Method for preparing scheelite type red fluorescent powder by combustion method

Abstract

The invention discloses a method for preparing Sr < 0.6 > Ba < 0.4-x > MoO4: xPr < 3 + >, yPEG-200 system scheelite type red fluorescent powder by a combustion method, Sr (NO3) 2, Ba (NO3) 2 and (NH4) 6Mo7O14. 4H2O are used as reaction raw materials, Pr < 3 + > is used as rare earth ion doping, citric acid is used as a combustion improver, and the Sr < 0.6 > Ba < 0.4-x > MoO4: xPr < 3 + > fluorescent powder is synthesized by combustion. A combustion method is adopted for synthesis, the advantages of being low in reaction temperature, short in time and small in synthesized sample particle are achieved, and the Sr0. 6Ba < 0.4-x > MoO4: xPr < 3 + >, yPEG-200 red fluorescent powder synthesized through the experiment is high in luminescence performance and can be used as red fluorescent powder for a white light LED. According to the invention, the surfactant PEG-200 is added to improve the morphology of the sample and enhance the luminescence property of the sample, and the trivalent praseodymium ions are doped in the molybdate with the scheelite structure, so that the luminescent material has high emission intensity in a dark red region.

Description

Technical Field

[0001] The invention relates to a method for preparing scheelite-type red fluorescent powder. Background Art

[0002] Against the backdrop of a deteriorating global environment and dwindling resources, people are turning their attention to energy-saving and environmentally friendly materials. As living standards improve, a significant portion of the world's energy is consumed by lighting. Traditional light sources, such as incandescent lamps, consume considerable energy when emitting light. However, the successful development of semiconductor light-emitting diodes (LEDs) has significantly reduced energy consumption for lighting and has been dubbed the "fourth generation of lighting sources." White LEDs, with their high efficiency, long life, short response time, recyclability, and pollution-free properties, have become green lighting sources that meet energy-saving and environmental requirements, offering promising prospects in lighting and display applications. With the advancement of new processes and the development of new materials, the luminous intensity and efficiency of LEDs have been continuously enhanced, and they are now widely used in commercial applications such as lighting sources, display screens, automotive lighting, and home decoration.

[0003] However, the phosphors for white light LEDs synthesized by existing technologies generally have defects in sample morphology, sample luminescence performance, etc., and need to be further improved. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing scheelite-type red phosphor by a combustion method, which can effectively improve the sample morphology and enhance the luminescence performance of the sample.

[0005] The technical solution of the present invention is:

[0006] A combustion method for preparing Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method of preparing yPEG-200 system scheelite type red phosphor is characterized by: using Sr(NO3)2, Ba(NO3)2 and (NH4)6Mo7O 14 4H2O is the raw material of the reaction, with Pr 3+ As rare earth ion doping, citric acid was used as a combustion aid to synthesize Sr 0.6 Ba 0.4-x MoO4:xPr 3+ Phosphor.

[0007] The surfactant PEG-200 was also added to the reaction.

[0008] The combustion method for preparing Sr 0.6 Ba 0.4-x MoO4:xPr3+ The method for preparing a PEG-200 system scheelite type red phosphor comprises the following steps:

[0009] (1) Weigh a certain amount of Pr6O 11 In the first beaker, take 2-4 ml of nitric acid and add it to the first beaker. Place it in a water bath and heat it to fully dissolve it until it evaporates to dryness. Then add deionized water to make a solution A with a concentration of 0.1 mol / L for later use. All the above operations are carried out in a ventilated place.

[0010] (2) Sr(NO3)2, Ba(NO3)2, (NH4)6MoO7, and citric acid monohydrate (C6H8O7·H2O) were weighed in sequence and placed in a second beaker. An appropriate amount of deionized water was added and stirred on a thermostatic magnetic stirrer until fully dissolved. Then, a certain amount of polyethylene glycol 200 (PEG-200) was added and the stirring was continued;

[0011] (3) Measure a certain amount of solution A and add it to the second beaker. Slowly evaporate and dehydrate it under electromagnetic stirring at 75°C ± 5°C for 0.5-0.8 hours. Transfer the light green sol-like substance obtained by stirring to a corundum crucible, cover it, and quickly place it in a muffle furnace preheated to the appropriate temperature for combustion;

[0012] (4) After keeping warm for a certain period of time, take out the fluffy product to obtain the target product Sr 0.6 Ba 0.4-x MoO4:xPr 3+ ,yPEG-200.

[0013] In step (3), the combustion temperature in the muffle furnace is 1100°C.

[0014] In step (2), the actual amount of citric acid used is twice the theoretical amount.

[0015] In step (1), press Pr 3+ Calculation, Pr 3+ Doping amount (i.e. in Sr 0.6 Ba 0.4-x MoO4:xPr 3+ Medium Pr 3+ Relative to Sr 0.6 Ba 0.4-x The percentage content of MoO4 is 1.5%.

