ti / al ) was formed . moreover , on top of the p - gan contact layer 94 , a p - type transparent electrode 96 ( pd ; 0 . 008 nm ) was formed , and on top of a portion thereof , a p - type electrode 97 ( pd / mo / au ) was formed . three types of inn nano - crystals were produced by laser ablation , namely those having volumes of 8 nm 3 to 27 nm 3 ( 2 nm to 3 nm along each side ), those having volumes of 10 . 7 nm 3 to 64 nm 3 ( 2 . 2 nm to 4 nm along each side ), and those having volumes of 17 . 6 nm 3 to 512 nm 3 ( 2 . 6 nm to 8 nm along each side ). then , as shown in fig1 , these three types of nano - crystals were dispersed in acrylic resin in three layers in such a way that the size of the inn nano - crystals decreases from the entrance side to the exit side of the primary light . the thicknesses of these three layers were , with consideration given to how each layer absorbed the primary light , so adjusted that the phosphorescence emitted from the individual layers and mixed together was white . when the led of the above light - emitting apparatus was energized to emit light , white light was obtained with energy conversion efficiency of 60 [ lm / w ]. a light - emitting apparatus structured as shown in fig5 was fabricated . as the primary light source , a stripe laser of an embedded type was used . in 0 . 95 ga 0 . 05 n nano - crystals having volumes of 125 nm 3 to 343 nm 3 ( 5 nm to 7 nm along each side ) were synthesized through chemical synthesis , and on the ingan , aln was synthesized through chemical synthesis in a similar manner to produce in 0 . 95 ga 0 . 05 n / aln nano - crystals having a quantum well structure as shown in fig2 . then , an optical fiber was produced of which the core had these nano - crystals dispersed therein . when the laser of the above light - emitting apparatus was energized to cause laser oscillation , phosphorescence of a wavelength 600 nm was obtained with energy conversion efficiency of 120 [ lm / w ]. a light - emitting apparatus structured as shown in fig6 was fabricated . in 0 . 95 ga 0 . 02 n 0 . 99 p 0 . 01 nano - crystals having volumes of 343 nm 3 to 512 nm 3 ( 7 nm to 8 nm along each side ) were synthesized through chemical synthesis , and then , by a sol - gel process , glass having the inganp nano - crystals dispersed therein was formed into a film ( 1 mm thick ). when the laser of the above light - emitting apparatus was energized to cause laser oscillation , phosphorescence of a wavelength 560 nm was obtained with energy conversion efficiency of 100 [ lm / w ]. a light - emitting apparatus structured as shown in fig7 was fabricated . as the primary light source , the same laser as used in example 1 was used . inn nano - crystals having volumes of 343 nm 3 to 1 000 nm 3 ( 7 nm to 10 nm along each side ) were synthesized through chemical synthesis , and then , by a sol - gel process , a glass film ( 10 μm thick ) having the inn nano - crystals dispersed therein was formed on a light guide plate . when the laser of the above light - emitting apparatus was energized to cause laser oscillation , phosphorescence of a wavelength 550 nm was obtained with energy conversion efficiency of 100 [ lm / w ]. obviously , many modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understood that within the scope of the appended claims , the invention may be practiced other than as specifically described .