[0016] The amount of PEG-200 added (i.e. in the product Sr 0.6 Ba 0.4-x MoO4:xPr 3+ , PEG-200 in yPEG-200 relative to Sr 0.6 Ba 0.4-x MoO4:xPr3+ The percentage content) is 6%.

[0017] The red phosphor prepared by the present invention has the best luminous intensity; the combustion method has the advantages of low reaction temperature, short reaction time and small sample particles. 0.6 Ba 0.4-x MoO4:xPr 3+ ,yPEG-200 red phosphor has strong luminescence performance and can be used as red phosphor for white light LED. The present invention adds surfactant polyethylene glycol 200 (PEG-200) to improve the sample morphology and enhance the sample luminescence performance, and selects trivalent praseodymium ion (Pr 3+ ) is doped in molybdate with a scheelite structure and has a higher emission intensity in the deep red region.

[0018] The present invention will be further described below with reference to the embodiments. DETAILED DESCRIPTION

[0019] A combustion method for preparing Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method for preparing a PEG-200 system scheelite type red phosphor comprises the following steps:

[0020] (1) Weigh a certain amount of Pr6O 11 In the first beaker, add 3 ml of nitric acid to the first beaker and heat it in a water bath to fully dissolve it until it evaporates to dryness. Then add deionized water to make a solution A with a concentration of 0.1 mol / L for later use. All the above operations are carried out in a ventilated place;

[0021] (2) Sr(NO3)2, Ba(NO3)2, (NH4)6MoO7, and citric acid monohydrate (C6H8O7·H2O) were weighed in sequence and placed in a second beaker. An appropriate amount of deionized water was added and stirred on a constant temperature magnetic stirrer until fully dissolved. Then, a certain amount of PEG-200 was added and continued to stir. The actual amount of citric acid used was twice the theoretical amount.

[0022] (3) Measure a certain amount of solution A and add it to a second beaker. Slowly evaporate and dehydrate the solution at 75°C ± 5°C under electromagnetic stirring for 0.5-0.8 hours. Transfer the resulting light green sol-like substance into a corundum crucible, cover it, and quickly burn it in a muffle furnace preheated to 1100°C.

[0023] (4) After keeping warm for a certain period of time, take out the fluffy product to obtain the target product Sr 0.6 Ba 0.4-x MoO4:xPr 3+ ,yPEG-200.

[0024] In step (1), press Pr 3+ Calculation, Pr 3+ Doping amount (i.e. in Sr 0.6 Ba 0.4-x MoO4:xPr 3+ Medium Pr 3+ Relative to Sr 0.6 Ba 0.4-x The percentage content of MoO4 is 1.5%.

[0025] The amount of PEG-200 added (i.e. in the product Sr 0.6 Ba 0.4-x MoO4:xPr 3+ , PEG-200 in yPEG-200 relative to Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The percentage content) is 6%.

[0026] In order to explore Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The optimal combustion synthesis temperature conditions were determined. Under the condition of a holding time of 40 minutes, comparative experiments were carried out at ignition temperatures of 800°C, 900°C, 1000°C, 1100°C and 1200°C. The product obtained at 800°C was a white powder with obvious black-brown impurities. The reason for the production of such impurities was that the ignition temperature was too low and the raw materials could not be completely burned. At an ignition temperature above 900°C, the product obtained became a light green powder with good fluorescence properties. At an ignition temperature above 900°C, high-purity scheelite-type Sr can be synthesized. 0.6 Ba 0.4-x MoO4:xPr 3+ Phosphor. As the ignition temperature increases, Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The excitation peak (λ ex =451nm) emission peak and (λ em =648nm), the peak narrows and becomes higher, and the luminescence intensity of the sample increases. At ignition temperatures of 1100°C and 1200°C, the intensities of the emission and excitation peaks do not increase significantly. This suggests that further increases in temperature beyond 1100°C have little effect on the fluorescence performance of the sample.

[0027] Sr was prepared by reacting at 1100℃ for 10min, 20min, 30min, 40min and 50min respectively. 0.6 Ba 0.38 MoO4:0.02Pr3+ The excitation spectrum (λ ex =451nm) and emission spectrum (λ em =648nm). The samples prepared under different holding time are all light green powders with good luminescence performance. 0.6 Ba 0.38 MoO4:0.02Pr 3+ The excitation peak and emission peak intensities of the sample increased continuously. When the holding time was changed to 40 min, the luminescence intensity of the sample reached the highest. The reason may be that with the increase of the holding time, Sr 0.6 Ba 0.38 MoO4:0.02Pr 3+ During its grain growth process, Pr 3+ It can obtain enough kinetic energy and time to enter the lattice, forming enough effective and stable luminescence centers, thereby enhancing the luminescence intensity. When the holding time is 50min, the luminescence intensity is greatly weakened. The possible reason is that the grains grow fully, the crystal structure tends to be complete, the internal defects are greatly reduced, and the luminescence center Pr 3+ The symmetry of the crystal field increases and the deformation force decreases, resulting in the partial luminescence center Pr 3+ Because the extranuclear electrons cannot obtain enough energy to undergo transitions, they lose their ability to emit light. Therefore, a long holding time will cause the luminescence intensity to drop significantly. Therefore, the subsequent experiments all used a holding time of 40 minutes.

[0028] When the amount of citric acid is more than its theoretical amount, Sr 0.6 Ba 0.38 MoO4:0.02Pr 3+ The excitation spectrum (λ ex =451nm) and emission spectrum (λ em =648nm) intensity is higher, illustrates that the amount of the citric acid added this moment has good promotion to combustion reaction, and the luminous property of sample also has greatly improved.When citric acid added reaction with 5 times of theoretical amounts, the emission peak of sample was lower, and its reason is that citric acid added too much and caused the reaction too violent, caused sample sintering, and the luminous efficiency of sample was sharply reduced.When the ratio of citric acid and theoretical amount was 2: 1, the luminous intensity of sample was the highest, illustrates that the citric acid addition at this moment both can guarantee the sufficient carrying out of combustion reaction, can not be because of excessive and remain in the sample and can not burn out again.Therefore, the citric acid addition in subsequent experiments all tests with 2 times of theoretical value.

[0029] Different Pr 3+ Sr doping amount 0.6 Ba 04-x MoO4:xPr 3+ The excitation spectrum (λ ex=451nm) and emission spectrum (λ em =648nm) comparison, it can be found that as Pr 3+ As the amount of doping increases, the excitation peak and emission peak of the sample first increase and then decrease. 3+ When the doping amount reaches 1.5%, the excitation peak and emission peak of the sample reach the highest. This is because 3+ It acts as an activator in the sample and 3+ When the average distance between 3+ With the increase of concentration, the number of luminescence centers increases accordingly, and the luminescence intensity also increases accordingly. 3+ When the concentration of Pr is too high, the adjacent 3+ The average distance between them is shortened, and even multiple Pr 3+ coexist in the same unit cell, which increases the crystal field symmetry within the unit cell and reduces the asymmetric crystal field force. 3+ If the distance between them is too short, cross relaxation may occur, which results in the energy 3+ The mutual relaxation process between them continuously dissipates, resulting in concentration quenching, which greatly reduces the luminescence intensity. 3+ The optimal doping amount is 1.5%.

[0030] PEG-200 was used as the surfactant to be added. It can be found that the addition of PEG-200 has a significant effect on the luminescence intensity of the sample, and as the amount of PEG-200 increases, the luminescence intensity first becomes stronger and then weakens. When the amount of PEG-200 added is 6%, Sr 0.6 Ba 0.4-x MoO4:xPr 3+ , yPEG-200 has the best luminescence performance.

Claims

1. A combustion method for preparing Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: With Sr(NO3)2, Ba(NO3)2 and (NH4)6Mo7O 14 4H2O is the raw material of the reaction, with Pr 3+ As rare earth ion doping, citric acid was used as a combustion aid to synthesize Sr 0.6 Ba 0.4-x MoO4:xPr 3+ Phosphor.

2. Preparation of Sr by combustion method according to claim 1 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: The surfactant PEG-200 was also added to the reaction.

3. The combustion method according to claim 2 prepares Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: The following steps are involved: (1) Weigh a certain amount of Pr6O 11 In the first beaker, take 2-4 ml of nitric acid and add it to the first beaker. Place it in a water bath and heat it to fully dissolve it until it evaporates to dryness. Then add deionized water to make a solution A with a concentration of 0.1 mol / L for later use. All the above operations are carried out in a ventilated place. (2) Sr(NO3)2, Ba(NO3)2, (NH4)6MoO7, and citric acid monohydrate were weighed in sequence and placed in a second beaker. An appropriate amount of deionized water was added and stirred on a thermostatic magnetic stirrer until fully dissolved. Then, a certain amount of polyethylene glycol 200 (PEG-200) was added and the stirring was continued; (3) Measure a certain amount of solution A and add it to the second beaker. Slowly evaporate and dehydrate it under electromagnetic stirring at 75°C ± 5°C for 0.5-0.8 hours. Transfer the light green sol-like substance obtained by stirring to a corundum crucible, cover it, and quickly place it in a muffle furnace preheated to the appropriate temperature for combustion; (4) After keeping warm for a certain period of time, take out the fluffy product to obtain the target product Sr 0.6 Ba 0.4-x MoO4:xPr 3+ ,yPEG-200.

4. The combustion method according to claim 3 prepares Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: In step (3), the combustion temperature in the muffle furnace is 1100°C.

5. The combustion method according to claim 3 prepares Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: In step (2), the actual amount of citric acid used is twice the theoretical amount.

6. The combustion method according to claim 3 for preparing Sr 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: In step (1), Pr 3+ The added amount is 1.5%.

7. The combustion method for preparing Sr according to claim 3 0.6 Ba 0.4-x MoO4:xPr 3+ The method for producing yPEG-200 system scheelite type red phosphor is characterized by: The added amount of PEG-200 is 6%.